Trace Elements in Sphalerite from the Dadongla Zn-Pb Deposit,Western Hunan–Eastern Guizhou Zn-Pb Metallogenic Belt,South China

The western Hunan-eastern Guizhou Zn-Pb metallogenic belt is one of the important Zn-Pb mineralization regions in China.The Dadongla deposit,located in the northeast of Guizhou Province,is one of the typical Zn-Pb deposits in the region and has estimated resources more than 12 million metric tons(Mt) with an average grade of 4.11 wt% Zn+Pb.Its orebodies are hosted in the lower Cambrian Aoxi Formation dolomite,occurring as bedded,para-bedded in shape,and in conformity with the wall rock.The ore m...     

In Situ Analyses of Trace Elements,U–Pb and Lu–Hf Isotopes in Zircons from the Tongshankou Granodiorite Porphyry in Southeast Hubei Province,Middle-Lower Yangtze River Metallogenic Belt,China

The Tongshankou Cu-Mo deposit, located in southeast Hubei province, is a typical skarn–porphyry type ore deposit closely related to the Tongshankou granodiorite porphyry, characterized by a high Sr/Y ratio.Detailed in situ analyses of the trace elements and U–Pb and Lu–Hf isotopes in zircons from the Tongshankou granodiorite porphyry were performed.Scarcely any inherited zircons were observed, and the analyzed zircons yielded highly concordant results with a weighted mean 206Pb/238 U age of 143.5 ± 0.45 Ma(n=20, mean square weighted deviation was 0.75), which was interpreted to represent the crystallization age of the Tongshankou granodiorite porphyry.The chondrite-normalized rare-earth element pattern was characterized by a slope that steeply rises from the light-group rare-earth elements(LREE) to the heavy-group rare-earth elements(HREE) with a positive Ce-anomaly and inconspicuous Eu-anomaly, which was coincident with the pattern of the zircons from the Chuquicamata West porphyry, Chile.The analyzed zircons also had relatively low 176Hf/177 Hf ratios of 0.282526–0.282604.Assuming t=143 Ma, the corresponding calculated initial Hf isotope compositions(εHf(t)) ranged from-5.6 to-2.9.The results of the in situ analysis of trace elements and U–Pb and Lu–Hf isotopes in zircons from the Tongshankou granodiorite porphyry suggest that a deep-seated process involving a thickened-crust/enriched-mantle interaction may play an important role in the generation of high Sr/Y-ratio magma and potentially in the generation of porphyry Cu-Mo systems.     

Trace Element Geochemistry of Magnetite from the Fe(-Cu) Deposits in the Hami Region, Eastern Tianshan Orogenic Belt, NW China

Laser ablation–inductively coupled plasma–mass spectrometry(LA–ICP–MS) was used to determine the trace element concentrations of magnetite from the Heifengshan, Shuangfengshan, and Shaquanzi Fe(–Cu) deposits in the Eastern Tianshan Orogenic Belt. The magnetite from these deposits typically contains detectable Mg, Al, Ti, V, Cr, Mn, Co, Ni, Zn and Ga. The trace element contents in magnetite generally vary less than one order of magnitude. The subtle variations of trace element concentrations within a magnetite grain and between the magnetite grains in the same sample probably indicate local inhomogeneity of ore–forming fluids. The variations of Co in magnetite between samples are probably due to the mineral proportion of magnetite and pyrite. Factor analysis has discriminated three types of magnetite: Ni–Mn–V–Ti(Factor 1), Mg–Al–Zn(Factor 2), and Ga– Co(Factor 3) magnetite. Magnetite from the Heifengshan and Shuangfengshan Fe deposits has similar normalized trace element spider patterns and cannot be discriminated according to these factors. However, magnetite from the Shaquanzi Fe–Cu deposit has affinity to Factor 2 with lower Mg and Al but higher Zn concentrations, indicating that the ore–forming fluids responsible for the Fe–Cu deposit are different from those for Fe deposits. Chemical composition of magnetite indicates that magnetite from these Fe(–Cu) deposits was formed by hydrothermal processes rather than magmatic differentiation. The formation of these Fe(–Cu) deposits may be related to felsic magmatism.     

