by Yuri SAFONOV, Corresponding Member, Russian Academy of Sciences, Deputy Director of the Academy's Institute of Ore Deposits, Petrography, Mineralogy, and Geochemistry
At the start of this century Russia held the proud place of the world's second largest producer of gold, after the Republic of South Africa. Its annual production of gold at the time averaged 40 tons and its total reserves were just under 1,000 tons (rising to 1,248 tons in 1913). Closer to our time, in the 1970s, the former Soviet Union mined nearly 300 tons of this noble metal a year. The output has since been falling, especially dramatically in recent years. Now, we have been left behind by all major gold-producing nations, South Africa, the US, Canada, and Australia, and an outsider, China, too.
With its gold ore reserves, Russia comes third after South Africa and the US. The reserves of gold itself are believed to be considerable, only if the annual output of the precious metals is kept up at today's level. Stepping up production by as little as 50 percent would keep gold users busy for 15 to 20 years. This is a common practice around the world, which is normally followed as reserves are steadily depleted and replenished. Not in this country, though, in the past few years at least.
The quality of minerals mined is an important consideration in the industry. Elsewhere in the world, mining primary rocks is believed to be worth the effort if they contain 5 to 7 grams of gold per ton of ore, some ores being economically rewarding even when they contain a meager 2 to 3 grams per ton. A large proportion of gold ores in Russia have a low gold content (2-5 g/ton) and are difficult to dress, expensive technologies being required to recover the metal. The quality of the minerals processed by this country's gold mining industry is acquiring high urgency in our days.
Gold problems are specific because of the metal's "noble" status. The metal neither oxidizes nor dissolves in a natural environment. It is used but rarely in industrial goods. Most of the gold ever mined is either deposited in bullion and coins with banks, or held in private hands as jewelry To meet the stable demand for this precious metal, Russia and other countries have to look for new gold ore sources in the 21st century. Priority must, therefore, be given to the exploration of the known gold fields. Russia, however, is extremely constrained in its practical options to undertake the effort. Actually, the options it will largely affect its ability to reverse the unfavorable trends in the development of its mineral wealth.
THE MINERAL RESOURCES
Official statistics in recent years has registered continuing depression in gold mining. In the mid-1970, the territory of present-day Russia yielded nearly 200 tons a year. This was the peak the industry reached in its history. In the past two decades, gold production has dropped to 120 tons. This deep decline has been precipitated by two factors-the wretched state of the Russian economy in general and deterioration in the quality of diminishing gold fields.
A map of gold-ore regions in Russia and former Soviet republics. Legend: 1- hypothermal and mesothermal gold deposits; 2-epithermal gold deposits; 3-mining areas: A-Akselvozh, B-Berezovo, Y-Yenisei, P-Patomsk, 1-lndigirka, K-Kolyma, C- Chukotka (in Russian territory only); 4-gold sulfide deposits (with gold recovery as a sideline).
Overall, the known and projected gold resources in Russia are great. Their structure and the location and commercial quality of gold ores are hardly propitious, however. Between 70 percent and 80 percent of the metal is recovered from placer deposits, which account for only about 10 percent of the total gold ore resources. Besides, new prospected gold placers have been added at a much lower rate than is needed to keep up production for years, and their number has decreased even more alarmingly of late.
As a matter of record, placer deposits have been mined for over 200 years in this country. The highest-yielding regions successively rose and waned in importance, moving eastward: the Ural Mountains (beginning in 1814), the Yenisei Ridge (from 1839), Vitim-Bodaibo (from 1864), and the Kolyma (starting in 1930). In the last several decades, gold mining has been kept up at a vigorous pace in the country's northeastern comer, including the Chukotka area, and in the Amur valley. Each of these areas has produced more than 900 tons of gold in all, an output that gave little incentive to look for vein gold in ingenous rocks elsewhere. By way of diversion, the first vein (hydrother-mal) deposit was discovered in the Uralsbackin 1745.
The largest share of vein ore prospecting funds in the former USSR was channeled into areas with favorable climatic and economic conditions. A good example of this policy is the gold-bearing ores at Muruntaus, in the Southern Kyzylkum desert of Central Asia, which was discovered and rapidly explored in the early 1960s. Today, this gold deposit is the core of the gold industry in the Republic of Uzbekistan.
