我国主要汞矿床的辰砂硫同位素组成

SULFUR ISOTOPIC COMPOSITION OF CINNABAR FROM MAJOR MERCURY DEPOSITS OF CHINA

汞矿是我国重要有色金属矿产之一,和世界相比,有其独特之处。据26个汞矿床(点)229件辰砂硫同位素测定值统计,绝大部分辰砂的δ^(34)S都是正值,且与含矿地层中硫酸盐δ^((?)4)S的差值,大致有一个确定的变化范围。辰砂的δ^(34)S比含矿地层中硫酸盐的δ^(34)S平均低9.35‰。从时间的总体上看,各时代地层中辰砂的δ^(34)S变化曲线与海洋硫酸盐的δ^(34)S时间变化曲线,几乎具有相同的演化趋势。因而,在一般情况下,辰砂中的硫都是来自含矿地层中的海洋硫酸盐。

Mercury deposits in China, being one of the important metallic ore resources of the country, have their unique characteristics as compared with mercury deposits in other parts of the world. China's mercury deposits mainly have Paleozoic marine carbonate rock as the ore-bearing wall rock, their metallogenic epochs are Mesozoic and Cenozoic, and they are dominantly of hydrothermal type. Mercury deposits in carbonate rocks are intimately associated with sedimentary facies, and occur mainly in dolomite and limestone of evaporation facies—supratidal salar facies and frontal slope facies of the carbonate platform, with the deposits in the former facies related to anhydrite and those in the latter facies related to organic matters.According to sulfur isotopic determinations of 229 cinnabar samples from 26 mercury deposits (spots) in 7 systems, 13 groups and 18 formations, cinnabar from the overwhelming majority of ore deposits has positive δ^(34)S values. δ^(34)S values of cinnabar from strata of the same age in various places vary limitedly, generally not in excess of 10‰. δ^(34)S mean values of cinnabar from various strata are 3.8‰～14.4‰(averagely 9.35‰) lower than mean δ^(34)S values of oceanic sulfates in ore-bearing strata; that is to say, their differences are within a comparatively definite range. Viewed from the general temporal evolution, δ^(34)S variation curves of cinnabar from strata of various ages almost exhibit the same evolutionary trend as δ^(34)S temporal variation curves of oceanic sulfates compiled by G. E. Claypool et al. (1980). It is thus considered that, for the mercruy deposit in marine sedimentary rocks, sulfur in cinnabar came exclusively from oceanic sulfates of the strata where the ore deposit lies.