Evolution of hydrothermal fluids of HS and LS type epithermal Au–Ag deposits in the Seongsan hydrothermal system of the Cretaceous Haenam volcanic field,South Korea

The Haenam volcanic field was formed in the southern part of the Korean peninsula by the climactic igneous activity of the Late Cretaceous. The volcanic field hosts more than nine hydrothermal clay deposits and two epithermal Au–Ag deposits. This study focuses on the relationship between hydrothermal clay alteration and epithermal Au–Ag mineralization based on the geology, alteration mineralogy, geochronology, and mineralization characteristics.These clay and epithermal Au–Ag deposits are interpreted to have formed by the same hydrothermal event which produced two distinct types of mineral systems: 1) Au-dominant epithermal Au–Ag deposit and 2) clay-dominant hydrothermal clay deposit. The two types of mineral systems show a close genetic relationship as suggested by their temporal and spatial relationships. The Seongsan hydrothermal system progressively evolved from a low-intermediate sulfidation epithermal system with Au–Ag mineralization and phyllic alteration to an acid–sulfate high-sulfidation system with Au–Ag mineralization and/or barren advanced argillic/argillic alteration. The Seongsan system evolved during post volcanic hydrothermal activity for at least 10 Ma in the Campanian stage of the late Cretaceous.The Seongsan hydrothermal system shows the rare and unique occurrence of superimposed high to low (intermediate) sulfidation episodes, which persisted for about 10 Ma.     

Epithermal deposits in North Xinjiang, NW China

The North Xinjiang region (NW China) is an important part of the Central Asia Orogenic Belt, situated at the junction of Siberia, Tarim and Kazakhstan plates. It is an area characterized by multiple stages of Phanerozoic continental growth, during which several porphyry and epithermal systems were formed. The relationship of these mineral systems to the geodynamic evolution of the region has not yet been well understood. In this paper, we list the main geological characteristics of 21 significant epithermal precious and base metal deposits in North Xinjiang, and classify them into high-sulfidation and low-sulfidation styles, with the latter being predominant. We have selected seven epithermal deposits representing different styles formed under different tectonic regimes and discuss their geology and geochemistry in some detail. The deposit-scale geology and geochemistry of epithermal systems in North Xinjiang are essentially similar to those in other parts of the world. All epithermal deposits in North Xinjiang are hosted in volcanic rocks with ages ranging from Devonian to Triassic, with the Early Carboniferous volcanic sequences being the most important, followed by the Permian and Triassic. The Devonian–Early Carboniferous host rocks belong to the calc-alkaline series that developed in pre-collisional arc-back-arc basin systems; whereas the Permian–Triassic host volcanic rocks of shoshonite series formed in post-subduction regimes. Available isotopic ages of these epithermal systems cluster in two periods: Early Carboniferous (>320?Ma) and Late Carboniferous–Triassic (320–220?Ma), reflecting two metallogenic episodes that occurred during subduction-related accretion and post-subduction collision regimes, respectively. Accordingly, three groups of epithermal deposits in North Xinjiang can be recognized as (1) pre-collisional deposits without or with negligible collisional-related modification, (2) deposits formed in collision regime and (3) ore systems strongly overprinted by fluid flow in post-subduction collision regime.     

Mineral resources of high-tech metals in Russia: State of the art and outlook

Seven main ore-forming systems—porphyry and epithermal; orogenic related to granitic intrusions; magmatic ultramafic; volcanic-hosted massive sulfide and volcanic–sedimentary; sedimentary basins; related to alkaline magmatic activity; and placers and weathering mantles—are sources of high-tech critical metals. The following promising types of ore deposits containing high-tech critical metals as by-products are recognized: Cu–Mo porphyry, Fe–Cu–Au and Pb–Zn skarn, base-metal epithermal, volcanic-hosted massive sulfide, base-metal stratiform, various tin deposits, and placers containing rare metals including REE. The mineral resources of critical metals in Russia are compared with those known in other countries. The contents of high-tech critical metals in ores of some noble-metal deposits of the Russian Northeast are reported. It is shown that the subsurface of Russia possesses considerable mineral resource potential for hightech critical metals, which allows new enterprises to be created or production of operating enterprises to increase.     

