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V V Kolpakov - One of the best experts on this subject based on the ideXlab platform.
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native gold from the kamenka barabanovsky and kharuzovka alluvial Placers northwest salair ridge western siberia russia typomorphic features and possible bedrock sources
Ore Geology Reviews, 2020Co-Authors: Pavel A Fominykh, Peter A Nevolko, Tatyana V Svetlitskaya, V V KolpakovAbstract:Abstract Northwest Salair Ridge, is one of the oldest alluvial gold mining regions; it is located in the western part of the Altai-Sayan folded area. The Placers localized along the Kharuzovka and Kamenka-Barabanovsky creeks (the right-branch of the Suenga River) were chosen for investigation. The only bedrock deposit in the study area is the Novolushnikovsky gold deposit located in the Suenginsky placer field of the Egoryevsky district. The source of gold supply for the Kharuzovka and Kamenka-Barabanovsky Placers spatially related to the hypothetical continuation of the type II’ ore zones of the Novolushnikovsky deposit. The composition of gold grains derived from Placers was determined based on a representative collection. A distinctive feature of native gold from type II’ ores is unusually high content of Hg, up to 20 wt.%. The composition of gold grains from studied Placers shows that the average Hg content is 1.5-5 wt.%. However, there is a group of Hg-rich Placers (less than 1% of the collection), where the mercury content is as high as 16 wt.%. We suggest that possible alteration of the gold composition manifested both in the rims and in the cores is represented by significant loss of Hg, while the other analyzed components underwent relative enrichment. The first time reported demercurization processes occurring under the supergenic conditions determine this alteration. The erosion of Novolushnikovsky deposit type II’ ore zones are the source of supply of Hg-rich gold in the Kharuzovka and Kamenka-Barabanovsky Placers. These Placers were analyzed for the existence of mineral inclusions in gold grains. The presence of placer gold grains with mineral inclusions, that partially or fully correspond to mineral association of ores of the Novolushnikovsky deposit, as well as an unusual Hg-content of the native gold suggest several sources of gold with a similar mineralization style. The undiscovered sources of gold are might be also of intrusion related type.
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alluvial platinum group minerals as indicators of primary pge mineralization Placers of southern siberia
Russian Geology and Geophysics, 2016Co-Authors: G V Nesterenko, S M Zhmodik, V V Kolpakov, E V Airiyants, D K Belyanin, Yu M Podlipsky, N S KarmanovAbstract:Abstract The platinum-group minerals (PGM) in placer deposits provide important information on the types of their primary source rocks and ores and formation and alteration conditions. Different characteristics of minerals can be determined by a set of conventional and modern in situ analytical techniques (scanning electron microscopy (SEM) and electron probe microanalysis (EPMA)). A study of PGM from Placers of southern Siberia (Kuznetsk Alatau, Gornaya Shoria, and Salair Ridge) shows that the morphology and composition of PGM grains, the texture, morphology, and composition of silicate, oxide, and intermetallic microinclusions, and the type of mineral alteration can serve as efficient indicators of the primary sources of PGM. The widespread rock associations in the Kuznetsk Alatau, Gornaya Shoria, and Salair Ridge, the compositions of PGM and microinclusions in them, and the dominant mineral assemblages testify to several possible primary sources of PGE mineralization: (1) Uralian-Alaskan-type intrusions; (2) ophiolite associations, including those formed in a subduction zone; (3) ultramafic alkaline massifs; and, probably, (4) rocks of the picrite-basalt association. The preservation of poorly rounded and unrounded PGM grains in many of the studied Placers of the Altai-Sayan Folded Area (ASFA) suggests a short transport from their primary source.
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native gold in complex ti zr Placers of the southern west siberian plain
Russian Geology and Geophysics, 2013Co-Authors: G V Nesterenko, V V Kolpakov, L P BoboshkoAbstract:Abstract Typomorphic features of native gold and its contents in complex Ti–Zr Placers in the southern West Siberian Plain are reported. Three of the Placers are of littoral-marine genesis, and two formed under conditions of an alluvial piedmont plain. Native gold from the studied Ti–Zr Placers occurs mainly as flattened thin (−0.1 mm) particles which underwent mechanical action. It is marked by wide fineness variation and the abundance of a very fine (990–1000‰) variety. Most likely, this is chemically transformed clastogenic metal. The gold content of the productive bed (5–30 mg/m3 native gold and 8–140 ppb bulk gold) is consistent with the dispersion of heavy ore and accessory minerals during mechanical migration in water flows simultaneously with their concentration on geochemical barriers. The native-gold content of complex Ti–Zr Placers shows a higher negative correlation with the primary source–placer distance than those of Ti and Zr minerals and a positive correlation with the degree of hydrodynamic reworking (gravity concentration) of transit terrigenous material. On the southern framing of the West Siberian Plain, some regions of northern Kazakhstan are promising for gold of complex Ti–Zr Placers as well as fine- and thin-gold Placers, gold-bearing weathering crusts, and primary gold deposits.
