Geochemical indicators of gold-rich zones in the La Josefina epithermal deposit,Deseado Massif,Argentina

The gold deposit at La Josefina, in the Deseado Massif of Argentina, is a low-sulfidation epithermal deposit with some features of the intermediate sulfidation style; the Au occurs in quartz veins and hydrothermal breccias hosted by acid pyroclastic rocks produced by Jurassic bimodal volcanism. Exploration for this deposit type uses geochemical data for vectoring to mineralized rocks. Although a general suite of elements with anomalous concentrations around low-sulfidation deposits is known, that suite varies amongst individual deposits, which should be studied individually. The aim of this study was to determine, in the La Josefina deposit, geochemical indicators of Au-rich rocks at different scales and to assess the effects of weathering on those indicators. To reach these objectives, a mineralized zone (hosting Au-rich veins) and a non-mineralized zone (hosting barren veins) were compared in terms of vein mineralogy, alteration minerals and geochemistry. These zones were also compared with estimated element concentrations of the protolith. Element concentrations in the mineralized zone were then plotted against distance to the Au-rich veins, separating the dataset into two subsets: one from strongly oxidized rocks and the other from weakly oxidized rocks, considering the degree of oxidation as indicative of relative degree of weathering. Based on alteration and vein mineralogy, we interpret that the mineralized zone was hydrothermally active before, during and after Au-mineralization, while the non-mineralized zone was active only before Au-mineralization. Therefore, differences in element concentrations between the estimated protolith and the non-mineralized zone represent geochemical changes produced before mineralization, whereas differences between mineralized and non-mineralized zones represent changes produced during and after mineralization. We conclude that in rhyolitic to rhyodacitic pyroclastic rocks of the study area, affected by predominantly argillic and silicic hydrothermal alterations, high concentrations of Au, Cu, Hg, V, Co and P, and low concentrations of Ba are probably the best deposit-scale geochemical indicators to distinguish Au-mineralized zones from non-mineralized zones. High concentrations of As, Mn, Fe, Pb, Cr, Ni, MgO and Zn (as well as high values of chlorite-carbonate-pyrite index), and low concentrations of Be and CaO can also distinguish mineralized from non-mineralized zones. High concentrations of Au, Cu, Pb, As, Hg, and Co indicate Au-rich zones, independently of lithology and alteration, because they were introduced into the veins and host rocks together with Au. At detailed-scale, the concentrations of 15 elements vary with distance to Au-rich veins; therefore, those elements are considered potential indicators of proximity to Au-rich veins. Of those elements, Au, P, Cu, Pb, Hg, Ba and MgO are the strongest indicators of proximity to the Au-rich veins. In strongly oxidized rocks, some indicators of mineralized zones (Co, Mn, Pb, Zn and MgO) and some indicators of proximity to Au-rich veins (P, Au, Cu, Hg and Ba) should be used with caution or be avoided because weathering modifies their quality as indicators.     

哈萨克斯坦北东天山浅成低温热液型金矿床成矿时代及构造背景

哈萨克斯坦北东天山地区是中亚造山带重要的浅成低温热液型金矿床产出地区,但其成矿年代学研究非常薄弱。为确定成矿时代,作者运用高精度激光40Ar/39Ar定年法对阿尔哈尔雷金矿床和乌仁科布拉克金矿床的赋矿围岩进行了年龄测定。获得阿尔哈尔雷金矿床安山岩样品20个点40Ar/39Ar等时线年龄为304±7Ma(MSWD=6),乌仁科布拉克金矿床安山玄武岩样品21个点40Ar/39Ar等时线年龄为280±6Ma(MSWD=2.4),表明哈萨克斯坦北东天山地区浅成低温热液型金矿床主要形成于晚石炭世末期-早二叠世。初步的岩石学、地球化学研究表明,哈萨克斯坦北东天山地区晚石炭世末期-二叠纪火山岩主要为流纹岩、粗安岩、玄武粗安岩、玄武安山岩、粗面玄武岩和玄武岩,具双峰式特征,主体属于高钾钙碱性和橄榄玄粗岩系列。哈萨克斯坦北东天山地区晚石炭世末期浅成低温热液型金矿床形成于碰撞晚期向裂谷的转换阶段,而二叠纪浅成低温热液型金矿床产出于陆内裂谷环境。     

