秦岭热水沉积铅锌矿床中硅质岩特征及成因

硅质岩是秦岭中泥企世铅锌矿床中的主要含矿层,呈层状与围岩整合接触,但因受海底同生断裂控制呈线状延伸。化学成分及其Fe、Ti、Al、Mn比值变化范围与现代或古代热水沉积物一致或相似。稀土元素以总量低、LREE>HREE、有明显的Ce亏损和中等的Eu正异常为显著特征。氢氧同位素测试数据表明,形成硅质岩的介质水主要为原生建造水。锶初始比及铅单阶段演化模式年龄反映硅质主要来自硅铝质地壳基底地层或岩石。

Characteristics and Cenesis of the Silicalites in Hot-Water Sedimentary Lead-Zinc Deposits in the Qinling Mountains

The silicalites dealt with in this paper are a kind of silica-rich rockwhich occur in the middle Devonian lead-zinc deposits in the Qinling Moun-tains. They take the form of layer which are conformable with theunderlying and overlying rocks. As they are controlled by a syndepositionalfault system, the silicalites are distributed in the form of lines. The geochemical properties of Fe, Ti, Al, Mn and other elements arecoincident with or similar to those of Iecent and fossil hot water sediments.Moreover, the silicalites are also characterized by lower REE contents,LREE>HREE, apparently negative Ce anomaly and weakly positive Eu ??anomaly. The hydrogen and oxygen isotope data of the inclusions suggest thatthe metallogenic fluids forming the silicalites mostly came from the hydro-thermal solutions in deep-seated rocks. According to the Doe method, thelead single-stage model ages calculated are mainly between 390--552Ma,olderthan those of the middle Devonian strata thus also implying that lead wasderived possibly from the basement rocks. As main ore-bearing rocks, the silicalites are neither the product ofvolcanic exhalation, nor the product of marine deposition, but their featuresare similar to those of the sea-floor exhalogene deposit.