TESTING OF SEDIMENTARY DEPOSITS AT DIAMOND SEARCHING WORKS
Аннотация и ключевые слова
Аннотация (русский):
The book contains materials on the search for modern and buried alluvial and primary deposits of diamonds. Much attention is paid to prospecting testing of potentially diamondiferous deposits and provides information on all types of diamondiferous rocks currently known. It is addressed primarily to young geologists who have embarked on a search for diamond deposits. It will find the answer to many questions by many geologists, prospectors and prospectors, leading the search for gold and diamonds. While this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Ключевые слова:
diamonds, deposits, Basaltoids, Impactites, Tuffisites, Metamorphites, Lamproites, Kimberlites, placers, Angarida
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RUSSIAN ACADEMY OF SCIENCES

SIBERIAN BRANCH

 

 

INSTITUTE OF THE EARTH'S CRUST

 

 

 

 

Nikolay Ivanovich Akulov

 

SEDIMENT TESTING

DURING DIAMONDS SEARCH

 

 

Scientific editor

Doctor of Geological and Mineralogical Sciences

A. V. Tolstov

RUSSIAN ACADEMY OF SCIENCES

INSTITUTE OF THE EARTH'S CRUST

 

 

N.I. Akulov

TESTING OF SEDIMENTARY

DEPOSITS AT

DIAMOND SEARCHING WORKS

Scientific Editors

D. Sc. in Geological and Mineralogical Sciences A.V. Tolstov

                                                                                                                                

The book contains materials on the search for modern and buried alluvial and primary deposits of diamonds. Much attention is paid to prospecting testing of potentially diamondiferous deposits and provides information on all types of diamondiferous rocks currently known.

It is addressed primarily to young geologists who have embarked on a search for diamond deposits. It will find the answer to many questions by many geologists, prospectors and prospectors, leading the search for gold and diamonds.

While this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

 

Suggested citation:

Akulov N.I., 2022. Testing of sedimentary deposits at diamond searching works.

Irkutsk, Academic Publishing IOTEC, 140 p.

 

ISBN 978-1-922756-10-7

 

 

 

 

K 549.12

LBC 26.31

А 941

 

Akulov N. I.

    Sediment Testing During Diamonds Search

 

Sci. ed. A.V. Tolstov

The Russian Academy of Sciences; Siberian branch;

Institute of the Earth's Crust (IEC).

Irkutsk, 2022.140 p.

ISBN 978-1-922756-10-7

 

The book contains materials on prospecting for modern and buried alluvial diamond deposits. Much attention is paid to prospecting testing of potentially diamondiferous deposits and information is given on various types of diamond-bearing rocks known at present.

It is addressed primarily to young geologists who have embarked on prospecting for diamond deposits. They will find there the answer to many questions geologic-prospectors and prospectors conducting searches for gold and diamonds.

Reviewers:

 

Dr. of Geol. and Min. Sciences S. I. Kostrovitsky

Dr. of Geol. and Min. Sciences V. A. Skvortsov

Cand. of Geol. and Min. Sciences S. A. Prokopiev

 

© N. I. Akulov

ISBN 978-1-922756-10-7

 

 

 

 

 

 

 

 

 

 

List of content

BY EDITOR………………………………………………………………………………………………….………………………………….5

INTRODUCTION………………………………….…………………………………..………………………………….....................7

1. THE PHILOSOPHY OF SEARCH AND THE BASIS OF GEOLOGICAL JURISPRUDENCE. 11

1.1. Specifics of acquiring the right to use subsoil. 11

2. DIAMONDS OF RUSSIA.. 14

3. GENETIC TYPES OF DIAMOND-BEARING ROCKS. 17

3.1. Basaltoids. 17

3.3. Tuffisites. 19

3.4. Metamorphites. 22

3.5. Lamproites. 23

3.6. Kimberlites. 25

4.1. Weathering crust of kimberlites. 30

4.2. Types of diamond placers and tasks of the first stage of their search. 34

5. TYPES OF TESTING WORKS IN SEARCHING FOR DIAMONDS. 40

6. METHOD OF OBTAINING DIAMOND-CONTAINING CONCENTRATES IN FIELD CONDITIONS. 47

6.1. Elementary Jigging Basics. 47

6.2. Obtaining concentrates using jigging devices. 50

7. SCHEMES OF ENRICHMENT OF DIAMOND-BEARING SEDIMENTS. 54

7.1 Features of laboratory studies of concentrates. 57

8. SEARCH FOR DIAMANTIFEROUS PLACERS AND SELECTION OF THE OBJECT OF TESTING (ON THE EXAMPLE OF THE SIBERIAN PLATFORM) 63

8.1. Channel placers. 70

8.2. Terrace placers. 79

8.3. Deluvial-proluvial placers. 83

8.4. Buried placers of Angarida. 86

8.5. Riphean sources of diamonds in the south of Angarida. 87

8.6. Coastal-sea placers of Angarida. 89

9. PRELIMINARY WORKS FOR DIAMONDS IN THE SOUTH-EASTERN PART OF THE SIBERIAN PLATFORM... 93

9.1. Conditions for the accumulation of diamond deposits in the Angara region. 93

9.2. Composition of diamondiferous deposits of the Tusham paleobasin. 94

10. THE STORY OF ONE DISCOVERY. 108

CONCLUSION.. 110

Reference. 111

 

 

 

 

 

 

 

 

 

 

 

 

 

 

BY EDITOR     

 

The relevance of this work, despite its seeming archaism is quite high, oddly enough. Prospecting for diamonds is in many ways specific, and, first of all, due to the peculiarities of the object itself, which is a unique mineral from many sides. Diamond with a higher specific gravity like its invariable companions, better known as indicator minerals of kimberlite (magnesian garnet pyrope, picroilmenite, olivine, chrome diopside and chrome spinels), is much lighter than traditional, from the point of view of prospectors, useful components, such as, first of all, gold. And if, we use the traditional method during diamond prospecting operations, which has proven itself for hundreds of years in the search for gold, when the sampled material that entered the schlich sample, after "elutriation", "cut-off" and sieving by fractions, is blown in a tray to black concentrate, then diamonds, as well as the indicator minerals of kimberlite,  there can be definitely no more in the concentrate. This is the main specificity, the main problem and the main mistake of novice diamond prospectors. "Gray concentrate" is the only opportunity to identify diamonds or kimberlite indicator minerals in sedimentary deposits in new territories, regardless of their genesis.

Therefore, the author devotes rightly a lot of time to the sampling method and the peculiarities of sample washing, in particular, the problem of choosing a sampling point, which, as a rule, a geologist should outline directly in the field. Surely, this should be the most informative part of the river-bed sediments, as a rule, the so-called "spit head", where the maximum amount of the heavy fraction, including diamond and indicator minerals, will be concentrated. At the same time, the author paying apparently tribute to history, gives numerous, and sometimes overly detailed examples of sampling from various sediments, referring mainly to the experience of work in the 40s - 60s of the last century.

It should be given credit that the author notes that it is also in many respects specific characterizing the material entering the sample. It will not necessarily be a classic coarse-grained, well-sorted and washed oblique material. Quite the opposite, often the deepest near-bedrock, clayey part of the section should be taken into the sample, where the maximum amount of minerals of the heavy fraction can be concentrated, which is rightly emphasized by the author.

The proposed monograph is devoted to the features and specifics of sampling of sedimentary deposits during diamond prospecting. However, in fairness, the author manages to tell about the history of the development of the Siberian platform, starting from the Paleozoic, the time of the formation of productive kimberlites, as well as about the history of prospecting for diamonds in Siberia. The Institute of the Earth's Crust, in the depths of which this monograph has matured, glorious history of prospecting for diamond deposits on the Siberian platform, dated back over 70 years. Thanks to generations of Irkutsk scientists and geologists, the methodology has improved in relation to various geological settings, before spilling into this thorough work, claiming to be fundamental. Much of the author's ideas in the monograph has been translated into reality, the necessary corrections were made in a timely manner, in the course of work with the editor.

The confidence of the author of the monograph that new discoveries of diamond deposits on the Siberian platform are still ahead is conveyed to the readers. And it is no coincidence that, completing the work, the author dwells in a very original way on the history of one of the last vivid and real discoveries of diamond deposits. He focuses on the final stage of the diamond rush in Canada, to which our compatriot, a geologist of the Soviet school, who had gone through more than a dozen field seasons in Yakutia and received a wealth of experience in prospecting for diamond deposits.

It is very noteworthy and symbolic when a convinced geologist, proving his innocence, persistently goes to the intended goal and, as a result, finds a deposit contrary to the opinion of the authorities and the confidence of the majority, in defiance of the leadership. This is a worthy and instructive example in many ways, when the result of many years of creative work, multiplied by experience, finds its embodiment in such a bright discovery. The example given by the author will allow young subsoil explorers to believe in their strengths and capabilities, to be inspired by the confidence that new discoveries are ahead. It is hoped that this monograph will contribute to this.

This monograph, according to the editor, deserves to be published and accessible to every novice young geologist who has devoted himself to prospecting for diamonds.

 

 

 

Director of RGE AK ALROSA (PJSC),

Discoverer of the "Mayskoye" diamond deposit,

Honored Geologist of the Republic of Sakha (Yakutia),

Honored Geologist of the Russian Federation,

Doctor of Geological and Mineralogical Sciences                                                          A. V. Tolstov

07.09.2021

Novosibirsk c.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

INTRODUCTION

Many researchers, embarking on prospecting for diamonds, are not familiar with this area of ​​the geological service, and therefore face a number of difficulties. In addition, every year young specialists who have no experience in sampling diamond-bearing formations come to diamond prospecting expeditions. The main purpose of this book is to provide practical assistance to prospecting geologists involved in the search for primary sources of diamonds.

The application of the methodological techniques given in this work will allow obtaining extensive geological prospecting information, the completeness and quality of which is sufficient for making decisions on further search for diamonds.

The relevance of prospecting for diamonds is well known. At all times, there have been enthusiasts and romantics who go in search of natural resources. One of them are geologists specilizing in diamonds. The knowledge and skills set forth in the book will assist them in conducting prospecting work.

The methodological basis for writing this book was the author's personal experience gained during diamond exploration in the middle reaches of the Viluy river, on the Nizhnyaya Tunguska river  (Preobrazhenka-Krasnoyarovo region), on the Tanguy-Udinsky and Ilimo-Katangsky confluences, as well as scientific works and publications of famous domestic and foreign geologists. The purpose of writing this work is the author's aspiration to give the reader a broader understanding of geological methods and techniques for conducting diamond prospecting.

Prospecting research is always associated with sampling promising (potentially diamondiferous) deposits and obtaining concentrates. A detailed study of which was previously carried out only in stationary laboratories, and is now being carried out in the field.

The sampling schemes presented in the work were drawn up taking into account the minimum financial costs for extracting diamonds and their satellite dikes from concentrates. The choice of a particular sampling scheme depends entirely on the type of diamond-bearing deposits and their mineralogical composition. So, when processing samples represented by loose sandy-clayey and boulder-pebble formations, the enrichment scheme is relatively simple. When sampling cemented diamondiferous rocks, represented by sandstones, gravelites or conglomerates, crushing aggregates and automatic screens with specially trained personnel appear in the enrichment scheme.

It is important to note that prospecting for diamonds is in many respects identical to prospecting for gold, platinum, silver, copper and other types of mineral raw materials. All of them are objects of various studies, but they are united by one natural property, a large specific gravity. Therefore, in the process of sizing, they end up in a concentrate (heavy fraction). In our case, the target for prospecting work is diamonds. Diamonds and diamond satellite minerals (MSA) define and direct the further procedure for prospecting sampling of sediments in order to obtain a concentrate for a more detailed laboratory study, the results of which will form the basis for further search for their primary deposit.

Information on conducting prospecting testing, set forth in various monographs and methodological recommendations, starting from V. M. Kreiter (1940) and ending with the manual on geological survey at a scale of 1:50000 (Methodical manual ..., 1978), as well as various sampling manuals (Prokopchuk, 1979; Methods of selection ..., 1984), do not give a complete picture of this process.

At the end of the last century, various requirements and instructions for conducting geological survey work for diamonds were published, which did not significantly clarify this issue (Instructions for compiling ..., 1995; Cameral processing ..., 1999; Field research ..., 2000, etc. .).

In the new century, the issues of prospecting for diamonds have already been raised more than once in various publications (Beskrovanov, Shamshina, 2000; Minorin, 2001; Afanasyev et al., 2002; Vaganov et al., 2002; Shatalov et al., 2002; Grakhanov, Koptil , 2003; Geology, forecasting ..., 2004; Akulov, Vladimirov, 2005; Afanasiev, Zinchuk, 2005; Kudryavtsev et al., 2005; Grakhanov, 2006; Placers of diamonds ..., 2007; Tolstov et al., 2007; Ustinov, 2008, 2009a, b; Grakhanov, Serov, 2009; Akulov, 2010b; Akishev et al., 2018; Posukhova, Sokolova, 2018, etc.). Among the most recent publications, the most interesting is a short but very laconic methodological work devoted to field studies of Guinean diamond placers (Chirico, Malpeli, 2014). Nevertheless, no summarizing public work on the search and exploratory sampling of diamondiferous deposits has been written.

The main task facing the author was not to describe expensive methods for the comprehensive study of promising territories using aeromagnetic surveys, geochemical methods of research and drilling, but based on modern knowledge and means of small-scale mechanization, promptly search for primary sources of diamonds in a small detachment.

This work is a revised and supplemented edition of the methodological manual “Sampling of potentially diamondiferous deposits and prospecting for diamonds placers” (Akulov, 1992), which was approved by such remarkable geologists, discoverers of diamond deposits, such as V. N. Shchukin (pipes Udachnaya, Sytykanskaya and Aikhal), B. M. Vladimirov (diamondiferous dikes of the Sayan region and kimberlite fields of West Africa), G.Kh. Feinstein (Yakutian diamondiferous province). The wishes and comments expressed by them were taken into account in this edition.

It should be noted that the first edition was very popular among geology students. According to the “teacher of teachers” S. N. Kovalenko, who turned to me with a request to republish it, is a handbook for students when writing term papers on placers.

The author is deeply grateful to B. M. Vladimirov, S. F. Pavlov, V. N. Shchukin, A. E. Bessolitsyn, K. N. Yegorov, S. A. Kashik, I. G. Korobkov, A. I. Melnikov and V. S. Imayev, who showed great interest in this work and made a number of valuable suggestions and comments that contributed to its improvement.

Special thanks to the reviewers: Doctor of Geological and Mineralogical Sciences, Professor V.A. Skvortsov and doctor of geological and mineralogical sciences, diamond geologist (kimberlitch) S.I. Kostrovitsky, as well as a specialist of the highest category in the field of sampling and enrichment of gold and diamonds, candidate of geological and mineralogical sciences S.A. Prokopyev, undertaking the work of reviewing the monograph and noting its great importance and relevance.

 

 

1. THE PHILOSOPHY OF SEARCH AND THE BASIS OF GEOLOGICAL JURISPRUDENCE

 

After the collapse of the USSR and the liquidation of the Ministry of Geology, a crisis hit in Russian geology. The Marxist-Leninist direction of development of the national economy has ceased to play a leading role in the country's economy.  While in the "battles for history" Russian philosophers-skeptics are fighting Anglo-American hyperglobalists (colonialists), we are trying to understand at what social stage of development is domestic geology.