大别山北麓斑岩型钼矿床地质特征、成矿时代及其成矿构造背景

在野外调查和测试分析的基础上,结合前人的研究成果,综合论述了大别山北麓斑岩型钼矿床的地质特征、形成时代和构造背景。大别山北麓斑岩型钼矿床总体沿区域构造线呈北西向狭长带状展布,具有近东西向成带、南北向成群的空间展布特征,其形成与燕山期中酸性浅成-超浅成小型花岗斑岩体有关,钼矿床直接产于岩体内外接触带及其附近的围岩中,矿床类型主要为斑岩型、斑岩-矽卡岩型及少量热液石英脉型。结合Re-Os同位素年龄数据,探讨了大别山北麓斑岩型钼矿床的成矿物质来源、成矿流体、成矿时代、主要成矿作用的时限以及成矿地球动力学背景。结果表明:大别山北麓地区钼矿床的主要成矿作用时限为142~137 Ma和127~110 Ma,对应的地球动力学背景为中国东部地球动力学体制大转换晚期的岩石圈拆沉及伸展减薄的构造背景。     

Provenance analysis and tectonic setting of the Ordovician clastic deposits in the southern Puna Basin, NW Argentina

Provenance studies on Early to Middle Ordovician clastic formations of the southern Puna basin in north-western Argentina indicate that the sedimentary detritus is generally composed of reworked crustal material. Tremadoc quartz-rich turbidites (Tolar Chico Formation, mean composition Q_t89 F7 L4) are followed by volcaniclastic rocks and greywackes (Tolillar Formation, mean Q_t33 F42 L25). These are in turn overlain by volcaniclastic deposits (mean Q_t24 F30 L46) of the Diablo Formation (late Arenig–early Llanvirn) that are intercalated by lava flows. All units were deformed in the Oclóyic Orogeny during the Middle and Late Ordovician. Sandstones of the Tolar Chico Formation are characterized by Th/Sc ratios > 1, La/Sc ratios ≈ 10, whereas associated fine-grained wackes show slightly lower values for both ratios. LREE (light rare earth elements) enrichment of the arenites is ≈ 50× chondrite, Eu/Eu* values are between 0·72 and 0·92, and flat HREE (heavy rare earth elements) patterns indicate a derivation from mostly felsic rocks of typical upper crustal composition. The ε_{Nd(t = sed)} values scatter around −11 to −9. The calculated Nd-T_DM residence ages vary between 1·8 and 2·0 Ga indicating contribution by a Palaeoproterozoic crustal component. The Th/Sc and La/Sc ratios of the Tolillar Formation are lower than those of the Tolar Chico Formation. Normalized REE (rare earth elements) patterns display a similar shape to PAAS (post-Archaean average Australian shale) but with higher abundances of HREEs. Eu/Eu* values range between 0·44 and 1·17, where the higher values reflect the abundance of plagioclase and feldspar-bearing volcanic lithoclasts. Average ε_{Nd(t = sed)} values are less negative at −5·1, and Nd-T_DM are lower at 1·6 Ga. This is consistent with characteristics of regional rocks of upper continental crust composition, which most probably represent the sources of the studied detritus. The rocks of the Diablo Formation have the lowest Th/Sc and La/Sc ratios, lower LREE abundances than the average continental crust and are slightly enriched in HREEs. Eu/Eu* values are between 0·63 and 1·17. The Nd isotopes (ε_{Nd(t = sed)} = −3 to −1; T_DM = 1·2 Ga) indicate that one source component was less fractionated than both the underlying Early Ordovician and the overlying Middle Ordovician units. Synsedimentary vulcanites in the Diablo Formation show the same isotopic composition. Our data indicate that the sedimentary detritus is generally composed of reworked crustal material, but that the Diablo Formation appears to contain ≈ 80% of a less fractionated component, derived from a contemporaneous continental volcanic arc. There are no data indicating an exotic detrital source or the accretion of an exotic block at this part of the Gondwana margin during the Ordovician.     

