Geological and Industrial Types of Gold Ore Deposits in Kazakhstan
Abstract Generated abstract
This paper surveys the metallogeny and industrial classification of gold ore deposits in Kazakhstan, emphasizing that the region is a major ore gold province with numerous districts and more than 1,000 known mineralization points, occurrences, and deposits. Drawing on accumulated prospecting, exploration, and mining data, it distinguishes gold mineralization across Precambrian, Caledonian, and Variscan epochs and organizes deposits into ore formations and structural morphological groups, including quartz-vein, veinlet-disseminated stockwork, and metasomatic silicification types. The study identifies the gold-quartz-sulfide, secondary quartzite, and pyrite-polymetallic formations as having primary industrial significance, describes representative deposit types such as Bestyube, Bakyrchik, Maikain, and Vasilkovskoye, and argues for balanced exploration of large, medium, and small deposits, including renewed assessment of conserved sites and Precambrian gold potential.
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GEOLOGICAL AND INDUSTRIAL TYPES OF GOLD ORE DEPOSITS IN KAZAKHSTAN
V. A. NARSEEV, V. A. GLOBA, N. G. GRAZHDANTSEV, O. A. SINEV
(KazIMS, TsKGU)
Kazakhstan is among the largest gold-bearing provinces of the Union. It includes 13 gold-ore districts, in which more than 1,000 points of mineralization, ore occurrences, and gold deposits are known. Unlike other gold-bearing provinces of the country, Kazakhstan is a supplier only of ore gold. Placer deposits have occupied a subordinate place in gold mining and at present are of no practical interest. Along with gold-ore deposits proper, complex deposits play a significant role in the metal balance.
An analysis of the regional metallogeny of gold, carried out under the direction of Academician K. I. Satpaev, made it possible to compile prognostic-metallogenic maps for gold for Kazakhstan at scales of 1:500,000 and 1:200,000, and to distinguish on its territory the following gold-bearing districts: 1. Dzhetygara, 2. Mugodzhar, 3. Stepnyak, 4. Maikain, 5. Balkhash-bordering, 6. Chingiz-Tarbagatai, 7. Kalba, 8. Altai, 9. Dzhungar, 10. North Tien Shan, 11. Betpakdala–Chu-Ili, 12. Karatau, 13. Dzhezkazgan–Ulutau. Each of them is characterized by distinctive features of development and metallogeny.
One of the characteristic features of the metallogeny of gold in Kazakhstan is the presence of deposits in all epochs from the Precambrian through the Permian inclusive.
The Precambrian metallogenic epoch until recently was regarded as unpromising for gold. However, studies in recent years have established an elevated gold content in Precambrian deposits of a number of districts of the republic. Of special interest are the pyritized quartzites of the Bekturgan Series of the Archean in Ulutau and of the Kokchetav Formation of the Lower Proterozoic within the area of the Kokchetav block. Gold mineralization is also recorded in sedimentary deposits of quartz composition in the Karsakpai Series of the Upper Proterozoic. The gold content in these deposits sporadically exceeds the Clarke value by one or two orders of magnitude, and in individual cases is higher. In connection with the deep metamorphism of Precambrian sediments, the primary nature of the gold mineralization has not yet been fully determined.
decoded, but regardless of genesis it undoubtedly deserves attention. In this type of mineralization a lithological control is clearly expressed—the confinement of gold mineralization to monoquartzites containing iron minerals: pyrite, hematite, and magnetite.
A number of vein occurrences of gold in the framing of the Kokchetav block and within the Mointy–Kyzyl-Espe uplift are also associated with the Precambrian epoch.
The Caledonian metallogenic epoch is characterized by varied and intense gold mineralization. Gold mineralization of this epoch was manifested chiefly in Northern Kazakhstan, where such large gold-ore districts as Stepnyak and Maikain are known. The formation of Caledonian gold-ore deposits is connected with the development of geosynclinal zones from the Riphean to the Lower Paleozoic and corresponds to their middle and late stages. The mineralization is associated mainly with Ordovician intrusions of moderately acidic composition. It is characterized by a diversity of morphology, conditions of occurrence, and mineral types. The structural position of the ore fields is determined by folded disjunctions. Lithologic-stratigraphic control is expressed in the predominant confinement of gold mineralization to the Ordovician flysch formation. Commercial deposits are known only for the Late Caledonian stage. Early Caledonian ore genesis is characterized by small occurrences. Mineralization was manifested chiefly in areas of development of the Caledonides proper, partly in activated Precambrian zones and as fragments within Variscan structures.
