吉林临江荒沟山铅锌矿床流体包裹体特征及矿床成因

摘要

In order to determine the ore-forming fluid and metallogenic mechanism of the Huanggoushan Pb-Zn deposit in Linjiang area,the authors undertook petrography,micro-thermometry and C-H-O-S-Pb stable isotope analysis of fluid inclusions in lead-zinc ores from the main metallogenic stage (polymetallic sulfide stage).The results show that the inclusions are gas-liquid two-phrase belonging to NaCl-H2O system.The main metallogenic stage's fluid is characterized by medium temperature (209℃ ～276℃),medium salinity (1.98 ～16.34wt％) and low density (0.79 ～0.96 g/cm3).Themetallogenic pressure ranges approximately from 16.8 to 33.0 MPa with depth mainly in 1.68 ～ 3.30 km.The hydrogen and oxygen isotope analysis indicate that the δ18OH2O and δD values are 3.3 × 10-3 ～9.9 × 10-3 and-115 × 10-3 ～-74.8 × 10-3.Combining with the δ18O-δ13C diagram of carbon and oxygen isotopes,it can be concluded that the metallogenic fluids are mainly from mantle-derived fluids and may have mixed with the meteoric water.The δ34S values of sulfur isotopes range from 2.6 × 10-3 to 18.9 × 10-3,representing the enrichment of heavy sulfur.The 206pb/204 Pb,207pb/204 Pb and 20spb/204pb ratios of lead isotopes vary from 15.43 to 15.57,15.25 to 15.33 and 34.88 to 35.07,respectively,indicating that the metallogenic materials were derived from Zhenzhumen Formation,but does not rule out the mixing of materials from deep source.Combining with the regional geology,the deposit belongs to mesothermal veintype lead-zinc deposit formed in the subduction background of the Paleo-Pacific Plate to the North China Plate,and the metallogenic age is the Late Yanshanian.%为确定临江荒沟山铅锌矿床成矿流体特征及矿床形成机制,笔者对矿区主成矿阶段(多金属硫化物阶段)中的铅锌矿石进行了流体包裹体岩相学、显微测温及稳定同位素研究.结果显示,包裹体均为气液两相包裹体,属NaCl-H2O体系,且成矿流体具有中温(209℃ ～ 276℃)、中盐度(1.98～16.34wt％)、低密度(0.79 ～0.96 g/cm3)的特点;成矿压力约为16.8 ～33.0 MPa,成矿深度为1.68～ 3.30 km.氢氧同位素结果显示δ18 OH2O和δD值分别为3.3 ×10-3 ～9.9×10-3,-115×10-3～-74.8×10-3,结合碳氧同位素δ18O-δ13C图解说明成矿流体以幔源流体为主,可能有大气降水混入.硫同位素δ34 S值为2.6 ×10-3 ～18.9×10-3,具有富集重硫的特点;铅同位素206 pb/204 Pb,207 pb/204 Pb,208 pb/204 Pb值分别为15.43 ～ 15.57,15.25 ～ 15.33,34.88～ 35.07,说明成矿物质来源于珍珠门组地层,但不排除有深源物质混入.结合区域地质,认为该矿床的成因类型为中温热液脉型铅锌矿,形成于环太平洋体系向华北板块俯冲的构造背景下,形成时代为燕山晚期.