Ore Genesis for Stratiform Ore Bodies of the Dongfengnanshan Copper Polymetallic Deposit in the Yanbian Area, NE China：Constraints from LA-ICP-MS in situ Trace Elements and Sulfide S–Pb Isotopes

The Dongfengnanshan Cu polymetallic deposit is one representative deposit of the Tianbaoshan ore district in the Yanbian area, northeast(NE) China. There occur two types of ore bodies in this deposit, the stratiform ore bodies and veintype ones, controlled by the Early Permian strata and the Late Hercynian diorite intrusion, respectively. Due to the ambiguous genetic type of the stratiform ore bodies, there has been controversy on the relationship between them and veintype ore bodies. To determine the genetic type of stratiform ore bodies, laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS) in situ trace elements and S–Pb isotope analysis have been carried on the sulfides in the stratiform ore bodies. Compared with that in skarn, Mississippi Valley-type(MVT), and epithermal deposits, sphalerite samples in the stratiform ore bodies of the Dongfengnanshan deposit are significantly enriched in Fe, Mn, and In, while depleted in Ga, Ge, and Cd, which is similar to the sphalerite in volcanic-associated massive sulfide(VMS) deposits. Co/Ni ratio of pyrrhotites in the stratiform ore bodies is similar to that in VMS-type deposits. The concentrations of Zn and Cd of chalcopyrites are similar to those of recrystallized VMS-type deposits. These characteristics also reflect the intermediate ore-forming temperature of the stratiform ore bodies in this deposit. Sulfur isotope compositions of sulfides are similar to those of VMS-type deposits, reflecting that sulfur originated from the Permian Miaoling Formation. Lead isotope compositions indicate mixed-source for lead. Moreover, the comparison of the Dongfengnanshan stratiform ore bodies with some VMStype deposits in China and abroad, on the trace elements and S–Pb isotope characteristics of the sulfides reveals that the stratiform ore bodies of the Dongfengnanshan deposit belong to the VMS-type, and have closely genetic relationship with the early Permian marine volcanic sedimentary rocks.     

Geochronology, Geochemistry and Tectonic Setting of the Bairiqiete Granodiorite Intrusion (Rock Mass) from the Buqingshan Tectonic Mélange Belt in the Southern Margin of East Kunlun

This study focuses on the zircon U–Pb geochronology and geochemistry of the Bairiqiete granodiorite intrusion(rock mass) from the Buqingshan tectonic mélange belt in the southern margin of East Kunlun. The results show that the zircons are characterized by internal oscillatory zoning and high Th/U(0.14–0.80), indicative of an igneous origin. LA–ICP–MS U–Pb dating of zircons from the Bairiqiete granodiorite yielded an age of 439.0 ± 1.9 Ma(MSWD = 0.34), implying that the Bairiqiete granodiorite formed in the early Silurian. Geochemical analyses show that the rocks are medium-K calc-alkaline, relatively high in Al2O3(14.57–18.34 wt%) and metaluminous to weakly peraluminous. Rare-earth elements have low concentrations(45.49–168.31 ppm) and incline rightward with weak negative to weak positive Eu anomalies(δEu = 0.64–1.34). Trace-element geochemistry is characterized by negative anomalies of Nb, Ta, Zr, Hf and Ti and positive anomalies of Rb, Th and Ba. Moreover, the rocks have similar geochemical features with adakites. The Bairiqiete granodiorite appears to have a continental crust source and formed in a subduction-related island-arc setting. The Bairiqiete granodiorite was formed due to partial melting of the lower crust and suggests subduction in the Buqingshan area of the Proto-Tethys Ocean.     