Vein or primary gold ore deposits in Russia have continuously been discovered over the 20th century, and their number now has reached nearly 180. Today, vein gold is mostly mined in the Magadan Region (Kubaka, for example) in Russia's northeast. Relatively small quantities of the metal are produced in Transbaikalia and the
Amur valley near Russia's southeastern frontiers, and larger quantities are recovered in the Central Aldan area (at Kuranakh), the Yenisei Ridge (Sovetskoye and Olympiada), and south of Lake Baikal (Zun-Kholbinsk). Finally, very small amounts of gold are mined in the south of the Krasnoyarsk Territory and in the Ural Mountains. Kubaka is the biggest producer of vein gold, with a yield of around 16 tons in 1998 alone.
Developing stand-by deposits is a hard task today, since most of them consist of primary ores that are difficult to dress and contain relatively little gold. Enormous investments (from several hundred million to billions of dollars) and much time are, therefore, required to develop new ore processing technologies. Deposits of this variety include, in the first place, Olympiada (with a total content of over 400 tons of gold), which we referred to above, Nezhdaninskoye in Yakutia (about 300 tons), and Sukhoi Log in Transbaikalia, for which no reliable estimates are available.
The profitability of gold deposit development depends, about all, on the quality of the ores and mining methods-open-pit (or strip) mining or underground mines (shafts). Gold mines around the world reach phenomenal depths: in Kolar, India, the descend to 3,200 m, in Moro Belho, Brazil, 3,400 m, and in Witwatersrand, South Africa, as much as 3,800 m (exploratory wells to be sunk soon will go down to 6,000 m).
Russia is not yet ready to plunge to these great depths. At Berezovo and Kochkar in the Urals, gold mines are some 600 m under the surface, and nearly the same depths have been hit at Sovetskoye (Yenisei Ridge) and Darasun (Eastern Transbaikalia). Most of the primary ores in Russia are, however, mined within the depth range of only a few hundred meters.
This leads us to the conclusion that the deposits available to the gold mining industry are too limited to expect major breakthroughs, unless drastic measures are taken to turn the situation around.
HOW CAN GOLD ORE CONCENTRATIONS BE PREDICTED?
A reliable prediction of the gold content in gold-bearing ores could only be made after a considerable body of knowledge about the reserves and projected resources of gold in the depleted and prospected deposits had been built up. As soon as we have the figures we see a striking difference between the quantity of the noble metal deposited in the rocks of specific geologo-genetic types. The largest deposits (taking into account the extent of their erosion) serve as benchmarks helping estimate the maximum gold concentration levels in the so-called ore-forming systems associated with the formation of a particular deposit or a group of deposits. True, the concept of "ore-forming system" is still construed differently in different situations. In the case of hydrothermal gold ore deposits it normally implies a combination of regions where ore-bearing solutions form and migrate, to eventually settle as ores. The conditions in which such systems arise and their evolution have been studied but very little so far.
The highest known concentration of gold occurs in the deposits of Witwatersrand, South Africa, where the total gold reserves are estimated at between 70,000 and 100,000 tons. The famous region of some 250,000 km2 in area has six distinctly recognizable main fields, each containing from a few thousand
to a few dozen thousand tons of the noble metal. Such high concentrations are not to be found in gold-bearing conglomerates elsewhere in the world-Brazil, Central Africa or Canada.
The overwhelming majority of hydrothermal deposits (at least 1,500 around the world) contain up to 100 tons of gold each. Some 150 of them only have stored up more than this. Actually, they contain at least 70 percent of the total known reserves of gold and some 80 percent of the projected resources. The latter include nine gold- ore giants each holding around 1 million tons of gold. Taking account of their eroded particles creating placer deposits under favorable conditions, these figures give an idea of the maximum yields of the respective ore-forming systems. For example, the gold field system at Muruntaus has, by this measure, proved to be the most productive of all (with an estimated 3,000 tons of gold deposited within its boundaries). The maximum productivity of some ore-forming systems of other types can be put at 3,000, 1,200, 1,000, 500, 300, 200, and 100 tons. These are very approximate estimates, of course, being based on the figures available for deposits that have been discovered to this day. They are important, however, for future projections, providing a yard-stick in assessing the gold-bearing capacity of existing and new gold-rich regions by analogy.