At present, the philosophy of conducting geological surveys in Russia is clearly divided into two stages - Soviet and neo-capitalist (modern). If in Soviet times prospecting work in geological surveys parties was accompanied by transparencies and slogans calling for geologists to discover new mineral deposits for the national economy, then after the collapse of the USSR, domestic neo-capitalists began a rapid division among themselves of all explored mineral resources of the country's resources. They were dividing them into distributed and unallocated subsoil use funds (RF Law ..., 2008).

In Soviet times, geological prospecting works were poorly supported by a material base, but they had tremendous fortitude and an indestructible search enthusiasm. Soviet geologists worked wonders, sparing neither time nor health. Deposits were discovered for the future. The liquidation of the USSR Ministry of Geology and the distribution of permits for the right to use subsoil to individuals and legal entities led to the emergence of a new type of people - subsoil users. It turned out that a subsoil user is a subject of entrepreneurial activity, regardless of the form of ownership, including a legal entity or a citizen (colonialist) of another state. It is empowered to engage in the corresponding type of activity in the use of subsoil by the legislation of the Russian Federation and the legislation of the constituent entities of the Russian Federation (Order ..., 1998).

The unallocated fund consists of unused subsoil plots where it is possible to carry out geological survey for the development of subsoil use objects, but permits are not issued to anyone. Thus, the main part of the economically efficient operating and already explored by the state deposits of various minerals, including diamonds, found new owners i.e. subsoil users, represented mainly by colonists (shareholders of various countries and metropolises, the main goal of which is aimed at personal enrichment through export port of natural resources of Russia). There were new requirements and procedures for considering applications for obtaining the right to use subsoil for the purpose of geological study of subsoil areas, for the purpose of collecting mineralogical, paleontological and geological collection materials (Order ..., 2004a; 2004b; 2005), which were subsequently clarified by the Ministry of Natural Resources and Ecology of the Russian Federation (About introduction ..., 2017).

 

1.1. Specifics of acquiring the right to use subsoil

In accordance with Art. 11 of the Law of the Russian Federation No. 2395-1 of 21.02.1992 "On Subsoil", the provision of subsoil for use, including their provision for use by the state authorities of the constituent entities of the Russian Federation, is issued with a special state permit in the form of a license for geological survey as well as exploration and mining.

A license can be obtained on the basis of the application principle without holding a tender or an auction on the fact of “pioneering” subject to the following restrictions (order of the Ministry of Natural Resources of Russia No. 583 dated November 10, 2016):

  1. There is already data on the presence of reserves of solid minerals or probable resources of solid minerals of category P1 or P2 for the declared area. In case of discovery of oil or gas, if there is already data on the probable resources of hydrocarbon raw materials of category Dо or Dl;

No more than 3 subsoil plots can be obtained per applicant for the purposes of geological exploration, the size of each of which is no more than 100 km (this rule does not apply to "Rosgeologia" JSC  - clause 1.8 of the Order of the Ministry of Natural Resources of Russia No. 583 dated November 10, 2016).

When establishing the fact of the discovery of a mineral deposit on a subsoil plot of federal significance (hereinafter referred to as SPFS) or on a subsoil plot that is classified as a subsoil plot of federal significance as a result of the discovery of a mineral deposit, the right to use such a subsoil plot is granted only on the basis of decisions of the Government of the Russian Federation. The subsoil plots of federal significance includes areas with recoverable oil reserves of more than 70 million tons, with primary (ore) gold reserves of more than 50 tons, etc.

It is necessary to pay a one-time payment when a subsoil user opens a deposit and for obtaining the right to use subsoil under a combined license for the mining and prospecting of a mineral in accordance with Art. 39 of the Subsoil Law. In the environment of subsoil users, such a one-time payment is called a “fine for the discovery of a deposit”. The procedure for determining the size of a one-time payment for the use of subsoil is established by the Rules approved by the Government of the Russian Federation dated February 4, 2009 No. 94. The size of a one-time payment is equal to 10% of the estimated amount of mineral extraction tax (MET) received from the planned average annual howling capacity of the mining organization.

The total period for issuing licenses should not exceed 65 days (clause 15 of the Regulation on the issuance and renewal of licenses). The flow chart is reduced to the following steps:

 

  1. publication of the order of Rosnedra or its territorial body on the registration of a license for the use of subsoil;
  2. registration and signing of 2 copies of licenses from the head or authorized deputy head of Rosnedra, or its territorial body;
  3. direction for registration of a license for the use of subsoil;
  4. registration of a license for the use of subsoil;
  5. issuance of a license to the applicant.

According to the information published by the editors in the "Zoloto i Tekhnologii" magazine No. 4, 2018, the average estimate of a turnkey diamond pipe search abroad is about $ 7 million, and a large liquation-type nickel, nonferrous or precious metal deposit is $ 500 mln. The search for a diamond pipe within the Yakutsk diamond-bearing province previously cost about 2 billion rubles. (about $ 30 million).

The license is issued for five years, and the procedure for further actions is carried out according to the scheme:

  1. obtaining a license;
  2. writing a project for search and evaluation;
  3. obtaining a positive expert opinion on the project;
  4. obtaining permission to conduct geological survey without the right to cut forest plantations.

It should be emphasized that 25 years have passed since the start of market reforms in the Geological Survey of Russia. In almost all developed countries, when putting into circulation new deposits, the leading role belongs to junior companies. Junior companies do not have direct government participation, and in exceptional cases they are very limited. Usually, an investor or oligarch enters into an agreement with a junior company to transfer all rights to conduct exploration work in a selected promising area in order to obtain assets in the form of protected reserves of raw materials and the right to develop them. Within two years, the junior company is allowed to sell the field discovered by it, and if it does not work out, then it can turn to the state, which will auction off the field. A junior company can obtain itself a license for exploration and mining of minerals in the deposut it discovered.

It is interesting to note that in Canada in the period from 2004 to 2014, junior companies accounted for 75% of all discovered fields with annual investments of about $ 1.7 billion. In Australia, the share of juniors does not exceed $ 22.4 million, while during the same period the number of discovered fields increased from 55 to 66%.

In conclusion, it should be said that the philosophy of diamond prospecting has a special theoretical status. The initial stage of the search involves the selection of a promising research area, which, first of all, must meet the following three rules:

  1. rule of Clifford (Clifford, 1966): “… diamondiferous kimberlites are always coincide with cratons of the Archean consolidation”;
  2. rule of group intrusion from one ultrabasic source: “... there are no single-located kimberlite pipes, finding a new pipe is a sure sign of the presence of a new kimberlite field”;
  3. rule of placing kimberlite bodies on positive geological structures: “… diamondiferous kimberlite bodies are always located on positive structures of platforms (anteclises, shields and uplifts)”.

 

 

2. DIAMONDS OF RUSSIA

On the territory of the Russian Federation (East Siberian diamondiferous province) in the process of schlich-mineralogical research the the VSEGEI staff L. A. Popugayeva and N. N. Sarsadskikh  discovered the first kimberlite pipe “Zarnitsa” in 1954. Several decades have passed and in 2017 in St. Petersburg (FSBI VSEGEI) the first working meeting of companies-subsoil users of the diamond mining industry was held (Fig. 1) “Scientific, methodological and technological problems of forecasting and searching for low-contrast kimberlite pipes in East European and East Siberian  diamond-bearing provinces”. The Program Conclusion noted:

 

 

Недропользователи

 

Fig. 1. Subsoil users of the Russian Federation. Session of the workshop on June 8, 2017 in St. Petersburg (Photo by FSBI VSEGEI).

 

  1. In terms of diamond reserves, the Russian Federation ranks first in the world. The reserves of 80 deposits amount to 1.2 billion carats, including one billion carats of proven reserves are concentrated in three constituent entities of Russia: the Republic of Sakha (Yakutia), the Perm Krai and the Arkhangelsk Oblast.
  2. 218 new kimberlite bodies have been identified in the Yakutsk diamondiferous province in the period 1997-2016. In 2006, the Mayskoye primary diamond deposit (with resources of about 20 million carats) was discovered on Nakyn; million carats). In addition, in 2010 the reserves of the buried Nyurbinskaya placer (over 20 million carats) were added to the balance sheet. In 2015, the first kimberlite body of the new Syuldyukar kimberlite field was discovered. Exploration of deep horizons of the Udachnaya, Yubileinaya and Mir pipes resulted in an increase in reserves in the tens of millions of carats (Maltsev et al., 2016; Maltsev and Tolstov, 2018). Prospecting work in the Arkhangelsk Oblast also did not lead to the discovery of new large deposits, and the fund of high-amplitude local magnetic anomalies promising for the identification of kimberlite pipes (prospecting reserve) had exhausted itself by the beginning of this century.
  3. It is necessary to develop new innovative technologies to search for low-contrast diamondiferous kimberlite bodies hidden at depth and to intensify forecasting and prospecting work in promising areas of the Republic of Sakha (Yakutia), Krasnoyarsk Krai, Murmansk, Arkhangelsk Oblast and Irkutsk Oblast, the Urals and Karelia.
  4. Scientific institutions should be involved in the development of “Methodological guidelines for prospecting for diamond deposits on the Siberian platform”, as well as models for the formation of dispersion halos of minerals-indicators of diamond content in various depositional environments.

According to the Ministry of Natural Resources and Ecology, set forth in the State Report on the State and Use of Mineral Resources of the Russian Federation in 2016-2017, the quality of kimberlite in domestic developed deposits is high. The average diamond content exceeds 1 ct/t, with five large and giant pipes in terms of the amount of reserves are characterized by a unique diamond content i.e. more than 3 ct/t (On the state..., 2018). The quality of the diamonds themselves is generally rated as average. According to the Russian Ministry of Finance, the average price of diamonds mined in 2016 was 88.75 doll./ct, while Russia's main competitor, Botswana, reached 138.8 doll./ct.

If we compare the Russian diamonds mined from kimberlites with diamonds from other countries, then, for example, the entire volume of production of Australia, which ranks fourth in the world, is provided by the giant highly diamondiferous pipe of Argyle olivine lamproites (Lamproity ..., 1991). The quality of the diamonds from the deposit is generally low. In 2016, their average price was only  15.5 doll./ct. The kimberlite deposits of diamonds in Canada, which is the last of the five leading producers, are significantly inferior to domestic ones in terms of reserves. The quality of the ores of the Canadian objects is different, the average diamond grade varies from 0.1 to 3 ct/t.

The main industrial deposits of the Russian Federation are concentrated in three diamond-bearing regions: the Republic of Sakha (82.4% of reserves and 99.7% of production), the Perm Oblast (0.1% of reserves and 0.3% of production) and the Arkhangelsk region (17.5% of reserves) (On the state ..., 2018). Kimberlite deposits form the backbone of the Russian raw material base of diamonds, as they contain 93% of precious raw materials. The remaining 7% of diamond reserves are concentrated in placers. The main deposits of the country are located in the bowels of the Sakha Republic: the kimberlite pipes Udachnaya, Mir, Yubileinaya, Botuobinskaya, Aikhal, Nyurbinskaya, Internatsionalnaya and Zarnitsa, as well as the Nyurbinskaya and Ebelyakh placers, which are gigantic in terms of the amount of reserves. Many of them are unique in terms of diamond concentration. Thus, the kimberlites of the Internatsionalnaya pipe contain about 9.2 ct/t, Botuobinskaya - 6.2 ct/t, Aikhal - 5.8 ct/t, Nyurbinskaya - 4.6 ct/t, and the sands of the placer of the same name - 4.9 ct/m3. m.

At the expense of the federal budget in 2015–2017, the company "Rosgeologia" JSC carried out advanced geological and geophysical work for primary diamonds within the Ilimo-Katangsky diamondiferous region (Irkutsk Oblast), in which the author of this book also took part. Based on the results, the forecast reserves of the P3 category were calculated in the amount of 45 million carats.

The main buyers of Russian diamonds are Belgium, India, Israel and China (Hong Kong). In Russia, the main production of polished diamonds is carried out at the state polishing plant "Kristall-Smolensk", at the joint Russian-Israeli enterprise "Ruiz Diamonds" CJSC, at the company "EPL Diamond", as well as at the enterprise "Diamonds ALROSA".

It should be noted that in the opinion of the remarkable geologist E.N. Ehrlich (Ehrlich, 2016), who predetermined the discovery of the richest rare metal and rare earth deposit Tomtor, the epochal history of the discovery of diamond deposits in the USSR ended in the post-perestroika period with the shameful deal of the Russian government with the De Beers company, which took control of the entire the market for diamonds mined in Russia.

According to RosBusinessConsulting (http://ecsocman.hse.ru/data /383/537/1217/Almazodobyvayushchaya_promyshlennot.pdf) the largest diamond deposits in Russia are the Udachnaya pipe, containing 22.9% of Russian reserves, and Jubilee (20.3%). The Nyurbinskaya and Botuobinskaya pipes, which are being prepared for development, contain about 10.6% of the reserves, in the deep horizons of the Mir and Internatsionalnaya pipes - 9.9% and 5.4%, respectively, in the Zarnitsa pipe - 3.9%.

The content and quality of diamonds are highest in the pipes "Internatsionalnaya", "Muno-Olenekskaya", "Vodorazdelnaya" and "Mir", then (in descending order of these indicators) there are pipes of the Nakyn field, "Udachnaya" (with the highest level of diamond production today) and Yubileinaya There are low grades and quality of diamonds are compensated by their significant reserves.

The second largest diamondiferous region in Russia is the Arkhangelsk region, where two deposits named after M.V. Lomonosov and named after Grib are located which account for 16.8 and 4.4% of the country's reserves, respectively. The content of diamonds in them is lower than in the deposits of the Republic of Sakha (Yakutia), and the quality of diamonds corresponds to the average quality of the Yakut or slightly lower.

The cost of diamonds depends on many factors, the main ones being: size, shape, color and transparency, absence of inclusions, cracks, origin. The range of prices for diamonds is very large: from $ 6,000 per carat to $ 0.8 per carat. The evaluation of diamonds and polished diamonds is carried out by experts, that is, it is subjective. As a result, the error in setting prices can reach up to 15%. More than 50% of physical supplies to the world market are the lowest-grade small diamonds with an average price of about  1 $/ct. Approximately 35% are low-grade diamonds (the so-called "Indian commodity") at an average price of $ 50 per carat. Diamonds of medium and high quality (average price $ 350 per carat) are relatively small - 15%. Weighted average cost of diamonds S ~ $ 70.

The cost of diamonds is quite high: an ordinary diamond of average quality with a mass of 1 carat (1 carat is equal to 0.2 gram) costs 3-4 thousand dollars, that is, 15-20 thousand dollars per gram. It should be recalled that the cost of gold on the International market as of 06/08/2021 is 62 dollars per gram or 4526 rubles.

 

 

3. GENETIC TYPES OF DIAMOND-BEARING ROCKS

 

At present, six types of bedrock containing diamonds are known in the Earth: 1) kimberlites; 2) lamproites; 3) metamorphites; 4) tuffisites; 5) impactites and 6) basaltoids.