Emplacement Ages and Petrogenesis of the Molybdenum–bearing Granites in the Jinduicheng Area of East Qinling, China: Constraints from Zircon U–Pb Ages and Hf Isotopes

The Mesozoic porphyry assemblage in the Jinduicheng area is a special molybdenum area in China, the Mo deposits, including the Jinduicheng, Balipo, Shijiawan, Huanglongpu, are distributed. The emplacement age and geochemical features of the granites in the Jinduicheng area can provide essential information for the exploration and development of the porphyry molybdenum deposit. In this study, we report LA–ICP–MS zircon U–Pb age and zircon Hf isotopic compositions of granite porphyries from the Jinduicheng area, and provide insights on the petrogensis and source characteristics of the granites. The results show that the zircon U–Pb ages of the Jinduicheng granite porphyry (143±1 Ma) and the Balipo granite (154±1 Ma), agree well with the Re–Os ages of molybdenite in the Jinduicheng molybdenum polymetallic deposit (139±3 Ma) and the Balipo molybdenum polymetallic deposit (156±2 Ma), indicating that the emplacement of granite porphyries occurred between Late Jurassic and Early Cretaceous. Zircons granite from the Jinduicheng area give the εHf(t) values mainly ranging from ?10 to ?16, and ?20 to ?24, respectively, corresponding to two–stage model ages (tDM2: mainly focused on 1.86–2.0 Ga, and 2.2–2.6 Ga, respectively) of zircons of the granite from the Jinduicheng values. The ore–forming materials are mainly derived from crust, with minor mantle substances. Zircons of the granite from the Balipo area give εHf(t) values ranging from ?18 to ?20, ?28 to ?38, and ?42 to ?44, respectively, corresponding to two–stage model ages (tDM2: mainly focused on 1.88–3.0 Ga, and 3.2–3.90 Ga, respectively). the εHf(t) values of the Jinduicheng porphyry more than that of the Balipo porphyry, and two–stage model ages (tDM2) less than that of the Balipo porphyry, shows that he source of the porphyries originated from ancient lower crustal materials in the Jinduicheng area, and mixed younger components, more younger components contributed for the source of the Jinduicheng porphyry.     

Genetic Types and Metallogenic Model for the Polymetallic Copper–Gold Deposits in the Tongling Ore District,Anhui Province,Eastern China

The Tongling ore district is one of the most economically important ore areas in the Middle–Lower Yangtze River Metallogenic Belt, eastern China. It contains hundreds of polymetallic copper–gold deposits and occurrences. Those deposits are mainly clustered(from west to east) within the Tongguanshan, Shizishan, Xinqiao, Fenghuangshan, and Shatanjiao orefields. Until recently, the majority of these deposits were thought to be skarn-or porphyry–skarn-type deposits; however there have been recent discoveries of numerous vein-type Au, Ag, and Pb-Zn deposits that do not fall into either of these categories. This indicates that there is some uncertainty over this classification. Here, we present the results of several systematic geological studies of representative deposits in the Tongling ore district. From investigation of the ore-controlling structures, lithology of the host rock, mineral assemblages, and the characteristics of the mineralization and alteration within these deposits, three genetic types of deposits(skarn-, porphyry-, and vein-type deposits) have been identified. The spatial and temporal relationships between the orebodies and Yanshanian intrusions combined with the sources of the ore-forming fluids and metals, as well as the geodynamic setting of this ore district, indicate that all three deposit types are genetically related each other and constitute a magmatic–hydrothermal system. This study outlines a model that relates the polymetallic copper–gold porphyry-, skarn-, and vein-type deposits within the Tongling ore district. This model provides a theoretical basis to guide exploration for deep-seated and concealed porphyry-type Cu(–Mo, –Au) deposits as well as shallow vein-type Au, Ag, and Pb–Zn deposits in this area and elsewhere.     

