The Engineer Mine,British Columbia: An example of epithermal Au-Ag mineralization with mixed alkaline and subalkaline characteristics     

《Ore Geology Reviews》2017

The Engineer Mine epithermal precious metal deposit in British Columbia, Canada, is related to Eocene Sloko-Skukum-Group (SSG) volcanism and, according to previous studies, contains roscoelite in intimate association with electrum. Roscoelite, a vanadian mica, is considered characteristic of low-sulfidation epithermal deposits related to alkaline magmatism. This contradicts the fact that the SSG volcanics are subalkaline. In order to address this ambiguity and to accurately classify the style of epithermal mineralization at the Engineer Mine we conducted detailed petrographic, mineralogical, geochronological, fluid inclusion, and stable isotope studies.The principal ore assemblage of the Engineer Mine epithermal veins precipitated in response to boiling during a hydrothermal event at 49.90 Ma ± 0.25 Ma. During this event electrum, arsenopyrite, pyrite ± chalcopyrite ± sphalerite ± löllingite ± tetrahedrite-group phases ± allargentum ± acanthite ± hessite ± dyscrasite ± stibarsen ± galena and an unidentified Ag-rich phase were deposited in conjunction with amorphous silica, platy and rhombic calcite, K-feldspar, and vanadian illite. Fluid inclusion and stable isotope data suggest that the ore-forming fluid was boiling at ∼220 °C during vein mineralization and had an isotopic composition derived from local meteoric water. Based on these results the Engineer Mine is classified as an epithermal low-sulfidation deposit, which shares similarities with alkaline and subalkaline epithermal low-sulfidation deposits. This is attributed to the fact that the SSG volcanic rocks are borderline subalkaline to alkaline in character and that the sedimentary host rocks are vanadium-bearing. These sedimentary rocks contributed the bulk of the vanadium to the Engineer Mine epithermal system. The presence of roscoelite at the Engineer Mine could not be confirmed during this study. The mica referred to as roscoelite in previous publications instead is vanadian illite. To our knowledge the only alkaline low-sulfidation epithermal precious metal deposit that contains V-mica which exclusively qualifies as true roscoelite is the Porgera deposit, Papua New Guinea.  相似文献   

Cenozoic metallogeny of Greece and potential for precious,critical and rare metals exploration     

《Ore Geology Reviews》2017

The Cenozoic metallogeny in Greece includes numerous major and minor hydrothermal mineral deposits, associated with the closure of the Western Tethyan Ocean and the collision with the Eurasian continental plate in the Aegean Sea, which started in the Cretaceous and is still ongoing. Mineral deposits formed in four main periods: Oligocene (33–25 Ma), early Miocene (22–19 Ma), middle to late Miocene (14–7 Ma), and Pliocene-Pleistocene (3–1.5 Ma). These metallogenic periods occurred in response to slab-rollback and migration of post-collisional calc-alkaline to shoshonitic magmatism in a back-arc extensional regime from the Rhodopes through the Cyclades, and to arc-related magmatism along the active south Aegean volcanic arc. Invasion of asthenospheric melts into the lower crust occurred due to slab retreat, and were responsible for partial melting of metasomatized lithosphere and lower crustal cumulates. These geodynamic events took place during the collapse of the Hellenic orogen along large detachment faults, which exhumed extensive metamorphic core complexes in mainly two regions, the Rhodopes and the Cyclades. The detachment faults and supra-detachment basins controlled magma emplacement, fluid circulation, and mineralization.The most significant mineralization styles comprise porphyry, epithermal, carbonate-replacement, reduced intrusion-related gold, intrusion-related Mo-W and polymetallic veins. Porphyry and epithermal deposits are commonly associated with extensive hydrothermal alteration halos, whereas in other cases alteration is of restricted development and mainly structurally controlled. Porphyry deposits include Cu-Au-, Cu-Mo-Au-Re, Mo-Re, and Mo-W variants. Epithermal deposits include mostly high- and intermediate-sulfidation (HS and IS) types hosted in volcanic rocks, although sedimentary and metamorphic rock hosted mineralized veins, breccias, and disseminations are also present. The main metal associations are Cu-Au-Ag-Te and Pb-Zn-Au-Ag-Te in HS and IS epithermal deposits, respectively. Major carbonate-replacement deposits in the Kassandra and Lavrion mining districts are rich in Au and Ag, and together with reduced intrusion-related gold systems played a critical role in ancient economies. Finally hundreds of polymetallic veins hosted by metamorphic rocks in the Rhodopes and Cyclades significantly add to the metal endowment of Greece.  相似文献   

