Ore-bearing fluids of the Eldorado gold deposit (Yenisei Ridge,Russia)

The Eldorado low-sulfide gold-quartz deposit, with gold reserves of more than 60 tons, is located in the damage zone of the Ishimba Fault in the Yenisei Ridge and is hosted by Riphean epidote-amphibolite metamorphic rocks (Sukhoi Pit Group). Orebodies occur in four roughly parallel heavily fractured zones where rocks were subject to metamorphism under stress and heat impacts. They consist of sulfide-bearing schists with veins of gray or milky-white quartz varieties. Gray quartz predominating in gold-bearing orebodies contains graphite and amorphous carbon identified by Raman spectroscopy; the contents of gold and amorphous carbon are in positive correlation. As inferred from thermobarometry, gas chromatography, gas chromatography-mass spectrometry, and Raman spectroscopy of fluid inclusions in sulfides, carbonates, and gray and white quartz, gold mineralization formed under the effect of reduced H₂O-CO₂-HC fluids with temperatures of 180 to 490 °C, salinity of 9 to 22 wt.% NaCl equiv, and pressures of 0.1 to 2.3 kbar. Judging by the presence of 11% mantle helium (³He) in fluid inclusions from quartz and the sulfur isotope composition (7.1-17.4‰ δ³⁴S) of sulfides, ore-bearing fluids ascended from a mantle source along shear zones, where they “boiled”. While the fluids were ascending, the metalliferous S- and N-bearing hydrocarbon (HC) compounds they carried broke down to produce crystalline sulfides, gold, and disseminated graphite and amorphous carbon (the latter imparts the gray color to quartz). Barren veins of milky-white quartz formed from oxidized mainly aqueous fluids with a salinity of < 15 wt.% NaCl equiv at 150-350 °C. Chloride brines (> 30 wt.% NaCl equiv) at 150-260 °C impregnated the gold-bearing quartz veins and produced the lower strata of the hydrothermal-granitoid section. The gold mineralization (795-710 Ma) was roughly coeval to local high-temperature stress metamorphism (836-745 Ma) and intrusion of the Kalama multiphase complex (880-752 Ma).     

Tectonometamorphic evolution of the Garevka polymetamorphic complex (Yenisei Ridge)

The Garevka metamorphic complex (GMC), located at the junction of the Central Angara and Isakovka terranes (western part of the Transangarian Yenisei Ridge), was studied in terms of its tectonometamorphic evolution and geodynamic processes in the Neoproterozoic history of the region. Geological, structural, geochronological, and petrological data permitted the recognition of two stages in the GMC evolution, which differ in thermodynamic regimes and metamorphic field gradients. These stages were related to crustal contraction and extension within the Yenisei regional shear zone, a large lineament structure in the region. Stage 1 was marked by the formation of metamorphic complexes in the middle to upper amphibolite facies moderate-pressure regional metamorphic settings at ～ 960 Ma, P = 7.7–8.6 kbar, and T = 582–631 °C. This suggests subsidence of the area to the middle continental crust with dT/dH = 20–25 °C/km. During stage 2, the rocks experienced Late Riphean (～ 880 Ma, SHRIMP II U–Pb and ⁴⁰Ar–³⁹Ar dating) dynamic metamorphism under epidote-amphibolite facies conditions (P = 3.9–4.9 kbar; T = 461–547 °C), indicating a metamorphic field gradient of dT/dH no greater than 10 °C/km, with the formation of blastomylonites in narrow zones of ductile and brittle deformations. In these zones, high-grade GMC blocks were exhumed to the upper continental crust and underwent low-temperature metamorphism. Comparison of the structural, geologic, and other evolutionary features (nearly identical age constraints in view of exhumation rate, similar PT-paths, and different types of metamorphism associated with different geodynamic settings, etc.) of the Garevka and Teya complexes suggests that they constitute a single polymetamorphic complex.     

