Metal sources for the polymetallic Ni–Mo–PGE mineralization in the black shales of the Lower Cambrian Niutitang Formation,South China

Total organic carbon content (TOC), trace element and platinum-group element (PGE) concentrations were determined in the black shales of the Lower Cambrian Niutitang Formation in the Nayong area, Guizhou Province, South China, in order to study the polymetallic Ni–Mo–PGE mineralization. The results demonstrate that numerous elements are enriched in the polymetallic ores compared to those of the nearby black shale, particularly Ni, Mo, Zn, TOC and total PGE, which can reach up to 7.03 wt.%, 8.49 wt.%, 11.7 wt.%, 11.5 wt.% and 943 ppb, respectively. The elemental enrichment distribution patterns are similar to those in the Zunyi and Zhangjiajie areas except that the Nayong location is exceptionally enriched in Zn. Whereas positive correlations are observed between the ore elements of the polymetallic ores, no such correlations are observed in the black shale. These positively correlated metallic elements are classified into three groups: Co–Ni–Cu–PGE, Zn–Cd–Pb and Mo–Tl–TOC. The geological and geochemical features of these elements suggest that Proterozoic and Early Palaeozoic mafic and ultramafic rocks, dolomites and/or Pb–Zn deposits of the Neoproterozoic Dengying Formation and seawater could be the principal sources for Co–Ni–Cu–PGE, Zn–Cd–Pb, and Mo–Tl–TOC, respectively. Furthermore, the chondrite-normalized patterns of PGEs with Pd/Pt, Pd/Ir and Pt/Ir indicate that PGE enrichment of the polymetallic ores is most likely related to hydrothermal processes associated with the mafic rocks. In contrast, PGE enrichment in the black shale resembles that of the marine oil shale with terrigenous and seawater contributions. Our investigations of TOC, trace elements and PGE geochemistry suggest that multiple sources along with submarine hydrothermal and biological contributions might be responsible for the formation of the polymetallic Ni–Mo–PGE mineralization in the black shales of the Lower Cambrian Niutitang Formation across southern China.     

中、下扬子地区下寒武统黑色页岩微量元素富集特征

中国南方扬子地区下寒武统黑色页岩分布广泛,主要由黑色页岩、黑色白云质页岩,黑色粉砂质页岩和黑色硅质页岩等组成;并伴生有较厚的磷块岩矿床、钒矿床和镍、钼多元素硫化物矿床。对黑色页岩岩石学特征、元素地球化学特征进行系统研究,并详细分析微量元素的富集成因,结果表明：黑色页岩主要形成于静水还原的浅海-半深海缓坡环境,层状元素富集带为沉积成因,海底热流体提供了丰富物质来源。总体上,Co、Be、Mn、Ga等元素含量较低;Cu、V、Ni、Mo等元素的含量较高,多数超过北美页岩平均值;以Ni、Mo为主的多元素富集层通常位于磷块岩之上,以黑色页岩、黑色白云质页岩中的硫化物和硫酸盐矿物为主要载体,其中有机碳（TOC）含量可达12.2%以上,远高于其他元素富集层,随着页岩内硅质成分增加,Ni、Mo、Fe、Co等元素含量明显降低;以V为主的多元素主要赋存于黑色硅质页岩中的水云母,与页岩内硅质成分具有较好的正相关关系;黑色页岩中稀土元素含量为(76.22~290.67)×10-6,轻重稀土比值LREE/HREE介于1.21~4.22,说明轻稀土更为富集,Sr/Ba值为0.04~0.34,δEu正异常,且北美页岩标准化配分曲线呈现平缓左倾,为沉积过程中存在海底热水流体提供了进一步证据。     

华南下寒武统镍钼矿层中铜铅锌矿物的发现及意义

华南扬子地块是我国古热水沉积成矿作用最为发育的地区之一,其热水沉积特性最早引起我国学者的关注。华南下寒武统黑色岩系中赋存多个与热水沉积成矿作用相关的大型、超大型重晶石矿床与N i-Mo-U-V多金属富集层。进一步研究分布在华南扬子地块黑色岩系中的金属、非金属矿床成因及其地球化学特征,对认识华南乃至全球晚震旦—早寒武世生物与环境演化有着十分重要的意义。本文对华南下寒武统镍-钼富集层矿石进行电子探针研究,识别出黄铜矿、黝铜矿等铜的独立矿物;闪锌矿等锌的独立矿物;方铅矿、白铅矿等铅的独立矿物。研究表明,在镍-钼矿石中这些矿物的发现为镍-钼矿层是热水沉积作用产物提供了直接的矿物学证据。     