U–Pb Zircon Geochronology and Geochemistry of the Neoproterozoic Liujiaping Group Volcanics in the Northwest Margin of the Yangtze Block: Implications For the Breakup of the Rodinia Supercontinent

Investigation of the petrogenesis and the origin of zircons from the volcanic rocks of the Liujiaping Group of the back-Longmenshan tectonic belt in the northwest margin of the Yangtze Block is conducted by analysis of U–Pb geochronology and geochemistry. Results show that selected zircons are characterized by internal oscillatory zonings and high Th/U ratios (0.43–1.18), indicating an igneous origin. Geochronological results of LA–ICP–MS U–Pb dating of the Liujiaping Group zircons yield an age of 809 ± 11 Ma (MSWD = 2.2), implying that the volcanic rocks were formed in the Late Neoproterozoic. Geochemical analysis shows that the rocks are calc-alkaline, supersaturated in Al, and metaluminous to weakly peraluminous. Rare-earth elements are present at high concentrations (96.04–265.48 ppm) and show a rightward incline and a moderately negative Eu anomaly, similar to that of continental rift rhyolite. Trace element geochemistry is characterized by evident negative anomalies of Nb, Ta, P, Th, Ti, inter alia, and strong negative anomalies of K, Rb, Sr, et al. We conclude that the Liujiaping Group volcanic rocks resulted from typical continental crust source petrogenesis and were formed in a continental margin setting, which had no relation to subduction, and thus, were the products of partial melting of the lower crust due to crustal thickening caused by active continental margin subduction and arc–continent collision orogeny in the northwestern Yangtze Block and were triggered by the breakup of the Rodinia supercontinent during the Neoproterozoic.     

U–Pb Zircon Geochronology and Geochemistry of the Neoproterozoic Liujiaping Group Volcanics in the Northwest Margin of the Yangtze Block:Implications For the Breakup of the Rodinia Supercontinent

Investigation of the petrogenesis and the origin of zircons from the volcanic rocks of the Liujiaping Group of the back-Longmenshan tectonic belt in the northwest margin of the Yangtze Block is conducted by analysis of U–Pb geochronology and geochemistry. Results show that selected zircons are characterized by internal oscillatory zonings and high Th/U ratios(0.43–1.18), indicating an igneous origin. Geochronological results of LA–ICP–MS U–Pb dating of the Liujiaping Group zircons yield an age of 809 ± 11 Ma(MSWD = 2.2), implying that the volcanic rocks were formed in the Late Neoproterozoic. Geochemical analysis shows that the rocks are calc-alkaline, supersaturated in Al, and metaluminous to weakly peraluminous. Rare-earth elements are present at high concentrations(96.04–265.48 ppm) and show a rightward incline and a moderately negative Eu anomaly, similar to that of continental rift rhyolite. Trace element geochemistry is characterized by evident negative anomalies of Nb, Ta, P, Th, Ti, inter alia, and strong negative anomalies of K, Rb, Sr, et al. We conclude that the Liujiaping Group volcanic rocks resulted from typical continental crust source petrogenesis and were formed in a continental margin setting, which had no relation to subduction, and thus, were the products of partial melting of the lower crust due to crustal thickening caused by active continental margin subduction and arc–continent collision orogeny in the northwestern Yangtze Block and were triggered by the breakup of the Rodinia supercontinent during the Neoproterozoic.     

