Research On The Geochemical Characteristic And Genesis Of The Xiwan Lead-zinc Deposit In Anhui Province

The Xiwan lead-zinc deposit is located in the northern margin of Luzong volcanic basin.Since the Geological Exploration Technology Institute of Anhui Province carried out its work in the study area,great breakthroughs have been made in mineral exploration for many years.However,there is still a lack of systematic research on the geochemical characteristics of the deposit and the genesis of the deposit.This paper takes Xiwan lead-zinc deposit as the research object.On the basis of collecting and sorting out the predecessors'data in detail,field geological survey and systematic sample collection,combined with modern analysis and testing techniques such as indoor light?thin?section identification,electron probe analysis,sulfur and carbon-oxygen isotope analysis,fluid inclusion composition analysis,etc.The Geological survey,mineralogical characteristics,sulfur isotope,carbon and oxygen isotope geochemical characteristics and fluid inclusion composition characteristics of Xiwan lead-zinc deposit have been studied and the following results have been achieved:?1?According to the spatial distribution characteristics of ore bodies,ore types,ore structure and the interpenetration relationship of minerals in the Xiwan lead-zinc deposit,the metallogenic process can be divided into sedimentary diagenesis,hydrothermal mineralization period and supergene period.Among them,hydrothermal mineralization period is the main metallogenic period of the deposit,during which hydrothermal activity led to a large number of metals to migrate and precipitate.The hydrothermal mineralization period can be divided into pre-sulfide period,carbonate-sulfide period and sulfide period.?2?The results of EPMA analysis of sphalerite,galena and pyrite show that the Zn/Cd ratio of sphalerite is 56.18-371.86,the average value is 209.013,the Zn/Fe ratio is 36.15-913.25,and the average value is 235.572.It shows that sphalerite is formed in medium-low temperature hydrothermal mineralization.The ratio of Pb/S atoms in galena ranges from 0.98 to 1.04,with an average of 1.015.It shows that the sulfur fugacity of ore-forming fluids changes in varying degrees during migration and precipitation,but the sulfur fugacity of ore-forming environment remains relatively stable.The average value of Fe/?S+As?of pyrite in the pre-sulfide stage is 0.869,and that of pyrite in the carbonate-sulfide stage is 0.885.It indicats that pyrite was formed in a medium-shallow environment,and the depth of the former to the latter gradually becomes shallow.The values of Co and Ni,their ratios,As-Co-Ni diagrams and?Fe-?S diagrams of pyrite in the two stages can be used to judge that the deposit is mainly medium-low temperature hydrothermal deposit.?3?The distribution of?¹³C in calcite and limestone ranges from-0.1‰-3.9‰,indicating that their carbon originates from marine carbonate strata.It can be seen from the diagrammatic comparison of?¹⁸O_SMOW-?¹³C_PDB that carbon and oxygen in ore-forming fluids are mainly derived from carbonate dissolution.?4?The value of?³⁴S in the sulphide of the deposit is concentrated in the range of4‰-6‰.According to the diagram of Pinckney method,the value of?³⁴S_?SS is about4.5‰,which indicates that the sulfur source is relatively complex and may mainly come from disseminated sulfides in the surrounding rocks.?5?The gas phase composition of fluid inclusions in the deposit is characterized by rich H₂O and CO₂,and a small amount of reducing gases such as H₂,CO and CH₄.The characteristics of anionic and cationic components in liquid phase of fluid inclusions indicate that the ore-forming fluids are mainly Ca²⁺-Na⁺-SO₄^2--Cl^-type fluids.?6?In Xiwan area,volcanic activity is frequent,multi-stage and multi-stage fault structures provide external driving force for the migration of ore-forming fluids.Volcanic hydrothermal fluids migrate upward along fault structures.In this process,mineralizing elements and mineralizer elements in surrounding rocks are extracted.With the decrease of temperature and pressure or the fluid mixing with atmospheric precipitation,lead and zinc deposits and other ore-forming materials precipitate and mineralize.The deposit may be a volcanic hydrothermal deposit of medium-low temperature.