四川石棉西部地区金矿床形成时代

四川石棉西部地区金矿床和矿点分布在扬子地块盖层碳酸盐岩和基底元古宙变质闪长岩以及中生代石英斑岩中的北北西和北北东走向断裂中。矿脉为含金黄铁矿-（黝铜矿）-多金属硫化物-石英脉、含金黄铁矿-石英脉和含金硅化糜陵岩等,围岩蚀变为硅化、白（绢）云母化、碳酸盐化、绿泥石化和黄铁矿化等。用40^Ar／39^Ar阶段加热法测定瓦斯沟、黄水沟、大岩房、金洞子和金台子5个金矿床蚀变白云母。4^Ar／39^Ar坪年龄分别为约22Ma、25～28Ma、20Ma、20Ma和32-34Ma,代表该地区主要金矿床的矿化蚀变时间。石棉西部地区金矿床是在渐新世和中新世早期的伸展构造背景下形成的。     

Blastomylonite Complexes of the Western Yenisei Ridge (Eastern Siberia,Russia): Geological Position,Metamorphic Evolution and Geodynamic Models

Geotectonics - Metapelites and metabasites within the Yenisei regional shear zone of the Yenisei Ridge underwent strong deformations with substrate recrystallization and blastomylonite formation...     

Geochemistry,Formation Settings,Composition, and Age of the Protolith for the Fe- and Al-Rich Metapelites of the North Yenisei Ridge

Doklady Earth Sciences - The Fe- and Al-rich metapelites of the North Yenisei Ridge are redeposited and metamorphosed products of Precambrian kaolinite-type weathering crusts of predominantly...     

P-T-X parameters of metamorphogene and hydrothermal fluids,isotopy and age of the Bogunai gold deposit,southern Yenisei Ridge (Russia)

Fluid inclusions in quartz, sulfides from quartz veins, and quartz, garnet, plagioclase, and orthoclase from granulites of the Bogunai gold deposit located in the granulites of the Angara-Kan block of the Yenisei Ridge were studied by thermobarometry, gas chromatography, chromato-mass-spectrometry, Raman spectroscopy, and mass spectrometry with inductively coupled plasma. The formation temperatures (850-950 °C) and pressures (8.5-9.0 kbar) of minerals of the granulite metamorphic facies are much higher than the crystallization temperatures (220-420 °C) and pressures (0.1-1.6 kbar) of gold-quartz veins of the Bogunai deposit. These veins formed with the participation of H₂O-CO₂-hydrocarbon fluids with a salt (predominantly MgCl₂) concentration of 2-19 wt.% NaCl equiv. The gas phase of fluid inclusions from quartz, pyrite, chalcopyrite, galena, and sphalerite contains not only H₂O, CO₂, CH₄, and N₂ but also the first found compounds of sulfur (CS₂, O₂S, COS, C₂H6S₂) and nitrogen (C3H₇N, C3H₇NO, C₄H8N₂O) and numerous hydrocarbons of different classes (paraffins, arenes, naphthenes, alcohols, aldehydes, ketones, carbonic acids, and furans). The age of the Krasnoyarsk mineralized zone, one of the sites of the Bogunai deposit, is 466 ± 3.2-461.6 ± 3.1 Ma, which is almost 1400 Ma younger than the age of granulite metamorphism and 255 Ma younger than the age of diaphthoresis but is close to the age of the Lower Kan granitoid pluton (455.7 ± 3.4 Ma). The sulfur isotope ratios (5³⁴S) of sulfides (pyrite, chalcopyrite, sphalerite, and galena) are close to the mantle values, 0.8 to 3.5%c, and are in the range of the granitoid values, which indicates the crustal source of the fluid sulfur. Gold of the Bogunai deposit accumulated with the participation of H₂O-CO₂-hydrocarbon fluids generated both in deep-fault zones and in granitoid intrusions.     