3.1. Basaltoids

Data on the diamond content of basaltoids appeared in the last century (Kutuyev and Kutuyeva, 1975). Using modern methods of studying rocks V. I. Silaev and colleagues (Silayev et al., 2015) carried out a detailed study of Kamchatka basaltoids and also found diamonds, but already in the products of the latest fissure Tolbachik (Kamchatka) eruption in 2012. Diamonds are well-formed micron crystals up to 700 μm in size with approximately equal faces of the octahedron and cube (Fig. 2). In the depressions and pits on the crystal faces, precipitations of Mg-Fe and Fe silicates, Ca-Mg silicates, aluminosilicates, sulfates, iron oxides, native metals and alloys of the composition Fe, Ni-Cu, Cu-Sn-Fe are observed. In their opinion, the originality of crystal morphological, spectroscopic, mineralogical-geochemical and isotope-geochemical properties gives grounds to classify the Tolbachik diamonds as a previously unknown fluid-volcanogenic-eruptive genetic type.

 

µm

µm

µm

рис

 

 

Fig. 2. Photographs of diamond lava crystals of the Tolbachik fissure eruption, obtained using a scanning electron microscope (after EI Gordeev et al., 2014).

 

At the “Volcanism and Related Processes” conference held in Petro-Pavlovsk-Kamchatsky in 2015, L. A. Anikin and colleagues presented data on a new find of diamonds in Kamchatka near the Plosky Tolbachik volcano (upper reaches of the Tolud River) in the products of lava flows erupted in 2013 (Anikin et al., 2015). It was found that diamond-bearing basalts do not contain xenoliths of deep rocks and high-pressure minerals. Heavy diamond concentrates (HDC) in them are corundum, silicon carbide - moissanite, native metals and organic compounds. The synthesis of diamonds and its satellite dikes took place at relatively low temperatures and pressures under reducing conditions from carbon-containing gases (Gordeyev et al., 2014).

popigai-crater_1

 

Fig. 3. General view of the Popigai astrobleme (impact crater) from one of the sides of the Popigay river (photo by Vitaly Gorshkov vitaly-gorshkov.livejournal.com).

 

3.2. Impactites

One of the most famous places in the Earth is the Popigay meteorite crater (astroblema). Its inner diameter is about 90 km, and its depth reaches 200 m (Fig. 3). It was formed 35.7 million years ago, and in 1971, impact diamonds were found in the crater rocks (Masaitis et al., 1975). Large-scale prospecting and exploration work was launched, carried out by the Polar Expedition of the Krasnoyarsk Territorial Geological Administration. Geologists have drilled and documented about 450 wells up to 1500 m deep. A large number of large-volume samples were taken. This made it possible to obtain concentrates with a large amount of impact diamonds, which were not of jewelry value and were sent for technological tests (Fig. 4). According to the results of the tests carried out in the expert opinion of the V. N. Bakul Institute for Superhard materials states that: “... the abrasive ability of the samples provided is on average two times higher than that of synthetic and natural diamonds of similar grain size” (Masaitis et al., 1998).

Russian researchers also point out that the use of impact diamonds in the tool industry is promising and highly profitable (Afanasiev, Pokhilenko, 2013; Kryukov et al., 2016; Nikolaev et al., 2017).

According to N. P. Pokhilenko and his colleagues (Pokhilenko et al., 2012), the explored reserves of the Udarnoye and Skalnoe deposits, which occupy about 3% of the astrobleme (impact crater) area, amount to 147 billion carats. Thus, the total resources of impact diamonds contained in the bedrock of the Popigai impact deposits are more than an order of magnitude higher than the total reserves of all diamondiferous provinces known in the Earth (Fig. 5).

 

Рис

 

Fig. 4. Impact diamonds from the Popigai astrobleme (photo by V. P. Afanasyev, IGM SB RAS).

3.3. Tuffisites

          The Vishera group of tuffisite diamond deposits is located in the  Vishera river basin (a tributary of the Kama River, Perm Krai). The term “tuffisite” denotes a volcanic rock like tuff or tuff breccia, which arose in connection with the metasomatic processing of sedimentary rocks by volcanic fluids. It is a product of highly fluidized magmatogenic systems capable of forming not only stockwork and dyke-like bodies, but also stratal sill-like formations, layer-by-layer injection into the enclosing sedimentary rocks. Thus, tuffisites of the Krasnovisherskiy complex compose thin stratal bodies, sometimes veins and small stockworks in sedimentary carbonate-terrigenous strata (quartz sandstones, dolomites) of Vendian-Permian age.

 

Рис

 

Fig. 5. One of the slopes of the “Variegated Rocks” in the Popigai astroblem, composed of chaotically mixed blocks, cemented by loose fine-grained rock with pieces and bombs of glass:

a - breccia, b - tagamite (based on photographs by Vitaly Gorshkov vitaly-gorshkov.livejournal.com).

As a result of the state geological survey carried out on this territory, the confinement of tuffisites to all Ural diamond-bearing placers was established. Their occurrence among from Riphean to Lower Permian rocks indicates post-Early Permian intrusion, which is consistent with the wide distribution of redeposited pyroclastic material in the Triassic-Jurassic deposits of the Upper Kama depression. The difficulty in identifying these rocks is that they are almost completely replaced by clay minerals and are, in fact, mudstone. Their primary nature is established quite definitely i.e. according to intersecting contacts with the host sedimentary rocks, according to a set of specific relict minerals (diamond, pyrope, ilmenite, chromite, sodium richterite, phlogopite, etc.), according to such textures, structural features such as breccia, fluidity and saturation with xenogenic material (Anfilogov et al., 2000). All these features of tuffisites allowed A.Ya. Rybalchenko and his colleagues attribute them to the injection type of rocks (Rybalchenko et al., 1996).

According to information obtained by N. S. Ivanova (2011), in the bedrock-adjacent parts of almost all diamond deposits of the Krasnovishersk region, there are unusual rocks of clay and sandy-clay composition, previously attributed to secondary diamond reservoirs. Traces of pelitized ash material were found in the composition of these problematic diamondiferous rocks, which allowed her to consider these rocks as volcanogenic-sedimentary and compare them with the “sandy” tuffs of lamproites in Australia. Thus, the bodies containing diamonds and previously called the secondary reservoir are not redeposited material, but the primary source of diamonds - tuffisites.

According to A.Ya. Rybalchenko (Rybalchenko et al., 1997), tuffisites contain minerals of clearly deep origin - chromium knorringite-bearing garnets, chrome spinels, picroilmenites, olivine, phlogopite, and others. Later, lamproites were found in the Southern Urals (Chelyabinsk Region, Kuibasovsky District) (Lukyanova et al., 1992; Bogatykh et al., 2000; Busharina, 2002).

It should be noted that the idea of ​​the tuffisite type of diamondiferous rocks was objected to by some researchers (Bogatykh et al., 2000; Malakhov, Busharina, 2000; Anfilogov, 2001, etc.). Later A.Ya. Rybalchenko and colleagues conducted additional studies in the Ural-Timan diamondiferous province and found that many geological, petrographic, and mineralogical-geochemical features of diamondiferous rocks of the Ural type deposits indicate their primacy and belonging to the tuffisite facies of mantle kimberlite-lamproites (Rybalchenko et al. others, 2011).

 

f

e

d

c

b

a

Рис

 

 

Fig. 6. Morphological types of Ural diamonds:

 

 a - a fragment of an individual of the rhombododecahedroid habit (Talitsa-Blagodat, No. 9), b - a single-crystal of a rhombododecahedroid habit (Talitsa-Blagodat, No. 41), c - a fragment of an individual of the combined "EO" habit (Rassolninsky, No. 17), d - a single crystal rhombododecahedroid habit (Rassolninsky, no. 340), e - a fragment of the twin of individuals of the rhombododecahedroid habit (Rassolninsky, no. 64), f - single crystal Janus of the combined “OTSE” habit (Rassolninsky, no. 292) (after Silaev et al., 2010 p. changes).

 

Ural diamonds are relatively small (no more than 2 cm, and the maximum weight of a diamond found in 2004 is 35 carats), but they are distinguished by their chemical purity and high quality. They are mostly colorless or pale in color (bluish, golden-yellow, honey-yellow, amethyst-red) and are ten times more expensive than the Yakutian ones - about $ 700 per carat (Fig. 6).

The company "Uralalmaz" CJSC based on the results of exploration work carried out on the right bank of the Sukhaya Volinka river, calculated the reserves of diamonds of categories C1 + C2 in the amount of 13.8 thousand carats, while the placer of Sukhaya Volinka river, was accepted to the State Balance of Reserves and is listed in the unallocated subsoil fund (On the state ..., 2018).

3.4. Metamorphites

In the period from 1968 to 1973, geologist of the Kokchetav         geological survey expedition (Republic of Kazakhstan) A. A. Zayachkovsky discovered the Kumdykol diamond deposit (Kokchetav massif). Subsequently, it was attributed to a new genetic type of diamond deposits - metamorphogenic (Ekimova et al., 1992; Lavrova et al., 1999). Diamonds were found in sedimentary metamorphic complexes.

Earlier, it was assumed that diamonds were formed within the Earth's crust as a result of local tectonic overpressures in the massifs of eclogite and apoeclogite rocks (Rosen et al., 1972). As a result of the exploration and industrial assessment of the Kumdykol deposit carried out by geologists of the Kokchetav GSE in 1983-1986, it was established that the main reserves of diamond are concentrated in gneisses (85.5%), much less in carbonate rocks (5.6%), chlorite-tremalite-quartz rocks (4.2%), garnet pyroxenites (3.4%) and only 1.3% in eclogites. The explored deposit contains huge reserves of diamonds, but they are all very small (technical) and necessary only for the production of abrasive products. Nevertheless, the Kumdykul deposit attracts the attention of scientists all over the world (Claoue-Long et al., 1991; Sobolev et al., 1990).

According to L. D. Lavrovoy (Lavrova et al., 1999) the age of regional metamorphism at the Kumdykol deposit, during which diamond-bearing gneisses, pyroxenites, eclogites and other rocks were formed, is Proterozoic, and the age of diamond formation is Cambrian (about 530 Ma). Diamond-bearing rocks are linearly distributed along the main tectonic zone and are confined to the most reworked rock blocks. Blocks of rocks within the ore zone, little affected by metasomatic processing, do not contain diamonds or are poorly diamondiferous. This indicates the formation of diamonds in situ and does not agree well with the paradigm of their crystallization in the subduction zone.

Diamonds from metamorphogenic rocks differ significantly from diamonds from deposits of other genetic types. They are small (on average 30 microns), imperfect in shape (lamellar, skeletal, spheroidal) and contain a large number of impurities.

Apparently, the diamond content of metamorphic rocks is determined by the “shock heating” of the microscopic accumulations of hydrocarbons present in them. The most probable cause of shock heating is contact metamorphism during intrusive massif intrusion, and with distance from the contact zone, pyrolysis of hydrocarbon inclusions occurs and graphite is formed.

It is quite possible that the metamorphic rocks on the Kokchetav massif were formed at high pressure, which arose as a result of the collision of two giant continental plates (suture zone).

3.5. Lamproites

Lamproites are ultrabasic igneous rocks rich in leucite and sanidine. The name lamproite was given from the Greek "lampros". It is brilliant because of the phlogopite phenocrysts characteristic of this group. The main minerals of lamproites are magnesian olivine (forsterite), phlogopite, diopside, leucite, sanidine, richterite, as well as specific minerals vadeite, priderite. They form small bodies in terms of volume: dikes and tubes, which are easily subject to destruction and weathering. Lamproite lavas and lamproite tuffs are described. There are 24 known areas in the Earth with finds of lamproites, while the total volume does not exceed 100 m3. Lamproites are found both on ancient platforms and in fold belts. They have a wide range of ages from 1.4 billion years to 56 thousand years. Lamproites contain a large number of pyrope-bearing xenoliths of deep rocks (eclogites, peridotites, etc.). The discovery  of diamondiferous lamproites in 1979 in Western Australia (the Argile pipe), thanks to which in the first year of operation (1986), about 29 million carats of diamonds were mined. It amounted to more than 40% of the total world production, significantly expanded search area for both primary and alluvial diamond deposits (Temporary methodical ..., 1988). Nevertheless, the bulk of them (about 95%) are industrial diamonds (Fig. 7). Diamond-bearing lamproites in Western Australia are represented by two petrochemical rock types - olivine and leucite. This is a typical association of diaschist (split) rocks, in which melanocratic olivine lamproite can be attributed to lamprophyres (these are fine-grained rocks rich in dark-colored minerals, included in the vein formation together with leucocratic vein aplites and pegmatites), and lamproitic feldspathoid aplite.

The average weight of Argal diamonds is 16 mg, and the weight of the largest diamond found in 1990 is 14.34 carats. The Argyle pipe is surrounded by diamondiferous placers, as its erosional section is estimated at 400 m (Shigley et al., 2001).

Most likely, the formation of lamproite magmas is associated with the partial melting of the lithospheric mantle at depths of more than 150 km (Lamproity ..., 1991; Jakes, 1989; Petrographic ..., 2009). Apparently, the layering of lamproite magma occurred after it acquired a diamond-bearing specificity in deep chambers, which grew due to pyrope peridotites and partly inherited their high-pressure mineralization. In this regard, both types of lamproites are diamondiferous, but in the melanocratic the diamond content is more stable. Apparently, during stratification, melanocratic melts were located in the lower parts of magma chambers, where diamond crystals could submerge due to their high density.

Lamproites differ from kimberlites in high concentration of titanium, potassium, phosphorus and some other elements. They are characterized by low contents of calcium, aluminum, sodium and extremely high contents of trace elements (Kononova et al., 2011).

However, there are no significant differences between diamonds of these two types of magmatics. Despite the fact that the Argyle deposit has colossal reserves of diamonds and only about 5% of them can be used in the jewelry industry. The beauty of their colors from light yellowish (champagne) and greenish to pink and pinkish purple is striking (fig. 8). The fame of Argyle was because of pink crystals, recognized as the finest gemstones in the world, which became the brand of Argyle. In 1989, a 3.14-carat crystal was sold at a Christie's auction for $ 1.5 million. The Argyle company privately sells its diamonds at a price of up to $ 1 million per carat (Lamproites ..., 1991).

It should be noted that 35 lamproite dikes and 9 lamproite explosion tubes were found on the Taimyr Peninsula. Several diamonds were found. Perhaps, in the future, another diamondiferous province will be discovered here.

 

Fig. 7. Rough diamonds from lamproites from the Argyle pipe. A variety of crystalline forms are present, including a relatively small fraction of octahedra and a large number of rounded and shapeless formations. These crystals range in weight from about 0.5 to 1 carat, but most of them are less than 0.1 carat. Photo by James E. Shigley (Shigley et al., 2001).

3.6. Kimberlites

Back in the early 19th century, A. F. Williams wrote: “… there are reservoirs of molten magma at some hypothetical unknown depth, which, due to changes in temperature and pressure, slowly crystallize and turn into deep ultra-basic (peridotite, pyroxenite and eclogite) rocks and diamond crystals” (Williams, 1932).