Geology and ages of porphyry and medium- to high-sulphidation epithermal gold deposits of the continental margin of Northeast China

The continental margin of Northeast China, an important part of the continental margin-related West Pacific metallogenic belt, hosts numerous types of gold-dominated mineral deposits. Based on ore deposit geology and isotopic dating, we have classified hydrothermal gold–copper ore deposits in this region into four distinct types: (1) gold-rich porphyry copper deposits, (2) gold-rich porphyry-like copper deposits, (3) medium-sulphidation epithermal copper–gold deposits, and (4) high-sulphidation epithermal gold deposits. These ore deposits formed during four distinct metallogenic stages or periods, at 123.6 ± 2.5 Ma, 110–104 Ma, 104–102 Ma, and 95.0 ± 2 Ma, corresponding to periods of Cretaceous intermediate–acid volcanism and late-stage emplacement of hypabyssal magmas along the northern margin of the North China platform. The earliest stage of mineralization (123.6 ± 2.5 Ma) corresponds to the formation of medium-sulphidation epithermal copper – gold deposits and was associated with a continental margin magmatic arc system linked to subduction of the Pacific Plate beneath the Eurasia. This metallogenesis is closely related to high-K calc-alkaline intermediate–acid granite and pyroxene – diorite porphyry magmatism. The second and third stages of mineralization in the study area (110–104 Ma and 104–102 Ma, respectively) correspond to the formation of gold-rich porphyry copper, porphyry-like copper, and high-sulphidation gold deposits, with metallogenesis closely related to sodic or adakitic magmatism. These magmas formed in a continental margin magmatic arc system related to oblique subduction of the Pacific Plate beneath the Eurasia, as well as mixing of crust-derived remelted granitic and mantle-derived adakitic magmas. During the final stage of mineralization (95.0 ± 2 Ma), metallogenesis was closely related to sodic or adakitic magmatism, with diagenesis and metallogenesis related to the disintegration or destruction of the Pacific Plate, which was subducted beneath the Eurasian Plate during the Mesozoic.     

Types,features, and prospecting potential for Mesozoic metal ore deposits in Zhejiang Province,southeast China

The geotectonic units of Zhejiang Province include the Yangtze Plate in the northwest juxtaposed against the South China fold system in the southeast along the Jiangshan–Shaoxing fault. The South China fold system is further divided into the Chencai–Suichang uplift belt and the Wenzhou–Linhai geotectogene belt, whose boundary is the Yuyao–Lishui fault. The corresponding metallogenic belts are the Mo–Au(–Pb–Zn–Cu) metallogenic belt in northwest Zhejiang, the Chencai–Suichang Au–Ag–Pb–Zn–Mo metallogenic belt, and the coastal Ag–Pb–Zn–Mo–Au metallogenic belt. The main Mesozoic metal ore deposits include epithermal Au–Ag(Ag), hydrothermal vein-type Ag–Pb–Zn(Cu), and porphyry–skarn-type Mo and vein-type Mo deposits. These ore bodies are related to the Mesozoic volcanic-intrusive structure: the epithermal Au–Ag(Ag) deposits are represented by the Zhilingtou Au–Ag deposit and Houan Ag deposit and their veins are controlled by volcanic structure; the hydrothermal vein-type Ag–Pb–Zn deposits are represented by the Dalingkou Ag–Pb–Zn deposit and also controlled by volcanic structure; and the porphyry–skarn-type Mo deposits are represented by the Tongcun Mo deposit and the vein-type Mo deposits are represented by the Shipingchuan Mo deposit, all of which are related to granite porphyries. These metal ore deposits have close spatio-temporal relationships with each other; both the epithermal Au–Ag(Ag) deposits and the hydrothermal vein-type Ag–Pb–Zn deposits exhibit vertical zonations of the metallic elements and form a Mo–Pb–Zn–Au–Ag metallogenetic system. These Jurassic–Cretaceous deposits may be products of tectonic-volcanic-intrusive magmatic activities during the westward subduction of the Pacific Plate. Favourable metallogenetic conditions and breakthroughs in the recent prospecting show that there is great resource potential for porphyry-type deposits (Mo, Cu) in Zhejiang Province.     