The Variscan metallogenic epoch in Kazakhstan is characterized by the most diverse types of deposits. Gold is widely distributed in Eastern Kazakhstan, Dzungaria, the Balkhash region, Central Kazakhstan, the Northern Tien Shan, and the Mugodzhar. Ore districts are localized within the Variscan geosynclines—the Dzungarian-Balkhash, Zaisan, and others—corresponding in time of formation to the final orogenic stages of development. The most interesting deposits are epithermal, near-surface ones associated with volcanogenic formations of the Upper Paleozoic. Recent studies have established Variscan mineralization also in the Caledonian structural-metallogenic zones proper, which emphasizes the throughgoing development of gold metallogeny. Upper Paleozoic gold deposits are characterized by a great variety of morphological and formation types, and by the association of mineralization with magmatic formations of near-surface facies of varied composition. Subvolcanic intrusions and extrusions of complex volcano-plutonic structures play a notable role in ore formation. The largest deposits of this epoch are known in Western Kalba, Dzungaria, and the Balkhash region. A number of them are being exploited, while others are at the exploration stage.
On the basis of the extensive information accumulated over more than a century of prospecting, exploration, and gold mining in Kazakhstan, it is now possible to distinguish six gold-ore formations: skarn gold-ore, gold-quartz-sulfide, secondary quartzite, gold-tourmaline, listvenite, and pyrite-polymetallic (Table 1). At present, among them the gold-quartz, secondary-quartzite, and pyrite-polymetallic formations are of industrial significance.
The skarn gold-ore formation is represented by a small number of objects. They are observed in the exocontacts of large
masses of granitoids in the form of zones and bodies of veinlet-disseminated ores. Among the ores occur both gold-copper and gold-silver types. Gold is associated with silver, copper and iron sulfides, and tellurides. Deposits of this formation are small in size (Ichkeulmes, Slushoky, and others).
The gold-quartz-sulfide formation occupies the dominant place in the series under consideration. Characteristic representatives are the worked-out deposits Dzhetygara and Stepnyak; those being exploited—Bestyube, Bakyrchik, Dzhelambet, Kvartsitovye Gorki, Vasil'evskoe, Arkharlin; and those at the exploration stage—Vasil'kovka and others.
By mineralogical associations, structural-morphological features, relation to magmatic bodies, and other positions, all deposits of this formation can be divided into five unequal groups.
The first group includes deposits with arsenopyrite-bearing veinlet-disseminated ores localized in the zone of exo- and endocontacts of large intrusions of increased basicity. A representative of this group is the Vasil'kovskoe deposit, recently discovered on the Kokchetav block. This mineral type is currently regarded as highly promising.
A large group comprises a number of deposits of the gold-quartz-sulfide formation on the basis of their close connection with small intrusions and the commonality of their mineral composition, which is determined to a considerable degree by the level of erosional truncation. Some of them are localized in supra-intrusive zones (Stepnyak, Kvartsitovye Gorki), others in the apical parts of small intrusions (Akzhal, Akbeit, Dzhelambet, and others). Under special conditions, deposits of the so-called thermostated stocks were formed (Bestyube). In this group almost all morphological types of mineralization occur—veinlet-disseminated, stockwork, mineralized zones, and vein.
A distinctive group is formed by deposits with arsenic-bearing gold mineralization (Bakyrchik, Vasil'evskoe, and others) in flyschoid sequences.
A special position in the formation under consideration is occupied by deposits carrying gold-silver mineralization in zones of propylitization (Arkharlin) or adularization (Kuder) in association with subvolcanic intrusions of increased alkalinity. They are, as it were, transitional to deposits of the secondary-quartz formation.
The gold-ore formation of secondary quartzites has been known in Kazakhstan since long ago, but its industrial significance has been proved only in recent years after the discovery of a number of deposits of this type in the Mugodzhary, Dzhungaria, and the Balkhash region (Yubileinoe, Dalabai, Taskora, Naurazbai, and others). Their characteristic features are: association with shallow intrusions and paleovolcanoes, confinement to volcanogenic formations, a specific set of wall-rock alterations (propylitization, adularization, kaolinization, silicification), original textures and structures of the ores, the silver-bearing character of the gold, and the presence of sulfosalts, tellurides, argentite-acanthite, antimonite, and others.
The gold-tourmaline formation is widely developed, but so far has no major representatives. It is associated with subvolcanic bodies of moderately acidic composition. Small deposits belong to this type (Zheleznaya Gorka, Air, and others).
The listvenite formation has been distinguished as an independent type on the basis of study of the Maralikhinskoe deposit in Southern
in Altai, Vera-Char in Kalba, and a number of others. Its connection with hypabyssal intrusions of intermediate composition and its association with gabbroids—hyperbasites of deep-fault zones—are established. It is of no substantial importance.
