Abstract:

Chert, mainly composed of silica, are widely and stably distributed in the orogenic area.  The results of Raman and SEMEDS analyses of cherts indicate that the microfabric information of chert from the BafangshanErlihe PbZn ore deposit can be used to study the reconstruction of orogeny, of metallogenesis and of recrystallization. The SEM analysis show that the quartz grains in cherts are tiny and closely packed, which is in accordance with the characteristics of high nucleation rate of hydrothermal sedimentation. Despite of the high stability, the recrystallization of the quartz can be clearly proved by the Raman analysis showing that the FWHM value of the characteristic peak (463 cm-1) of quartz after the Gaussian Fitting decreases from the rim to the core of the quartz grain, which indicates the increasing of crystallinity towards the core caused by the recrystallization of the quartz grain. For the quartz grains that were in contact with the carbonate vein, the crystallization degree of the quartz is increasing from the inner to the rim of the grain, implying that the quartz grains had been affected by the upper fluids. This is also supported by the SEM analysis showing that there are floccules at the interface between quartz and carbonate mineral. Some carbonate minerals were broken up and deformed under the stress during the orogenic activities, resulting in the fissures and holes filled up with metal sulphides. Under SEM, it can be seen that metal sulphides are distributed in the fissures and holes with linear and disseminated structures. In addition, in the interpenetration of different veins, there existed multiple stages of fluids evolution, which is similar to that in the Eastern Qinling orogen, with the order of carbonate (ankerite) fluids→metal sulphides fluids→siliceouscarbonate(calcite) fluids.

Key words: Western Qinling, Pb-Zn ore, microfabric, hydrothermal sedimentation, fluid