Texture and chemistry of pyrite at Chah Zard epithermal gold–silver deposit,Iran     

《Ore Geology Reviews》2017

Gold mineralization at Chah Zard, Iran, is mostly concentrated in breccia and veins, and is closely associated with pyrite. Optical and scanning electron microscopy-backscattered electron observations indicate four different pyrite types, each characterized by different textures: porous and fractured py1, simple-zoned, oscillatory-rimmed, framboidal and fibrous py2, colloform py3, and inclusion-rich py4. Laser ablation ICP–MS analysis and elemental mapping reveal the presence of invisible gold in all pyrite types. The highest concentrations (161–166 ppm Au) are found in py2 and py4, which correlate with the highest As concentrations (73,000–76,000 ppm). In As-poor grains, Au concentrations decrease by about two orders of magnitude. Copper, Pb, Zn, Te, Sb, and Ag occur with invisible gold, suggesting that at least part of the gold occurs in nanoparticles of sulfosalts of these metals and metalloids. Gold distribution patterns suggest that only negligible Au was originally trapped in py1 from the initial ore fluids. However, most, if not all, Au was transported and deposited during subsequent overprinting hydrothermal fluid flow in overgrowth rims around the margins of the py2 and within microfractures of py4 grains. Oscillatory zonation patterns for Co, Ni, Sb, Cu, Pb, and Ag in pyrite reflect fluctuations in the hydrothermal fluid chemistry. The LA-ICP–MS data reveal that Cu, Pb and Ag show systematic variations between different pyrite types. Thus, Cu/Pb and Pb/Ag ratios in pyrite may provide a potentially powerful exploration vector to epithermal gold mineralization at Chah Zard district and elsewhere.  相似文献   

Deriving Optimal Exploration Target Zones on Mineral Prospectivity Maps     

Pravesh Debba  Emmanuel J. M. Carranza  Alfred Stein  Freek D. van der Meer 《Mathematical Geosciences》2009,41(4):421-446

This paper describes a quantitative methodology for deriving optimal exploration target zones based on a probabilistic mineral prospectivity map. The methodology is demonstrated in the Rodalquilar mineral district in Spain. A subset of known occurrences of mineral deposits of the type sought was considered discovered and then used as training data, and a map of distances to faults/fractures and three band ratio images of hyperspectral data were used as layers of spatial evidence in weights-of-evidence (WofE) modeling of mineral prospectivity in the study area. A derived posterior probability map of mineral deposit occurrence showing non-violation of the conditional independence assumption and having the highest prediction rate was then put into an objective function in simulated annealing in order to derive a set of optimal exploration focal points. Each optimal exploration focal point represents a pixel or location within a circular neighborhood of pixels with high posterior probability of mineral deposit occurrence. Buffering of each optimal exploration focal point, based on proximity analysis, resulted in optimal exploration target zones. Many of these target zones coincided spatially with at least one occurrence of mineral deposit of the type sought in the subset of cross-validation (i.e., presumed undiscovered) mineral deposits of the type sought. The results of the study showed the usefulness of the proposed methodology for objective delineation of optimal exploration target zones based on a probabilistic mineral prospectivity map.  相似文献   

黑龙江省黑河市争光金矿流体包裹体研究及矿床成因   总被引：4，自引：1，他引：3  

邓轲  李诺  杨永飞  张成  于援邦  张东才 《岩石学报》2013,29(1):231-240

黑龙江省黑河市争光金矿床位于大兴安岭东北缘的多宝山矿集区,矿体呈脉状产于闪长岩体与中奥陶统多宝山组凝灰岩的接触带,受断裂构造控制.流体成矿作用可分为4个阶段:石英-黄铁矿阶段、石英-多金属硫化物阶段、方解石-石英-硫化物阶段、碳酸盐阶段.其中阶段2和3具有复杂的金属硫化物组合并含金,即黄铁矿-闪锌矿-方铅矿-黄铜矿±自然金.石英及方解石中流体包裹体类型单一,主要为气液两相水溶液包裹体,大小集中于3 ～ 15μm,气液相比集中于5％～10％.包裹体均一温度介于119 ～ 305℃,盐度集中于0.3％ ～ 10.4％ NaCleqv,密度介于0.760.99g/cm3.从阶段2至阶段4,流体均一温度从150～ 220℃,经140～190℃,降为130～150℃.综合矿床地质特征和成矿流体研究,认为争光金矿床属低硫型浅成低温热液矿床.  相似文献   