The noble metal distribution in the black shales of the Degdekan gold deposit in Northeast Russia

The mineral and chemical composition of the carbon-bearing rocks of the Late Permian Pionerskaya Formation containing the Degdekan gold deposit has been studied. The bulk contents of Au, Ag, Pt, and Pd in the black shales and their light, sulfide, and electromagnetic fractions were determined by electrothermal atomization. The mineral composition and the phase analysis of the rocks were studied using a scanning electron microscope. Gold is present as fine xenomorphic grains of high fineness with an Fe admixture of up to 4 at %, as well as intergrowths of kustelite and electrum. The Au and Pt contents in the black shales and ores vary in a wide range (g/t): Au 0.01–13.12, Pt 0.001–1.34. The highest Au contents (up to 1748 g/t) were noted in the sulfide fraction. The Pt-bearing phases were not found, whereas a Pt content of about 0.61 wt % was determined using an electron microscope in a carbonaceous matrix. The initial rocks have a steady and low Pt content (less than 0.007 g/t). A stable even Au distribution in the studied rocks was established within 1.14–2.46 g/t. The chemical analysis of the soluble fraction of the carbonaceous matter extracted from the black shales showed the presence of Au 0.375, Ag 3.68, Pt 0.147, and Pd 0.052 g/t. It has been concluded that the carbon-bearing rocks of the Pionerskaya Formation play a resource role in the accumulation of noble metals, whereas economic concentrations of the latters are formed in the course of the superimposed metamorphic-hydrothermal processes.     

Trace- and rare-earth element geochemistry and Pb–Pb dating of black shales and intercalated Ni–Mo–PGE–Au sulfide ores in Lower Cambrian strata, Yangtze Platform, South China

The Lower Cambrian black shale sequence of the Niutitang Formation in the Yangtze Platform, South China, hosts an extreme metal-enriched sulfide ore bed that shows >10,000 times enrichment in Mo, Ni, Se, Re, Os, As, Hg, and Sb and >1,000 times enrichment in Ag, Au, Pt, and Pd, when compared to average upper continental crust. We report in this paper trace- and rare-earth-element concentrations and Pb–Pb isotope dating for the Ni–Mo–PGE–Au sulfide ores and their host black shales. Both the sulfide ores and their host black shales show similar trace-element distribution patterns with pronounced depletion in Th, Nb, Hf, Zr, and Ti, and extreme enrichment in U, Ni, Mo, and V compared to average upper crust. The high-field-strength elements, such as Zr, Hf, Nb, Ta, Sc, Th, rare-earth elements, Rb, and Ga, show significant inter-element correlations and may have been derived mainly from terrigenous sources. The redox sensitive elements, such as V, Ni, Mo, U, and Mn; base metals, such as Cu, Zn, and Pb; and Sr and Ba may have been derived from mixing of seawater and venting hydrothermal sources. The chondrite-normalized REE patterns, positive Eu and Y anomalies, and high Y/Ho ratios for the Ni–Mo–PGE–Au sulfide ores are also suggestive for their submarine hydrothermal-exhalative origin. A stepwise acid-leaching Pb–Pb isotope analytical technique has been employed for the Niutitang black shales and the Ni–Mo–PGE–Au sulfide ores, and two Pb–Pb isochron ages have been obtained for the black shales (531±24 Ma) and for the Ni–Mo–PGE–Au sulfide ores (521±54 Ma), respectively, which are identical and overlap within uncertainty, and are in good agreement with previously obtained ages for presumed age-equivalent strata.Editorial handling: R. Coveney Jr.     

