内蒙古敖仑花钼铜矿床成矿流体来源及成矿作用机制

Source of ore-forming fluids and metallogenic mechanism in Aolunhua Mo-Cu Deposit,Inner Mongolia

敖仑花钼铜矿床为典型的斑岩型矿床,矿体主要赋存于早白垩世二长花岗斑岩中。成矿作用可以分为4个阶段:石英+黄铁矿+辉钼矿阶段(Ⅰ)、石英+辉钼矿+黄铁矿+黄铜矿阶段(Ⅱ)、石英+黄铁矿+黄铜矿+闪锌矿阶段(Ⅲ)、石英+碳酸盐脉阶段(Ⅳ)。矿物学、流体包裹体岩相学、包裹体显微测温、稳定同位素研究表明:成矿Ⅰ、Ⅱ阶段成矿流体为高温(316℃~462℃)、高盐度(2.23%~45.54%)的NaCl-H 2O-CO_(2)体系热液;成矿Ⅲ阶段成矿流体为高温(300℃~368℃)、低盐度(3.37%~9.34%)的NaCl-H_(2)O体系热液;成矿Ⅳ阶段为低温(130℃~260℃)、低盐度(3.53%~11.95%)的NaCl-H_(2)O体系热液;总体具有成矿温度、盐度逐渐降低的特征。氢、氧同位素分析结果表明,早期成矿流体以岩浆水为主,晚期逐渐混入大气降水;δ^(34)S值为1.9‰~4.9‰,指示硫同位素主要来源可能是岩浆。由于温度、压力降低,流体发生沸腾作用,CO_(2)挥发,流体pH升高,导致Mo、Cu等成矿元素开始沉淀,最后富集成矿。

Aolunhua Mo-Cu Deposit is a typical porphyry deposit.The ore bodies mainly occur in the monzonitic granite porphyry in the Early Cretaceous.The hydrothermal mineralization can be divided into 4 stages:quartz+pyrite+molybdenite stage(Ⅰ),quartz+molybdenite+pyrite+chalcopyrite stage(Ⅱ),quartz+pyrite+chalcopyrite+sphalerite stage(Ⅲ),quartz+carbonate veins stage(Ⅳ).The study on mineralogy,petrography of fluid inclusions,micro-thermometry of inclusions,and stable isotope analysis shows that the primary ore-forming fluids in StageⅠandⅡare high temperature(316℃-462℃),high salinity(2.23%-45.54%)NaCl-H 2O-CO 2 type solutions;the ore-forming fluids in StageⅢare high temperature(300℃-368℃),low salinity(3.37%-9.34%)NaCl-H 2O type solutions;the ore-forming fluids in StageⅣare low temperature(130℃-260℃),low salinity(3.53%-11.95%)NaCl-H 2O type solutions,indicating the trend of decreasing ore-forming temperature and salinity.H,O isotope analysis shows that early ore-forming fluids are mainly magmatic water,meteoric water blended in later;δ34 S value is 1.9‰-4.9‰,indicating magmatic source of S isotope.Due to decreasing temperature and pressure,the fluids boil,CO 2 vaporizes,fluid pH increases,so that ore-forming elements such as Mo,Cu precipitates and eventually concentrates into deposits.