In his opinion, crystallization and solidification of ultrabasic rocks, continued for a long time, during which the magma was thoroughly mixed until it acquired a kimberlite composition. Together with xenoliths of deep rocks, kimberlite magma carried diamond crystals to the Earth's surface. Almost a hundred years have passed, and the idea of ​​the origin of diamonds has hardly changed.

 

Алмаз аргайл

 

Fig. 8. Employees of the Rio Tinto company, which operates the Argyle diamond mine in Western Australia, found a rare pinkish-purple diamond (photo https://diamond-gallery.com.ua).

 

Kimberlite is a rock with predominantly breccia-like texture and porphyritic texture. It looks like a bluish-gray breccia, which consists of fragments (xenoliths) of sedimentary rocks of the platform cover (limestones, sandstones, dolomites, etc.), crystalline fragments of the platform basement (gneisses, crystalline shales, etc.) and fragments of deep-seated magmatic formations (eclogites, garnet peridotites, etc.).

The morphology of kimberlite pipes and their mineral composition are very diverse (Fig. 9). Usually kimberlites are represented by protomagmatic minerals (olivine, pyrope, chrome diopside, picroilmenite, phlogopite, diamond) and minerals of kimberlite melt (polycrystalline diamond - ballas or carbonado, olivine, phlogopite, perovskite, apatite, magnetite and diopside) and postmagmatic (serpentine, calcite, magnetite, chlorite, barite, sulfides). The distribution of diamonds in kimberlites is extremely uneven. Their average content in industrial pipes ranges from 0.17 to 8.09 carats per ton of rock, and it decreases with the depth of the pipe. Not all kimberlite pipes are diamondiferous and only 2-3% of them are of industrial value (Fig. 10).

S

N

N

S

Satellite dike-2

Satellite dike

Autolithic kimberlite breccia

Dike of subalkaline mafic rocks

Autolithic kimberlite breccia

xenoliths

porphyritic kimberlites

kimberlite breccia

Nyurbinskaya

Yubileynaya

Udachnaya

Mir

 

Fig. 9. Volumetric models of kimberlite pipes of the Yakutian diamond province:

 

Pipe Mir: 1 - dikes composed of porphyry kimberlite; 2 - kimberlite breccia of the first phase of intrusion; 3 - kimberlite breccia of the second phase of intrusion; 4 - porphyritic kimberlites of the third intrusion phase; 5 - autolithic kimberlite breccia of the fourth intrusion phase.

Pipe Udachnaya : 1 - porphyritic kimberlites of the first intrusion phase; 2 - kimberlite breccia of the second phase of intrusion; 3 - autolithic kimberlite breccia of the fourth intrusion phase; 4 - porphyritic kimberlites of the fourth intrusion phase; 5 - xenoliths of the sedimentary cover of the platform in kimberlite; 6 - zone of crushing of host rocks (according to Kostrovitsky et al., 2015 with changes).

 

When kimberlite magma penetrated the earth's crust, it broke through the basement and sedimentary cover of ancient platforms and consolidated in the form of tubular bodies (diatremes), less often in the form of veins or dikes. The dip of the tubes is usually very steep and there is often a crater (caldera) at the top of the tubes. The diameter of the tubes varies from 40 to 60 m. Near the earth's surface, at a depth of about 200 m, the diatremes are funnel-shaped, the angles of incidence of the walls of which are from gentle (about 25°) at the top of the bell to steep at the bottom. Weakly eroded tubular bodies are often crowned with a crater filled with tuffaceous sedimentary formations.

Sometimes tuffites and their varieties have industrial diamond content. The contacts of kimberlite pipes with the host sedimentary rocks are distinct, rarely gradual through the crushing zones. The more deeply, pipe-like bodies narrow, change shape, and blow out and turn into swelling dikes at a depth (usually 1000 m and more).

 

https://scfh.ru/files/medialibrary/e51/e51b9bef01145c7aeee3761b9593c18f.jpg

 

 

 

Fig. 10. Morphology of diamonds in the Yakutian diamond province (Photo by A. Pavlushin, IGAiBM SB of RAS, Yakutia).

 

   According to the shape of the horizontal section, kimberlite pipes are divided into simple (round, oval) single-channel, complex (pear-shaped, dumbbell-shaped) two-channel, and very complex (lenticular with swelling or irregular shape) multichannel.

 The internal structure of kimberlite pipes is complex, due to the multiphase nature of their formation. Each phase was accompanied by the introduction of a certain variety of rocks (kimberlite breccias, tuff breccias, massive kimberlites, etc.), which differ from each other not only in structural and textural features and material composition, but also in the content of diamonds in them. Usually, diamondiferous rocks of one variety contain a stable amount of diamonds, while their content is distributed extremely unevenly throughout the pipe. And in some places there are areas of kimberlite rocks with substandard diamond content. Kimberlite rocks contain up to 50% of xenoliths of host rocks ranging in size from fractions of a millimeter to chunks and blocks.

Kimberlite dikes and sills rarely form independent deposits and are found in South Africa and Canada (Snap Lake). Kimberlite dikes are steeply dipping bodies ranging from 1 to 5 km long and 1 to 180 m thick. The diamond content in dikes ranges from low to high, and the size of crystals is from medium to large.

The Pipe Mir is one of the most famous kimberlite formations of the Yakutian diamondiferous province. It is a steeply dipping funnel-shaped body (0-600 m), below it is cylindrical. At a depth of about 1000 m, the diatreme sharply narrows and turns into a subvertical kimberlite dike. The diatreme is filled with kimberlite formations formed during the three-phase intrusion of kimberlite magma. According to S. I. Kostrovitsky (Kostrovitsky et al., 2015), kimberlite breccias of the first phase formed the northwestern half of the pipe, and kimberlite breccias of the second phase occupied the southeastern part of the pipe (Fig. 11). The third phase includes dyke-like bodies of porphyric kimberlites. Despite this, the rocks of different phases of introduction differ little from each other. They have the same physical and mechanical properties and the diamond content established during operation with a content of 8.09 carats per ton.

According to the most widespread point of view, kimberlite diamonds crystallized in a static environment at a depth of about 150-250 km at a temperature of about 1200 °C and a pressure of at least 45 GPa. Their parent rocks were hyperbasites (chromium-pyrope dunites, harzburgites, and lherzolites) and mafic rocks (garnet pyroxenites and eclogites). The rise of kimberlite magma took place during the Middle Paleozoic (D3 – C1) tectonic-magmatic activation in an environment of stretching of the earth's crust (Akulov, 2003b).

f

e

d

c

b

a

 

 

Fig. 11. Reference samples of kimberlites and xenoliths from various kimberlite pipes of the Yakutian diamondiferous province (after Kostrovitsky et al., 2015 with changes):

 

a - kimberlite breccia with inclusions of garnet serpentinite (Mir pipe), b - kimberlite breccia (Udachnaya pipe), c - autolithic kimberlite breccia (Nyurbinskaya pipe), d - porphyric kimberlite (Yubileynaya pipe), e, f - eclogite inclusions of diamonds (pipe Mir).

 

Apparently, the melt was characterized by a high content of the fluid phase. In near-surface conditions (at a depth of about 1–2 km), an explosion occurred due to the separation of volatile components, which contributed to the formation of kimberlite pipes (diatremes). In the process of near-surface crystallization of kimberlite, fine-crystalline aggregates were formed, which make up the bulk of the rocks of the second phase. Due to the action of a powerful fluid flow coming from the bowels through the formed channel of the pipe, autometamorphism took place with the formation of postmagmatic minerals of the third phase. Thus, kimberlite magma could only serve as a “transporter” for the transport of eclogites and diamonds to the Earth's surface (Anand and al., 2004).

Мирр

 

Fig. 12. View of the Mir pipe after the flooding of underground workings in the process of breaking through the mud-like water-mud-stone mass. Currently, the deposit is suspended. Photo: Sergei Subbotin (RIA Novosti).

 

It should be noted that in 2001, at a depth of 525 m, open pit mining of diamondiferous kimberlites was suspended. And underground mining began, which continued until 2017, when (according to preliminary data) a water breakthrough occurred at the mine with the formation of mudflow-like mud-like water-mud-stone mass (Arkhipov, 2019). At that time, there were 151 people in the mine. 142 miners were promptly evacuated, and one more was rescued the next day. The search for the eight people remaining in the mine continued for several weeks, but to no avail. Then the search and rescue operations were stopped, and the deposit was suspended (Fig. 12). A detailed investigation showed that the mine was flooded due to the breakthrough of subpermafrost high-mineralized waters. At present, additional exploration of the deep horizons of the pipe continues and options for its further development are being worked out.

In total, more than 4000 kimberlite and lamproite bodies have been identified in the Earth, of which about 500 contain diamonds. The main volume of production is provided by only 15 kimberlite and lamproite diamond deposits (Vaganov et al., 2002). The main criteria for the search for kimberlites in new areas are being actively developed (Protsenko et al., 2018), with great attention being paid to geochemical prospecting for kimberlites in closed areas (Tolstov et al., 2007; Simonenko et al., 2008; Sobolev et al. ., 2018).

Various types of exogenous processes have been affecting various types of diamond-bearing formations for many millions of years, destroying and redeposing them, due to which numerous alluvial diamond deposits have been formed. The richest diamond placers were formed in the Yakutian diamond province (on the Irelyakh river, the "Vodorazdelnye galechniki" placer, placers in the Anabar region on the Ebelyakh, Billyakh, Mayat and other rivers) (Tolstov and Grakhanov, 2014; Tolstov et al., 2019).

 

 

4. FROM THE THEORY OF SEARCH TO THE PRACTICE

Modern diamond prospecting is impossible without knowledge of the laws governing the change in diamond-bearing formations in the hypergenesis zone.

4.1. Weathering crust of kimberlites

The formation of the weathering crust of diamondiferous rocks is due to the influence of the environment (water, atmosphere, solar insolation, temperature, life of various organisms, including plants and fungi). Meteoric water and ambient temperature play a major role in weathering. Therefore, the elementary weathering process should be considered in the water-rock interaction system. Practically distilled rain (melt) water is very “aggressive”. Therefore, seeping through the rock, it gradually imbibes (leaches) its mineral components. In this case, an increase in the mineralization of meteoric water occurs, which leads to a weakening of its chemical activity and, accordingly, to attenuation of the leaching processes. An example is the crust of chemical weathering on the shores of the lake Baikal and in the south of the Siberian Platform (Akulov et al., 1992; 1996). In this regard, the winding crust profile is formed from top to bottom. On the surface of such a profile, developed along the granitoids of Khamar-Daban, there is an intensely weathered zone, represented by a member of white kaolinite clays.  And its weakly weathered lower part by disintegrated granitoids with spots of iron and manganese hydroxides.

The conditions of their formation and the duration of weathering are important factors contributing to the weathering of diamondiferous rocks. Rocks formed at great depths, where high temperature and pressure prevail, and then brought to the surface, fall into completely different thermodynamic conditions, which leads to their destruction. The age of the kimberlite bodies of the Yakutian diamond province is from 350 to 430 Ma, which indicates the possibility of prolonged weathering. Therefore, it is not surprising that kimberlites are considered the least resistant rocks to weathering processes.

According to N. N. Zinchuk et al. (Zinchuk et al., 1997) and E.A. Shamshina (1979), three zones are distinguished on kimberlites. The upper almost 30-meter zone of strongly weathered kimberlites is represented by grayish-brownish-yellow lumpy clay impregnated with iron hydroxides, in which the structural and textural features of the original rock are not preserved, but a clay mass composed of kaolinite, hydromica and montmorillonite. The middle one which is  almost 100-meter hydromica-montmorillonite zone consists of brownish-gray moderately weathered kimberlites, in which relict structures are preserved, but obscured by clayey new formations colored with iron hydroxides. The lower one is composed of slightly altered greenish-gray, strongly cemented rocks, in which the structural and textural features of kimberlites are almost completely preserved (Fig. 13).

 

Montmorillonite

garnets

picroilmenite

Clay fraction

Heavy residue

Power

More

Lower

Middle

Upper

Zone

Minerals composition

Weathering crust lithological profile

Кора выветр

 

 

Fig. 13. Lithological and mineralogical section of the weathering crust on one of the kimberlite pipes explored by boreholes (built using the Zinchuk data et al., 1997):

 

1 - kimberlites, 2 - weakly weathered kimberlites, 3 - strongly weathered kimberlites, 4 - picroilmenite, 5 - leucoxene, 6 - micas and amphiboles, 7 - apatite and epidote, 8 - garnets, 9 - tourmaline, 10 - zircon, 11 - resistant minerals led by diamond, 12 - hydromica, 13 - kaolinite, 14 - montmorillonite.

 

It is important to note that picroilmenite (up to 40%) and garnets (up to 25%) remain in the composition of the minerals of the heavy fraction of the upper weathering zone. This is due to their resistance to weathering. The stability of minerals is determined by their mechanical strength and chemical resistance. A. A. Kukharenko (1961) suggested using the following scheme to compare the minerals of rocks by their stability in the hypergenesis zone (Table 1).

Precipitation, mm

Semi-deserts and deserts

Steppe

Evaporation

Savannah

Tropical forest area

Fallen leaves

Savannah

Tundra

Taiga-podzol zone

Precipitation

Кора выветр страхов

 

 

 

FIg. 14. The classical scheme of the formation of the weathering crust in tectonically inactive areas (according to N. M. Strakhov, 1962):

 

 1 - fresh rock, 2 - grit zone, chemically slightly altered, 3 - hydromica-montmorillonite-beidellite zone, 4 - kaolinite zone, 5 - ocher, aluminum oxides, 6 - clivvy, iron and aluminum oxides.

 

N. M. Strakhov (1962) constructed a very graphic diagram on the formation of the weathering crust on ancient platforms, on which he showed that it reaches its maximum values ​​on cratons with a humid and hot climate (Fig. 14). These paleoclimatic conditions prevailed on the Siberian platform 350-370 mln. years ago, when, according to the theory of continental drift, the Siberian craton was located in the tropical climatic zone (Khramov, 1991). Thus, if a kimberlite body was located for a long time in the hypergenesis zone, then it turns into a plastic mud-like grayish-brownish-yellow clay, which is a good aquiclude. Usually, the diatreme has a rounded shape in plan, and under the influence of exogenous processes its caldera often turns into a rounded lake.

There is a legend about the discovery of one of the kimberlite pipes in South Africa. It was as if an African had weaved a hut out of branches and coated it with yellow clay, which lies near the hut on the shore of a rounded (caldera) lake. The clay dried up and the sun shone brightly small colorless minerals, which later turned out to be diamonds.

 

Table 1

Unstable

Moderately stable

Sustainable

Very stable

Olivine

Pyroxene

Augite

Vesuvian

Hornblende

Pyrite

Cinnabar

Melanitis

 

Apatite

Diopside

Ortit

Pomegranates (pyrope)

Actinolite

Tremolite

Epidote

Zoisite

Wolframite

Scheelite

Ottrelite

Axinite

Barite

Sillimanite

Anataz

Stavrolite

Distin

Ilmenite (picroilmenite)

Hematite

Sfen

Titanomagnetite

Magnetite

Monazite

Xenotime

Perovskite

Columbite

Cassiterite

Andalusite

Topaz

Brookit

Leucoxen

Chrome spinellide

Rutile

Tourmaline

Gold

Platinum

Osmous iridium

Spinel

Zircon

Corundum

Diamond

Stability of minerals during weathering (according to A. A.Kukharenko, 1961)

Note: the increasing resistance of minerals to weathering is shown in the columns from top to bottom.