Multiple Sources of Metals of Mineralization in Lower Cambrian Black Shales of South China: Evidence from Geochemical and Petrographic Study

Black shales of the Lower Cambrian Niutitang Formation in southern China (Huangjiawan mine, Zunyi region, northern part of the Guizhou Province) host regionally distributed stratiform polymetallic Ni‐Mo‐platinum group elements (PGE)‐Au phosphate‐ and sulfide‐rich ores. These are confined to a ≥0.2‐m thick ore horizon composed of mineralized bodies of algal onkolites, phosphate nodules, and sulfide and shale clasts in a mineralized phosphate‐ and organic matter‐rich matrix. Compared to footwall and hanging wall shales, the ore bed is strongly enriched in Ni (up to 100‐fold), As (up to 97‐fold), Mo (up to 95‐fold), Sb (up to 67‐fold), Rh (up to 49‐fold), Cu (up to 37‐fold), Pd (up to 33‐fold), Ru (up to 24‐fold), Zn (up to 23‐fold), Pt (up to 21‐fold), Ir (up to 15‐fold), Co (up to 14‐fold), and Pb (up to 13‐fold). Even footwall and hanging wall black shales are significantly enriched by Mo (21‐fold) and Ni (12‐fold) but depleted in Cr in comparison to average Cambrian black shale. Organic matter is represented by separate accumulations dispersed in the rock matrix or as biotic bitumen droplets and veinlets in ore clasts. Similar organic carbon (C_org) values in an ore bed and enclosing footwall and hanging wall shales of little mineralization indicate that metal accumulation was not controlled only by biogenic productivity and organic matter accumulation rate. Evaporitic conditions during sedimentation of the basal part of the Niutitang Formation were documented by an occurrence of preserved Ni‐, V‐, Cr‐, and Cu‐enriched phosphate‐rich hardground with halite and anhydrite pseudomorphs on the paleosurface of the underlying Neoproterozoic carbonates. Neoproterozoic black shales of the Doushantuo Formation are characterized by increased metal concentrations. Comparison of metal abundances in both hardground and Doushantuo black shales indicate that black shales could have become a source of metal‐rich hardground during weathering. The polymetallic Ni‐Mo‐PGE sulfide‐rich ore bed is interpreted to represent a remnant of shallow‐water hardground horizon rich in metals, which originated in a sediment‐starved, semi‐restricted, seawater environment. During the Early Cambrian transgression an influx of fresh seawater and intensive evaporation, together with the hydrothermal enrichment of seawater in a semi‐restricted basin, resulted in the formation of dense metalliferous brines; co‐precipitation of metals together with phosphates and sulfides occurred at or above the oxic–anoxic sediment interface. Metal‐enriched hardground was disintegrated by the action of waves or bottom currents and deposited in a deeper part of the anoxic basin. Contemporaneously with the formation of a polymetallic Ni‐Mo‐PGE‐Au sulfide ore bed, economic sedimentary exhalative (SEDEX)‐type barite deposits were forming in a stratigraphically and geotectonically similar setting. The results of geochemical study at the Shang Gongtang SEDEX‐type Ba deposit indicate that concentrations of Ag, As, Cr, Cu, Fe, Mn, Ni, Pb, Sb, V, Zn and other metals decrease from top of the barite body toward the hanging wall black shale. Lower Cambrian black shales of the Niutitang Formation above the barite body also display similar element abundances as Neoproterozoic black shales of the Doushantuo Formation, developed in the footwall of the barite body. But the geochemical composition of the sulfide layer is different from the Ni‐Mo ore bed, showing only elevated Pb, Cu, Ni and Mo values. It is suggested that hydrothermal brines at Shang Gongtang might have leached metals from footwall Neoproterozoic sequences and became, after mixing with normal seawater, an additional source of Ag, Cr, Cu, Pb, Sb, Zn, Ni, PGE, V and other metals.     

Seawater contribution to polymetallic Ni–Mo–PGE–Au mineralization in Early Cambrian black shales of South China: Evidence from Mo isotope,PGE, trace element,and REE geochemistry

