湘南黄沙坪矿区花岗岩的硫同位素特征及其地质意义

Sulfur Isotopic Characteristics of the Huangshaping Granite and Their Geological Significance in Southern Hunan Province

黄沙坪矿床是湘南地区最大的铅锌多金属矿床。矿区内发育的花岗岩出露面积最大仅为0.6km2,却导致铅、锌等金属巨量堆积,因此明确其成矿物质来源是理解矿床成因的关键。为探究矿床内硫的来源,本次研究在已有工作的基础上,对黄沙坪矿区石英斑岩和花岗斑岩进行了系统的全岩硫同位素分析,并与已有硫化物硫同位素数据进行了对比研究。结果显示,矿区石英斑岩和花岗斑岩的δ34 S范围分别为+4.1‰^+7.5‰和+4.9‰^+11.4‰,与典型的S型花岗岩硫同位素组成基本一致,而明显低于区内矿石δ34S值(+2.3‰^+17.5‰)。综合上述,我们认为矿区岩浆硫的同位素组成应接近或略低于花岗质岩石全岩硫同位素组成,成矿物质硫除部分来自岩浆外,很大程度上有地层或膏盐层硫的加入,这可能是黄沙坪成为区域上最大铅锌多金属矿床的重要原因。

The Huangshaping deposit is the largest lead-zinc polymetallic ore deposit in southern Hunan Province.The biggest granite occurred in mining area occupies only 0.6 km^2,which are responsible for the accumulation of huge amounts of metals.The sources of ore-forming materials are critical to understand the ore genesis.Based on the previous studies,we systematically studied the sulfur isotopic composition of quartz porphyry and granite porphyry samples collected from the different locations of mining area to clarify the source of sulfur in the Huangshaping deposit.The results show that the δ^34S values of quartz porphyry and granite porphyry range from ＋4.1‰ to ＋7.5‰,and from 4.9‰ to ＋11.4‰,respectively.Considering the influence of the alteration by the fluid with high δ^34Svalue,the δ^34S values of the granitoid rocks （＋4.1‰ to ＋11.4‰） are probably slightly higher than these of corresponding granitic magma,but they are also well consistent with the δ^34Svalue of typical S-type granites.Based on the above,it is indicated that the sulfur of sulfides with high δ^34Svalues was partly originated from the carbonate strata besides the magmatic sulfur,which is probably one of the most important reasons that the largest lead-zinc deposit in southern Hunan Province occurred in the Huangshaping mining area.