 

N. A. Shilo (2002) investigated the migration properties of placer-forming minerals and found that due to their properties (increased density, hardness, chemical stability in a wide alkaline-acid range, etc.). They are accumulated in certain deposits, thus determining the concentration of ore matter above the clarke values. He proposed to use the accumulative indicator as a constant of hypergene stability (Chs), which takes into account the hardness of minerals, the energy state of the structure of minerals (H), and their density (r).

Chs = lg (rH)

According to his data, Chs for diamond and zircon is 1.54, for gold - 1.66, and for picro-ilmenite - 1.41. For comparison, quartz, which is one of the most widespread placer minerals, has Chs  = 1.26. Quartz serves as a range mark, above which Chs are located for most placer-forming minerals, the amount of which is about 50.

In the process of weathering, stable and partially stable minerals accumulate in the zone of destruction of the original outlet, forming eluvial deposits, represented by accumulations of minerals at the site of destruction. Their further transportation by temporary water flows leads to the formation of spoon placers, and their merging with river flows contributes to the formation of various types of near-drift placers. Coastal placers are formed in the deltas of rivers flowing into large lakes or seas.

It should be noted that the products of the redeposited weathering crust have an “inverted” rhythm with respect to the original weathering crust, which occurs in situ and is easily recognized in the field. At the bottom of such a section, there is usually a fine-grained or pelitic material, and at the top it is coarse-grained, often transformed into conglobreccias. An example is the redeposited products of the Lower Carboniferous weathering crust developed in the southwestern part of the Siberian platform near the Yenisei Ridge. Here, on the eroded surface of Devonian carbonate rocks,  kaolin-rich mudstones of the “flint clay” type occur, which transform up the section into quartz sandstones, and then into a thick 25-meter member of conglobreccias.

It should be noted that until 1960, the main production of diamonds fell on dewy deposits. Shiny crystals in river sand and pebble deposits attract the attention of not only geologists. Many diamond-bearing placers have been discovered by children. Thus, the first Ural diamond was found by a serf Pavel Popov in 1829. In South Africa, on the banks of the Orange and Vaal rivers, the children of farmers found the first diamond crystals. Despite the apparent ease of development of alluvial diamond deposits, their miners always face one big drawback i.e. fast areal mining of alluvial deposits. This is due to the fact that the construction of a MPP (a) on the basis of an open field, in the hard-to-reach conditions of Siberia, becomes profitable in the case when there are enough explored reserves and will last for at least 30 years of its operation. This requirement is usually met by the discovery of a primary deposit. In this regard, the primary task of geologists is to find the primary source of diamonds. Thirty years have passed and this task has been solved, which was facilitated by the numerous previously discovered diamond-bearing placers. After 1990, almost 80% of the world's diamond production was produced from primary deposits. At present, in Russia, despite the abundance of dews, more than 95% of diamonds are mined from primary deposits (On state..., 2018).

4.2. Types of diamond placers and tasks of the first stage of their search

V. P. Afanasyev and colleagues (Afanasyev et al., 1984, 2008, 2010) carried out an experimental study of the abrasive resistance of diamond and its companions - pyrope, picroilmenite, olivine, apatite, as well as fragments of diamondiferous kimberlites. The following series of their decreasing abrasion resistance was obtained: pyrope-picroilmenite-apatite-olivine-kimberlite. The diamond practically did not change during the experiment. Fragments of kimberlite turned out to be quite stable, and their relics survived almost until the end of the experiment, while all satellite minerals acquired the form of wear. Pyrope, olivine and apatite are characterized by oval wear type. Picroilmenite forms tablets with hexagonal outlines typical of ancient halos.

The ratio of the abrasive resistance of pyrope and picroilmenite showed that in coastal marine conditions, picroilmenite is completely abraded, while rounded pyrope and diamonds are preserved. In this case, a stable diamond-pyrope mineralogical association is formed with an insignificant admixture of chrome spinellides, which are smaller in size than pyropes and diamonds. Mechanical changes were noted in diamond crystals due to their chipping, abrasion of edges and tops (Afanasyev, 1989).

The main features of schlichineralogical analysis indicate that clastic material, or as it is called terrigenous material from erosion of kimberlite pipes, is found only in those watercourses that drain them, while the distribution of minerals of diamond satellite dikes is linear (scattering flux).

According to V. I. Vaganov and his colleagues (Vaganov et al., 2002), placer diamonds make up a small (about 10%) part of the world production of natural the importance of placer deposits. Among the known industrial alluvial diamond deposits, the following main genetic types stand out: alluvial, deluvial-proluvial (including karst depressions), and coastal-marine. In Yakutia, deluvial and alluvial (terrace and valley) diamond deposits are widely developed. They were formed in the process of long-term destruction and redeposition of bedrock diamond-bearing kimberlite rocks. Among the valley placers, there are trailing, alluvial and channel ones.

The second region in terms of the size of exploited diamond-bearing placers is located in the Northern Urals. The Ural placers were formed as a result of the destruction of diamond-bearing tuffisites.

The Arkhangelsk Oblast is the third alluvial diamondiferous area, which was discovered relatively recently and is located within the primary deposits of diamondiferous kimberlites.

Let us note the main features of these processes without dwelling on the characteristics of the transport mechanisms and the concentration of placer-forming minerals in various environments, which are discussed in detail in the following works: A. A. Kukharenko (1961), B. I. Prokopchuk (1979), B. N. Sokolov (1982), S. S. Voskresensky (1985), Yu. A. Burmin (1988), V. E. Minorin (2001), N. A. Shilo (2002), A.A. Kremenetsky with colleagues (2006), S. A. Grakhanov with colleagues (2007), N. G. Patyk-Kara (2008), O. K. Kilizhekov with colleagues (2017).

The main mechanism for the formation of placers is their separation  by size (mass), density and chemical stability. The last two indicators are taken into account by the constant of hypergene stability, which makes it possible to compare the migration ability of minerals of equal, mainly sandy dimension. It is noted that the same mineral, depending on the granulometric class in which it is located, has a different migration ability. The migration ability of diamonds is also influenced by the shape of the crystals and hydrophobicity. Two tendencies on the way of their migration along with indicator minerals or minerals-satellites from the primary source are well recognized: on the one hand, gradual destruction, abrasion and dispersal, and on the other hand, this is the removal of unstable minerals along the path of their long-distance transport and the formation of new ones. stable terrigenous-mineralogical associations. Thanks to this, the concept of the genetic category of the placers is autochthonous and allochthonous, as well as local and regional.

According to the degree of their remoteness from the primary sources of diamonds, they are subdivided into placers of near drift and long-range transport (redeposited). The first group includes eluvial-deluvial and alluvial placers. They are characterized by a high concentration of diamonds, and in the areas of karst distribution they give large and sometimes unique deposits.Вторая группа россыпей алмазов представлена россыпями, удаленными от источника питания на десяткисотни километров; среди них преобладают озерно-морские (россыпи конечных водоемов), аллювиальные и ледниковые.

G. Kh. Feinstein (1977) divided secondary sedimentary diamond collectors into 3 groups according to the distance of transfer of fragmentary material into 3 groups: 1) the nearest transport (0-5 km); 2) short-range transport (5-30 km) and 3) long-range transport (more than 30 km). He writes that the distance of up to 5 km from the power source for sedimentary reservoirs of the nearest transfer was established using the example of modern spoon and Rhaetian-Lias placers of diamonds in Yakutia, as well as placers of titanium ores (ilmenite placers).

According to S. A. Grakhanov and V. I. Koptil (Grakhanov and Koptil, 2003), the transfer of diamonds downstream or along the coast can be traced for many hundreds of kilometers. For example, they managed to trace a halo of diamonds coming from the Pipe Mir along the Irelyakh-Mal water system, Botuobia - Vilyui at a distance of more than 500 km.

These two types of placers differ significantly not only in the mechanism of concentration of useful minerals, but also in terms of feeding the placer-forming process.

So, near-drift placers represent a local result, often of a relative concentration along the path of the closest scattering of diamonds. These are scattering streams or mechanical halos of a local root source.

Long-range transfer placers are formed without a visible connection with a specific primary source as a result of prolonged, usually multiple redeposition of clastic material, often through intermediate reservoirs, accompanied by its perfect separation. Long-range transport placers are well preserved in the composition of fossil    alluvial formations.

All currently known diamondiferous placers, according to one or another feature (morphological, genetic, morphogenetic, dynamic, etc.), are divided into a number of types of placers. In our opinion, the most important feature that allows one to clearly distinguish diamond placers in the field is the genetic one. In nature, there are many genetic types of terrigenous deposits, to which diamond-bearing placers are confined. Thus, the genetic types of terrigenous formations containing diamonds also determine the genetic type of diamondiferous placers. Among them, there are proluvial, colluvial, eluvial-deluvial, alluvial, lacustrine, coastal-marine and other less significant genetic types.

 

Fig. 15. The sequence of exploration work on alluvial gold-bearing and diamond-bearing placers (according to A. S. Ageikin et al., 1982 as amended):

 

Stage: a - general search, b - preliminary reconnaissance, c - detailed reconnaissance;

1 - alluvial deposits, 2 - bedding rocks, 3 - edge of the erosional-accumulative terrain, 4 - exploratory lines, 5 - areas with established industrial gold content.

 

It should be noted that in terms of diamond reserves in the world among the Cenozoic placers (without Russia), the first place is occupied by deluvial-karst placers (more than 60% of reserves), the second place belongs to alluvial placers, and the third place belongs to various types of coastal-marine placers and open shelf (Dictionary on Geology ..., 1985).

Among the main tasks that have to be solved at the first stage of the search for diamonds, first of all, it is necessary to find out in the studied deposits at least single grains of heavy diamond concentrates (HDC): pyropes, olivines, moissanite, chrome diopsides, picroilmenites, chromites, etc. Solution of this task is possible only with knowledge of the main laws governing the formation of various genetic types of diamond placers, on the basis of which it is necessary to make a local forecast of the most favorable potentially diamondiferous areas (geological bodies) and carry out their preliminary sampling.

If HDC is found, the studied deposits are subjected to detailed sampling in order to establish the length, width and thickness of the open placer, as well as the average diamond content in them. It is interesting to note that during the open development of the Pipe Mir, it was experimentally established that one ton of kimberlite contains about 20 kg of indicator minerals, including more than five kilograms of chromium-containing pyrope. Such kimberlite pipes form an HDC plume near them, which made it possible to detect it. A geologist walking along the river channel in the footsteps of the HDC will certainly come to the kimberlite pipe.

The sequence of exploration work on alluvial placers is conventionally shown in Fig. 15.

It should be emphasized that diamond in placer samples is extremely rare, since the volume of one such sample is only 10-15 liters of sand-and-shingle or argillo-arenaceous material, and not every cubic meter of diamond-bearing deposits or weathered kimberlite contains at least one crystal diamond.

This means that it is practically impossible to search for both primary and alluvial diamond deposits by the appearance of crystals of this mineral in concentrates. For these purposes, small-volume sampling is carried out or the main attention is focused on heavy diamond concentrates: blood-red pyrope, pitch-black picroilmenite and emerald-green chrome diopside (Fig. 16).

Searches for kimberlite pipes using schlich sampling along the scattering halos of diamond satellite minerals are widely known in the geological literature (Zinchuk et al., 2004) and, in principle, do not present any particular difficulties. They are very vividly and colorfully described and demonstrated in photographs in the monograph by A.M. Khmelkov (2008).

Минералы спутники3

Fig. 16. Heavy diamond concentrates: blood-red pyrope from the Mir pipe and emerald-green chrome diopside from the Inagli massif on Aldan (photo by A. A. Yevseyev).

 

Starting from the earliest prospecting works for diamonds, it was found that rivers, streams and channels are the most favorable for schlich sampling (Burov, 1957). Sampling is usually carried out at intervals of about 1 km and in the direction from the mouth to the source of the river. After washing the schlich sample, the geologist is obliged to carefully study it in order to detect blood-red pyropes or other visually recognizable satellite dikes of diamonds. As he moves along the river to its upper reaches, the researcher finds himself in the province of feeding the river channel with terrigenous material. If the amount of pyrope in the concentrates increases and their size increases, then it is on the right track to the kimberlite pipe. When the schlichs are washed out above the area of ​​the removal of terrigenous components from the kimberlite body, pyropes and other satellite dikes of diamonds abruptly disappear. In this case, it is necessary to study in detail the places of schlich sampling of the valley slopes or tributaries of the river located between the last “empty” sample and the penultimate one with pyropes. Thus, it is possible to find both primary (kimberlite) bodies and ancient intermediate diamond collectors. The ultimate goal of prospecting is to identify an industrial primary or placer diamond deposit.

 

4.3. Criteria and signs of diamond-bearing placers

The criteria and features of diamondiferous placers make it possible to judge the prospects of this or that territory for the discovery of placer diamondiferousness. The basis for their identification is a systematic analysis of the main prerequisites for the formation of diamond placers.

To date, it has been established that the most important criteria indicating that the territory is promising for prospecting for alluvial diamonds are: 1) the presence of primary sources of diamonds in the area under study; 2) the presence in the section of sedimentary strata of stratigraphic horizons, the time of formation of which corresponds to the erosion and denudation of the primary diamond sources (epochs of placer formation); 3) paleogeographic conditions for the formation of potentially diamondiferous deposits (type of sedimentation basin or weathering crust and products of its redeposition); 4) sources of nutrition for sedimentary paleobasins, as well as the type and conditions of transportation of terrigenous material (features of the formation, transformation and conservation of placers).

Along with the search criteria, uniting consistent, statistically stable indicators, a huge role is played by less stable indicators - signs of diamond-bearing placers. Prospecting signs of diamond placers include: 1) the presence of an erosion-denudation cut of the primary source (kimberlite pipe or buried placer) of diamonds in the study area; 2) finds of fragments of bedrocks (kimberlites) in terrigenous deposits; 3) the presence of heavy diamond concentrates in rudaceous fractions; 4) information about the finds of diamonds among the alluvial deposits of the study area.

In addition to the listed criteria and features, diamond-bearing placers have a number of characteristic features that determined their formation. These features are based, firstly on the behavior of diamonds in the process of transfer and sedimentation, as well as on data on the structure and composition of the enclosing and underlying rocks. These characteristic features include the following: 1) confinement of diamond-bearing placers to rudaceous deposits (granulometric factor); 2) close connection of the most diamond-enriched terrigenous material with near-bedrock layers (factor of high specific gravity); 3) the presence of enriched zones among the redeposited products of the weathering crust (a factor of high diamond stability); 4) the ability of diamonds to form placers of long-range drift and multiple redeposition, due to their high hardness and hydrophobicity (physical and mechanical factor); 5) geomorphological features of the site, which direct the formation of the placer, including control of the basis of erosion, areas of avalanche discharge of terrigenous material (geomorphological factor).