The Early Cambrian black shale sequence of the Niutitang Formation in South China hosts a synsedimentary, organic carbon-rich, polymetallic sulfide layer with extreme metal concentrations, locally mined as polymetallic Ni–Mo–PGE–Au ore. In combination with previously reported data, we present Mo isotope, platinum-group element (PGE), and trace and rare-earth element (REE) data for the polymetallic sulfide ores and host black shales from four mine sites (Dazhuliushui and Maluhe in Guizhou Province, and Sancha and Cili in Hunan Province, respectively), several hundred kilometers apart. The polymetallic sulfide ores have consistently heavy δ^98/95Mo values of 0.94 to 1.38‰ (avg. 1.13 ± 0.14‰, 1σ, n = 11), and the host black shale and phosphorite have slightly more variable δ^98/95Mo values of 0.81‰ to 1.70‰ (n = 14). This latter variation is due to variable paleoenvironmental conditions from suboxic to euxinic, and partly closed-system fractionation in isolated marine sedimentary basins. Both the polymetallic sulfides and host black shales show PGE distribution patterns similar to that of present-day seawater, but different from those of ancient submarine-hydrothermal deposits and modern submarine hydrothermal fluids. The polymetallic sulfide bed has a generally consistent metal enrichment by a factor of 10⁷ compared to present-day seawater. PAAS-normalized REE + Y patterns of the polymetallic sulfide bed are characterized by a remarkably positive Y anomaly, consistent with an origin of the REE predominantly from seawater. Small positive Eu anomalies in some of the sulfide ores could reflect minor hydrothermal components involved. The Mo isotope, PGE, and trace and rare-earth element geochemical data suggest that metals in the polymetallic Ni–Mo–PGE–Au sulfide ore layer were scavenged mostly from Early Cambrian seawater, by both in-situ precipitation and local re-deposition of sulfide clasts.     

A laser ablation inductively coupled plasma mass spectrometry study of the distribution of chalcophile elements among sulfide phases in sedimentary and magmatic rocks of the Duluth Complex,Minnesota, USA

Nickel-copper sulfide deposits occur in the basal unit of the Partridge River Intrusion, Duluth Complex (Minnesota, USA). Many lines of evidence suggest that these sulfides are formed after assimilation of the proterozoic S-rich black shales, known as the Bedded Pyrrhotite Unit. In addition to S, black shales are enriched in Te, As, Bi, Sb and Sn (TABS) and the basaltic magma of the intrusion is contaminated by the partial melt of the black shales. The TABS are chalcophile and together with the platinum-group elements, Ni and Cu partitioned into the magmatic sulfide liquid that segregated from the Duluth magma. The TABS are important for the formation of platinum-group minerals (PGM) thus their role during crystallization of the base metal sulfide minerals could affect the distribution of the PGE. However, the concentrations of TABS in magmatic Ni-Cu-PGE deposits and their distribution among base metal sulfide minerals are poorly documented. In order to investigate whether the base metal sulfide minerals host TABS in magmatic Ni-Cu-PGE deposits, a petrographic and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) study has been carried out on base metal sulfide and silicate phases of the Partridge River Intrusion, Duluth Complex.Petrographic observations showed that the proportions of the base metal sulfide minerals vary with rock type. The sulfide assemblage of the least metamorphosed Bedded Pyrrhotite Unit from outside the contact metamorphic aureole consists of pyrite with minor pyrrhotite plus chalcopyrite (<5%), whereas within the contact aureole the sulfide assemblage of the Bedded Pyrrhotite Unit rocks consists dominantly of pyrrhotite (>95%) with small amount of chalcopyrite (<2%). The sulfide mineral assemblage in the xenoliths of the Bedded Pyrrhotite Unit and in the mafic rocks of the basal unit contains two additional sulfides, pentlandite and cubanite.Our LA-ICP-MS study shows that sulfides of the Bedded Pyrrhotite Unit are rich in TABS; consistent with these S-rich black shales being the source of TABS that contaminated the mafic magma. Most of the TABS are associated with sulfides and platinum-group minerals in the rocks of the Bedded Pyrrhotite Unit from the contact aureole, the Bedded Pyrrhotite Unit xenoliths and the mafic rocks of the Duluth Complex. In addition to these phases the laser maps show that silicate phases, i.e., orthopyroxene and plagioclase contain Sn and Pb respectively. In contrast, in the least metamorphosed samples of the Bedded Pyrrhotite Unit from outside the contact aureole although the pyrite contains some TABS mass balance calculations indicates that most the TABS are contained in other phases. In these rocks, galena hosts significant amounts of Te, Bi, Sb, Sn and Ag and few very small grains of Sb-rich phases were also observed. The host phases for As were not established but possibly organic compounds may have contributed.     