Genesis of the Ciemas Gold Deposit and Relationship with Epithermal Deposits in West Java, Indonesia: Constraints from Fluid Inclusions and Stable Isotopes

The Ciemas gold deposit is located in West Java of Indonesia,which is a Cenozoic magmatism belt resulting from the Indo-Australian plate subducting under the Eurasian plate.Two different volcanic rock belts and associated epithermal deposits are distributed in West Java:the younger late Miocene-Pliocene magmatic belt generated the Pliocene-Pleistocene epithermal deposits,while the older late Eocene-early Miocene magmatic belt generated the Miocene epithermal deposits.To constrain the physico-chemical conditions and the origin of the ore fluid in Ciemas,a detailed study of ore petrography,fluid inclusions,laser Raman spectroscopy,oxygen-hydrogen isotopes for quartz was conducted.The results show that hydrothermal pyrite and quartz are widespread,hydrothermal alteration is well developed,and that leaching structures such as vuggy rocks and extension structures such as comb quartz are common.Fluid inclusions in quartz are mainly liquid-rich two phase inclusions,with fluid compositions in the NaCl-H20 fluid system,and contain no or little CO_2.Their homogenization temperatures cluster around 240℃-320℃,the salinities lie in the range of 14-17 wt.%NaCl equiv,and the calculated fluid densities are 0.65-1.00 g/cm~3.The values of δ~(18)O_(H2O-VSMOW)for quartz range from +5.5‰ to +7.7‰,the δD_(VSMOW) of fluid inclusions in quartz ranges from-70‰ to-115‰.All of these data indicate that mixing of magmatic fluid with meteoric water resulted in the formation of the Ciemas deposit.A comparison among gold deposits of West Java suggests that Miocene epithermal ore deposits in the southernmost part of West Java were more affected by magmatic fluids and exhibit a higher degree of sulfldation than those of Pliocene-Pleistocene.     

浅成低温热液金银多金属矿床矿化分带及找矿标志

自20世纪70年代环太平洋地区发现大批浅成低温热液型矿床以来,浅成低温热液矿床业已成为贵金属矿床和Cu、Pb、Zn等有色金属矿床的重要工业类型。文章依据主要工业组分对我国浅成低温热液Au、Ag多金属矿床进行了分类,并讨论了成矿系列及矿化分带特征,即按成矿深度浅成低温热液Au、Ag多金属矿床自下而上可分为:Au-Cu/Cu-Au矿床;Au/Au(Ag)矿床;Au-Ag矿床;Ag/Ag多金属矿床;Pb-Zn-Ag矿床。同时,根据我国浅成低温热液Au、Ag多金属矿床特征尝试性提出了浅成低温热液型银矿床的成矿规律与找矿标志。     

Cu–Ag sulfides as indicators of pre-porphyritic epithermal Au–Ag deposits in Northeastern Russia

Au–Ag mineralization of the Olcha and Teploe epithermal deposits underwent thermal metamorphism due to porphyritic intrusions. The presence of Bi-bearing galena and matildite in the ores (Teploe), Cu–Te-bearing naumannite (Olcha), the occurrence of middle- and high-temperature facies of metasomatic rocks (epidote and actinolite), and temperature formation conditions are related, firstly, to the influence of granitoids on the ore process, which supplied not only Cu and Mo, but also Bi, Te, and, secondly, to the heating of host rocks containing pre-porphyritic epithermal Au–Ag mineralization. The abundance of Cu–Ag sulfides and Cu-acanthite resulted from the enrichment of later mineral phases in Cu and Ag under the substance redistribution with the formation of Ag-acanthite ores. The data considered in the paper are of practical importance for regional forecasting of metallogenic constructions, exploration, and evaluation of the epithermal Au–Ag deposits.     