 

 

5. TYPES OF TESTING WORKS IN SEARCHING FOR DIAMONDS

 

No researcher will begin the study of the diamond content of an unfamiliar river by studying the roundness of pebbles or their granulometry, as rightly pointed out by one of the experienced diamond geologists, B.M. Sokolov (1982). First of all, he will begin by testing it for diamonds and their paragenetic satellite dikes.

Depending on the purpose, an ordinary, special technical, technological and operational sampling of diamond-bearing placers is distinguished. In this book, we will only deal with the issues of ordinary sampling, which is carried out at all stages of geological exploration and includes a system of operations that ensure the study of the mineral composition of the heavy fraction of terrigenous sediments in order to identify and determine among them the content of diamonds or their heavy concentrate (HC). The data obtained in the course of routine sampling are the initial material for delineating and calculating the reserves of the identified placer. Both pits and ditches are tested vertically along the walls. The volume of each sample is one placer watersink (10 l). In the event that it is cemented, it is preliminarily disintegrated mechanically in a mortar (it is desirable to obtain a crumbling without disturbing the structure of mineral grains). To do this, the cemented fragments are poured with water if the cement is clayey or 5% HCl if it is carbonate. When taking a bulk sample (small-volume or large-volume), it contains all the material obtained when driving a dug hole. Bulk samples taken from trenches or ditches are usually 10-40 m (or more) sections for the entire thickness of the potentially diamondiferous formation.

When testing wells, the core is divided along the long axis and half or a quarter of it enters the sample. The entire core is used as a sample out of the most interesting intervals of the well, which allows obtaining more reliable information.

Thus, at present, four types of sampling work are distinguished as part of ordinary sampling: schlich, crushing, drilling (core and sludge) and gross (small-volume and large-volume).

Slice sampling is the most common type of sampling in prospecting for diamond deposits. Thanks to the schlich sampling, the scattering halos of the HDC are established and the paths of the drift of the terrigenous material are determined. To increase the reliability of the study, sometimes two trays of terrigenous material (20 l) are washed.

Sampling for crushing to determine the mineral composition of ancient rocks and the detection of HDC is carried out from near-bed areas. The sample must include material from the “scuff” (from a depth of up to 20 cm from the surface of the raft). For the manufacture of crushed conglomerates, cement is selected in the places of its greatest accumulation. After grinding, the sample is poured into a placer watersink and sieved.

The results of the analysis of crushed samples, as well as other information on prospecting and sampling, are plotted on the prospecting map (plan).

Small drill rigs of the UPB-25 type are used to open a relatively shallow-lying bedrock, as well as to study loose productive sediments.

Cable-tool drill is usually used to open and sample sand-and-shingle deposits of terraces and floodplains under a thick layer of fine-grained formations. Drilling is carried out along profiles across the valleys from bedrock on one side to bedrock on the other. Sampling should preferably be done with a Canadian spoon.

Small-volume samples are taken in areas most enriched in paragenetic satellite dikes of diamonds. Such areas are outlined in the course of schlich sampling. The volume of samples varies from 0.5 m3 to 1.5 m3, depending on the nature of the tested deposits and the degree of their diamond content. Samples are taken using pits, ditches, sometimes using a bulldozer or excavator. In connection with the discovery of new sources of diamonds - lamproites, new recommendations for small-volume sampling appeared (Temporary methodological ..., 1988). In particular, it is indicated that small-volume sampling in the search for lamproites and diamond-bearing placers developed on them, due to the fact that the average background concentrations of

Suppose that in the course of prospecting for diamonds, one cubic meter of sand and gravel deposits is washed. How much should the resulting concentrate weigh?

Based on the experience of geological exploration, it is assumed that one cubic meter of sand and gravel deposits weighs 1.5 tons, and the mass of the heavy fraction minerals contained in it (minerals with a density of more than 2.9 g/cm3) averages 0.5-3 kg. For every ton of small-volume samples washed in the field, we have from 0.3 to 2 kg of concentrate. Due to the fact that the concentrate is washed to a gray concentrate, its weight is always much higher and reaches 3 kg or more. G. F. Feinstein (Feinstein, Lebed, 1988) wrote that when the first diamond-bearing pipes were opened, from each cubic meter of “sands” supplied to beneficiation, from 5 to 50 liters of concentrate was obtained, which indicates a large underwash of the tested sediments.

It is important to emphasize that in the course of obtaining a concentrate in the field, all mineral grains must be washed from clay smears and clay “aggregates” (pellets). Washing is usually carried out immediately after unloading the shaker (before depositing) in a sieve, with holes smaller than the size of the washed fraction, in running water. Washing goes on until the release of clay "turbidity" and light gray minerals of the light fraction stops.

Large-volume sampling is carried out to confirm the presence of diamonds found in small-volume sampling and to determine the diamond grade. According to G. Kh. Feinstein (1968), this sampling is especially necessary where the alluvium of streams draining the development fields of diamond-bearing and pyro-bearing deposits is devoid of diamond satellite dikes. And in the adjacent areas, river sediments contain large diamonds with an average weight of more than 10-15 mg. The frequency of detecting such diamonds is several times less than in placers with small diamonds, and therefore the probability of finding at least one such crystal in a small-volume sample is small.

The required sample volume for large-scale sampling is usually calculated using the Burov-Volorovich formulaSuppose that in the course of prospecting for diamonds, one cubic meter of sand and gravel deposits is washed. How much should the resulting concentrate weigh?

Based on the experience of geological exploration, it is assumed that one cubic meter of sand and gravel deposits weighs 1.5 tons, and the mass of the heavy fraction minerals contained in it (minerals with a density of more than 2.9 g/cm3) averages 0.5-3 kg. For every ton of small-volume samples washed in the field, we have from 0.3 to 2 kg of concentrate. Due to the fact that the concentrate is washed to a gray concentrate, its weight is always much higher and reaches 3 kg or more. G. F. Feinstein (Feinstein, Lebed, 1988) wrote that when the first diamond-bearing pipes were opened, from each cubic meter of “sands” supplied to beneficiation, from 5 to 50 liters of concentrate was obtained, which indicates a large underwash of the tested sediments.

It is important to emphasize that in the course of obtaining a concentrate in the field, all mineral grains must be washed from clay smears and clay “aggregates” (pellets). Washing is usually carried out immediately after unloading the shaker (before depositing) in a sieve, with holes smaller than the size of the washed fraction, in running water. Washing goes on until the release of clay "turbidity" and light gray minerals of the light fraction stops.

Large-volume sampling is carried out to confirm the presence of diamonds found in small-volume sampling and to determine the diamond grade. According to G. Kh. Feinstein (1968), this sampling is especially necessary where the alluvium of streams draining the development fields of diamond-bearing and pyro-bearing deposits is devoid of diamond satellite dikes. And in the adjacent areas, river sediments contain large diamonds with an average weight of more than 10-15 mg. The frequency of detecting such diamonds is several times less than in placers with small diamonds, and therefore the probability of finding at least one such crystal in a small-volume sample is small.

The required sample volume for large-scale sampling is usually calculated using the Burov-Volorovich formula

                                       , where

P is the volume of the most representative sample; A - average weight of diamonds in placers adjacent to the prospecting area; С - average diamond content in placers adjacent to the prospecting area; K is the reliability factor, conventionally taken equal to 2.

  

What should be the minimum bulk sample volume? Let's conditionally establish that the average weight of diamonds in the placer is 100 mg (so as not to miss a diamond with a size of 0.5 ct), and the average minimum (borne) content in the placer is 0.1 ct/m (20 mg/m3). Substituting the given data into the above formula, we obtain

To enrich the analyzed material and obtain the necessary concentrate, a primitive field processing plant is being built. Its construction and operation is carried out by a special enrichment detachment, provided with an excavator or bulldozer and an all-terrain vehicle for transporting the test material, the volume of which varies from several tens to several thousand cubic meters. For example, in 1954, the party No. 47 of the Oryol expedition from alluvial deposits of one of the sections of the Chuny river (south of the Siberian platform) 2112 m3 of sands were sampled. As a result of their enrichment, 16 diamond crystals with a total weight of 113.2 mg were recovered. It is easy to calculate that the average grade in this placer is 0.00027 carats/m3. Is it a lot or a little? It is known that in foreign practice, primary deposits are exploited with a diamond content usually from 0.5 to 5-10 carats/t, and placer deposits  with a diamond content of about 0.1-0.3 carats/m3 and higher (Berlinsky, 1988). Thus, this placer is characterized by a very low or poor diamond content.

Table 2

Classification of diamond placer deposits (Placers of diamonds ..., 2007)

Parameter

Size, level

 

Size, mln ct

Unique

Over 20.0

Large

5-20

Average

1-5

Small

Up to 1.0

 

Diamond content, ct/m3

Unique

Over 5.0

High

1-5

Average

0.5-1.0

Low

lower 0.5

 

Price, USD/ct

Unique

Over 100.0

High

50-100

Average

30-50

Low

Up to 30.0

 

S. A. Grakhanov et al. (Placers of diamonds ..., 2007) proposed the following variant of the classification of alluvial diamond deposits (Table 2). In this regard, it should be noted that the main reserves of placer diamonds in Russia are concentrated in Western Yakutia and are distributed over the following regions: Anabarsky (64.2%), Sredne-Markhinsky (13.8%), Malo-Botuobinsky (12.3%), Prilensky ( 4.6%), Muno-Tyungsky (2.3%) and Daldyno-Alakitsky (1.4%). The missing interest belongs to another region of Russia - the Perm Oblast (1.4%). It should be noted that the richest place is the river basin Ebelyakh (Anabar region), where 52.3% of all Russian reserves of placer diamonds are concentrated (Placer diamonds ..., 2007).

An important condition for prospecting for diamond-bearing placers is the production of high-quality diamond-bearing concentrates, as well as their thorough analysis at stationary installations, excluding the possibility of contamination with diamonds from other samples. It is noted that in Western Australia, mass finds of diamonds in lamproites began only after a new processing plant was commissioned in August 1978 (Temporary methodical ..., 1988).

 

5.1. Equipment: tools and materials for field work

 

When carrying out expeditionary work, an ordinary geologist must have: a geological hammer, a mountain compass, a set of topographic maps, a field book, pencils, a geological satchel, a knife, a tape measure, 5% hydrochloric acid, labels and bags for samples. A diamond geologist will need a whole range of equipment and tools, which includes: 1) a set of sieves (roar), which is often mounted in the form of a single, easily movable mechanism - a shaker; 2) marching flush lock; 3) a jigging plant of the Ji-gi type or a portable screw separator; 4) wooden or plastic sizing trays; 5) entrenching tool: a set of shovels (pick and bayonet), pick, crowbar, wedge, chisel, ax, chainsaw; 6) a cast-iron mortar (2-3 l volume) for the manufacture of prototypes from cemented rocks; 7) tarpaulin (awning) of dimensions 2x3 m; 8) a awning and everything you need for sleeping and cooking.

In addition to base maps, you must have: 1) 2-3 copies of field maps for applying data (actual material); 2) satellite dikes navigation system and portable position control system (GPS) for binding precise geographic coordinates and altitude data; 3) laptop for registering important objects and data; 4) digital camera and video camera for shooting each tested area and documenting mine workings (pits, ditches); 5) an aircraft - a quadrocopter or drone for aerial survey of the research area; 6) documents for carrying out geological exploration works; 7) a ruler with micron divisions for measuring HDC mineral grains and diamond crystals.

Personal protective equipment plays an important role: hunting knife and rifle; mosquito nets and insect repellents; sun hat, gloves and mountain boots for outcrop work; portable generator or small-sized power plant; gas cylinders for cooking; money to buy the necessary things, as well as a first-aid kit.

The data collection methodology is further subdivided into three categories, each of which represents a collection technique: observation, diary, photography, and video filming. In the diary, each field route is recorded by the date of its conduct, the composition of the search group according to surname, the purpose of the route and the exact binding of each described observation point. All this will serve as the basis for reporting on the results of the exploration work. The researcher records measurements and observations related to specific outcrops, their general characteristics. It is very important that all documentation is completed at the outcrop or mine working itself, and not carried out after returning to the camp.

Geological observations include a description of the composition of the bedrock, geological features of occurrence and types of overlying deposits. A preliminary assessment of the environmental conditions in the area of ​​the future mine and in the adjacent territory should be carried out.

When carrying out work in areas with identified diamond content, drilling crews with self-propelled drilling rigs are involved, and when tracing paleovalleys and preliminary contouring of ore bodies - geophysical research methods (VES survey, magnetic survey, etc.).

Since the extensive literature is devoted to drilling and geophysical research methods, and the main attention will be paid to jigging devices below, here we will focus only on tools for driving mine workings manually and sampling for the purpose of flushing them on a jig plant. Bayonet and pick-up shovels are used as such tools, and when working with cemented deposits - picks and metal wedges (Fig. 17). In the process of driving workings, workers (miners) often use home-made, improved varieties of shovels: bayonet - tunneling and collecting - shovel (loading). The choice of a shovel with a particular width of the working blade should be made on the basis of the following rule: the higher the specific gravity of the rock, the smaller the blade of the shovel should be. This is because it has been established in practice that the least fatigue of the worker and higher labor productivity are achieved when placed on shovel no more than 8-9 kg of rock.

Often, the rocks of the block, which are of primary interest in diamond prospecting, turn out to be strongly cemented or represent a monolithic conglomerate. In such cases, a pick, crowbar, chisel and wedges are used. A pick can be one-sided (one-blade), two-sided and a pick-hoe (see fig. 17). The peculiarity of the latter is that instead of a point, it ends with a blade. In most cases, in double-sided tools, one blade has a tip, like a regular pick, and the other has a blade, like a pick-hoe.

Usually, experienced miners sharpen, harden and beat off tools before starting tunneling work. Their hardening is carried out by heating over a fire to a red-hot color and shaping with a hammer, and then cooled in cold water with tempering to a purple color.

It is no coincidence that we dwelt in such detail on mining tools, since all geological exploration work is based on mine workings, the competent implementation of which can greatly facilitate the work of miners, save time or conduct mining work not where it is good to “dig”, but there, where it is truly necessary.

The search for paleo placer deposits is accompanied by a whole complex of lithological studies. First of all, natural outcrops of rocks are comprehensively studied. In their absence, excavation of pits, ditches or clearing is carried out. Description of sedimentary rocks along the section is carried out from bottom to top, in the following sequence:

 

  1. Granulometric type (sandstones, mudstones, etc.).
  2. Form of occurrence (formation, lens, interlayer, etc.).
  3. Power.
  4. Structural and textural features.
  5. Color.
  6. Material composition (roundness, sorting, field mineralogy).
  7. Genetic traits (wave-break marks, traces of turbidity and underwater landslides, drying cracks, nodules, etc.).
  8. Type of cement (clay, carbonate, quartz, ferruginous, etc.), the nature of cementation (basal, pore, contact, etc.).
  9. Paleontological remains (flora, fauna, ichthyofauna, etc.).
  10. Contact (blurry, clear, gradual, unclear).
  11. Cyclicity and rhythm (rhythms, cycles, mesocycles, macrocycles).
  12. Sampling for granulometric (30 g), petrographic (thin section, 30 g), palinological (150 g) and clay (100 g) analyzes.