Ore Genesis of the Kalatongke Cu–Ni Sulfide Deposits, Western China: Constraints from Volatile Chemical and Carbon Isotopic Compositions

The Kalatongke Cu–Ni sulfide deposits located in the East Junggar terrane, northern Xinjiang, western China are the largest magmatic sulfide deposits in the Central Asian Orogenic Belt (CAOB). The chemical and carbon isotopic compositions of the volatiles trapped in olivine, pyroxene and sulfide mineral separates were analyzed by vacuum stepwise-heating mass spectrometry. The results show that the released volatiles are concentrated at three temperature intervals of 200–400°C, 400–900°C and 900–1200°C. The released volatiles from silicate mineral separates at 400–900°C and 900–1200°C have similar chemical and carbon isotopic compositions, which are mainly composed of H2O (av. ~92 mol%) with minor H2, CO2, H2S and SO2, and they are likely associated with the ore-forming magmatic volatiles. Light δ13CCO2 values (from ?20.86‰ to ?12.85‰) of pyroxene indicate crustal contamination occurred prior to or synchronous with pyroxene crystallization of mantle-derived ore-forming magma. The elevated contents of H2 and H2O in the olivine and pyroxene suggest a deep mantle-originated ore-forming volatile mixed with aqueous volatiles from recycled subducted slab. High contents of CO2 in the ore-forming magma volatiles led to an increase in oxygen fugacity, and thereby reduced the solubility of sulfur in the magma, then triggered sulfur saturation followed by sulfide melt segregation; CO2 contents correlated with Cu contents in the whole rocks suggest that a supercritical state of CO2 in the ore-forming magma system under high temperature and pressure conditions might play a key role in the assemblage of huge Cu and Ni elements. The volatiles released from constituent minerals of intrusion 1# have more CO2 and SO2 oxidized gases, higher CO2/CH4 and SO2/H2S ratios and lighter δ13CCO2 than those of intrusions 2# and 3#. This combination suggests that the higher oxidation state of the volatiles in intrusion 1# than intrusions 2# and 3#, which could be one of key ore-forming factors for large amounts of ores and high contents of Cu and Ni in intrusion 1#. The volatiles released at 200–400°C are dominated by H2O with minor CO2, N2+CO and SO2, with δ13CCO2 values (?25.66‰ to ?22.98‰) within the crustal ranges, and are considered to be related to secondary tectonic– hydrothermal activities.     

新疆南天山成矿带矿床成矿系列

在系统分析南天山成矿带地质构造演化和成矿特点基础上,划分了5个矿床成矿系列、5个矿床成矿亚系列和13个矿床式。南天山成矿带矿床成矿系列的分布受区域构造－岩浆演化制约,具有鲜明的古生代,尤其是晚古生代成矿作用特点。区域构造演化的规律, 决定了矿床成矿系列的分布规律,即构造－岩浆演经随时间推移有由北向南推进的趋势。     

新疆库鲁克塔格成矿带主要矿床类型及成矿系列划分

库鲁克塔格是新疆前寒武纪出露较全的地区,然而该区区域成矿规律研究程度非常低.通过对研究区已有资料进行总结分析,系统阐述研究区矿床类型,并对其成矿系列进行划分.研究区从太古代到早古生代形成了7个主要的岩浆构造演化阶段:古太古代陆核形成阶段(3.3~3.0 Ga)、新太古代-古元古代陆壳增生改造阶段(2.6~2.3 Ga)、古元古代中晚期陆壳改造阶段(2.1~1.8 Ga)、中元古代晚期-新元古代早期造山运动阶段(1.1~0.86 Ga)、新元古代中期后碰撞伸展阶段(830~800 Ma)、新元古代中晚期陆内裂解阶段(770~600 Ma)和早古生代造陆运动阶段.成矿作用主要发生在古元古代、新元古代及早古生代.依据各构造演化阶段、含矿建造特征及矿床成因特征,将库鲁克塔格成矿作用类型总结为以下6个主要成矿系列,即形成于古元古代陆壳增生改造环境下的Fe-P-Cu-Au系列、新元古代俯冲碰撞环境下的Cu-Au系列、新元古代后碰撞环境下的Cu-Mo-Au-Fe-P-REE系列、新元古代裂解环境下的Cu-Ni系列、早古生代沉积盆地中Ag-V-Mo-Au-U-P系列和早古生代俯冲岛弧环境下的Cu-Au系列.      

