The Geochemical Forming Mechanism Of Copper-Silver Polymetallic Mineralization Field Of Baiyangping Region

Based on Geological investigation in the field and a lot of analytical data in the laboratory, this paper has discussed settings of the regional Geology and structure, the ore-forming Geochemical process of Cu -Ag polymetallic mineralization field of Lanping Baiyangping, Yunnan province. The study covers regional Geology, the physicochemical conditions of Cu-Ag polymetallic mineralization area, transport forms of Copper and Silver, the ore-forming Geochemical mechanism of Cu & Ag, the Geochemical characters of major element, trace element and lanthanon in mineralization field, the ore-forming age and Geochemical mode, and so on. The result is as follows:(1) Cu-Ag polymetallic mineralization field lied in the north of Lanping Basine between Jinshajiang fissure and Lancangjiang fissure, whose internal mid-axis fissures and different subfissures formed the fissure system of the basin. They were the transport system of the ore-forming fluid, which was important to the formation of Copper-Silver polymetllic deposits.(2) The special fissures and lithology controlled the deposits. Deep and sub fissures were advantageous fields for ascending and assembling of the ore-forming thermal fluid. In addition, gritstone and mudstone provided the condition for the atmospheric water's descending.(3) The mineral source was provided by both lower crust, upper mantle and upper crust, obviously from crust-mantle mixing.(4) The polymetallic deposits formed at middle or low temperature, and hydrothermal solution was neutral. Mineralizing agent of Cu & Ag was mainly Cl- S2O32- S2-and HS- Copper and Silver were mainly induced and transported by Cl- S2O32-, S2-and HS-.(5) Copper in the solution was transported mainly in form of CuCl42-, Cu(H2O)42+, Cu(S2O3)46- CuS46-, Cu(HS)42- and Cu(SbS3)410-; Silver in the solution was transported by AgCl2-, Ag(S2O3)23- Ag(HS)2-, AgS23- and Ag(SbS3)25-; and which precipitated from the solution when physicochemical conditions, such as T P , pH, fo2 and fs2, were lower. As a result, CuFeS2, (Cu, Ag)12Sb4S13 CuS, Ag2S, etc. were formed.