| 我国南方下寒武统黑色岩系及其中的层状矿床 |
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| 引用本文：.1982.Lower Cambrian black argillaceous and arenaceous rock series in south China and its associated stratiform deposits[J].Mineral Deposits,1(2):39~51 |
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| Lower Cambrian black argillaceous and arenaceous rock series in south China and its associated stratiform deposits |
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| Abstract:Widespread in more than ten provinces of south China is the Lower Cambrian black argillaceous and arenaceous rock series, which consists of black carbonaceous shale (termed black shale for short hereafter), black carbon argillosiliceous rocks, black carbonaceous silicostone and black silicostone (termed black silicostone for short hereafter) and black carbon-argillaceous siltstone. The Ni, Mo, V, Cu, U, Ba, Ag, P contents of this series are usually several to decades of times higher than their average values in shales. Based on the lithological sequence, element association and evolution, this series can be divided into two types. The first type is characterized by Ni, Mo multimetal element association and the lithological sequence phosphorite→black shale and Ni, Mo multimetal element concentrated layers→black carbon-argillosiliceous rocks→black carbonaceous hydromica shale. The second type is characterized by V, Cu, U, Ba mul.timetal element association and the lithological sequence black silicostone and siliceous rocks black arenaceous shale and vanadium ore layer→black shale. There occur a variety of deposits in this series, such as phosphorite deposits, Ni-, Mo-, V-bearing multimetal element deposits and "stone coal" deposits. According to ore composition, textures and structures, the phosphorite deposits fall into three types, i.e. thick-bedded, lenticular and nodular phosphorite deposits. The Ni-, Mo-, V-bearing multimetal element deposits can be subdivided into Ni-, Mo-bearing multimetal element deposits, vanadium deposits and sedimentary-transformed Cu-, U-, Cd-bearing multimetal element deposits interms of their element association and ore genesis. As for the stratiform deposits in this series, three minerogenetic stages have been recognized, i. e. the stage of the formation of phosphorite deposits, that of the formation of Ni-, Mo-bearing multimetal element deposits and that of the formation of V-, Cu-, U-, Cd-bearing multimetal element deposits and "stone coal” deposits. There is ample evidence that low organisms played an important part in the mineralization. Their contributions were. (1) low organisms themselves could take up some elements to form tissue of their bodies which were then to become part of the source of "stone coal" and phosphorite deposits; (2) low organisms would decompose into such organic matters as amino-acid and porphyrin after their death which later combined with some metallic elements, producing organic-metallic complexes and metal-porphyrin compounds. These compounds were inherently very unstable and readily decomposed, losing metallic elements which were probably to be accumulated afterwards; (3) the decomposition of organisms would consume a lot of oxygen and release hydrogen sulphide. There also existed another factor facilitating the release of hydrogen sulphide, i. e. the reduction of sulfate radical by sulfate-reducing bacteria in seawater. Thus auiacid and highly reductive environment would be formed at the sea floor where metal ions easily combined with hydrogen sulfide, forming metal sulfides. The Ni-, Mo-, Cu-, and Fe-bearing sulfide deposits in the Lower Cambrian basal part of south China are products of these processes. Our studies indicate that Lower Cambrian black argillaceous and arenaceous rock series in south China and its associated stratiform deposits occur generally in the basal part of a big sedimentary cycle, i. e. the initial period of a transgression, or in the finely detrital-siliceous formation between two carbonate formations, formed in a humid climatic zone between two arid climatic zones. As regards the environment of deposition, we suggest that Lower Cambrian black argillaceous and arenaceous rock ser/es and its associated stratiform deposits (excluding thick-bedded phosphorite deposits) were mainly formed in a restricted and nonsupplemental sea basin of stagnant shallow water containing abundant low organisms and organic matters and dominated by calm hydrodynamic conditions, where reductive-highly reductive conditions prevailed under which the dolomitic-siliceous-clay facies were formed. |
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