青海祁漫塔格楚阿克拉千隐爆角砾岩型铅锌矿床成矿模式及发现意义

青海省东昆仑成矿带西段的祁漫塔格地区与三叠纪花岗岩、斑岩有关的斑岩型、接触交代矽卡岩型、热液型矿产广泛分布。近年以缺位预测成矿理论为指导,在祁漫塔格发现了一处新类型矿床——楚阿克拉千隐爆角砾岩型铅锌矿床。开展了流体包裹体和氢、氧、硫同位素研究,结果表明矿床内存在明显的2类流体,一类为中高温低盐度低密度NaCl-CO2-H2O流体,另一类为低温中等盐度中低密度NaCl-H2O流体,2类流体反映的成矿压力明显不同,与隐爆作用吻合,压力的突然释放是成矿的关键。氢、氧同位素结果表明,成矿热液来源于岩浆水和大气降水的混合,硫同位素显示硫来源于岩浆。对矿床特征分析总结,综合认为,矿床的形成与斑岩活动密切相关,结合卡尔却卡A区斑岩成矿特征,建立了楚阿克拉千矿床成矿模式,提出了楚阿克拉千地区具有斑岩型找矿潜力的认识。该矿床的发现对于促进东昆仑地区斑岩找矿突破和斑岩成矿规律研究具有重要的科学意义和勘查意义。     

秦岭成矿带成矿特征和找矿方向

秦岭成矿带是我国有色、贵金属工业的重要矿产资源基地,也是最具成矿潜力和找矿远景的地区之一。近年的综合研究工作表明,秦岭造山带是一个多旋回复合大陆碰撞造山带,自太古代以来经历了多种构造体制的转化和多期构造热事件发生,伴随有多个构造成矿旋回,所形成的含矿建造、成矿作用及矿床组合具有多样性。根据成矿时代、构造、建造、成矿作用及矿床组合特征分析,认为秦岭造山带铜、钼、铅、锌、银、金、汞、锑等内生金属矿床主要受7个主要的成矿系统控制,形成了18个主要成矿系列,并对各成矿系列及其典型矿床的地质特征和近几年找矿新发现进行了系统的论述,建立了铜、金、铅、锌、银等矿床系列的区域成矿模式。对区域优势矿种的成矿谱系研究表明,本区成矿在时间演化上表现出明显多旋回性、继承性、新生性和叠加性特征,华力西期与印支末-燕山期是成矿大爆发期,最有利于大型超大矿床形成;在空间分布上,具有明显的侧向和垂向分带性。在此基础上,对秦岭成矿带的成矿潜力及成矿远景区进行了评价和划分,指出秦岭地区热水喷流沉积型与密西西比型铅锌银矿床、微细浸染型与石英脉构造蚀变岩型金矿床、斑岩型钼钨铜矿床及低温热液型汞锑矿床等具有很大的找矿前景。并划分出5个区域成矿远景带和17个重要成矿预测区。     