 

h

g

f

e

d

c

b

a

Рис

 

 

Fig. 17. Tools for driving mine workings manually (according to A. R. Sushon, 1976):

 

shovels: a - spade, b - tunneling, in - loading (scoop);

picks: d - one-sided (straight and oblique), d - double-sided;

wedges: e - square, g - rectangular, and h - round.

 

As a result, the bag with the selected sample should weigh 300-350 g. Thus, the sample volume for all types of lithological analyzes should be equal to the volume of a 200-gram glass. Samples of rocks for all types of analyzes are taken from each type of rocks or lithological variety, and in homogeneous strata - every 5 m. It should be remembered that samples are taken for chemical analysis only from the weathering crust, as well as from various chemogenic formations (10 g each of them). The chemical composition of the fine-pellet fraction is performed after its laboratory elutriation and drying (2-3 g is required for analysis). Particular attention is paid to sampling for crushing with the purpose of detecting HDC. Its volume is usually 15-20 kg.

The rocks that make up the ancient sedimentary bodies enriched with diamonds or their satellite dikes are usually called intermediate reservoirs, although oil geologists are very indignant about this and demand to call reservoirs only those rocks that contain oil fluids and ensure their mobility. Nevertheless, the term intermediate reservoirs is deeply rooted and is widely used by diamond geologists.

Intermediate reservoirs are usually consolidated and overlain by “waste” rock strata. Consequently, all diamondiferous paleoros are intermediate collectors of diamonds, but not all intermediate collectors are paleoros.

The most expedient search for paleo placer deposits in places where intermediate diamond collectors emerge on the day surface. Such places are usually located along the outskirts of such large structures as the ancient mainland of Angarida and the Anabar anteclise on it. If shallowly buried intermediate diamond collectors are found within a promising area, it is most reasonable to drill shallow wells that open the intermediate collector along a sparse grid over the entire area. Based on the data obtained during drilling, a plan of the investigated area is built taking into account the location of the found diamonds and their satellite dikes. Based on this, further, more detailed searches for paleo-placer deposits are being carried out, but already proceeding from the analysis of the regularities of the formation of an intermediate reservoir, its enclosing sediments and the supposed locations of their primary sources.

6. METHOD OF OBTAINING DIAMOND-CONTAINING CONCENTRATES IN FIELD CONDITIONS

 

The main purpose of any type of sampling in the search for diamonds, gold or other placer-forming minerals is to obtain a concentrate by dividing the initial sample into light and heavy fractions, followed by pouring the light fraction into a dump. The concentrate is a  schlich consisting of heavy fraction minerals, which may include HDC, diamonds, gold, platinum and other valuable minerals and their aggregates. During operational work, mineralogists examine concentrates under a binocular microscope in the field, but this is usually done in the winter during the office period. Prospector trays, various depositing devices or mechanical depositing machines are used to obtain concentrates.

Fig. 18. Korean-style prospectors are made from poplar or aspen: small, medium, giant, and supergiant.

small

Supergiant

Giant

 

Middle

 

 

 

6.1. Elementary Jigging Basics

         Jigging is a method of separating mineral grains of the investigated sediments by specific gravity. In the field, jigging is always done in an aquatic environment. As a result of repeated shaking and swaying, the terrigenous material is repeatedly weighed and loosened, and then sank to the bottom and compacted. In this case, the heaviest fraction is located in the lower part of the sand mixture, and the light fraction (tails) settles on its surface. Then it is gradually washed out by a scraper during water washing. All jigging machines, cradles and butars are based on the same principle.

 

Fig. 19. Prospector tray with grooves on the flush plane and a paddle for removing coarse-fragmented material, and crushing clay pellets during screening.

 

The specific gravity of the heavy fraction is usually more than 3.2 g/cm3, and the light fraction is 2.7 g / cm3. The more intermediate fraction in the material (specific gravity 2.7 - 3.2 g/cm3), the worse the jigging occurs, and the resulting concentrate is not black (dark), but gray or light gray. Sometimes geologists deliberately force the scrappers to wash up to gray concentrate in order to preserve the heavy fraction as much as possible. This is very negatively perceived by mineralogists, who have to carry out additional work to remove minerals of the light fraction in laboratory conditions using bromoform.

One of the simplest methods of depositing is washing the sample in a prospector's tray (Fig. 18). Before washing, the tested material is subjected to wet screening on a sieve, the mesh size of which is adopted by the researcher himself (from 5 to 2 mm), depending on the dimension of the studied components. Screening is usually carried out in shallow water, where a sieve is placed on a tray immersed in water, into which the material to be tested is poured with shovels. After screening in water (until the tray is full), the oversized sample remains are abruptly turned over and the gravel-pebble material is carefully poured onto the sandy bank. Here, they scan the washed pebbles and gravel in order to visually search for large diamonds and fragments of diamond-bearing rocks. The concentrate is washed off from the material that turned out to be in the tray. The finishing of the concentrate must be completed when the concentrate acquires a dark gray color. This careful flushing (leaving a small amount of light fraction minerals) is necessary to avoid loss of HDC.

h

g

f

e

d

c

b

a

 

Fig. 20. Prospector trays made of plastic and metal:

 

a - Australian (gateway in a tray) Hillier's plastic tray (Turbopan), b - black plastic (Estwing BP-16), c - green plastic (Garret Gravity Trap), d - rectangular plastic green trap (LeTrap), e - combined, multifunctional with catching grooves and a micro-lock at the bottom (Trinity Bowl), e - steel grooved with three retaining grooves (Estwing), g - prospector's set, h - hexagonal plastic blue (JOBE Hex). The hexagonal shape contains two faces of deep grooves (6 on each) for primary processing of the material, two faces of sixteen secondary grooves for main processing and two sides with a textured surface for finishing washing.

 

The washing of the concentrate samples and the production of the diamond-bearing concentrate is carried out in ordinary Korean-type prospector trays (see Fig. 18). An experienced washer can wash from 20 to 50 trays per shift, i.e. 0.2-0.5 m3 of rock. The loss during washing in such a tray reaches 15% or more (Crater, 1940). In order to reduce the loss of useful components, trays with a corrugated surface of the flush plane are used (Fig. 19). For the first time, a tray with a corrugated surface was developed and applied by M. V. Solodyankin. Laboratory tests have shown that the Solodyankin tray surpasses even the Wilfley jigging table in terms of the quality of extraction of heavy fraction minerals (Crater, 1940).

The reader should be reminded that already at 80% recovery of the heavy fraction into concentrate, almost all diamonds are in concentrate (Romanchikov, 1983). This is explained by the high penetrating ability of diamonds down to the sieve of the jigging chamber due to their high specific gravity and low coefficient of friction for most minerals and rocks (high migration ability). Therefore, it is permissible to operate jigging devices and machines, on which the yield of the heavy fraction is at least 80%. Manufacturers currently offer a variety of plastic and metal trays (Figure 20).

 

 

Fig. 21. Portable foldable airlock (Royal backpack). Mini-sluice four-kilogram installation: general view in assembled and disassembled state.

6.2. Obtaining concentrates using jigging devices

 

At the heart of all modern jigging devices is the sluice operation scheme, copied from the principle of the elementary operation of a bootara, cradle or American rocker.

The sluice is a simple yet effective setup that can handle much more material than manual flushing in a sludge trough. Unlike the bootar, cradle and American rocker, which have wooden structures, modern portable sluices are made of aluminum or stainless steel and installed at an angle of 5-7° directly on the shallow but running bottom of the river (Fig. 21). The streams of water, passing through a sluice hidden under the water, wash the poured alluvial material. They are used for gravitational enrichment by separating mineral grains from the pulp of a large specific gravity in vortex flows and obtaining a concentrate as part of an enriched complex of heavy fraction minerals. The principle of operation of the sluice is based on the separation of two flows of pulp movement: upper and lower. Downstream speed, slower and considering upstream pressure, heavy mineral grains sink into PVC mats. Corrugated  rubber carpet are often used as mats. Under the influence of a turbulent water flow, heavy mineral grains are deposited (retained) on the corrugations of rubber mats. Minerals of the light fraction are carried away by water flows outside the sluice.

 

Fig. 22. American rocker (dimensions are given in millimeters) (after V. M. Kreiter, 1940).

 

Vashgerd is one of the oldest and simplest devices for the enrichment of sands, it consists of a receiving hopper with a bang (5 mm sieve) and a sluice (with a special bedding), barred by slats. Water is supplied to the cradle through a special chute, but most of all it is simply poured onto the sand and gravel mixture that is in the receiving hopper from a bucket. Having passed through the bang, the water-sandy-clay mixture flows down the plane of the cradle, taking away lighter particles with it. In the process of rock movement, heavy concentrate accumulates at the slats on the litter, from where it is carefully collected after washing the sample. To facilitate the collection of the concentrate, the bottom of the cradle is covered with a cloth, which, after washing, is removed and the concentrate is collected from it. Sometimes, instead of cloth, the bottom is covered with felt or straw boards. Jigging operations on it are usually carried out by three workers. The washing capacity is from 3 to 6 m3 per shift, depending on the washability (clay content) of the rock. Loss during flushing usually does not exceed 10% (Zakharova, 1974). If diamonds and their satellite dikes are confined to small granulometric classes, their washout with light fraction minerals can reach 30-50%.

When developing placers of gold, diamonds and other valuable minerals, an improved version of a cradle is used. A hydrosherd, the work of which is based on the effect of a pressure jet from a hydraulic monitor on loose deposits. The apparatus consists of a disintegrator-classifying part and a hydromonitor (Methods of selection ..., 1984).

Butara is an enrichment plant, which, in contrast to the cradle, is equipped with many locks of different sizes, which generally resemble a ladder. A cloth is laid on the bottom of the butar, which creates a wavy surface that helps to trap heavy minerals less than 0.25 mm in size. In addition, the butara is equipped with a device for rock disintegration and cleaning of minerals from clay additives. This device is located immediately below the screen (5 mm sieve) near the hopper.

The American rocker has a device for swinging (shaking) the test material from side to side during flushing (Fig. 22) in contrast to the bootar and the cradle. In it, the system of locks is simplified to a minimum, and its length reaches 1.7 m. Rokker, like butara, is equipped with a device for disintegration of adhered minerals, which contributes to their better washing from clay material. Due to the presence of a swinging device (rounded unstable base), the rocker has a higher productivity and quality of concentrate washing than the above-described jigging devices.

A very interesting simple and fast way of enriching the initial small-volume sample was proposed by V. D. Skulsky (Feinstein, Lebed, 1988). A sieve with 1 mm holes is tied to a tripod made of poles. A sand-pebble mixture is poured onto a rhythmically swinging sieve and portion by portion is washed with water from a bucket. All material smaller than one millimeter is discarded after viewing, as are pebbles and coarse gravel. With a rocking sieve, the heavier material is concentrated at the bottom, and the lighter one at the top. The first becomes dark gray, the second - light gray tones. Light sand is raked up and thrown away. The dark sand remaining on the sieve is a potentially diamondiferous concentrate, which is stored in bags. The resulting concentrate is sent for research under stationary conditions.

Currently, in geological organizations engaged in the search for diamonds, manual mechanical machines (field dressing machines) POM-2, known as "Jiga", have become widespread. Jigs are made in a homemade way, mainly from durable and lightweight duralumin materials. A characteristic feature of jigging machines of this type is the presence of a cylindrical movable chamber, which, during jigging, produces a complex movement, consisting of a forward-reverse movement downward - upward and balance-pendulum rolling in the horizontal plane. This movement of the chamber ensures the concentration of the heavy fraction on the sieve in the central part of the chamber. These are machines of periodic action. The material is deposited on them in portions of 2.5-3 liters. The procedure for working with them is as follows (Romanchikov, 1983):

1. The jigging machine is installed in a pond (stream, lake or simply in a metal half-roll) so that the water mirror is parallel to the chamber sieve, and the water should be at the level or slightly below the upper edge of the chamber.

2. The sample is loaded into the chamber in portions, from which it is necessary to obtain a concentrate.

3. When you press your hands on the drive spring-loaded handle of the machine, the camera goes down. In this case, the water passes through the sieve and loosens (agitates) the test material.

4. When the hands are weakened (pressing stops), the chamber returns under the action of the spring upward, the material is compacted, thereby depositing it, that is, the heavy fraction passes into the lower part of the chamber to the sieve, and the light fraction remains on top.

It is important to note that the camera is secured in the frame of the machine with three rigid and three rubber braces, which, when the camera moves down, rotate it by a certain angle to the right, and when it moves up, return it to its initial position. The movement of the chamber from side to side (right-left) forces the heavy fraction to concentrate on the central part of the sieve. It takes one to two minutes to deposit one portion of the material to be tested.

Spiral separators are much less widespread. This is explained by the fact that they are intended for enrichment of only small diamond-bearing concentrate, usually –0.5 mm, less often –1 + 0.5 mm. In addition to the above jiggers, heavier (20 kg), which are more productive (up to 100 l / h), R0M-1 jigging machines are also used.

Before starting direct enrichment using mechanical machines, unlike jigging devices (cradles, etc.), the sampled material must undergo preliminary washing and granulometric classification. For these purposes, homemade shakers or search vibrating screens (GRP-1) are usually used.

A shaker is a simple device consisting of a densely packed set of sieves (usually four) with meshes of different sizes. Their size depends on the task and the methodological features of laboratory processing. So, M. I. Malanin and A. P. Krupenin (Enrichment of diamond-bearing ..., 1961) give the following data on their size (from top to bottom) 8; 4; 2 and 1 mm. Geologists PGO "Irkutskgeologiya" (Verkhnechonskaya party) used sieves of size 5; 3; 2 and 1 mm. Diamond prospectors VostSibNIIGGiMS (a) used a grid of 4, 2, 1, and 0.2 mm, respectively. For the pyrope survey we used a shaker consisting of three sieves with a mesh size of 2; 1 and 0.3 mm.

The net is attached to a frame with high sides (15-20 cm). At the base of the sieves, a pallet box is placed in dimensions equal to the sieves. Small rinsed material accumulates in the pallet box. After installing the entire set of sieves (shaker) on a log (16-20 cm in diameter), it acquires an unstable (rocking) position like that of an American rocker, which is very favorable for washing the material under study.

For a more rigid attachment of shaker screens, a frame is often used, formed by four racks fastened together. The base of the frame is made like a sled with two rounded slots for installation on a log.

Sometimes, stops are attached to the frame, which, when they hit the ground, shake the material being tested for shaking the material on sieves.

Shaker operaton is carried out in the following sequence. One person, usually a walker, shovels the material to be examined onto a sieve. The second person pours water from a bucket or scoop on a long handle onto the grid with a sample, and the third person shakes the shaker and at times (with a special scraper) loosens the sample. Lumps of clay are rubbed with fingers, and large pebbles are thoroughly washed and discarded.

After the shaker sieves are sufficiently filled, they are unloaded. The largest oversize material is gently poured onto the sand by a sharp turn to visually study the composition of pebbles and search for large diamond crystals. All the rest of the washed oversize material is loaded one by one into hand-held gardening machines or spiral separators to obtain a concentrate. Jigging is usually done by experienced workers, as well as the geologist himself, who maintains all the documentation. From the material of the finest fraction that has accumulated in the pallet box, the concentrate is washed in an old-fashioned tray.