To make projections, the manifestation of ore-forming systems of different genetic types is related to the differentiated gold-bearing capacity of different metallogenic provinces, zones and belts, even though the causes of this differentiation are not completely clear. Actually, some areas up to 1,000 km long may have just a few deposits with total reserves of a few hundred tons, while others, for example, the Abititi on the- Canadian Shield (less than 300 km long) encompass dozens of fields with a total content in excess of 10,000 tons of the noble metal. The Canadian belt includes three clusters of very high concentration (2,000 to 3,000 tons). Similar clusters of gold within ore regions have been established in some other metallogenic provinces and belts as well.
The ideas we have about the differentiated productivity of ore-forming systems and its maximum levels, and also about the linear cluster disposition of highly productive systems provide a basis for projections of new gold-bearing regions and for a reassessment of the prospects in those already discovered in Russia.
SOURCES OF VEIN GOLD IN RUSSIA
Nearly all Russian specialists share the view that the short-term prospects for the gold-mining industry in this country are linked to primary deposits. To remind, we have over 150 of them, only a few of them past the prospecting stage. The majority of these deposits date from the Phanerozoic (the last 600 million years) and are mostly gold-quartz and gold-carbonate veins. No major ancient Pre-cambrian deposits (over 600 million years old), the likes of Wit-watersrand (2.9 to 2.5 billion years) or the gold-ore giants in Australia and India, have been discovered in Russia as yet. True, signs of such deposits have been found in Russia's Kola Peninsula and Karelia, the Aldan Shield, and the Voronezh land mass of the East European Platform.
This promise regardless, Russia looks set to depend on placer gold in the next 10 to 15 years. There are, however, very slim hopes of any new discoveries of placer deposits (similar to Kolyma or
Yenisei). On the bright side, the existing placer deposits have not been fully exhausted, according to specialists, Nikolai Shilo, Boris Benevolsky, and Natalia Patyk-Kara. Expectations of a significant growth in reserves are now tied to the smaller ones which have been passed up previously because of their difficult geological conditions.
Promising sources of vein gold in the Urals and southern Siberia may be found in gold-bearing weathering crusts, both young and buried ancient formations. Deposits of this kind are expected to be discovered under the platform shield of the Voronezh land mass.
About 40 known and projected gold ore regions existing in Russia today are shown on a unique map. Some of them, perhaps the most promising ones, deserve special attention. Two regions, Berezovo and Kochkar, are in the Urals, the best studied gold- bearing belt in the country. The former has not yet been fully exhausted to be written off, despite its long-standing operation (around 300 tons of metals have been extracted at Berezovo). The fluid-magmatic system manifesting here has a very high productivity (gold concentrations of as much as 600 tons commonly occur in similar systems, within a combination of various gold ore bodies, with mineralization frequently going more than a kilometer down). The Kochkar gold-bearing cluster south of Berezovo can be assessed in much the same terms: some of the deposits discovered there resemble gold-bearing weathering crusts. The quality gives much hope to developers.
The young, and promising, regions in the Urals are, above all, the Akselvozh (Kozhim) area in the Komi Republic, where the local geologists have recently identified gold-bearing stockwork zones,(*) also containing platinum-palladium and rare earth minerals. I must emphasize that the ores found here are easy to dress. Besides, the new mineralogo-geochemical type of gold mineralization discovered here is associated with the late Hercynian (about 300 million years ago) metallogenic activity in the northern part of the Ural mobile belt. Curiously, mineralization in this region is similar to the ores of the unique Olympic Dam ore field in southeast Australia, where large deposits of copper, uranium, and gold (about 1,200 tons) have been discovered.
Russia has its chief stand-by gold deposits, Olympiada and Sukhoi Log, in the gold ore regions of the Yenisei Ridge and the Patomsk uplands in Siberia. The Yenisei Ridge, the locus of Olympiada, is
* Stockwork is an ore body of irregular shape formed by rocks cut through by a dense cobweb of mineral veins and veinlets.- Ed.
an old development region, from which over 900 tons of gold have been extracted. Olympiada itself contains reserves in the same class. A part of it lying in the weathering crust is being mined today. Its primary impregnated gold sulfide ores are hard to dress, however, requiring expensive specialized technologies to release gold.