贺兰山北段牛头沟金矿床成矿流体和成矿物质来源:来自H-O-S-Pb同位素的证据

贺兰山北段牛头沟金矿床为华北克拉通西北缘新发现的金矿床,包括构造破碎带蚀变岩型和石英脉型两种矿化类型,后者可进一步细分为低缓石英脉型和陡窄石英脉型2个亚类。矿区所有矿体均赋存在古元古界贺兰山群变质杂岩和混合花岗岩内,受主干断裂F_1及其上盘次级断裂体系控制。综合本文及前人研究成果表明,破碎带蚀变岩型石英流体包裹体以纯液相水溶液包裹体为主,而低缓石英脉型和陡窄石英脉型石英流体包裹体则以气液两相水溶液包裹体为主,不同矿化类型成矿流体均为中低温(160~210℃)、中低盐度(6%~12%NaCl_(eq))的H_2O-NaCl流体。对矿区内3种矿化类型石英流体包裹体和硫化物分别开展的H-O和S-Pb同位素研究显示:破碎带蚀变岩型和陡窄石英脉型流体包裹体δD_(H2O)组成相近,分别为-75.2‰~-89.3‰和-87.0‰~-93.8‰,而低缓石英脉型流体包裹体则具有较高的δD_(H2O)值(-45.7‰~-67.7‰);流体包裹体δ~(18)O_(H2O)值则由破碎带蚀变岩型(3.7‰~4.4‰)→低缓石英脉型(1.9‰~3.3‰)→陡窄石英脉型(0.5‰~0.9‰)依次降低。破碎带蚀变岩型和陡窄石英脉型δ~(34)S组成均为正值,分别为1.3‰~6.9‰和2.2‰~5.8‰,而低缓石英脉型则具有较低的δ~(34)S值(-5.1‰~-2.6‰)。低缓石英脉型金矿具有明显不同的δD_(H2O)和δ~(34)S组成,可能与含矿断裂性质及其距离导矿构造F_1断裂较远等因素所共同导致的成矿流体氧逸度升高有关。3种矿化类型对应的矿石均表现出明显富集Th放射成因Pb的特点,~(206)Pb/~(204)Pb(16.467~17.994)和~(207)Pb/~(204)Pb(15.382~15.582)组成相对均一,而~(208)Pb/~(204)Pb变化较大(37.413~42.345)。总体上,石英流体包裹体H-O同位素组成表明成矿流体均为岩浆水和大气降水形成的混合流体,其大气降水比例自破碎带蚀变岩型→低缓石英脉型→陡窄石英脉型依次升高;矿石S-Pb同位素指示成矿物质为深部岩浆和具有高Th/U比的基底围岩双重来源。结合区域构造–岩浆演化,笔者将牛头沟金矿床成矿过程概括为晚古生代裂陷盆地形成阶段、中晚侏罗世区域挤压推覆阶段和晚侏罗世至早白垩世岩浆热液活动阶段等3个阶段。     

Trace Elements and Rare Earth Elements of Sulfide Minerals in the Tianqiao Pb-Zn Ore Deposit, Guizhou Province, China

Trace elements and rare earth elements (REE) of the sulfide minerals were determined by inductively-coupled plasma mass spectrometry. The results indicate that V, Cu, Sn, Ga, Cd, In, and Se are concentrated in sphalerite, Sb, As, Ge, and Tl are concentrated in galena, and almost all trace elements in pyrite are low. The Ga and Cd contents in the light-yellow sphalerites are higher than that in the brown and the black sphalerites. The contents of Ge, Tl, In, and Se in brown sphalerites are higher than that in light-yellow sphalerites and black sphalerites. It shows that REE concentrations are higher in pyrite than in sphalerite, and galena. In sphalerites, the REE concentration decreases from light-yellow sphalerites, brown sphalerites, to black sphalerites. The ratios of Ga/In are more than 10, and Co/Ni are less than 1 in the studied sphalerites and pyrites, respectively, indicating that the genesis of the Tianqiao Pb–Zn ore deposit might belong to sedimentary-reformed genesis associated with hydrothermal genesis. The relationship between LnGa and LnIn in sphalerite, and between LnBi and LnSb in galena, indicates that the Tianqiao Pb–Zn ore deposit might belong to sedimentary-reformed genesis. Based on the chondrite-normalized REE patterns, δEu is a negative anomaly (0.13–0.88), and δCe does not show obvious anomaly (0.88–1.31); all the samples have low total REE concentrations (<3 ppm) and a wide range of light rare earth element/high rare earth element ratios (1.12–12.35). These results indicate that the ore-forming fluids occur under a reducing environment. Comparison REE compositions and parameters of sphalerites, galenas, pyrites, ores, altered dolostone rocks, strata carbonates, and the pyrite from Lower Carboniferous Datang Formation showed that the ore-forming fluids might come from polycomponent systems, that is, different chronostratigraphic units could make an important contribution to the ore-forming fluids. Combined with the tectonic setting and previous isotopic geochemistry evidence, we conclude that the ore-deposit genesis is hydrothermal, sedimentary reformed, with multisources characteristics of ore-forming fluids.     