Epithermal deposits in South China: Geology,geochemistry, geochronology and tectonic setting

South China Block (SCB) is the broad area including the Yangtze Craton in the northwest and Huanan Orogen in the southeast. It is an important epithermal metallogenic province in China, containing at least 1 high-sulfidation (HS) and 42 low-sulfidation (LS) Au-Ag ± Cu ± Pb-Zn ± Sb epithermal deposits. Porphyry-type mineralization was recognized in four of the LS deposits, and thus they were regarded as LS–P type. These 43 deposits are mainly located in: (1) the Lower Yangtze River Belt and (2) the Northeastern Jiangnan Orogenic Belt in the Yangtze Craton, (3) the Wuyi-Yunkai Orogenic Belt and (4) the Southeast Coastal Volcanic Belt in the Huanan Orogen. They are mostly located in Mesozoic volcanic basins, especially where the regional faults and their subsidiaries occurred. The host rocks include Jurassic–Cretaceous volcanic-sedimentary rocks, coeval or slightly older subvolcanic, granitoids and breccias, and metamorphic basement rocks. The alteration of the HS epithermal deposit (Zijinshan Cu-Au) zoned from silicic (vuggy quartz), through alunite, to dickite and phyllic alteration zones, from the ore veins outwards. The alteration of the LS deposits is zoned from adularia-chalcedony-bladed calcite (or quartz pseudomorphs after bladed calcite) in ore veins to distal illite-sericite-chlorite-kaolinite assemblages. For those LS–P systems, besides the dominated LS alteration assemblages, phyllic and potassium silicate alteration related to porphyry mineralization were identified. Acid leaching textures and vein, stockwork and breccia structures are common in HS deposit, while the LS epithermal deposits are characterized by open-space filling, crustifications, colloform banding and comb structures. The ore-forming fluids are low-temperature, low-salinity meteoric water-dominated in most epithermal deposits in SCB, with variable input of magmatic water. The ore components were derived from both the deep magma and host rocks, and transported upwards or laterally and precipitated in the fracture systems by fluid boiling, mixing and cooling. Most of the epithermal deposits are formed at depth of < 1.5 km and < 300 °C, with few exceptions containing porphyry-type mineralization, such as the Zhilingtou, Yinshan and Longtoushan deposits. Deep drilling is suggested in these deposits as more epithermal and/or porphyry mineralization could be expected. The mineral systems were formed in Early Yanshanian (180–130 Ma) and Late Yanshanian (120–90 Ma) periods. The Early Yanshanian epithermal ore systems are mainly located in a series of E–W-trending metallogenic belts to the west of the Lishui–Haifeng Fault, which were formed in a syn- or post-collision tectonic setting by the collision between the SCB and its surrounding plates. The Late Yanshanian epithermal deposits are mainly located in Southeast Coastal Volcanic Belt, genetically related to the westward subduction of the paleo-Pacific plate.     

浅成低温热液型金矿特点、分布和找矿前景

浅成低温热液矿床的概念,最初由Lindgren首先提出.20世纪80年代以来环太平洋活动带上一系列大型、超大型金矿床的发现,在世界范围内掀起了一股空前的"浅成低温金矿"热.浅成低温金矿具有低温、低压、低盐度、成矿深度浅的特点.矿化作用发生在火山活动晚期,最终定位于火山地热系统波及范围内.全球浅成低温金矿明显呈集中成带分布的特点,绝大多数分布在著名的环太平洋带、古特提斯带和中亚-蒙古(古亚洲)带.此类金矿成矿在时间上的分布特点大体是①第三纪(最重要)、②第四纪更新世(次重要)、③中生代(重要)、④石炭-二叠纪(次要).成矿环境主要为岛弧带、板内走滑断裂带和上叠火山盆地、陆内裂谷.我国地处三大浅成低温成矿带分布区,已经发现诸如阿希、团结沟、紫金山等金(铜)矿床,找寻同类矿产前景广阔.     