The pyrite-polymetallic formation belongs to the number of promising formations, with stable mineralization of gold, nonferrous metals, and barite in bodies of massive and disseminated ores. Ores of this type are mined as complex ores for gold, copper, lead, silver, zinc, and barite. Representatives of this formation are the deposits of the Maikain group, as well as Kosmurun, Mizek, Tortkuduk, and others.
According to conditions of occurrence, structural-morphological features, characteristic mineral associations, the form in which the metal occurs, and the scale of mineralization, the gold deposits of Kazakhstan can be combined into three major morphogroups: quartz-vein, veinlet-disseminated, and metasomatic silicification, and subdivided into 12 geological-industrial types (Table 2).
In the quartz-vein group, the Bestyube type is of greatest interest. This type is characterized by thermostated conditions of formation and, in connection with this, a considerable vertical extent of productive mineralization. Industrial mineralization has been intersected by boreholes at a depth of 1000 m without substantial signs of its pinching out. The quartz-vein bodies form a framework network of several systems in the heating zone of pipe-like granitoid stocks among flysch deposits. Of the series of quartz veins, the diagonal ones are the most productive; on the whole, they may be regarded as ore shoots. The ores are low-sulfide, represented by pyrite, sphalerite, arsenopyrite, pale ores, antimonite, and free gold. In terms of scale, Bestyube is among the largest in the province and, in a number of features, is unique. It is noteworthy that the deposit has not been affected by erosion; therefore its volumetric study appears possible from the supra-ore halos down to the root parts.
Other types of the quartz-vein group—Stepnyak, Aksu, and Dzhetygara—are characterized by small and medium scales. Some of them are represented by low-sulfide ores (Stepnyak, Aksu), others by moderately sulfide ores (Dzhetygara), with free and bound gold. The vertical extent of industrial mineralization ranges from 200 to 800 m. Gold is distributed in the veins very unevenly, with clearly expressed shoots. All the types of this group considered belong to the hydrothermal class.
The group of veinlet-disseminated (stockwork) mineralization combines five industrial types of deposits.
The Bakyrchik type occupies the principal place among them. A 10-year period of intensive prospecting for deposits of this type, known as “mineralized zones,” is associated with the history of its discovery. The Bakyrchik deposit differs from all others above all in its large scale. The ore bodies are mineralized rocks—carbonaceous-clayey shales and sandstones. The mineralization is essentially arsenic, with finely dispersed gold in arsenopyrite and pyrite. The distribution of gold is comparatively uniform. In connection with the clearly expressed lithological-stratigraphic control of mineralization, in recent years the question has been raised of a sedimentary-hydrothermal genesis of the mineralization.
Table 2
Geological-industrial types of gold-ore deposits of Kazakhstan
| No. | Deposit type | Structural-morphological group | Mineral associations | Form of ore bodies | Ore scale | Vertical extent of mineralization, m |
|---|---|---|---|---|---|---|
| 1 | Bestyubinsky | Quartz-vein | Low-sulfide: pyrite, sphalerite, arsenopyrite, tellurides, pale ores, free gold. | Veins. | Large | more than 1000 m |
| 2 | Stepnyaksky | Quartz-vein | Low-sulfide: pyrite, galena, pale ores, carbonates, free gold and gold in pyrite. | Veins. | Medium | more than 700 m |
| 3 | Dzhetygarinsky | Quartz-vein | Moderately sulfide: pyrite, arsenopyrite, free gold and gold in sulfides. | Veins. | Medium | more than 800 m |
| 4 | Aksuysky | Quartz-vein | Low-sulfide: pyrite, arsenopyrite, carbonates, free gold and gold in sulfides. | Veins. | Small | up to 200 m |
| 5 | Bakyrchiksky | Veinlet-disseminated (stockwork), mixed. | Arsenopyrite, pyrite, stibnite, gold in sulfides. | Lenses, deposits, ribbons. | Very large | 1000 m |
| 6 | Dzhelambetsky | Veinlet-disseminated (stockwork), mixed. | Pyrite, pale ores, tellurides, free gold and gold in sulfides. | Lenses, deposits, ribbons, stockworks. | Large | about 1000 m |
| 7 | Quartz Hills | Veinlet-disseminated (stockwork), mixed. | Pyrite, arsenopyrite, stibnite, pale ores, galena, gold in sulfides. | Lenses, deposits. Pipe-shaped deposits. | Medium | about 800 m |
| 8 | Maikainsky | Veinlet-disseminated (stockwork), mixed. | Pyrite–copper–barite–polymetallic. | Deposits. | Large | more than 800 m |
| 9 | Vasilkovsky | Veinlet-disseminated (stockwork), mixed. | Arsenopyrite, bismuthinite, pyrite, gold in sulfides. | Lens-shaped stockworks, lenses. | Medium | more than 300 m |
| 10 | Arkharlinsky | Metasomatic silicification. | Pyrite, galena, argentite, free gold and silver. | Lenses and deposits, series of veins. | Small | up to 200 m |
| 11 | Yubileiny | Metasomatic silicification. | Pyrite, chalcopyrite, stibnite, gold. | Deposits. | Medium | about 500 m |
| 12 | Naurzbaĭsky | Metasomatic silicification. | Pyrite, galena, stibnite, tellurides (?), gold. | Stock-shaped, pipe-shaped bodies, lenses. | Small | about 200 m |
Complex gold-bearing deposits (copper and polymetallic deposits).