 

Thus, for the rational conduct of small-volume sampling with the use of a shaker and manual jigging machines, a “calculation” of at least four people is required.

Search vibrating screen GRP-1 is a continuous-action apparatus. It is presented as a set of four sieves measuring 500 x 170 mm with openings of 8, 4, 2 and 1 mm. The sieves are clamped between two side plates that form a sort of screen body. The screen is suspended by eight springs from a frame mounted on four legs. It is driven manually through two gear stages and an elastic (spring) connection to the shaft. At the ends of the shaft, for better shaking of the material, balancers are attached to the sieves. The screen is very convenient for transportation, as it can be easily disassembled into its component parts. It is made almost entirely of duralumin at the factory. The device weighs 13 kg, but has a low productivity - up to 0.08 m3/hour.

                                                                 

 

 

7. SCHEMES OF ENRICHMENT OF DIAMOND-BEARING SEDIMENTS

 

Conducting many types of sampling during prospecting work for nemyslimo diamonds without preliminary (field) enrichment. One of the elementary schemes of enrichment of terrigenous material in order to obtain minerals of the heavy fraction (concentrate with a specific gravity of more than 2.88 g/cm3) was shown by the example of washing a sample in a concentrate tray (Fig. 23).

For mineral analysis

Concentrates

Review oversize material (visual search for fragments of kimberlites and diamonds in a fraction of more than 2 mm)

Fractions

Underflow material

Schlich

Schlich

Schlich

Kimberlite (ore)

Drying

Drying

Drying

Gray sand

Gray sand

Gray sand

- 0,3 mm

From 1 to 0,3 mm

Sieve 0,3 mm

From 2 to 1 mm

Less than 1 mm

Sieve 1 mm

Sieve 2 mm

INITIAL SAMPLE

WATER

 

 

Fig. 23. Elementary enrichment scheme by obtaining a concentrate from the investigated loose deposits in a placer tray.

 

Slightly more complicated is the field scheme of the enrichment of terrigenous material using a shaker and jigging machines (Fig. 24). As a result of the simultaneous three-time wet screening of the test material through sieves with a mesh size of 2, 1 and 0.3 mm, as well as their subsequent jigging on a "Jig", a screw separator or a concentrate tray, we obtain three concentrates for laboratory enrichment (magnetic separation, etc.) and the extraction of diamonds in stationary installations. Paragenetic satellite dikes of diamonds are extracted when studying concentrates under binoculars. The size of the mesh of the sieves is taken depending on the most probable size of the desired diamonds or their satellite dikes, distributed in the region under study.

M. I. Malanin and A. P. Krupenin (Enrichment of diamond-bearing ..., 1961) indicate that the choice of the upper limit of size when processing samples is determined by the need to have a 1.5-fold margin for free passage through a sieve of large diamond crystals found in placers. The lower size limit is due to economic considerations, the difficulty of extracting diamond grains finer than 0.5 mm, which are not taken into account even when calculating reserves. In the case of a significant content of crystals less than 0.5 mm in size in the growth rash, the lower limit decreases to 0.2 mm. In this regard, in order to concentrate sands under stationary conditions, sands (with large-volume sampling) are pre-washed on sieves of 16 mm and 0.5 mm in size (wet screening). Products with a particle size of more than 16 mm and less than 0.5 mm are sent to the dump, and all sand and gravel material is screened in 4 classes: - 16 +8; -8 + 4; -4 + 2; +2 mm. Class 2 mm is sent to the hydroclassification apparatus, where the remaining sludge is released. The classified granular material is sent to jigging on piston jigging machines (41V-0T, 20VM-1, 0B-1, OMSK-2, etc.), where diamond-containing concentrates are obtained.

The concentrates obtained in the field are dried in the sun or in a metal ladle over a low fire. Avoid strong heating of the concentrate, which leads to a discoloration of some minerals. After drying, the concentrates are poured into special bags, which are delivered to hospitals for further research. In those cases when operational data on the obtained concentrates are needed for successful prospecting work, then in the field, their X-ray luminescence separation and mineralogical diagnostics are carried out. Under stationary conditions, the concentrate is, first of all, subjected to preliminary selective grinding in a screw mill (SM-1) or a laboratory grinder (LI-2). The screw mill works on the principle of crushing the material supplied by the screw on the plate. As a result of selective grinding, weak in hardness and brittle minerals of the heavy fraction (limonite, goethite, barite, disthene, pyrolusite, pyrrhotite, fluorite, chalcopyrite, celestine, scheelite, etc.) are crushed and together with water in the form of sludge leave from concentrate. The reduced concentrate is dried and fed to various types of separation.

 

Concentrate for

mineralogical

analysis

Into waste dump

Minerals of light and argillaceous-silt fraction

Underflow material

Schlich

Gray sand

Drying

Review oversize material (visual search for fragments of kimberlites and diamonds in a fraction of more than 5  mm)

Sieve 5 mm

INITIAL SAMPLE

WATER

 

 

Fig. 24. The scheme of small-volume concentration of sand-gravel-pebble deposits on a shaker, used by the author in the field.

 

Separation is the separation of mineral mixtures into fractions enriched with individual minerals, or entirely monomineral. Its methods are different, but the most widespread are the following: 1) gravitational separation of minerals (on concentration tables, screw separators and in heavy liquids; 2) magnetic separation of minerals according to their magnetic susceptibility (manual permanent magnet, electromagnet, magnetic isodynamic separator SIM-1); 3) electrical separation of minerals: according to their electrical conductivity in an electric field (in electro-static separators), in a corona discharge field (in corona electric separators) and according to the dielectric constant of minerals (in dielectric separators); 4) flotation separation of minerals based on the different ability of minerals to be wetted with water (in the presence of flotation reagents) and carried out on flotation machines of various designs); 5) visual selection of minerals with a steel needle under a binocular or microscope, etc.

The choice of this or that type of separation and the sequence of their complex use entirely depend on the task facing the researcher. Suppose it is necessary to check the field concentrate for the presence of diamonds in it. To achieve this goal, the concentrate is sent to electromagnetic separation, which is based on the differences in the electrical conductivity of minerals and the knowledge that diamond is a non-magnetic mineral. Moreover, it is an excellent dielectric. Separation is carried out on an electric separator PS-1 or ES-2, and sometimes using SIM-1 or 138T-SEM. For a single passage of material through the separator, it is difficult to obtain a satisfactory result. Therefore, the non-conductive fraction is subjected to double cleaning. The degree of reduction of the concentrate during electromagnetic separation ranges from 20 to 50 times (Burmin, 1988).

The reduced concentrate is usually sent to luminescent separation, which is a method of extracting crystals of various minerals that luminesce with visible light (glow) when they absorb various radioactive radiation. Depending on the type of radiation used, luminescent separation is divided into two types: X-ray luminescent and radioluminescent. X-ray luminescence separation is based on the use of X-rays. About ten brands of similar units are produced (LSh-2M, AR-1, AD-2M). Radioactive strontium beta rays are used in radioluminescent separation (90). An example is the PASA-1M radio luminescent apparatus.

The sensitivity limit of luminescent separators is usually limited by the size of mineral crystals, equal to 0.5 mm. Separator performance depends entirely on the grain size of the minerals. So, on the LSh-2M apparatus with a concentrate size of –16 + 8 mm, the productivity is 450 l/shift, and when analyzing the fraction –4 + 2 mm - 80-150 l/shift.

It is important to note that in addition to diamonds, barite, apatite, beryl, calcite, fluorite, zircon, scheelite and some other minerals have luminescence.

After passing through the luminescent separation, the substantially reduced concentrate can be sent for mineralogical analysis or for grease separation. Separation on sticky surfaces is based on one of the physical properties of diamonds - hydrophobicity. Due to their hydrophobicity, diamond crystals adhere to a sticky surface at the interface with water, while hydrophilic grains (wetted with water) do not adhere to fatty surfaces. The approximate composition of the fat mixture is as follows: petrolatum, autol No. 15 or No. 18 and cylinder oil.

After processing the concentrate on a sticky separator (for example, ZhA-1), the ointment with adhered grains is removed from the concentrator belt with a knife located under the tension drum of the conveyor. Then adhering grains of minerals are melted out of it in a water bath (95 °C). The melted mixture is poured through a mesh with holes of 0.2 mm, and the remaining solid fraction is washed 3-4 times with a 3% solution of liquid glass, and then with hot water until complete degreasing.

It should be emphasized that the degree of material reduction on separators with sticky surfaces depends on the material composition of the concentrate and varies from 350 to 10,000 times with a high quality of diamond extraction (96-98%) (Methods of selection ..., 1984). The separation efficiency depends on the grain size of the analyzed concentrate. According to the technical characteristics of the separator SLB-500, when processing material with a particle size of –8 + 2 mm, the productivity reaches 2 t/h, and when processing a concentrate with a size of –2 + 0.5 mm - 0.2 t/h.

In addition to the above methods of enrichment and extraction of diamonds from field concentrates, froth flotation, froth separation and film flotation are also used. According to M.I. Malanyin and his colleagues (Methods of selection ..., 1984), the average degree of diamond recovery during flotation and film separation varies from 75 to 98%. The most interesting are the methods of flotation, focused on the enrichment of large volumes of the smallest particle size classes (from 0.2 to 0.05 mm).

In recent years, a number of methodological techniques have been developed for extracting diamonds from concentrates using thermochemical enrichment (methods of the PGO “Yakutgeologiya”, IMR (a) and TsNIGRI).

Thermochemical enrichment is based on the high chemical resistance of diamonds. It is used both for the enrichment of small (50-60 g) diamond-containing concentrates, and for relatively large volumes, the CM-100 EL unit with a bath capacity of 100 liters is used. The thermochemical enrichment process begins with the fusion of the concentrate (the grain size of which is from 0.5 to 0.05 mm, and, if necessary, even less) with chemical reagents of a certain composition. A. I. Berlinsky (1988) describes this procedure in this sequence. Fusion of the concentrate is carried out at a temperature of 500-520 °C with sodium hydroxide. The alloy is carefully poured into a metal vessel, leached with water and passed through a metal sieve with 0.05 mm apertures. The enriched concentrate remains on the sieve, after which it is transferred to a glass beaker and treated with hydrochloric acid, first in the “cold”, and then when heated. After that, the concentrate is passed through a metal sieve and examined under a binocular microscope (diamond grains with a particle size of +0.05 mm are selected). Diamonds are weighed on a VLM-1 microanalytical balance with a scale division of 0.01 mg.

It should be noted that during thermochemical dissolution in the insoluble residue, in addition to diamonds, there are zircon, rutile, chromite, picroilmenite, moissanite, garnet, graphite and some other minerals.

If the amount of the insoluble residue is large (150 mg or more), then it is separated in the Clerici liquid diluted with water to a density of 3.6 g/cm3 to remove zircon, rutile, chromite, picroilmenite, and a part of garnet into a heavier fraction. Removal of magnetic minerals (garnet, chromite, etc.) with the help of Sochnev magnet is possible.

7.1 Features of laboratory studies of concentrates

The discovery of diamond crystals during prospecting is usually very rare, therefore, the main attention is focused on identifying the following satellite minerals (MCA): 1) pyropes Mg3Al2 (SiO4) 3 (hardness 6.5-7.0; pink, orange, red, often with purple shades; grain size from 0.1 to 3 cm, most often 2-3 mm; refractive index 1.725-1.780. In addition to kimberlites, they are part of rocks with a high degree of metamorphism, and sometimes lamproites; in the process of weathering pyrope as relatively chemically stable minerals pass into placer); 2) picroilmenites (Fe, Mg) TiO3 (hardness 5-6; resinous black with a greasy luster, this is how they differ from black trap ilmenites with a metallic luster; the grain size is from 0.1 mm to one centimeter; in the process of chemical weathering, their intense leucoxa occurs - reduction, and then complete decomposition; along the migration routes, they quickly wear out, and therefore an increase in the size and morphological preservation of grains is a reliable indicator of the proximity of the primary source); 3) olivines (Mg, Fe) 2 SiO4 (hardness 6.5; from colorless to olive green with a glassy luster, weakly pleochroic; in the process of chemical weathering they are completely destroyed and converted into clay products). 4) chrome diopside Ca (Mg, Fe, Cr) (A1, Si) 2O6 (hardness 6; emerald green, grass green and dirty green with a glassy luster; fragile, very sensitive to weathering and mechanical wear; as a rule , in placers they are found in very small concentrations); 5) chromites and chrome spinels FeCr2O4 (black with a metallic luster; grains ranging in size from 0.1 to 3.5 mm; hardness 5.5-7.5; very resistant to chemical weathering); 6) zircons, ZrSiO4 (grain size from 0.1 to 1.5 mm; as chemically very stable minerals, during the weathering of rocks, they are easily freed from their satellite dikes and mechanically pass into placers, and then, in the form of rounded grains, into sedimentary rocks); 7) apatites Ca (PO4) 3 (F, C1, OH) 7 (hardness 5; chemical composition and optical properties are similar to fluorapatite; from colorless to blue, green, yellow, brown and violet with glass luster; belong to the group minerals not resistant to weathering); 8) moissanite SiC (hardness 9.5; green-gray, black; grain size from 0.05 to 1.7 mm; very resistant to weathering); 9) magnetites Fe3O4 (hardness 5.5-6; iron-black; brittle; magnetic; when weathering, they are stable and are difficult to hydrate); 10) perovskites CaTiO3 (hardness 5.5-6; grayish-black, red-brown, orange-yellow and light yellow with diamond luster, resistant to chemical weathering processes).

It is very important to note that in most lamproites garnets are either almost absent or present in small quantities. As in kimberlites, they belong to the pyrope - almandine series. In addition, the diamondiferous lamproites contain knorringite garnets, albeit in a number of single characters. Therefore, in Western Australia, the main prospecting satellite minerals are chromite, chrome diopside and zircon (Temporary methodological ..., 1988). Before starting laboratory research to identify satellite minerals, the concentrate is screened, often with the release of new (compared to field) intermediate classes. For example, if concentrates of the following granulometric classes were obtained in the field: –6 + 4; - 4 + 2; –2 + 1 –1 mm, then in laboratory conditions the following classes can be additionally distinguished: –4 + 3; –3 + 2; –1 + 0.5; –0.5 + 0.25 and –0.25 mm. The main goal of identifying new granulometric classes is to evenly distribute the studied concentrate by classes, which is necessary for its better processing.

Many minerals contained in the concentrate have a magnetic susceptibility, sufficient to extract them into a magnetic fraction using electromagnetic separation. Strongly magnetic minerals are magnetite, pyrrhotite and others. Medium magnetic and weakly magnetic minerals are chromite, ilmenite, picroilmenite, almandine, pyrope and others.

 

Acid "Tsar's water"

Diamonds pop up

Concentrate

Concentrate

Washing of floating grains with rectified alcohol

Discharge of floating grains with diamonds into a filter funnel (diamond density 3.51 g/cm3)

Discharge of floating grains with diamonds into a filter funnel (diamond density 3.51 g/cm3)

Heavy liquid "Clerici" (density 4.25 g/cm3)

Draining the solution into the disposal container

Thermochemical dissolution