西秦岭泥盆系Au背景值的确定、元素地球化学特征及地质意义

Determination of the Au background value and Au geochemistry in the Devonian of the West Qinling and their geological significance

根据地层地球化学研究,秦岭地区Au背景值为2.9×10-9,从西到东,自礼岷→文康→西成→凤太→板沙→镇旬→柞山地区金含量逐渐降低。凤太盆地、西成盆地、礼岷盆地泥盆系金背景值分别为3.1×10-9、3.2×10-9、4.7×10-9,为重要的金多金属地球化学成矿区。金在地层中的分布受岩性和沉积环境的控制,泥盆系是本区金成矿的矿源层,其中千枚岩、板岩、片岩、粉砂岩是金矿的重要源岩。与其他沉积盖层相比,秦岭中上泥盆统富集Au、Ag、Cu、Co、Ni、Cr、Pb、Zn。与上地壳丰度对比,Au、As、Sb、Ag、Co、Ni、Cr、V、Pb、Zn较富集。泥盆系中发育热水沉积岩,含Au较高。研究表明,在热水沉积中Au发生了预富集作用,沿海底同生断裂发育的钠质热水沉积过程中Au富集形成了矿源层。

Geological and geochemical studies indicate that the Au background value of the Qinling orogen is 2.89×10-9. The Au background values of the Fengtai basin, Xicheng basin and Limin basin, which are important gold polymetallic geochemical metallogenic provinces, are 3.1×10-9, 3.2×10-9, 4.7×10-9 respectively. From east to west, the Au background values gradually decrease from the Limin basin→Wenkang basin→Xicheng basin→Fengtai basin→Bansha basin→Zhenxun basin→Zhashan basin. The distribution pattern of Au in strata is controlled by the lithology and sedimentary environment. The Devonian is the source bed of gold, and phyllite, slate, schist and siltstone are important source rocks. Compared with other sedimentary covers in the area, the Mid-Upper Devonian in the Qinling orogen is rich in Au, Ag, Cu, Co, Ni, Cr, Pb and Zn, and compared with the upper crust, it is rich in Au, As, Sb, Ag, Co, Ni, Cr, V, Pb and Zn. The hydrothermal sedimentary rocks developed in the Devonian have higher Au contents. Study indicates that gold preconcentration took place in the hydrothermal sediments. It is suggested that Au was concentrated during Devonian sodic hydrothermal deposition along submarine contemporaneous faults to form the source bed.