Water/Rock Interaction During Mineralization Of Huize Super-large Lead-zinc Deposit,Yunnan Province

Yunnan Huize super-large Pb-Zn deposit is the most typical pb-Zn deposit in the important Sichuan-Yunnan-Guizhou pb-Zn ore concentration area in China.It has attracted the attention of ore deposit experts at home and abroad.Many high-level achievements have been made in metallogenic theory and significant breakthroughs have been made in metallogenic prediction.However,due to the limitations of analytical testing methods and research methods,the interaction between ore-forming fluid and wall rock（water/rock interaction）and its indication for mineralization and prospecting are weak,which restricts the fine characterization of mineralization process and affects the extraction of prospecting information.Taking the contact zone samples of ore body and wall rock of Huize Lead-zinc deposit as the research object,the characteristics of mineral structure,composition and isotope variation during the interaction between water and rock have been identified by using In-situ LA-ICPMS trace elements and In-situ S-Pb isotopes.the ore-forming process has been described in detail.The main insights gained are as follows:（1）To find out the variation characteristics of mineral structure,composition and isotope in the process of water/rock interaction:from ore body to contact zone to wall rock.The dolomite has a typical metasomatism structure,from irregular metasomatism grid,through a band with reaction edge at the edge of some particles,to the veins along the gap,with obvious recrystallization phenomenon.The contents of Ca,Mg and REE In dolomite increase,while the contents of Mn,Fe,Ga,Sr,In,Sn and V decrease.The contents of Cu,Zn,Ag,Cd and other ore-forming elements In dolomite In ore-body are much higher than those In contact zone and wall rock.Theδ³⁴S value of sphalerite decreases and theδ³⁴S value of sphalerite in contact zone decreases gradually from core to edge,while the Pb isotopic composition of galena increases.（2）The water/rock interaction delineates the ore-forming process:it reveals that the ore-forming materials are mainly derived from the ore-bearing carbonate rocks,the sulfur is mainly provided by the strata,and TSR plays an important role in the sulfate reduction process.The metallogenic process is summarized as follows:The ore-forming fluid with rich ore-forming elements,highδ³⁴S value and low Pb isotope composition enters the dolomite-rich wall rock`along the fault and interlayer fracture zone,and the strong water/rock interaction occurs.The sulfate TSR in the formation forms reduced sulfur,and the fluid property changes from alkaline to neutral and weak acidic.The ore with relatively highδ³⁴S value of sphalerite and high Pb isotope composition of galena was formed by sulfide precipitation.（3）The indicative significance of water/rock interaction for metallogenic prediction:both macroscopic and microscopic mineralization-alteration zoning reflect that the closer to the ore body,the stronger the water/rock interaction,and the higher the content of ore-forming elements obtained from ore-forming fluid.The formation of two types of special altered country rocks in the mining area is closely related to the water/rock interaction and the precipitation and mineralization of ore-forming elements.weakly marbled coarse-grained argillaceous dolostone（type-Ⅰ）provide favorable space for sulfide precipitation and mineralization,and dedolomitized giant crystalline limestone（type-Ⅱ）has experienced the mineralization,marbling and dolomitization successively.Therefore,the greater the intensity and the wider the distribution of alteration,t the more favorable it is to lead-zinc rich ore deposits.