Peculiarities of Ore Formation at the Teploe Ag–Au Deposit,Northeast Russia

The mineralogical–geochemical and thermobarogeochemical features of the Teploe Ag–Au epithermal deposit are considered. The dissolution and redeposition of ore minerals are a result of thermal metamorphism. The redistribution of Ag leads to the formation of lenaite and exsolution structures in minerals of the Cu–Ag–S system; abundant stromeyerite, jalpaite, and mckinstryite compose a significant amount of ores. The atypical physicochemical parameters of the formation of ores include high (for epithermal mineralization) temperatures and low salinity and density of the fluid typical of a dry vapor. The results of fluid inclusion study ascribe the Teploe deposit to an intermediate class of epithermal deposits.     

Paleozoic Epithermal Au and Porphyry Cu Deposits in North Xinjiang, China: Epochs, Features, Tectonic Linkage and Exploration Significance

Abstract. Based on field investigation of large number of ore deposits including some latest discoveries and multidiscipline comprehensive research, we demonstrated the general features of metallic deposits and we suggest that Paleozoic archipelago-type collisional orogen at North Xinjiang, northwestern China show intimate similarity with the metallogenesis of Southeast Asia Cenozoic archipelago. We briefly described the characteristics of major porphyry-type, skarn-type Cu deposits and typical high-sulfidation type (HS-type) and low-sulfidation type (LS-type) epithermal Au deposits as well as some latest discoveries. Systematic isotopic age-dating on the Tuwu-Yandong superlarge porphyry Cu deposits revealed that they formed in Late Devonian to Early Carboniferous in an accretionary arc setting. The tectonic settings of epithermal Au deposits and its linkage with porphyry Cu deposits are further discussed. The formation condition for porphyry Cu deposits is more strict than epithermal Au deposits. The distribution width for porphyry Cu deposits in the orogenic belts is more limited than epithermal Au deposits. The discovery and prospecting progress of the Kalatage HS-type Cu-Au deposit were reported. The significance in further exploration was suggested.     

斑岩型和浅成低温热液型矿床成矿流体与找矿预测研究:以华南若干典型矿床为例

斑岩型和浅成低温热液型矿床是全球铜、钼、金、银的主要来源之一,具有重要经济价值。这两类矿床之间通常存在紧密的时空关系,对其成矿流体性质和演化的解剖不仅有利于探究金属沉淀机制,也有助于揭示两者之间的内在成因联系。本文在综述国内外重要研究前沿基础上,以中国华南富家坞斑岩型铜钼(金)矿、桐村斑岩钼矿,以及邱村和安村浅成低温热液金矿为例,系统总结了斑岩型和浅成低温热液型矿床流体特征、演化规律和金属沉淀机制、探讨了从斑岩型到浅成低温热液型流体演化的“气相迁移”模型,并以福建紫金山铜金矿床为例,介绍了应用流体填图进行找矿预测的实例。     

中国东部中生代浅成热液金矿的类型、特征及其地球动力学背景

中国东部中生代浅成热液金矿可以划分为与花岗岩和与碱性岩有关的两种类型；也可以分为高硫型和低硫型两大类，而且以后一种为主。这些金矿的形成和分布受区域构造制约，具体地说是受破火山口、火山角砾岩筒以及与火山机构有关的断裂控制。成矿围岩为火山岩类及同源花岗质岩石和周围地层。主要的蚀变组合为冰长石一玉髓一绢云母或明矾石一高岭石一石英(玉髓)。成矿年龄分布在180～188Ma，135～144Ma，127～115Ma和94～105Ma四个区间，前三组年龄分别响应于中生代华北板块与扬子克拉通的造山碰撞后陆内造山的伸展过程、构造体制大转折以及岩石圈大减薄，后一组为华南地区岩石圈再一次强烈伸展期间的产物。虽然这些矿床的形成时间有差异，但都是发育于大陆伸展环境中。     