在裂变径迹测定年代中准确测定中子通量   总被引：1，自引：0，他引：1  

赵云龙  翟鹏济 《铀矿地质》1991,7(2):113-118

  相似文献   

湖南省热液硅化成矿作用与找矿   总被引：2，自引：0，他引：2  

童潜明 《湖南地质》1991,10(2):129-134

根据成矿作用与热液硅化极为密切的锡矿山锑矿床、康家湾铅锌金矿床、磺厂雄磺矿床和320铀矿床的地质特征,对热液硅化、角砾化、矿质沉淀和矿床剖面结构的形成机理进行了讨论,认为这类矿床属于浅成热液类型矿床或热泉型矿床,进而认为对司空见惯的硅化带的找矿意义要重新认识,由此提出了寻找这种类型矿床的地质、地球化学、地球物理的找矿标志。  相似文献   

浅成热液成矿系统模型研究评述   总被引：6，自引：0，他引：6  

张德会 《地球科学进展》1996,11(6):563-568

目前国内外矿床模型研究的一个明显发展势是研制成矿系统的地质成因模型，即建立具有一定的成因联系的不同矿种的矿系列成因模型。分析了近年来浅成热液矿床概念，分类、成模型式研究进展，评述了浅成热液矿床矿系统研究现状，并对我国此类矿床的研究提出建议。  相似文献   

Chemical,isotopic and mineralogical characteristics of volcanogenic epithermal fluorite deposits on the Permo-Mesozoic foreland of the Andean volcanic arc in Patagonia (Argentina)     

《Chemie der Erde / Geochemistry》2016,76(2):275-297

Epithermal deposits mined for fluorite in Patagonia, Argentina, are closely related to late Triassic through Jurassic magmatic activity which brought about felsic to intermediate magmatic rocks. The fluorite mineralization in the Patagonian epithermal system resulted from gaseous F-and CO₂-enriched magmas which lead to an explosive phreatomagmatic volcanism, when getting in contact with groundwater near the surface. As a result of these hydrothermal processes, rapid cooling took place in the epithermal mineralization. Changes in the viscosity along with the cooling down of mineralizing fluids caused mottled mineral colors blurring the boundaries between the stages and ore textures.The fluids accountable for the main constituents fluorite, quartz, barite and silica were operative over a vertical extension of roughly 600 m. Their temperature of formation dropped from 379 °C through 64 °C, while the pH decreased from the heat center towards the paleosurface under oxidizing conditions. This steep temperature gradient conducive to the telescoping of mineral associations into each other was accompanied by a rapid loss in CO₂, and a mixing of meteoric and magmatic fluids. Even the boundary between the hypogene and supergene alteration cannot be drawn precisely within the assemblage of Mn oxides, which bridge the gap between hypogene and supergen mineralization. The physical-chemical parameters of the fluids, particularly, the redox conditions did not allow sulfides to be preserved. A classification of the epithermal system as to its degree of sulfidation is based on K-feldspar and kaolinite which are present in significant amounts, whereas APS (aluminum-phosphate-sulfate) minerals are absent. Therefore a categorization as an epithermal fluorite deposit of low- to intermediate sulfidation is justified, because the only mineral of economic interest in the system is fluorite.The data obtained during this joint study render the Patagonian fluorite district a reference type of fluorite in an epithermal system of low- to intermediate sulfidation which are widespread in Argentina, e.g., Sierras Pampeanas, and evolved on part of the stable craton, called Gondwana and which grade into epithermal Au, Ag, In, Pb and Zn deposits.  相似文献   

江苏观山高硫型铜铅金矿床稳定同位素地球化学和成因意义   总被引：1，自引：0，他引：1  

梁业恒 《地质与勘探》2010,46(4)

江苏观山铜铅金矿是典型的高硫型浅成低温热液矿床。本文通过对观山铜铅金矿床氢、氧、碳、硫同位素组成的研究,探讨成矿溶液中水、碳、硫的来源以及成矿溶液的演化。同位素测定显示石英流体包裹体水的δD=-90‰～-70‰,δ18O水=-8.9‰～-1.1‰;热液方解石流体包裹体水的δD=-90‰～-81‰,δ18O水=0.1‰～2.3‰。氢氧同位素组成说明成矿流体主要为与围岩进行过水岩反应的循环大气降水,不排除有少量岩浆水的加入。黄铁矿与黄铜矿矿石的δ34SV-CDT=5.8‰～9.9‰,平均值为7.6‰,表明该矿成矿过程中的S很可能是沉积岩来源的硫与岩浆岩来源硫的混合。矿床中可见较多的重晶石等硫酸盐矿物,这种高价态硫的矿物的存在显示其成矿溶液具有富集34S的特征,加上成矿过程中流体的沸腾导致H2S等气体大量逸出和残余岩浆流体富集34S,使得沉淀的黄铁矿、黄铜矿等硫化物同样具有富集34S的特征;热液方解石碳同位素δ13C方解石=-4.1‰～6.1‰,平均为δ13C方解石=1.3‰,显示其中的C主要来源于流体对流循环过程中对基底岩石中碳酸盐地层的溶解。  相似文献