Neoproterozoic Alkaline Igneous Rocks,Carbonatites and Gold Deposits of the Yenisei Ridge,Central Siberia: Evidence of Mantle Plume Activity and Late Collision Shear Tectonics Associated with Orogenic Gold Mineralization

This paper discusses the plausible genetic relationship between disseminated Au‐sulfide mineralization and mantle plume‐related magmatism in the context of the tectonic evolution of the Yenisei ridge in central Siberia. The relationship is inferred based on structural and geochemical studies of the Blagodat Au deposit, and the Transangara alkaline syenite and Penchenga fenite‐carbonatite complexes. Analyses of Nd, Sr and Ar isotopic compositions of samples from these geological features show their possible close temporal relationships but different sources. Nevertheless, the present data sets suggest that thermal effects of mantle plume activity likely controlled hydrothermal fluid mobilization in metamorphic suites and further enrichment of gold. The structural setting of the Blagodat Au deposit demonstrates the typical example of Au‐sulfide mineralization controlled by late collisional shear deformations. The present example of Au deposit associated temporally and spatially with carbonatites and alkaline rock complexes is an exclusive case in the Earth's history supporting a plausible genetic relationship between mantle plume‐related magmatism and orogenic‐Au mineralization.     

The Blagodatnoe gold-sulfide deposit (Yenisei Ridge,Russia): the nature of geophysical anomalies and the succession and causes of formation of petrophysical zoning

Data on geophysical fields and petrophysical heterogeneity, parageneses and the thermodynamic conditions and age of their formation, and fluid inclusions were used for the genetic reconstruction of petrophysical zoning at the Blagodatnoe gold-sulfide deposit. Petrophysical associations of the preore and ore stages of the deposit formation are clearly reflected in anomalies of the magnetic and natural electric fields and the aureoles of radioactive elements. At the early preore stage (752 Ma), reduced solutions with high activity of K, enriched in U, Th, and, probably, Au, were supplied to intensely foliated tectonic zones. Their interaction with initial metasedimentary rocks gave rise to contiguous zones of quartz–muscovite and chlorite metasomatic rocks. Accompanying graphitization led to a high electrochemical activity of the metasomatic rocks, which generated anomalies of up to –300 mV in the natural electric field; the most intensely carbonized zones became enriched with U (up to 6.5 × 10^–4%) and, probably, Au. The quartz–muscovite metasomatic rocks accumulated Th and K (up to 29 × 10^–4% and 4%, respectively), whereas the chlorite metasomatic rocks accumulated rock-forming elements (particularly Fe), which led to the compaction of these rocks and the acceleration due to gravity in local positive anomalies. The nonmagnetic character of the fresh pre-ore metasomatic rocks suggests the predominantly pyritic composition of early sulfides. At the ore stage (698 Ma), the minerals were deposited from H₂O–CO₂–As–S solutions at 560 to 315 °C. The activity of these solutions caused a redistribution of radioactive elements and a high petrophysical differentiation of the ore-bearing structure. The amplitudes of the anomalies above this structure vary from 500 to 80 nT in the magnetic field and from –130 to + 10 mV in the natural electric field. It has been found that the hydrothermal fluid hardly affected the polarization properties of graphitized rocks at the maximum temperatures but caused an intense removal of U and the development of magnetic pyrrhotite after pyrite. The temperature decrease in the mineral-forming system was favorable for the formation of siderite. Carbonaceous schists which experienced carbonatization lost their electrochemical activity. The binding of carbon dioxide in the solid phase influenced the migration capability of trace elements and their zonal distribution. With this evolution of the solution, Th accumulated at the lower levels of the mineralized zone, whereas the upper levels of the deposit became enriched with U. Productive gold–arsenopyrite–pyrite–pyrrhotite paragenesis with anomalous magnetic susceptibility evolved at the ore stage. The late galena–sphalerite–chalcopyrite paragenesis (365 Ma) was of strictly local occurrence and reduced the magnetic susceptibility of ores.     

Features of Ore Formation of Gold Deposits of the Glukharinskii Ore Cluster (Cis-Kolyma Terrain)

Doklady Earth Sciences - This paper reports on new data on δ34S and δ18O isotopy for trace and rare-earth elements of the Au deposits of the Glukharinskii ore cluster. The geochemical...     