Geochemical features of Paleozoic Au–Ag epithermal deposits (Northeastern Russia)

The geochemical features and conditions of formation of the Paleozoic epithermal Au–Ag mineralization in the pre-accretion Kedon (D_2–3) volcanoplutonic belt located within the Omolon craton terrain are described. The new data on the composition and contents of trace and rare-earth elements (REEs) in igneous ores of epithermal deposits is provided. The elevated grades of a wide range of trace elements as compared to the average values of the upper crust have been identified.     

Role of basement in epithermal deposits: The Kushikino and Hishikari gold deposits,southwestern Japan

The magma–ore deposit relationship of most low-sulfidation epithermal ore deposits is still unclear, partly because many stable isotopic studies of such deposits have indicated the predominance of meteoric waters within hydrothermal fluids. However, it is certainly true that hydrothermal systems are ultimately driven by magmatic intrusions, and epithermal gold deposits might therefore be produced by magmatic activity even in deposits having has no obvious links to a magma. We re-examine the genesis of two typical low-sulfidation epithermal gold deposits, the Kushikino and Hishikari deposits, using structural simulations and isotope data.Many epithermal gold deposits including the Kushikino and Hishikari deposits have been discovered in Kyushu, southwestern Japan. The Kushikino deposit comprises fissure-filling veins within Neogene andesitic volcanics that overlie unconformably Cretaceous sedimentary basement. The veins consist of gold- and silver-bearing quartz and calcite with minor amounts of adularia, sericite and sulfides. Although carbon and oxygen isotopic data for the veins indicate a meteoric origin of the ore fluid, finite element simulations suggest that the vein system might have formed in direct response to magma intrusion. In particular, geophysical data suggest that intruding magma has uplifted the basement rocks, thereby producing fractures and veins and a positive Bouguer anomaly, and providing the heat necessary to drive an ore-forming hydrothermal system.The second component of this study has been to investigate the nature and evolution of the Kushikino and Hishikari epithermal systems. Isotope data document the geochemical evolution of the hydrothermal fluids. We conclude that the existence of sedimentary basement rocks at depth might have affected the strontium and carbon isotopic ratios of the Kushikino and Hishikari ore fluids. The ⁸⁷Sr/⁸⁶Sr ratios and δ¹³C–δ¹⁸O trend reveal that major ore veins in the Hishikari deposit can be distinguished from shallow barren veins. It was suggested isotopically that fluids responsible for the barren veins in nearby shallow and barren circulation systems were only controlled by the shallow host rocks. Such multi-isotope systematics provide a powerful tool with which to determine the center of hydrothermal activity and thereby document the evolution of hydrothermal fluids.     

The Late Paleozoic porphyry–epithermal spectrum of the Birgilda–Tomino ore cluster in the South Urals,Russia

The Birgilda–Tomino ore cluster in the East Uralian zone, South Urals, Russia, hosts a variety of Late Paleozoic porphyry copper deposits (Birgilda, Tomino, Kalinovskoe, etc.), high- and low sulfidation epithermal deposits (Bereznyakovskoe, Michurino), and skarn-related base metal mineralization (Biksizak) in carbonate rocks. The deposits are related to quartz diorite and andesite porphyry intrusions of the K–Na calc-alkaline series, associated to a subduction-related volcanic arc. We report microprobe analyses of ore minerals (tetrahedrite–tennantite, sphalerite, Bi tellurides and sulfosalts, Au and Ag tellurides), as well as fluid inclusion data and mineral geothermometry. On the basis of these data we propose that the Birgilda–Tomino ore cluster represents a porphyry–epithermal continuum, with a vertical extent of about 2–3 km, controlled by temperature decreases and fS₂ and fTe₂ increase from deeper to shallow levels.     

