| Southwestern part of the Jiangnan Old Land is adjacent to the Paleo-Asian metallogenic domain,the Paleo-Tethyan metallogenic domain and the Circum West Pacific metallogenic domain.It is situated in the collision and combinational belt between the Yangtze Block and Cathaysia Block,and is an important part of the western Nanling metallogenic belt,which is an important large-superlarge metallic deposits region in China and a vital part of the large-scale low-temperature metallogenic domain in southwestern margin of the Yangtze Block.There are a number of lead-zinc deposits related to layer-sliding,which are characterized by large amount of reserves,ore-rich and carbonate-bearing in the studied area.In this dissertation,based on layer-sliding effect,geological,orebody morphological,and geochemical characteristics of typical lead-zinc deposits in the studied area were systematically studied in order to unravel the mechanism of ore-controlling and ore-forming,the lead-zinc metallogenic mechanism and metallogenic age.The comprehensive model of regional layer-sliding metallogenic model is established.Since the Devonian,over 10,000 meters thick carbonate,sandstone,and interbedded mudstone and shale were developed in the studied area.Because different layers are soft and hard,regional layer-sliding was widely developed,with varied layer-sliding structure and assemblages.To sum up,there are four different layer-sliding structure assemblages,including:(1)layer-sliding—shear zone type(represented by the Jianzhupo Pb-Zn polymetallic deposit in Wuxu orefield);(2)layer-sliding—tensioned type(represented by the Siding lead-zinc deposit);(3)layer-sliding—karst cave type(representative by the Jiangyong lead-zinc deposit);(4)layersliding—breccia type(represented by the Kangjiawan lead-zinc deposit).The geochemical characteristics of trace elements,sulfur,lead,carbon-oxygen,hydrogenoxygen,and ore-forming fluids in the typical deposits,indicated that the ore-forming mechanisms of the various deposits in the region are generally similar.In all,three main mechanisms are proposed and further demonstrated:(1)associated with multi-source fluid mixing(represented by the Changpo-Tongkeng,Jiangyong,Huangshaping and Kangjiawan lead-zinc deposits);(2)associated with organic reduction(represented by the Beishan deposit);(3)associated with the paleo-oil and gas reservoirs destruction represented by the Siding deposit).According to the dating of structural analysis,the Changpo-Tongkeng deposit is a multi-factor complex metallogenic deposit that integrates the Hercynian,Indosinian and Yanshanian periods.It is also proposed that the principal contribution of Indosinian layer-sliding in regional mineralization,which is of great significance to establish the Indosinian metallogenic system that is relatively unknown in South China.The Rb-Sr isotopic dating of sphalerite in the Siding deposit revealed the existence of layer-sliding mineralization during the Hercynian period(360Ma±5Ma)in the studied area.Combined with the metallogenic geochronological data and structural analysis,it is considered that the layer-sliding mineralization is regional and common,indicating that there are ~360Ma,240~200Ma,165~95Ma layer-sliding mineralization events,which is consistent with the dynamic background of regional tension,Paleo-Tethys Ocean closing and the lithosphere stretching and thinning caused by the subduction of the Eurasian plate.The heterogeneity of the lithosphere structure and lithologic different composition is the material foundation of layer-sliding,which is universal and common.The difference in the formation of lead-zinc deposits related to layer-sliding in the studied area was controlled by different layer-sliding structure assemblages.Based on the study of "Structure geologyGeochemistry-Geochronology",the regional three stage layer-sliding mineralization is established for the first time. |
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