新疆北部古生代浅成低温热液型金矿特征及其地球动力学背景

文章在总结前人研究成果的基础上,提出新疆北部古生代浅成低温热液型金矿床可以划分为高硫型和低硫型两大类,以后一种为主。金矿的形成和分布受破火山口、隐爆角砾岩筒、与火山机构有关的断裂以及区域断裂控制。与金矿有关的火山岩,主要是一套以玄武岩_安山岩_英安岩_流纹岩及其火山碎屑岩组合为特征的钙碱性陆相火山岩,少数为海相_陆相火山岩。矿体赋存在火山岩、潜火山岩中,少数在斑岩中。主要的蚀变组合为冰长石_石英(玉髓)_绢云母或明矾石_高岭石_石英(玉髓)。金矿成矿时代在340~244Ma之间,金矿在时间和空间上与新疆古生代在(350±10)Ma、(300±10)Ma和(250±10)Ma3个阶段的大规模火山_潜火山活动有密切关系。金矿床形成的地球动力学背景为区域伸展环境或大范围挤压背景下的局部伸展环境。     

Origin and age of rift related fluorite and manganese deposits from the San Rafael Massif,Argentina

The San Rafael Massif is characterized by widespread fluorite and manganese epithermal ore deposits whose origin has been under debate to the present. Isotopic (Sm/Nd and K/Ar) and geochemical (trace elements and REE) data of fluorite and manganese ore allowed to establish the age and genesis of the deposits and to propose a regional genetic model. The fluorite deposits were formed during the Upper Triassic–Lower Jurassic as a result of the Triassic rifting that launched a hydrothermal activity at regional scale. The hydrothermal fluids had low T and high fO₂ with fluorine probably derived from a mantle source and REE scavenged from the volcanics of the Gondwanan Choiyoi Magmatic Cycle upper section. The manganese deposits were formed by oxidizing hydrothermal fluids that collected Mn from deep sources and also leached REE from the upper section of the Choiyoi Magmatic Cycle during two mineralization episodes. One episode was linked to the rift tectonic setting that remained active up to the Upper Cretaceous and the other was related to an Early Miocene back-arc extensional geodynamic setting. Both manganese and fluorite deposits were formed in extensional tectonic settings within an epithermal environment near the surface, and can be ascribed to the general model of detachment-related 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.     

Porphyry,epithermal, and orogenic gold prospectivity of Argentina

This paper presents a review of the available information on the significant porphyry, epithermal, and orogenic gold districts in Argentina, including the tectonic, geological, and structural settings of large deposits or deposits that have been exploited in the past. Based on this review of the geology and mineralization, targeting models are developed for epithermal and orogenic gold systems, in order to produce GIS-based prospectivity models. Using publically available digital geoscience data, weights of evidence and fuzzy logic prospectivity maps were generated for epithermal and orogenic gold mineralization in Argentina. The results of the prospectivity mapping highlight existing gold deposits within known mineralized districts throughout Argentina, as well as other highly prospective areas with no known deposits within these districts. Additionally, areas within Argentina that have no known gold mineralization (based on publically available information) were highlighted as being highly prospective based on the models used.     

中安第斯地区蒸发岩矿床成矿作用特征及构造背景

在中安第斯高原,包括玻利维亚西部、智利东部、阿根廷北部分布众多的盐湖,湖中含丰富的B、K、Li、Mg和其他蒸发盐类物质,封闭的盆地因蒸发作用使残留盐水中的成矿元素聚集并沉淀。这些矿床的形成与安第斯山的隆起和气侯变化关系密切。通过对该区蒸发岩型矿床的分布特征及成矿特征进行研究,讨论其形成的构造背景,分析成矿要素和找矿方向。     

Mineralogy and geochemistry of El Dorado epithermal gold deposit, El Sauce district, central-northern Chile