N. I. Boiko - One of the best experts on this subject based on the ideXlab platform.
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Paragenesis of upper cretaceous titanium-zirconium Placers and phosphate mineralization in the southern East European Platform
Lithology and Mineral Resources, 2011Co-Authors: R. G. Matukhin, N. I. BoikoAbstract:Association of titanium-zirconium Placers and phosphate mineralization in Upper Cretaceous rocks of the East European Platform is shown with the Tsentral’noe (Central) and Unecha deposits as example. This paragenesis is caused by interaction between the multicomponent placer ore (phosphate-rare metal) concentrations and mechanical-chemical differentiation that shows up periodically during the sub-aerial migration of sedimentary material. Clastic ore components were mainly derived from intermediate collectors, while the phosphate material was delivered by the phosphate-containing solutions and particulates in the chemical weathering crust. Such phosphorite-titanium-zirconium occurrences can also be detected in other regions, including areas with rare metal Placers.
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Titanium–Zirconium Placers of the Stavropol Region
Lithology and Mineral Resources, 2004Co-Authors: N. I. BoikoAbstract:Lithofacies analyses and paleogeographic reconstructions of the middle Sarmatian sequence in the central Ciscaucasus, which hosts the most promising titanium–zirconium Placers of the Stavropol region, indicate that ore components (rutile, ilmenite, leucoxene, and zircon) were mainly delivered to the Stavropol placer basin by the paleo-Volga River from a northern land. Bryozoan organogenic edifices played a significant role in the formation of Placers. The organogenic edifices appeared under anomalous (for bioherm formation) conditions of terrigenous sedimentation on the western and northwestern slopes of the Stavropol Uplift, hampered the transport of ore material to the deep-water zone of the basin, and promoted its differentiation in the paleouplift.
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titanium zirconium Placers of the stavropol region
Lithology and Mineral Resources, 2004Co-Authors: N. I. BoikoAbstract:Lithofacies analyses and paleogeographic reconstructions of the middle Sarmatian sequence in the central Ciscaucasus, which hosts the most promising titanium–zirconium Placers of the Stavropol region, indicate that ore components (rutile, ilmenite, leucoxene, and zircon) were mainly delivered to the Stavropol placer basin by the paleo-Volga River from a northern land. Bryozoan organogenic edifices played a significant role in the formation of Placers. The organogenic edifices appeared under anomalous (for bioherm formation) conditions of terrigenous sedimentation on the western and northwestern slopes of the Stavropol Uplift, hampered the transport of ore material to the deep-water zone of the basin, and promoted its differentiation in the paleouplift.
Dave Craw - One of the best experts on this subject based on the ideXlab platform.
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River drainage reorientation during placer gold accumulation, southern New Zealand
Mineralium Deposita, 2013Co-Authors: Dave CrawAbstract:Many alluvial placer deposits around the world occur in river systems that have been affected by tectonic events, causing drainage reorientation and severance of links between Placers and their sources. This study documents tectonic rejuvenation of topography in the Otago giant placer goldfield, New Zealand, which has resulted in numerous river capture and drainage reorientation events. These events have induced changes to gold transport directions and numerous stages of separation of detrital gold from primary sources. Goldfield-wide reconstructions of drainage patterns through time are as yet only possible for Miocene–Recent, and numerous earlier drainage changes back to Cretaceous primary orogenic mineralisation are probable. Variations in basement lithologies permit auriferous gravel provenance determinations, facilitating paleodrainage pattern reconstruction and documentation of river capture events. River capture events and timing of these events for gold-bearing paleodrainages have also been documented using genetic divergences of populations of freshwater galaxiid fish that were isolated by drainage reorientation. Gold-bearing quartz pebble conglomerates had a southeastward drainage in the Miocene. This was disrupted in the Pliocene by mountain range uplift and gold placer recycling, with deposition of lithic conglomerates containing only minor gold Placers. The most dramatic changes in gold transport directions occurred through the Quaternary, as antiformal ranges grew across the pre-existing drainages. Miocene and Pliocene Placers were recycled with numerous local (1–10 km scale) changes in river directions and numerous capture events. Large axial rivers were segmented into a more complex drainage pattern, and on-going river capture resulted in growth of the main Clutha River catchment at the expense of neighbouring catchments. The most productive Placers developed in the Clutha River in late Quaternary when increased discharge from captured mountain catchments enhanced gold transport and concentration. Similar river drainage reorientation has occurred in other placer fields around the world, but the lack of preserved evidence inhibits documentation of most such changes.
