湖南芙蓉锡多金属矿床成矿流体地球化学

Study on the ore-forming fluid geochemistry of the Furong tin polymetallic deposit, Hunan province, China.

湖南芙蓉锡多金属矿床是我国最近发现的与A型花岗岩具有成因联系的超大型锡多金属矿床。本文对该矿床主要的四种矿化类型(矽卡岩型、云英岩型、蚀变花岗岩型、锡石硫化物型)进行了系统的流体包裹体地球化学和稳定同位素地球化学研究。研究结果表明:该矿床中流体包裹体类型复杂,包括富含CO_2包裹体、气液包裹体、含子晶包裹体和气相包裹体。矽卡岩型矿石中流体包裹体均一温度主要集中在400～450℃,云英岩和蚀变花岗岩型矿石的均一温度相对下降,主要分布于250～350℃之间,锡石硫化物型矿石中包裹体温度进一步下降。成矿流体主要由高盐度CaCl_2-NaCl-KCI-HO_O流体(盐度多集中在32.2 wt%～50.6 wt%NaCl.eqv)和富含CO_2的CO_2-CH_4-NaCl-H_2O低盐度流体(盐度多集中在32.2 wt%～50.6wt%NaCl.eqv)组成。芙蓉锡矿云英岩型矿石成矿流体中的水主要以岩浆水为主,锡石硫化物型矿石成矿流体中的水具有岩浆水和大气降水混合的特征,成矿流体中的碳为岩浆碳与沉积碳酸盐不同比例混合的结果。芙蓉锡多金属矿床的成矿流体应主要来源于骑田岭黑云母二长花岗岩岩浆结晶期后分异出的岩浆热流体。岩浆热流体沿岩体周围裂隙对围岩和原生矽卡岩进行热液交代,在造成绢云母化、白云母化、绿泥石化等热液蚀变现象的同时,导致了大规模的锡矿化。减压沸腾和低温流体与高温流体混合造成的沸腾作用是导致芙蓉锡矿锡沉淀的主要机制。

Furong deposit is a recently discovered tin polymetallic deposit genetically related to A-type granite. This paper presents the fluid inclusion and stable isotope data of four types of ores from the deposit, i.e skarn, greisen, altered granite and sulfide vein. Four types of fluid inclusions have been observed, namely aqueous two-phase inclusions, M-bearing inclusions, gas-rich inclusions and daughter mineral-hearing inclusions. Homogenization temperatures of fluid inclusions in skam-type ores range from 400 degrees to 450 degrees C. The homogenization temperatures of fluid inclusions in greisen and altered granite range from 250 degrees to 350 degrees C, lower than those in skarns. The homogenization temperatures of fluid inclusions in sulfide veins are the lowest. The ore forming fluids have the composition of CaCl(2)(MgCl(2))-NaCl-KCl-H(2)O system with high salinity (32.2 wt% similar to 50.6 wt% NaCl. eqv) and CO(2)-CH(4)-NaCl-H(2)O system with low salinity (0.2 wt% similar to 12.4 wt% NaCl eqv). The results above and isotope data indicate that ore-forming fluids were dominantly of magmatic origin sourced from the Qitianling biotite granite during magma differentiation. Fluid boiling induced by pressure reduction and mixing of high and low temperature fluids are the main mechanisms of the tin precipitation of Furong tin polymetallic deposit.