Geochemistry of Platinum Group and Rare Earth Elements of the Polymetallic Layer in the Lower Cambrian, Weng’an, Guizhou Province

Abstract: The black shales of the Lower Cambrian Niutitang Formation in Weng’an, on the Yangtze platform of south China, contain voluminous polymetallic sulfide deposits. A comprehensive geochemical investigation of trace, rare earth, and platinum group elements (PGE) has been undertaken in order to discuss its ore genesis and correlation with the tectono-depositional setting. The ore-bearing layers enrich molybdenum (Mo), nickel (Ni), vanadium (V), lead (Pb), strontium (Sr), barium (Ba) , uranium (U) , arsenic (As), and rare earth elements (REE) in abundance. High uranium/thorium (U/Th) ratios (U/Th>1) indicated that mineralization was mainly influenced by the hydrothermal process. The dU value was above 1.9, showing a reducing sedimentary condition. The REE patterns showed high enrichment in light rare earth elements (LREE) (heavy rare earth elements (HREE) (LREE/HREE=5–17), slightly negative europium (Eu) and cerium (Ce) anomalies (dEu=0.81–0.93), and positive Ce anomalies (dCe=0.76–1.12). PGE abundance was characterized by the PGE-type distribution patterns, enriching platinum (Pt), palladium (Pd), ruthenium (Ru) and osmium (Os). The Pt/Pd ratio was 0.8, which is close to the ratios of seawater and ultramafic rocks. All of these geochemical features suggest that the mineralization was triggered by hydrothermal activity in an extensional setting in the context of break-up of the Rodinian supercontinent.     

Platinum group elements in gold-sulfide and base-metal ores of the Sayan-Baikal Fold Region and possible platinum and palladium speciation in sulfides

The concentration levels and distribution features of the platinum group elements (PGE) in quartz-sulfide and base-metal ores in deposits of the Sayan-Baikal Fold Region (SBFR) are discussed. Microfire assay neutron activation analysis (MF-NAA), which enables one to work on a nondestructive basis and allows one to avoid inaccuracies related to chemical sample preparation, was used as the main analytical technique. Three types of hydrothermal mineralization with elevated grades of PGE (especially Pt, Pd, and Ru) have been identified: (1) pyrite-pyrrhotite (massive sulfide) mineralization hosted in black shales of the Il’chir Sequence; (2) gold-sulfide ores of the Zun-Kholba, Tainsky, Kamenny, and some other gold deposits; and (3) silver-basemetal ores of the Dzhida-Vitim Zone. The PGE contents significantly vary, from global average values to tens of grams per ton. An absence of PGE minerals implies that these elements are finely dispersed in sulfide minerals and native gold. Taking into account difficulties in conversion of PGE into analytical forms, their nonuniform distribution in sulfide minerals, their high affinity to coordination compounds, and experimental results, cluster species of Pt and Pd in major minerals are suggested for the gold-sulfide and silver-base-metal ores in deposits, which are related to suprasubduction ophiolites and island-arc and intraplate settings in the SBFR.     

The Trace Element Distribution Patterns of Ediacaran-Early Cambrian Black Shales and the Origin of Selenium in the Guangning Area, Western Guangdong Province, South China

The Ediacaran and early Cambrian black shales are widespread across the South China Craton (Yangtze and Cathaysia blocks). However, the trace element distribution patterns of the Ediacaran and early Cambrian black shales in the Cathaysia Block are still unclear. In this study, thirty-four black shale samples in the Lechangxia Group (Ediacaran) and thirteen black shale samples in the lower Bacun Group (early Cambrian) from Guangning area, western Guangdong Province, South China, were analyzed for major and trace elements concentrations. Compared to the upper continental crust, the Ediacaran black shales exhibit strongly enriched Se, Ga, and As with enrichment factor values (EF) higher than 10, significantly enriched Bi and Rb (10>EF>5), weakly enriched Mo, Ba, Cs, V, In, Be, Tl, and Th (5>EF>2), normal U, Cr, Cd, Sc, Pb, Cu, and Li (2>EF>0.5), and depleted Ni, Zn, Sr, and Co. Early Cambrian black shales display strongly enriched Se, Ga, and As, significantly enriched Ba, Bi, and Rb, weakly enriched Mo, Cs, Cd, V, U, Be, In, and Tl, normal Sc, Th, Cr, Li, Cu, Ni, and Pb and depleted Co, Zn, and Sr. Moreover, Se is the most enriched trace element in the Ediacaran and early Cambrian black shales: concentrations vary from 0.25 to 30.09 ppm and 0.54 to 5.01 ppm, and averaging 4.84 and 1.72 ppm, with average EF values of 96.87 and 34.32, for the Ediacaran and early Cambrian shales respectively. The average concentration of Se in the Ediacaran black shales is 2.8 times higher than that of early Cambrian black shales. Se contents in the Ediacaran and early Cambrian black shales exhibit significant variation (P = 0.03). Provenance analysis showed that Se contents of both the Ediacaran and early Cambrian black shales were without detrital provenance and volcanoclastic sources, but of hydrothermal origin. The deep sources of Se and the presence of pyrite may explain the higher Se contents in the Ediacaran black shales. Similar with the Se-rich characteristics of the contemporaneous black shales in the south Qingling Mountain and Yangtze block, the Ediacaran and early Cambrian black shales in Guangning area, Cathaysia, are also enriched in Se, which may provide a clue for looking for the selenium-rich resources in western Guangdong Province.     