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delayed accumulation of Placers during exhumation of orogenic gold in southern new zealand
Ore Geology Reviews, 2010Co-Authors: Dave CrawAbstract:Abstract The giant gold placer system on the Otago Schist of southern New Zealand was derived from Mesozoic orogenic gold deposits in the underlying schist basement. The core of the schist basement was exhumed in the middle Cretaceous, coeval with the accumulation of the oldest preserved nonmarine sedimentary rocks in the area (ca 112 Ma). Those sedimentary rocks contain quartz clasts, with distinctive ductile deformation textures, that were derived from structural zones in, or adjacent to, major orogenic gold deposits. Quartz textures in these structural zones are readily distinguishable from the rest of the schist belt, and hence provide a fingerprint for erosion of gold. The earliest sedimentary rocks on the margins of the gold-bearing schist belt are immature, and were derived from unoxidised outcrops in areas of high relief. Gold was not liberated from unoxidised basement rocks during erosion, and was removed from the system without placer concentration. Placer concentration did not begin until about 20 million years later, when oxidative alteration of gold deposits had facilitated gold grain size enhancement from micron scale (primary) to millimetre scale (secondary). Subsequent erosion and recycling of gold in the early Cenozoic, and again in the late Cenozoic, caused additional concentration of gold in progressively younger deposits. The Klondike giant placer goldfield of Canada had a similar geological history to the Otago placer field, and Klondike placer accumulation occurred in the late Cenozoic, at least 70 million years after Mesozoic exhumation of orogenic gold. The giant placer deposit on the western slopes of the Sierra Nevada in California occurs in Eocene and younger sedimentary rocks, at least 40 million years younger than the timing of major exhumation of the source rocks. Circum-Pacific giant gold Placers formed under entirely different tectonic regimes from the emplacement of their source orogenic deposits, and these giant placer deposits do not form in foreland basins associated with convergent orogens. Formation of giant Placers requires less active erosion and more subdued topography than the collisional orogenic activity that accompanied emplacement of source gold deposits in basement rocks, as well as oxidative alteration of the primary deposits to liberate gold from sulfide minerals and enhance secondary gold grain size.
Yury D Kraynev - One of the best experts on this subject based on the ideXlab platform.
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gold and platinum group minerals in Placers of the south urals composition microinclusions of ore minerals and primary sources
Ore Geology Reviews, 2017Co-Authors: V. V. Zaykov, Irina Yu Melekestseva, Elizaveta V Zaykova, V A Kotlyarov, Yury D KraynevAbstract:Abstract Gold and platinum group minerals from the gold Placers of the South Urals are studied in order to identify the metal sources. In Placers from the Main Uralian fault zone (MUF), the primary gold contains Ag (up to 29 wt.%), Cu (up to 2 wt.%) and Hg (up to 4 wt.%) and its fineness ranges from 538 to 997‰. Tetra-auricupride and cupriferous gold (up to 20 wt.% Cu) are common for the Nizhny Karabash placer of the MUF zone. In the eastern part of the South Urals, the placer gold is mainly characterized by high fineness of 900–1000‰ and low Cu contents (max 1.38 wt.%). Most of the placer gold grains consist of the primary domains, which are rimmed by secondary high-fineness gold with diffuse and clear boundaries. The secondary gold also develops along the shear dislocations of primary gold. Gold contains microinclusions of geerite, balkanite, chalcopyrite, Se-bearing galena, sphalerite, pyrite, pyrrhotite, arsenopyrite and hematite. Twenty four (including five unnamed) platinum group minerals (PGMs) were found in 28 Placers; those from the Kialim and Maly Iremel Placers of the Miass placer zone were studied in details. In the Kialim placer, ruthenium is most abundant PGM, which hosts microinclusions of isoferroplatinum, ferroan platinum, laurite, cupriferous gold, a mineral similar in composition to tolovkite, heazlewoodite and unnamed RhSbS phase. The osmium contains microinclusions of erlichmanite and laurite. The iridium grains hosts various sulfides and arsenides of platinum group elements (PGEs). The inclusion-free PGMs form Ru compositional trend in contrast to Os–Ru trend of the Ir-depleted inclusion-hosted PGMs. The isoferroplatinum from the Maly Iremel placer hosts laurite, rhodarsenite, bowieite, a mineral similar in composition to miassite and unnamed sulfide of Pt (Pt 1.11 S 2.00 ) and antimonide of Pd ((Pd 2.41 Rh 0.43 Fe 0.17 ) 3.01 (Sb 0.91 Te 0.09 ) 1.00 ). Ruthenium is a host to isoferroplatinum, PGE sulfides and arsenides, and heazlewoodite. Osmium contains microinclusions of ferroan platinum; iridium is a host to a mineral similar in composition to hongshiite. Three types of PGM intergrowths were identified in the Maly Iremel samples: (1) the intergrowths of platy grains of ruthenium with isoferroplatinum and a mineral similar in composition to tulameenite; (2) the open-latticework intergrowths of platy crystals of ruthenium with interstitial aggregates made up of gold, isoferroplatinum and a mineral similar in composition to xingzhongite and (3) the intergrowths of osmium and irarsite and iridarsenite, which are developed along cleavage of the osmium grains. Nickel sulfides associated with some PGMs contain Ru (11.32 wt.