豫西崤山地区金矿成矿年龄的测定及其意义

＾４０Ａｒ／＾３９Ａｒ流体包裹体同位素测年法为金矿成矿年龄测定开辟了新的途径。但是,由于次生包裹体的存在及样品中存在过剩氩或氩丢失,常产生复杂的不一致年龄谱,难以获得准确可靠的成矿年龄。本文对豫西嵴山地区含金石英脉中的石英和方铅矿样品进行精选,采用阶段升温法测定出了可靠的＾４０Ａｒ／＾３９Ａｒ年龄。＾４０Ａｒ／＾３９Ａｒ等时线线性相关系数〉０．９９,＾４０Ａｒ／＾３９Ａｒ初始值分别为２９４．０和２     

右江盆地构造和演化及对卡林型金矿床的控制作用

右江盆地,又称南盘江盆地,是我国重要的多金属矿床富集地,广泛发育有Au-As-Sb-Hg低温热液矿床,也是我国 卡林型金矿大规模富集区之一。矿床地质特征表明,金矿床的形成明显受到构造的控制,因此,探讨盆地的构造演化对于 深入研究卡林型金矿的形成具有重要意义。通过结合前人大量研究认为：右江盆地内主要发育有NW和NE向两组构造, NW及NE向的边界断裂对盆地的演化及火成岩的发育起到重要作用;金矿床在平面上均分布于右江盆地范围内,具有明显 的岩性和构造控矿的特征;右江盆地形成及后续的构造演化可以分为六个阶段,即：早泥盆世中期滨浅海陆棚发育 （D2 1 ）,中泥盆世-中二叠世裂陷洋盆发育（D2-P2）,中二叠世末-中三叠世洋盆消失及前陆盆地发育（P3 2 -T2）,晚三叠世 -早侏罗世盆地消亡及碰撞后伸展（T3-J1）,中侏罗世-早白垩世中期NE向挤压构造发育（J2- K2 1 ） 和早白垩世晚期-古 近纪局部伸展作用（K3 1 -E）;右江盆地内卡林型金矿的成矿期集中在前陆盆地发育结束而褶皱成山后,成矿过程与伸展环 境密切相关。     

鲁西中生代金矿形成时代、物质来源及问题讨论

本文将鲁西地区"幔源岩浆型金矿"划归为"与中生代侵入岩有关的金矿",与金成矿相关的岩浆岩主要为产于断裂带及其附近或不同断裂交汇部位的中生代燕山期中性和碱性岩浆岩。根据碳、氢、氧、硫、铅等稳定同位素组成,金矿成矿作用过程中至少部分物质来源于下地壳或上地幔,局部有围岩物质成分的带入。鲁西地区各金矿成矿年龄相差较大,测得兰陵龙宝山含矿石英脉K-Ar年龄为96.2Ma,沂源金星基性岩床年龄为141Ma,代表了与其有关的层状金多金属矿成矿年龄。根据沂南金场早期矽卡岩和晚期矽卡岩黑云母Rb-Sr年龄分别为133±6Ma和128±2Ma,推测其成矿时间为128~121Ma。在剥蚀程度较浅或隐伏岩体及其周围是找矿有利地区。层状微细浸染型金矿的找矿方向重点在岩体外围,其它类型金矿找矿方向重点是在岩体或岩体接触带附近。该区中生代侵入岩缺乏深入系统研究,成矿时代缺乏精准的测年,平邑归来庄金矿尚无可行的测年方法。     

Geochemistry,Formation Settings,and Ore Potential of the Volcano-Sedimentary Complexes of Pryangarya,Yenisei Ridge

Doklady Earth Sciences - In the Angara part of the Yenisei Ridge, a sequential section of the metapicrite–basalt sequence and the overlying carbonate rocks of the Gorevskaya suite has been...     

Late Vendian postcollisional leucogranites of Yenisei Ridge

The Late Vendian (540–550 Ma) U–Pb zircon age of postcollisional granitoids in the Osinovka Massif was obtained for the first time. The Osinovka Massif is located in rocks of the island-arc complex of the Isakovka Terrane, in the northwestern part of the Sayany–Yenisei accretion belt. These events stand for the final stage of the Neoproterozoic history of the Yenisei Ridge, related to the completing accretion of the oceanic crust fragments and the beginning of the Caledonian orogenesis. The petrogeochemical composition and the Sm–Nd isotopic characteristics support the fact that the granitoid melt originated from a highly differentiated continental crust of the southwestern margin of the Siberian Craton. Hence, the granite-bearing Late Riphean island-arc complexes were thrust over the craton margin at a distance considerably exceeding the dimensions of the Osinovka Massif.     