Systematics of gold-ore deposits of Kazakhstan
Table 1
| Ore formation | Genetic or paragenetic relationship with intrusions | Position relative to magmatic bodies | Mineral types | Characteristic mineral associations | Structural–morphological characteristics | Host rocks | Wall-rock alterations | Examples of deposits and ore occurrences |
|---|---|---|---|---|---|---|---|---|
| Native gold | Deep intrusions of granitoid composition. | Proximity to magmatic bodies. | Gold-bearing, gold-serebryany. | Chalcopyrite, pyrite, gold, silver, tellurides of gold and silver. | Zones and veinlets of veinlet-disseminated ores. | Limestones and calcareous rocks. | Amphibolization, chloritization, epidotization, etc. | Nikulmes, Suluoky. |
| Skarn–gold-ore | Large intrusions of granitoid composition. | In the exocontact zone. | Gold–copper, gold–scheelite, gold–silver. | Chalcopyrite, pyrrhotite, gold, scheelite. | Veins, zones of veinlet-disseminated ores. | Granodiorites, diorites, quartz diorites. | Beresitization, skarnification, sulfidization, sericitization. | Bayarbayevskoye, Vasilkovka. |
| Gold–quartz–sulfide | Large intrusions of granitoid composition. | Endocontacts of intrusions, interior parts. | Gold–pyrrhotite–arsenopyrite. | Pyrite, chalcopyrite, galena, gold. | Deposits of large, stockwork-type quartz veins, systems of small veins. | Sandstone–siltstone sequences, granodiorites, quartz diorites, volcanic rocks. | Beresitization, propylitization, silicification, chloritization, sericitization. | Quartz Hills, Akzhal, Gorny, Stepnyak, Akzhal, Dzhar, Bestyube, Vasilkovsky, Baladzhal, Dzhelambet, Dzhentara, Bestyube. |
| Gold–quartz–sulfide | Small stocks of moderately acidic granitoids. | Marginal parts of stocks, their upper parts; especially the roof zones of granitoid massifs. | Antimonite, telluride, amalgam, arsenopyrite. | Characteristic mineral associations vary from the level of the section. | Sandstone–siltstone sequences, granodiorites, quartz diorites, volcanic rocks. | Beresitization, propylitization, quartzification, sericitization. | Bakyrchik, Eshkeolmes, Zhaima, Aleskoye, Kant-Chingiz, Amansai. | |
| Gold–quartz–sulfide | Series of dikes and granitoids (granite-porphyries) of acidic composition. | Dikes and granitoids. | Pyrite, arsenopyrite, galena, sphalerite, scheelite, chalcopyrite. | Pyrite, galena, sphalerite, chalcopyrite, scheelite, barite. | Sandstone–siltstone sequences. | Beresitization, skarnification. | Akzharli, Kuder. | |
| Gold–quartz–sulfide | Subvolcanic bodies of medium to high alkalinity. | Endo- and exocontact zones. | Pyrite, galena, sulfosalts of silver, argentite, etc. | Pyrite, galena, sphalerite, argentite, etc. | Veinlets of medium and basic composition. | Propylitization, alunitization. | Akzharli, Kuder. | |
| Gold–quartz–sulfide | Without visible connection with intrusions. | — | Pyrite, galena, carbonate, barite. | Pyrite, galena, carbonate, barite. | Various. | Various. | Sericitization, chloritization. | Taily. |
| Secondary quartzites | Small deep intrusions of acidic composition. | Endo- and exocontact zones. | Gold–polysulfide, alunite–pyrite, tourmaline–pyrite, chalcopyrite. | Pyrite, galena, sphalerite, chalcopyrite, sphalerite. | Lenses, deposits of veinlet-disseminated and ore breccia forms. | Volcanogenic sequences. | Propylitization, alunitization, kaolinization, silicification. | Dolobay, Akzhary, Naurzobay, Yubileiny, Taskora. |
| Secondary quartzites | Deep intrusions of acidic composition, subvolcanic bodies, dyke bodies. | Endo- and exocontact zones. | Pyrite–chalcopyrite, arsenopyrite. | Pyrite, chalcopyrite, arsenopyrite. | Veins, veinlets. | Volcanogenic sequences. | Tourmalinization, skarnification. | Zheleznyaya Gorka, Anir, etc. |
| Gold–tourmaline | Subvolcanic bodies of medium and acidic composition. | Endo- and exocontact zones. | Pyrite. | Pyrite, carbonate. | Veins, stockworks. | Ultrabasites, gabbroids. | Carbonatization, chloritization. | Maralikhinskoye, Vorchar. |
| Listvenite | Hypabyssal intrusions of acidic and intermediate composition. | Endo- and exocontact zones. | Barite, galena, sphalerite, gold, pyrite, chalcopyrite, pyrrhotite. | Barite, galena, sphalerite, gold, pyrite, chalcopyrite, pyrrhotite. | Lenticular and vein-shaped bodies. | Basic effusives. | Chloritization, sericitization. | Maikan, Tortkuduk, Mizhek, Komurshi, etc. |