Summary The El Dorado Au-Cu deposit is located in an extensive intra-caldera zone of hydrothermal alteration affecting Upper Cretaceous andesites of the Los Elquinos Formation at La Serena (≈ 29°47′S Lat., 70°43′W Long., Chile). Quartz-sulfide veins of economic potential are hosted by N25W and N20E fault structures associated with quartz-illite alteration (+supergene kaolinite). The main ore minerals in the deposit are pyrite, chalcopyrite ± fahlore (As/(As + Sb): 0.06−0.98), with electrum, sphalerite, galena, bournonite-seligmanite (As/(As + Sb): 0.21−0.31), marcasite, pyrrhotite being accessory phases. Electrum, with an Ag content between 32 and 37 at.%, occurs interstitial to pyrite aggregates or along pyrite fractures. Pyrite commonly exhibits chemical zonation with some zones up to 1.96 at.% As. Electron probe microanalyses of pyrite indicate that As-rich zones do not exhibit detectable Au values. Fluid inclusion microthermometry shows homogenization temperatures between 130 and 352 °C and salinities between 1.6 and 6.9 wt.% NaCl eq. Isotope data for quartz, ankerite and phyllosilicates and estimated temperatures show that δ¹⁸O and δD for the hydrothermal fluids were between 3 and 10‰ and between −95 and −75‰, respectively. These results suggest the mineralizing fluids were a mixture of meteoric and magmatic waters. An epithermal intermediate-sulfidation model is proposed for the formation of the El Dorado deposit. Author’s present address: J. Carrillo-Rosúa, Dpto. de Didáctica de las Ciencias Experimentales, Universidad de Granada, Campus de Cartuja, 18071, Granada, Spain     

Provenance and tectonic setting of the metapelites deposits in the Bulfat Complex,NE-Iraq

Major and trace elements including rare earth elements (REEs) chemistry of the metapelitic rocks of Bulfat Complex (Iraqi Zagros Suture Zone) indicate their enrichment in large-ion Lithophile, light rare earth (LREE) elements, and relative depletion of high field strength and heavy rare earth (HREE) elements. The linear correlation coefficients between TiO₂, K₂O, and Al₂O₃ and total REE reveal that phyllosilicates (e.g., mica) and accessory minerals mainly Ti-bearing phases (e.g., ilmenite) are likely the dominant hosts for REEs. Chondrite-normalized REE patterns typical of continental margin settings with significant enrichment of LREE, prominent negative Eu anomalies, and nearly flat HREE are positively correlated with post-Archean Australian shale (PAAS) and upper continental crust (UCC) patterns. Additionally, their consistent elemental La/Sc, Th/Sc, La/Co, Th/Co, Cr/Th, and Eu/Eu* values suggest that sediments may have been originally derived from an old post-Archean upper continental crust composed chiefly of granitic component. It seems most likely that the felsic source rocks were originated by a process of intra-crustal differentiation such as partial melting and/or fractional crystallization involving fractionation of Ca-plagioclase. The geochemical evidences particularly REEs evaluation show that deposition of clasts occurred in an active continental margin setting during lower–upper Cretaceous period contemporaneous with the igneous activities. It is evident therefore that the clasts source is from the north–northeast side, i.e., from the active margin of Iranian microcontinent (Sanandaj–Sirjan Zone).     

中国金矿床时空分布及成矿背景

中国金矿床的时空分布不均一,金矿主要产于稳定陆块边缘或稳定陆块内的活动带,形成了金的矿集区,成矿时代主要以中生代为主,其次为晚古生代及新生代,而早古生代和前寒武纪金矿床则处于相对次要地.从地质构造演化的角度探讨金矿形成的大地构造背景,认为金矿的形成及分布受控于壳幔相互作用及岩石圈不连续。     

华南稀有金属矿床:类型、特点、时空分布与背景

华南地区是我国重要的战略矿产资源基地,以发育大规模多时代、多旋回花岗岩和独特的中生代铜钼钨锡铌钽铍铀等大规模稀有金属和有色金属成矿作用而闻名于世.华南地区稀有金属(W-Sn-Nb-Ta-Li-Be)成矿作用主要与高度分异演化的花岗岩密切相关.稀有金属矿床的分布受区域性断裂控制,主要集中于南岭地区和钦-杭大断裂两侧.成矿...     