新疆天山黑色岩系型矿床的地质特征及找矿方向

概要介绍了中国天山黑色岩系分布和黑色岩系型矿床的地质特征。中国天山黑色岩系发育，主要集中在古生代，其次为中生代，目前发现与黑色岩系有关的矿种有金、钒、铀、磷、锑。中亚天山黑色岩系中发现了穆龙套和库姆托尔世界级金矿床，中国天山是其东延部分，发现了萨瓦亚尔顿、大山口、萨恨托亥等金矿床，呈现出良好的找矿前景。穆龙套金矿和萨瓦亚尔顿金矿是黑色岩系型金矿的典型代表，中国黑色岩系型金矿与中亚黑色岩系型金矿有许多相似之处。分析认为，吉根-塔尔特库里、乌兰赛尔-大山口、乌什北山、阿克牙孜河等地是最具前景的找金矿靶区，今后应加大萨瓦亚尔顿金矿的勘查和研究力度，同时注意寻找黑色岩系中的铂、钯、铜等矿种。     

Geochemistry of Platinum Group and Rare Earth Elements of the Polymetallic Layer in the Lower Cambrian,Weng'an,Guizhou Province

The black shales of the Lower Cambrian Niutitang Formation in Weng'an.on the Yangtze platform of south China,contain voluminous polymetallic sulfide deposits.A comprehensive geochemical investigation of trace,rare earth,and platinum group elements(PGE)has been undertaken in order to discuss its ore genesis and correlation with the tectono.depositional setting.The ore-bearing layers enrich molybdenum(Mo),nickeI(Ni),vanadium(V),lead(Pb),strontium(Sr), bariam(Ba),uranium(U),arsenic(As),and rare earth elements(REE)in abundance.High uranium/thorium(U/Th)ratios(U/Th>1)indicated that mineralization was mainly influenced by the hydrothermal process.The δU value Was above 1.9.showing a reducing sedimentary condition.The REE patterns showed high enrichment in Iight rare earth elements (LREE)(heavy rare earth elements (HREE)(LREE/HREE=5-17),slightly negative europium(EU)and cerium(Ce)anomalies(δEu=0.81-0.93).and positive Ce anomalies(δCe=0.76-1.12).PGE abundance was characterized by the PGE-type distribution patterns,enriching platinum(Pt),palladium(Pd),ruthenium(RuJ and osmium(Os).The Pt,Pd ratio was 0.8.which is close to the ratios of seawater and ultramafic rocks.AII of these geochemical features suggest that the mineralization was triggered by hydrothermal activity in an extensionai setting in the context of break-up of the Rodinian supercontinent.     

Black shales and massive sulfide deposits: causal or casual relationships? Insights from Rammelsberg, Tharsis, and Draa Sfar