藏南沙拉岗锑矿稀土和微量元素地球化学示踪及成矿物质来源

藏南沙拉岗锑矿赋存于下白垩统甲不拉组碳质板岩、泥质粉砂岩、硅质岩及燕山期辉绿岩和喜山期辉长岩中,受近东西向层间破碎带和近南北向构造破碎带控制。围岩蚀变较弱,围绕矿体呈对称性的面状、带状分布。稀土和微量元素测试结果表明碳质板岩和硅质岩具有与上地壳和太古宙后页岩非常相似的稀土配分模式。喜山期辉长岩以轻稀土相对亏损、重稀土相对富集和Eu轻度亏损的平坦型稀土配分模式有别于以轻稀土轻度富集、Eu无异常的稀土配分模式为特征的藏南燕山期辉绿岩。锑矿石具有轻稀土强烈富集、分馏程度高、Eu中度亏损、Ce强烈亏损的配分模式,与洋中脊黑烟囱-白烟囱中热液流体和喷流沉积物的Eu强正异常、海水的Ce中等负异常和重稀土富集的稀土配分模式及沃西Sedex型W-Sb-Au矿的稀土配分模式明显不同,但与喜山期辉长岩的稀土配分模式具有明显的互补关系。此外,锑矿石以其强Nb负异常及Ce和Ba正异常的微量元素特征,展示出与喜山期辉长岩的弱Nb负异常和强Rb正异常及碳质板岩-硅质岩的Nb、Ba负异常和轻度Ce、Rb、Th正异常的异同点,矿石δ³⁴S除个别样品为10.3‰和-41.6‰外,均分布在-2.6‰~-4.1‰区间,反映成矿物质主要来源于岩浆的特点。前人测定的流体包裹体氢、氧同位素值分别为δD=-151‰~-166‰,δ¹⁸O=9.4‰~12.3‰,显示岩浆水和地下水的混合性质。因此沙拉岗锑矿是形成于中新世、与藏南拆离系有关的浅成低温热液型矿床,成矿物质主要来源于喜山期辉长岩岩浆,少量来源于围岩,成矿流体部分来源于岩浆期后热液,部分来源于地下水。     

Trace Elements of Multi-stage Minerals and Titanite U-Pb Dating for the Gneisses from Liansan Island, Sulu UHPM Belt

Gneisses with anatectic characteristics from the Liansan island in the Sulu UHPM (ultra-high pressure metamorphic) belt were studied for petrography, titanite U-Pb dating and mineral geochemistry. Three origins of garnets are distinguished: metamorphic garnet, peritectic garnet and anatectic garnet, which are formed in the stages of peak metamorphism, retrograde anatexis and melt crystallization, respectively. The euhedral titanite has a high content of REE and high Th/U ratios, which is interpreted as indicating that it was newly-formed from an anatectic melt. The LA-ICP-MS titanite U-Pb dating yields 214–217 Ma ages for the titanite (melt) crystallization. The distribution of trace elements varies in response to the different host minerals at different stages. At the peak metamorphic stage, Y and HREE are mainly hosted by garnet, Ba and Rb by phengite, Sr, Nb, Ta, Pb, Th, U and LREE by allanite and Y, U and HREE by zircon. During partial melting, Y, Pb, Th, U and REE are released into the melt, which causes a dramatic decline of these element contents in the retrograde minerals. Finally, titanite absorbs most of the Nb, U, LREE and HREE from the melt. Therefore, the different stages of metamorphism have different mineral assemblages, which host different trace elements.