%) and Rh (2.21 wt.%) in millerite and Ir (31.00 wt.%), Ru (5.81 wt.%) and Rh (2.87 wt.%) in vaesite. The primary metal sources were determined on the basis of the mineral assemblages and composition of minerals, taking into account the nearby mineral deposits and directions of rivers. The rodingite-associated gold, gold-bearing massive sulfide and chromite deposits are major sources of gold and PGMs in Placers of the Miass placer zone confined to the MUF structure of the South Urals. In the southern part of this structure, gold was mainly originated from orogenic gold–sulfide deposits associated with volcanic/volcaniclastic rocks and listvenite-associated gold deposits. The placer PGMs were derived from the adjacent ultramafic massifs of ophiolitic origin. The distance between the Placers and primary deposits varies from 2 to 5 km (up to 20 km in the extended valley of the Miass River). Usage of ore microinclusions and associated PGMs in study of placer gold is far more advanced than an ordinary consideration of gold composition alone. This approach allowed us to identify the concrete sources for individual Placers and to predict some mineralogical findings in already known primary occurrences.
Elena Zhitova - One of the best experts on this subject based on the ideXlab platform.
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Platinum mineralization of the Epilchik Ural-Alaskan type zoned complex (Far East Russia)
Mineralium Deposita, 2020Co-Authors: Evgeniy Sidorov, Anton Kutyrev, Valery Chubarov, Elena ZhitovaAbstract:The Epilchik Ural-Alaskan type mafic-ultramafic zoned complex, located in the northernmost part of the Koryak-Kamchatka Platinum Belt (Russian Far East), contains lode platinum mineralization. The outcrops of the complex are crossed by the Snegovaya River, which hosts placer platinum-group minerals (PGM) occurrences. The primary PGM assemblage of the Epilchik lode chromitites is typical for Ural-Alaskan type complexes, dominated by Ir-rich isoferroplatinum which occurs as small euhedral inclusions within chromite. Secondary alloys include tetraferroplatinum (PtFe), tulameenite (Pt_2FeCu), an unnamed Fe_3Pt compound, and Pt-bearing native iron, which form alteration rims around isoferroplatinum or occupy fractures in chromite. Other secondary minerals from lode chromitites are hollingworthite (RhAsS) and Os-Fe alloy (“hexaferrum”). The PGM assemblages of the Snegovaya River placer occurrences are comparable with those of the lode chromitites with a predominance of Ir-rich isoferroplatinum and secondary alloys, including tetraferroplatinum, tulameenite, and an unnamed Fe_3Pt compound. However, placer occurrences are much richer in regard to mineral diversity, comprising native osmium (Os,Ir), native iridium (Ir,Os), laurite (RuS_2), erlichmanite (OsS_2), cuprorhodsite (CuRh_2S_4), cuproiridsite (CuIr_2S_4), Co-malanite (Cu(Pt,Co)_2S_4), unnamed sulfides Rh_3S_4, (Rh,Pt)S, sperrylite (PtAs_2), platarsite (PtAsS), irarsite (IrAsS), hollingworthite (RhAsS), osarsite (OsAsS), cooperite (PtS), native gold, unnamed telluride (Pt_2Te), and an unnamed Fe-Ir-Rh alloy. Similarities between lode and placer mineralization indicate that the Epilchik complex was the dominant source for the Placers. The larger diversity of PGM in Placers may be attributed to the heterogeneity of samples which could be derived from unsampled or unexposed outcrops of the complex. Alteration of isoferroplatinum to secondary intermetallic compounds occurred via progressive development of reduced conditions as a result of serpentinization. Subsequent pervasive As-mineralization redistributed platinum-group elements, including Os and Ir. A final mineralizing pulse deposited sporadic native gold and Pt telluride minerals. A comparison of key mineralogical and physical features between the Epilchik complex and other Ural-Alaskan type complexes is used to determine the economic potential for Placers along the Snegovaya River. Key criteria include (1) the size and degree of erosion of the outcrop area of the complex; (2) the predominance of isoferroplatinum over native platinum; (3) high Ir content in Pt-Fe alloys; and (4) the predominance of secondary intermetallic compounds over sulfides. Based on these criteria, the occurrences associated with the Epilchik complex are considered prospective for high volume and economic grade accumulations of PGE. This method is useful for assessing the economic potential of placer occurrences during indirect early-stage prospecting with a limited sample suite.