Black shales and massive sulfides represent reduced lithofacies that require isolation from oxic environments to be preserved. This, together with the sedimentary affinity of both lithofacies, can explain their common concurrence in the geologic record. The present study is based on the comparison of Rammelsberg in Germany, Tharsis in Spain, and Draa Sfar in Morocco, three massive sulfide deposits closely associated with black shales that are distributed along the European and North African Variscan orogen. The study entails geochemical, biostratigraphic, and stratigraphic analyses of the black shale sequences hosting the three deposits and mineralogical and textural analyses of the sulfides. All three deposits were formed in immature, tectonically unstable basins within an active continental margin or continental magmatic arc. Their stratigraphic records consist of a sequence of black shales enclosing massive sulfides and variable proportions of bimodal volcanic and subvolcanic rocks. The major differences among the three deposits concern the size, composition, and mineralogy. Regarding age, they are diachronous and younger southward: Rammelsberg is middle Eifelian, Tharsis latest Famennian, and Draa Sfar late Viséan. The study of redox conditions of the paleoenvironment using organic and inorganic proxies highlights similarities and significant differences among the three ore-hosting basins during massive sulfide and black shale deposition. The black shales generally display low C_org and high S_tot contents. At Rammelsberg, the S_tot/C_tot ratios provide values typical for normal Middle Devonian marine environments, which suggests that the original reactive organic C is now fixed in carbonates. At Tharsis, most of the samples have C_org >1 and S_tot/C_org values equivalent to those of Devonian?CCarboniferous normal marine sediments. However, some pyritic hanging-wall samples have C_org <1 and S_tot up to 5?wt.%, suggesting the epigenetic addition of HS^?. The S_tot/C_org ratio for the Draa Sfar samples resembles that of Middle Carboniferous normal marine environments. Geochemical inorganic proxies used to define the environmental conditions include the enrichment factors of U (U_EF) and Mo (Mo_EF) together with V/Cr and V/(V?+?Ni) ratios. Footwall shales at Filón Norte (Tharsis) show positive and eventually elevated U_EF and Mo_EF values, which suggests anoxic conditions, whereas at Rammelsberg and Draa Sfar oxic bottom water is indicated. The relations V/Cr and V/(V + Ni) in all three cases point to a redox boundary near the sediment?Cwater interface, although at Tharsis some samples indicate anoxic/euxinic conditions (i.e., V/(V + Ni) >0.9). Regarding the environmental conditions of the source areas, feldspar illitization and selective depletion in Na and Ca occurred at the three studies sites. Available sulfur isotopic data from the Rammelsberg and Tharsis sulfide ore indicate that biogenic reduction of marine sulfate was a major sulfur source during massive sulfide generation. Nevertheless, a hydrothermal sulfur source has also been detected. At Rammelsberg, this is indicated from the polymetallic sulfides that replace sedimentary and diagenetic pyrite. At Tharsis, the bacteriogenic sulfur signature is also restricted to sulfide with less evolved textures, whereas a hydrothermal source is more evident in sulfides showing evidence of recrystallization. Both geochemical and isotopic data suggest that the bacteriogenic reduction process was inhibited by rapid burial. The sedimentation rates calculated for Rammelsberg, Tharsis, and Draa Sfar were in the range 7?C13, 8?C14, and 19?C27?cm/ka, respectively. Continuous sedimentation of black shale favored the isolation of the massive sulfides and organic material from bottom waters and hence favored their preservation. Accordingly, the relationships between black shales and massive sulfides are considered to be casual. Nevertheless, the tectono-sedimentary evolution of each basin controlled the deposition of both black shales and massive sulfides and the parameters that favored their coeval deposition.     

内蒙古狼山—渣尔泰山地区与黑色岩系有关的铂族元素矿床找矿前景

铂族元素(PGE)为中国急缺的矿产资源。近年来,国外(如俄罗斯)在黑色岩系内发现了非传统类型的PGE矿床,中国南方也发现了与黑色岩系有关的PGE矿化。黑色岩系将成为PGE和稀有金属的一种新来源。内蒙古中西部狼山—渣尔泰山地区属中元古代裂谷系,具有类似的区域成矿构造背景,黑色岩系极为发育,并在黑色岩系分布区发现有砂铂矿床、PGE重砂异常及一系列与黑色岩系有关的金铜多金属矿床等良好的找矿线索,具有寻找与黑色岩系有关的PGE矿床的找矿前景。     