The Sovetskoye ore field 50 km south of Olympiada contains gold-quartz stockwork veins. The approximately 100 tons of gold recovered here and the depths of 500 meters reached by miners do not shut out the prospects of this deposit yielding more gold after many years in operation. Sovetskoye is a productive ore-forming system, like that at Muruntaus. By available estimates, Olympiada and Sovetskoye may have a very high ore potential.
Smaller gold ore deposits have been discovered in the central and southern parts of the Yenisei Ridge, but they have been little studied so far.
The Patomsk ore region, locked in between the Lena, Vitim, and Chara rivers, otherwise known as Bodaibo, holds a special place in Russia's inventory of noble metals. The area includes Sukhoi Log, the country's largest deposit containing gold and platinum as well.(*) Its ore-forming system has a very high fluid activity; the deposit shows signs of carbon-carrying gaseous flow rising from underlying depths. This gives us reasons to expect unique gold-ore concentrations (let me observe that carbon-containing gases played a key role in the transport of gold to the celebrated Witwatersrand deposit). Direct evidence of a highly productive ore-forming system that was at work at Sukhoi Log is provided by its satellite deposits-Pervenets, Golets, and Vysochaishy, among others, and the high gold-bearing capacity of the area as a whole.
There also is much gold in the placer deposits at Indigirka and Kolyma in East Siberia (which jointly contain some 2,500 tons of gold). The numerous primary deposits which have been discovered here lately include some big ones (like Natalkino, with over 100 tons). These regions are distinguished by a combination of different kinds of deposits which may only typify the top parts of the ore-deposition zones of different systems. This projection can also be applied to the Chukotka (Central Chukotka) region, where a major deposit, Maiskoye, with reserves of nearly 300 tons (at a relatively low gold content in the ores and generally hard to dress) has been discovered.
It is reasonable to expect discoveries of new gold-bearing ores to be made in Eastern Transbaikalia, where intensive Mesozoic (less than 230 million years ago) tectomagmatic activity is high. Discovery is about to be made of a major gold-bearing province, including a few uranium deposits. An identical combined mineralization was registered in the east of the Aldan Shield.
A special role in the projections of new major gold concentrations in Russia is assigned to epithermal deposits, frequently termed "volcanogenic". In the last few decades, they have contributed most to the growth of gold reserves in the world. Significant discoveries associated with them were made in the 1970s and 1980s in the southern part of the Pacific volcanic belt. A single major deposit, Kubaka (with over 100 tons of gold), already mentioned above, has so far been discovered in the Russian part of the belt. The Amethyst deposit (about 100 tons) in the northern Kamchatka Peninsula and the Mnogovershinnoye deposit in the southern part of the Okhotsk- Chukot volcanogenic belt can be put in this class in terms of reserve size. The remaining deposits in the area can, at best, be placed in the median category (such as Aginskoye, with up to 50 tons). The multiple development of highly productive ore- forming systems within these geological structures containing gold-silver and gold- bearing copper-porphyry deposits (for example, in the Carpathian Mountains and Chile) gives us reasons to assume that a more detailed exploration of the Okhotsk- Chukot volcanogenic belt and Kamchatka will produce new discoveries.
A significant proportion of gold (up to 15 percent of the total) in Russia is recovered from sulfide ores (at Norilsk, in the Urals, and elsewhere). This source will continue to play a role in the coming new century. Very probably, it will have an ever greater importance, above all, with the development of new gold winning technologies.
As technological progress continues around the world, the depth of gold mines is likely to grow in the next few decades. In this country, however, it will harly exceed one kilometer, given its geological and other conditions. Russian experts are, therefore, building their projections on this depth of gold ore occurrence in existing and new areas. Time is ripe to make prospecting to depths of up to 1 km (instead of the maximum 300-500 m today) the order of the day.
In other words, it is a realistic objective to raise annual gold production in Russia to 250 or even 300 tons in the 21st century.
* See: N. Laverov et al., "Platinum and Native Metals of the Sukhoi Log Deposit", Science in Russia, No. 2, 1999. -Ed.
Permanent link to this publication:
LUnited States LWorld Y G