Tectonic rotations in the Deseado Massif, southern Patagonia, during the breakup of Western Gondwana

Paleomagnetic investigation in the Deseado Massif, southern Patagonia, suggests that Triassic sedimentary rocks carry a latest Triassic to Jurassic remagnetization and that earliest Jurassic plutonic complexes carry a reversed polarity magnetization of thermoremanent origin. Despite uncertainties in the timing of the observed remanence in the Triassic rocks and the lack of paleohorizontal control on the plutonic complexes, comparison of the derived pole positions with the most reliable Late Triassic–Jurassic apparent polar wander paths indicates that the study areas underwent significant clockwise vertical-axis rotation. In contrast, paleomagnetic results from mid-Cretaceous rocks in the region indicate no rotation. The observed crustal rotations in the Deseado Massif are thus bracketed to have occurred between Jurassic and Early Cretaceous times, documenting southern Patagonian deformation during the breakup of Western Gondwana and then enlarging the regional record of clockwise rotations associated with this event. These results suggest a more complex than previously supposed tectonic evolution of this part of South America.     

桂东北钨锡稀有金属矿床的成矿类型、成矿时代及其地质背景

在大地构造位置上,桂东北地区位于江南造山带与华南褶皱带的过渡部位,具有独特的构造地理位置。在精细测试一系列典型矿床及其有关的花岗岩年代学的基础上,本文根据矿床类型、成矿元素组合,把该地区矿床分为6个成矿系统:①与志留纪花岗岩有关W-Mo矿;②与二叠世花岗岩有关Pb-Zn矿床;③与晚三叠世花岗岩有关W-Mo和Sn-Nb-Ta矿床;④与中—晚侏罗世花岗岩有关的W-Sn矿床;⑤与白垩世花岗岩有关的W-Sn矿床;⑥与花岗岩有关的铀矿。这些矿床的形成与不同时期构造-岩浆演化密切相关,主要形成于同碰撞挤压环境或者碰撞后伸展环境。     

Paleoproterozoic A- and S-granites in the eastern Voronezh Crystalline Massif: Geochronology,petrogenesis, and tectonic setting of origin

The eastern part of the Voronezh Crystalline Massif hosts coeval S- and A-granitoids. The biotite-muscovite S-granites contain elevated concentrations of Si, Al, and alkalis (with K predominance) and relatively low concentrations of Ca, Mg, Ti, Sr, and Ba, show pronounced negative Eu anomalies, and have low concentrations of Y and HREE. The biotite A-granitoids are enriched in Fe, Ti, P, HFSE, REE and have strongly fractionated REE patterns with deep Eu minima. According to their Rb/Nb and Y/Nb ratios, these rocks are classified with group A2 of postcollisional granites. The SIMS zircon crystallization age of the granitoids lies within the range of 2050–2070 Ma. Both the A- and the S-granitoids have positive ?_Nd(T) values, which suggests that they should have had brief crustal prehistories and were derived from juvenile Paleoproterozoic sources. The simultaneous derivation of the A- and S-granites was caused by the melting of the lower crust in response to the emplacement of large volumes of mafic magma in an environment of postcollisional collapse and lithospheric delamination with the simultaneous metamorphism of the host rocks at high temperatures and low pressures. The S-granites are thought to be derived via the melting of acid crustal material in the middle and lower crust. The A2 granites can possibly be differentiation products of mafic magmas that were emplaced into the lower crust and were intensely contaminated with crustal material.     

辽宁省清源县放牛沟含榴白云母花岗岩地质特征及构造环境探讨

辽宁省清源县放牛沟发现一含榴白云母花岗岩岩体,其锆石(U Pb)年龄为261±20M a,时代中二叠世,其岩石化学以富S iO2、富碱为特征,具Ⅰ型花岗岩特征,属晚华力两期同碰撞造山花岗岩晚期分异产物。     

Geochemistry, tectonic setting and geodynamic significance of late orogenic dikes in the Melibocus Massif, Bergsträsser Odenwald