塔里木盆地北部下寒武统底部黑色页岩形成的次氧化条件

富有机质黑色页岩的形成长期以来被认为是缺氧沉积环境的证据,并被作为全球缺氧事件的标志。塔里木盆地下寒武统底部黑色页岩的岩石学特征说明其沉积在受陆源有一定影响的陆棚环境中。矿物学研究表明,硫均以硫酸盐状态存在,没有见到黄铁矿,说明其形成在硫酸盐还原带以上。黑色页岩中结核状氟磷灰石的存在以及剖面底部结核状磷块岩的出现,表明了一种与现代热带太平洋东海岸和阿拉伯海相类似的广泛发育上升洋流的大陆边缘沉积环境。黑色页岩的地球化学特征中,Re和Mo的高度富集、高的Re/Mo比以及含有一定量的Mn,Cd和U的相对富集以及低的Cd/U比等,这些特点均支持了黑色页岩沉积于次氧化条件的认识。     

Lower Cambrian Black Rock Series and Associated Stratiform Deposits in Southern China

Widespread in more than ten provinces of southern China are the Lower Cambrian black argillaceous-arenaceous rock series consisting of black carbonaceous shales,black carbonaceousargillo-siliceous rocks,black carbonaceous silicolite and black silicolite and black carbonaceous argillaceous siltstone.The Ni,Mo,V,Cu,U,Ba,Ag,P contents of these series are usually several to tens of times higher than their average values in shales.As viewed from lithological sequence,element association and evolution,these black series can be diveided into two types.There occur a variety of deposits in the black rock series,such as phosphorite deposits,Ni-Mo-V polymetal deposits and “Stone coal“ seams.According to ore composition,texture and structure,the phosphorite deposits fall into three types,i.e.,thick-bedded,lenticular and nodular,The Ni-Mo-V polymetal deposits,V deposits and reworked sedimentary CU-U-Cd polymetal deposits in terms of their element assiciation and ore genesis.As for the stratiform deposits in the black rock series,three mineralization stages have been recognized,i.e.,the formation of phosphorite deposits,of Ni-Mo polymetal deposits and of V-Cu-U-Cd polymetal deposits as well as of “:stone coal“ seams.Evidence strongly suggests that lower organisms have played an important role in mineralization. Our studies indicate that the Lower Cambrian black argillaceous-arenaceous rock series in southern China and their associated stratiform deposits occur generally in the basal parts of a big sedimentary cycle,i.e.,the initial period of a transgression,or in the fine detrital-siliceous formation between two carbonate formatons,formed in a humid climatic zone between two arid ones.As for the environment of deposition,it is suggested that the Lower Cambrian black argillaceous-arenaceous rock series and associated stratiform deposits(excluding thick-bedded phosphorite deposits)were formed mainly in a restricted and poorly-fed sea basin of stagnant shallow water containing abundant lower or ganisms and organic matter under statically hydrodynamic conditions.     

贵州遵义黑色岩系多金属层中铂族元素的赋存状态

本文运用逐级化学提取和重液分离,结合电感耦合等离子体质谱分析,研究了遵义地区黑色岩系多金属层中铂族元素的赋存状态及其沉淀富集规律。实验结果表明,铂族元素主要赋存于硫化物类矿物中,其中Pt和Pd的赋存形式有所不同,有一部分Pt还存在于粘土矿物中,Pd则除部分在粘土矿物中外,还可能有独立矿物存在。结合前人的研究,可以认为成矿溶液中铂族元素可呈不同形式的络合物迁移;粘土矿物、有机质及金属硫化物在PGE富集过程中起着地球化学障的作用。     

湘西震旦—寒武纪交替时期古海洋环境的恢复

前寒武纪至寒武纪的交替时期是地质史和生命史的重要转折。中国南方地区广泛发育了上震旦统、下寒武统的黑色岩系。文中运用沉积学和沉积地球化学的理论和方法对湘西黑色岩系的岩石类型、矿物组成、元素地球化学特征、干酪根的结构以及碳同位素的组成等方面进行了研究 ,讨论了黑色岩系的形成条件 ,恢复了震旦纪 /寒武纪地史转折期的古环境。研究认为 ,湘西地区在晚震旦世和早寒武世地史转折期的生物爆发和高有机质的产率是形成缺氧环境的重要因素之一。     

新类型难识别矿地球化学勘查

讨论了4种新类型难识别矿的地球化学勘查研究进展,包括使用深穿透地球化学方法在吐哈盆地砂岩型铀矿的试验和在胜利油田伴生金的地表地球化学显示,从全国铂的地球化学分布看西南黑色岩系中寻找铂族元素的前景,地球化学填图增加到70余种元素分析对稀有、分散元素的研究和寻找将起到巨大的作用。