Formation and Significance of Chromium-Bearing Sericite in Granite-Hosted Gold Deposits

Please refer to the attachment(s) for more details.     

First Data on the Nature and Age of the Protolith of High-Pressure Tectonites of Yenisei Ridge: A Link to the Early Stage of Formation of the Paleoasian Ocean

Doklady Earth Sciences - The petrogeochemical characteristics of high-pressure mafic tectonites from the Yenisei suture zone of Yenisei Ridge indicate that N-MORB and E-MORB with an age of 701.6...     

Age and Source Areas of Detrital Zircons from the Rocks of the Yenisei Tectonic Zone: to the Problem of Identification of Archean Metamorphic Complexes in the Transangarian Yenisei Ridge

The petrogeochemical and geochronological correlations were carried out between boudined fragments of tonalitic rocks previously dated at Neoarchean, quartzite sandstones, and host amphibolites in the Yenisei Regional Shear Zone of the Yenisei Ridge in order to solve the problem of age of the Transangarian Yenisei Ridge basement. Detrital zircons in metasandstones can be derived from the Neoarchean–Paleoproterozoic crystalline rocks of the Angara–Kan block. Interpretation of available data does not confirm the inferred presence of the Early Precambrian basement of the Siberian Craton beneath the Transangarian Yenisei Ridge.     

Neoproterozoic Rare-Metal Subalkali Leucogranite from the Northern Yenisei Ridge

Petrochemical study and U–Pb SIMS (SHRIMP–II) zircon analyses of subalkaline leucogranite of the Khariusikha Massif have been carried out. They have revealed for the first time a rare-metal mineralization. The elevated concentrations of rare elements (wt %) are Nb (0.5–0.7), Ta (0.12–0.16), REEs (0.08–0.24), Y (0.06–0, 1), Zr (2.3–2.6), Hf (0.1–0.12), U (0.05–0.1), and Th (0.08–0.1) and are confined to albitized granites. The main mineral phases concentrating the rare elements, U and Th, are tantalo–niobates: fergusonite, euxenite, U–pyrochlore, tantalite, as well as thorite, monazite, zircon, and sphene. These minerals associate with cassiterite, sulfides, and gold. The simultaneity of the intraplate granitoid magmatism (753 ± 4 Ma) and bimodal rhyolite–basalt volcanism (753 ± 6 Ma) in the neighboring rift structure has been demonstrated. Presumably, the Neoproterozoic rifting and intraplate magmatism relate to the plume activity that caused the supercontinent Rodinia to break up.     

燕山-喜马拉雅旋回在中国内生金矿成矿作用中的重要意义及其原因探讨

中国内生金矿分布广，矿化产出层位多，矿床类型复杂。成矿物质主要来自四类含金地质建造。矿化与构造关系密切，与岩浆活动也有程度不同的联系。实际资料表明，燕山-喜马拉雅期是中国内生金矿的主要成矿期。中新生代中国大陆所处的特殊板块运动环境所导致的构造-岩浆事件及随之出现的前所未有的热效应和扩容空间效应，是中国内生金矿集中形成于这一时期的根本原因。本文最后对中国内生金矿成矿的演化过程作了归纳。     

Aggregation and Differentiation of Gold and Silver during the Formation of the Gold-Bearing Weathering Crusts (on the Example of Kazakhstan Deposits)

The supergene Au in weathering crusts of both the Suzdal and Raygorodok deposits is characterized by enhanced fineness, grain size, crystallinity, and the appearance of botryoidal aggregates of crystals. In the weathering crust of the Suzdal deposit, the exogenous Au is associated primarily with scorodite and carbonates; for Raygorodok, with chalcocite, bornite, hydrocarbonates and Cu hydrosulfates. The difference in the mineral associations of supergene Au at the deposits is determined by the occurrence of various mineral concentrators of Au in the primary endogenous substrate: arsenopyrite and pyrite at the Suzdal deposit and chalcopyrite with pyrite at the Raygorodok deposit. Due to the much greater mobility of Ag in the supergene zone, the weathering crusts are likely to contain submicron microinclusions of Ag minerals beyond the zones of Au concentration.