Base and precious metal mineralization in Middle Jurassic rocks of the Lesser Caucasus: A review of geology and metallogeny and new data from the Kapan,Alaverdi and Mehmana districts

The polymetallic Cu–Au–Ag–Zn ± Pb, Cu–Au and Cu deposits in the Kapan, Alaverdi and Mehmana mining districts of Armenia and the Nagorno–Karabakh region form part of the Tethyan belt. They are hosted by Middle Jurassic rocks of the Lesser Caucasus paleo-island arc, which can be divided into the Kapan Zone and the Somkheto–Karabakh Island Arc. Mineralization in Middle Jurassic rocks of this paleo-island arc domain formed during the first of three recognized Mesozoic to Cenozoic metallogenic epochs. The Middle Jurassic to Early Cretaceous metallogenic epoch comprises porphyry Cu, skarn and epithermal deposits related to Late Jurassic and Early Cretaceous intrusions. The second and third metallogenic epochs of the Lesser Caucasus are represented by Late Cretaceous volcanogenic massive sulfide (VMS) deposits with transitional features towards epithermal mineralization and by Eocene to Miocene world-class porphyry Mo–Cu and epithermal precious metal deposits, respectively.The ore deposits in the Kapan, Alaverdi and Mehmana mining districts are poorly understood and previous researchers named them as copper–pyrite, Cu–Au or polymetallic deposits. Different genetic origins were proposed for their formation, including VMS and porphyry-related scenarios. The ore deposits in the Kapan, Alaverdi and Mehmana mining districts are characterized by diverse mineralization styles, which include polymetallic veins, massive stratiform replacement ore bodies at lithological contacts, and stockwork style mineralization. Sericitic, argillic and advanced argillic alteration assemblages are widespread in the deposits which have intermediate to high-sulfidation state mineral parageneses that consist of tennantite–tetrahedrite plus chalcopyrite and enargite–luzonite–colusite, respectively. The ore deposits are spatially associated with differentiated calc-alkaline intrusions and pebble dykes are widespread. Published δ³⁴S values for sulfides and sulfates are in agreement with a magmatic source for the bulk sulfur whereas published δ³⁴S values of sulfate minerals partly overlap with the isotopic composition of contemporaneous seawater. Published mineralization ages demonstrate discrete ore forming pulses from Middle Jurassic to the Late Jurassic–Early Cretaceous boundary, indicating time gaps of 5 to 20 m.y. in between the partly subaqueous deposition of the host rocks and the epigenetic mineralization.Most of the described characteristics indicate an intrusion-related origin for the ore deposits in Middle Jurassic rocks of the Lesser Caucasus, whereas a hybrid VMS–epithermal–porphyry scenario might apply for deposits with both VMS- and intrusion-related features.The volcanic Middle Jurassic host rocks for mineralization and Middle to Late Jurassic intrusive rocks from the Somkheto–Karabakh Island Arc and the Kapan Zone show typical subduction-related calc-alkaline signature. They are enriched in LILE such as K, Rb and Ba and show negative anomalies in HFSE such as Nb and Ta. The ubiquitous presence of amphibole in Middle Jurassic volcanic rocks reflects magmas with high water contents. Flat REE patterns ([La/Yb]_N = 0.89–1.23) indicate a depleted mantle source, and concave-upward (listric-shaped) MREE–HREE patterns ([Dy/Yb]_N = 0.75–1.21) suggest melting from a shallow mantle reservoir. Similar trace element patterns of Middle Jurassic rocks from the Somkheto–Karabakh Island Arc and the Kapan Zone indicate that these two tectonic units form part of one discontinuous segmented arc. Similar petrogenetic and ore-forming processes operated along its axis and Middle Jurassic volcanic and volcanosedimentary rocks constitute the preferential host for polymetallic Cu–Au–Ag–Zn ± Pb, Cu–Au and Cu mineralization, both in the Somkheto–Karabakh Island Arc and the Kapan Zone.     

