Hydrothermal Exhalative Metallogeny Of Stratiform Pb-Zn Deposits On Western Margin Of The Yangtze Craton

A number of conformable stratiform Pb-Zn deposits and occurrences have been discovered in recent years along the Dadu River valley on western margin of the Yangtze Craton. The sulfide-bearing blackish siliceous rocks are interbedded in top of dolomite of Upper Sinian — Lower Cambrian Dengying Formation. Based on detail field and microscope observation and ore geochemical analyses, the author put forwards that these deposits are genetically SEDEX-type. In consideration of particular aspects of the deposits such as the combination of dolomite-blackish siliceous rocks-sulfide-dolomite in profile and the ore having formed in stable tectonic setting in early stage of the Yangtze Craton, the author names these deposits as Dadu River Valley Style deposits of SEDEX-type (abbreviated as DRVS deposits). Typical seismites sequence and seismic structures are recognized within the Pb-Zn orebeds, which might be the first case has ever been reported that seismites occur within Pb-Zn deposits. The author suggests that the hydrothermal exhalative metallogeny have been induced by severe submarine earthquakes in early Cambrian. Highly matured organic matters, e.g., hydrocarbon, bitumen, kerogen, and etc., have been identified in the ore. The organic matters are supposed to have evaluated from Proterozoic marine alga and bacteria, and have take significant roles in metals' accumulation in ore source bed, metal migration in ore-bearing fluid and deoxidization of SO₄^2- in seawater to S^2- to cause ore precipitation. Through the analysis of ore-forming lithofacies-paleogeographical conditions, the author points out that the DRVS deposits are controlled by both NEE-extending Hanyuan-Emei synsedimentary depression and contemporaneous fault system located at the axis of the depression during Upper Sinian—Lower Cambrian Dengying Period. The development of these synsedimentary depression and fault were affected by Proterozoic basement structures. There was another synsedimentary depression, the NE-extending Ningnan— Huili depression, existed at the same period, where might be the most hopeful region to discover the DRVS deposits. During the mineralization process of the DRVS deposits, two mineralization subsystems existed, one above the rock/ water boundary, which formed the conformable stratiform ores at temperature of 80⁸6℃; the other below the rock/ water boundary, which formed vein ores at temperature of 140-285 ℃. The ores...