秦岭泥盆系中铅锌矿床的热水沉积成因

THE SEDIMENTARY ORIGIN OF THE THERMAL WATER IN THE Pb-Zn ORE DEPOSITS OF THE QINLING DEVONIAN SYSTEM

秦岭泥盆纪铅锌成矿带提供了一种沉积岩中热水沉积矿床形成的典型构造背景,成矿作用发生在被动大陆边缘上的裂陷盆地中,与盆地造山前的发展和演化有关。同沉积期断裂控制着成矿洼地的发育,地热异常促使热水系统形成,已经识别出来若干古地热异常存在的标志。碰撞造山过程中盆地封闭,含矿沉积物受到不同程度的变形和变质改造。 可以把泥盆纪地层中的各种金属矿床纳入一个热水沉积成矿系列中,铅锌主要是在热水系统释放到海底时的沉积成岩过程中富集的,铜和金则表现有在热水系统晚期相中或后期改造中富集的趋势。

The most important Pb-Zn ore deposits in the Qinling Ranges are the sedimentary rock hosted hydrothermal sedimentary ore ones. The ore-bearing strata are the Devonian marine sedimentary rock series ,the sequence charc-teristics of which show that the mineralizing process took place while the hydrothermal system was getting into the seafloor during the synsedimentary tectonic activization. The host rocks consist mainly of the quarz-albitite, bari-tite, ankerite silica rocks, which are identified as the hydrotheraml-sedimentary rocks. The sedimentary banding and ribbon structures are well preserved in the concordant bedded sulfide orebodies. The complex variety in the shape and fabric of some orebodies is the result of the diagenetic and epigenetic reformation. Many kinds of deformation fabrics also indicate that they were formed before the principle deformation events. And the metal compositions, which are quite defferent from those of the magmatic hydrothermal Pb-Zn ore deposits, are Zn, Zn + Pb + (Cu), Pb + Zn+Ag, together with the accompanying elements of Fe, Ba, Aa, As and Sb. The formation of the ore deposits is related to the development of the Devonian sea basin and the evolution of the sedimentation,and is affected by the following collisional erogenic processes. It is demonstrated that the mineralizing metals were leached from the underlying sedimentary column and the bassement rocks. The high geothermal value in the fault basin serves as the heat source for the formation and development of the hydrothermal system. And the synsedimentary faults which are the boundaries of the basin are used to be the hydrothermal pathways.