STUDY ON TECTONIC FEATURE AND METALLOGENIC MECHANISM OF THE PENGSHAN Sn-Pb-Zn POLYMETALLIC OREFIELD,JIANGXI PROVINCE

摘要

The Pengshan Sn-Pb-Zn polymetallic orefield is located in the Jiujiang-Ruichang region, which is a segment of the middle-lower Yangtze River metallogenic belt. The Pengshan late Yanshanian buried pluton with granitic composition is a calc-alkaline pluton, intrusion of which is responsible for the formation of the Sn-Pb-Zn polymetallic deposit through providing thermodynamic condition and ore-forming material.The long-active basement rifts initially formed in the Jinning period and the domal structure with induced secondary order faults formed by emplacement of the pluton, such as ring-detachment fault,top-detachment fault and joint fissure, act as the passage-way for magma and ore-forming fluid and impounding structure for ore deposit. The magma to form the pluton with DI＞90 is intensively differentiated. The variation of the ore-forming fluid in composition with falling in temperature caused by action of magmatic hydrothermal convection system combined with groundwater convection system attributes to mineralization of various types in the orefield. The mineralization process can be divided into six stages, i.e., greisenization, skarnization of early stage, fluorite-stanniferous silication stage, skarnization of advanced stage, quartz and cassiterite-sulfuration stage and carbonation stage. The mineral assemblages formed in different mineralization stages are different owing to temperature changing and may be overlapped in space. Malayaite is recognized from the mineral assemblage formed in the fluorite-stanniferous silication stage. The ores in the Pengshan Sn-Pb-Zn polymetallic deposit are spatially zoned with variation from As-Sn mineral assemblage of high temperature in the inner zone through Sn-Pb and Pb-Zn-Ag mineral assemblage of middle temperature in the middle zone to fluorite mineral assemblage of low temperature in the outer zone.The exchanging of Sn,Mg and Fe between biotite and hydrothermal fluid resulted from variation of physicochemical condition during evolution processes of the hydrothermal fluid and its role in mineralization are also disussed in this paper.