The Dzhelambet type is widely known. It is especially characterized by localization of disseminated mineralization in intrusive bodies and by a stockwork form of the ore bodies with a low metal content. The depth of mineralization reaches 1000 m, with a number of stockworks being mined by open pits to 120 m.
The industrial type of Kvartsitovye Gorki differs from all the others in its isometric, pipe-shaped deposits of brecciated mineralized rocks, extending downward into the apical parts of intrusions. They are very similar to ore explosions. The gold is of fine class, of low concentration; the mineralization is of medium scale.
The Maikain type is widely known as gold–pyrite–polymetallic–barite, with the indicated components having almost equal importance. It is characterized by a folded distribution of sheet-like ore bodies, great depth of mineralization, and large scale.
The Vasilkovskoye industrial type is in the study stage. It significantly broadens the prospects for gold in the Kokchetav block and its margins. The ores of this type are highly arsenical, and the gold is finely dispersed. Ore formation at the deposit was preceded by intensive alkaline metasomatism. Stockwork-veinlet mineralization is confined to the apical parts of diorite intrusions. The mineralization has been traced to a depth of 500 m, and the lower boundary of mineralization has not been reached.
The group of deposits of metasomatic framing is represented by three industrial types. All of them are in the study stage; therefore, their prospects and scale have not yet been fully assessed.
The Arkharla type is associated with subvolcanic activity. The ore bodies have the form of lenses, deposits, vein series, and stockworks. Mineralization at the known occurrences has a limited vertical amplitude and an extremely uneven and pocket-like distribution of gold, with a high silver content. In the ore fields, metasomatic alteration of rocks with distinctly expressed volumetric zoning has been widely manifested.
The Yubileiny type is analogous in a number of features to the Arkharla type, but, unlike it, is localized in the exocontact zone of hypabyssal intrusions.
In speaking of industrial types of gold-ore deposits, one cannot pass over in silence a number of fundamental questions of the prospective assessment of regions.
In recent years, primary attention has been given to the search for large and unique gold deposits, and the very problem of expanding the raw-material base is placed exclusively on this foundation. Such a formulation of the question should, of course, be welcomed, but other factors must also be seen. During the last ten years, despite considerable efforts, very few large deposits have been discovered. The search for large objects inevitably weakens attention to the identification and especially the assessment of small and medium-sized deposits, as a result of which a number of operating mining enterprises find themselves in a difficult position. Such a one-sided approach fetters initiative and narrows the front of prospecting work in places where there are real prospects for identifying deposits of comparatively small scale.
In the questions touched upon, apparently, the most correct course will be a reasonable combination of the problem of searching for and assessing large, medium-sized, and small gold-ore deposits. The successful resolution of these questions is impossible without a deep study of the principal regularities
features of the localization and spatial distribution of ore fields of all scales and of different structural types. Conserved deposits play a significant role in this problem. An important task in this direction is the reassessment of their prospects. A fundamentally new direction is the study of Precambrian gold metallogeny in Kazakhstan. In view of the specificity of geosynclinal sedimentation, considerable attention must be given to studying the gold potential of both coarse terrigenous and flysch formations of quartz–iron composition of Precambrian age.