中硫型浅成低温热液金多金属矿床基本特征、研究进展与展望

继20世纪80年代以来低硫型和高硫型浅成低温金矿床概念提出及成矿模型建立之后,相继发现一些浅成低温热液矿床不具上述两类矿床端元的成矿特点,相反兼具过渡性质;很多学者将其作为单一矿床类型,定义为中硫型浅成低温热液矿床。作为一个新的矿床类型,中硫型矿床是否有单独划分的必要?该类矿床具有什么样的地质特征?长期以来这些问题令人困惑。本文从大量文献中,在全球范围内甄别出24个比较明确的中硫型浅成低温热液金(多金属)矿床,基于其基本特征和研究进展的系统梳理与分析,从中硫型矿床的时空展布、地质特征、矿物组合、金属源区特征、中硫型与高硫型金(铜)矿和低硫型金矿的主要区别,以及目前国际研究进展及难点等方面进行总结阐述。中硫型金多金属矿床具有如下六大特征:(1)发育富碳酸盐-贱金属硫化物成矿体系,碳酸盐矿物可见于各成矿阶段热液脉系中,尤其在热液晚阶段以碳酸盐矿物为主;贱金属硫化物主要为Cu、Pb、Zn、Fe等的硫化物;(2)发育中硫化态矿物组合,如贱金属硫化物黄铜矿、闪锌矿、方铅矿、黄铁矿、黝铜矿等;可少量发育明矾石和冰长石;(3)含矿脉系中富硫化物(总量大于5%),且在斑岩铜矿系统中较富黄铜矿;(4)普遍发育浅色贫铁闪锌矿(有待进一步证实);(5)普遍赋存在挤压岛弧背景下斑岩Cu-Au-Mo矿的外围;(6)空间上可与高硫型和低硫型金多金属矿床共存。普遍发育斑岩型Cu-Au-(Mo)矿床和浅成低温热液型矿床的世界著名三大成矿域(滨太平洋成矿域、古亚洲洋成矿域和特提斯-喜马拉雅成矿域),同样具有形成中硫型矿床的有利成矿条件。未来关于中硫型矿床的研究亟需解决以下几个关键问题:(1)目前尚未有文献对"富碳酸盐-贱金属(Cu、Pb、Zn、Fe等)"进行详细报道,这种成矿体系是如何形成的?流体中CO_2、H_2S及贱金属元素对Au的运移和沉淀有何影响?此问题是认识中硫型金多金属矿床成矿机制的关键所在。(2)中硫化态矿物的矿物(黄铁矿、闪锌矿、方铅矿、黝铜矿、砷黝铜矿、黄铜矿等)的沉淀环境?与高硫化态、低硫化态矿物有何区别?(3)从成矿系统、成矿过程和矿物形成的复杂性来考虑,显然以闪锌矿中Fe S的含量多少作为区别IS型、HS型、LS型矿床的特征地化标志过于简单,且与已有关于闪锌矿的矿物学研究成果相矛盾,因此仍需进一步工作。(4)早期形成的作为赋矿围岩的火山岩地层或者次火山岩体是否提供了成矿物质?是否充当了浅成低温热液矿物沉淀的地球化学屏障?其具体过程是怎样的?以上问题的解决可辅助揭示IS型矿床的成因机制和形成过程,并为同类型矿床的勘查工作提供支持。     

Geochemical patterns of epithermal ore formation in the Okhotsk–Chukotka volcanoplutonic belt (Northeast Russia)

Doklady Earth Sciences - Ores of epithermal Au–Ag deposits of the Okhotsk–Chukotka volcanoplutonic belt are characterized by enrichment in a wide spectrum of elements in relation to the...