Summary The Melibocus Massif forms a tonalite pluton in the W’ Bergstr?sser Odenwald, which is interpreted as part of a magmatic arc of Devonian to Carboniferous age. Dikes of various compositions intrude frequently this tonalite. Different dike-lithologies are associated with different strike directions. Most dikes show evidence of high-temperature shearing. A probable maximum paleostress direction of ca. 060° can be estimated, i.e. nearly parallel to the known Variscan subduction zone in the Northwest. Due to their ductile deformation under conditions around the Ar-closing temperature of amphibole, intrusion likely occurred during the Carboniferous (Mississippian). The gabbroic to dioritic dikes (malchites) have calc-alkaline composition. Comparison with modern analogues suggests subduction-related arc magmatism. Rare earth element distributions indicate more than 5% partial melting of the mantle source with limited amounts of residual garnet. In contrast to the tonalite pluton the granitoid dikes (alsbachites) are of S-type origin, as indicated by primary muscovite and chemical composition. This requires involvement of continental material in the dike’s source rather than in the tonalite host rock’s source. The trace element chemistry of these dikes indicates magma formation in a convergent plate tectonic situation, i.e. a magmatic arc regime. Therefore, the dikes are probably the late part of the same subduction-related magmatism, which produced the tonalitic and other plutons of the Bergstr?sser Odenwald. In contrast to the large pluton-forming magmas, formation of the dikes during late or post-collisional extension or transtension followed by a phase of compression or transpression is probable.

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Zusammenfassung Geochemie, tektonische Stellung und geodynamische Signifikanz sp?torogener G?nge im Melibocus Massiv, Bergstr?sser Odenwald Der Melibokus Tonalit-Pluton geh?rt zum Bergstr?sser Odenwald, der als Teil eines devonisch-karbonischen magmatischen Bogens interpretiert wird. In diesem Pluton treten sehr h?ufig magmatische G?nge unterschiedlicher Zusammensetzung auf. Die Arbeit zeigt, dass die G?nge unterschiedlicher Zusammensetzung unterschiedliche Streichrichtungen haben. Die meisten der untersuchten G?nge zeigen Hochtemperatur-Schergefüge. Aus der Lage der zerscherten G?nge l?sst sich eine Pal?ostressrichtung mit 060° für Sigma 1 ableiten. Diese Richtung weicht nur unwesentlich von der bekannten variskischen Subduktionszone im Nordwesten ab. Aufgrund ihrer Hochtemperatur-Gefüge, die im Bereich der Schlie?ungstemperatur von Ar in Hornblenden gebildet wurden, ist das Alter der G?nge wahrscheinlich ebenfalls als Karbon (Mississippian) einzustufen. Die gabbroiden bis dioritischen G?nge (Malchite) haben eine kalkalkaline Zusammensetzung. Der Vergleich mit rezenten Magmatiten deutet auf eine Entstehung in einem magmatischen Bogen (Kontinentalrand) hin. Die Seltenerdelementverteilung der G?nge zeigt einen wahrscheinlichen Aufschmelzungsgrad der Mantelquellregion von über 5% bei einem geringen Anteil von residualem Granat an. Im Gegensatz zu den tonalitischen Nebengesteinen zeigen die granitoiden G?nge anhand ihrer modalen (Muskovit) als auch chemischen Zusammensetzung S-Typ-Charakter. Dies bedeutet eine h?here Beteiligung krustaler Komponente in der Magmenquelle als dies für den Tonalit angenommen werden darf. Die Spurenelementchemie der granitoiden G?nge zeigt ebenfalls eine Bildung in einem konvergenten plattentektonischen Regime, d.h. innerhalb eines magmatischen Bogens. Die G?nge stellen somit vermutlich das Produkt eines sp?ten Abschnittes des subduktionsbezogenen Magmatismus, der auch die Tonalite und andere Plutone im zentralen Bergstr?sser Odenwald geschaffen hat, dar. Im Gegensatz zu dem Magmatismus der die Plutone erzeugt hat, sind die G?nge wahrscheinlich gegen Ende der Kollision oder nachfolgend auf diese in eine sich dehnende Kruste intrudiert und in einem nachfolgenden kompressiven Regime deformiert worden.

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Received August 31, 1999; revised version accepted October 9, 2000     

浅成低温热液型金矿研究综述

浅成低温热液型金矿是重要的金矿类型,近年来对该类矿床的地球化学特征、成矿岩浆背景、成矿机理及成矿模式等方面的研究取得了重大进展。研究表明,该类矿床形成时代主要是中、新生代,其次为晚古生代;高硫化型矿床主要形成于挤压应力场环境和流体混合导致成矿物质沉淀,而低硫化型矿床主要产于张性或中性环境下由于流体的沸腾使得成矿物质沉淀;蒸气冷却收缩模式合理地解释了浅成低温热液矿床和斑岩矿床在时间和空间上的共生关系,对指导找矿具有一定的实践意义。