湖南省黄铁矿床地质地球化学特征初步探讨

PRELIMINERY DISCUSSION ABOUT THE GEOLOGY AND GEOCHEMISTRY OF PYRITE DEPOSITS IN HUNAN PROVINCE

湖南省黄铁矿资源颇为丰富,已探明工业矿床50多处。矿床成因类型,可划分为岩浆热液型、层控型和沉积型3类6个亚类,以前两类最重要。岩浆热液型黄铁矿床,主要分布在湘东和湘南地区,与燕山期酸性小岩体密切有关,矿体形态复杂,矿石品位较富,矿物成分繁多,围岩蚀变发育,矿床规模较大;黄铁矿中Co/Ni>1、S/Se比值较低,矿石硫同位素组成具塔式分布效应,矿床硫源以岩浆硫为主,亦有部分地层沉积硫。层控型黄铁矿床,集中分布在湘西北和湘中地区,矿床的产出与岩浆岩无成因联系,受上震旦统陡山沱组和中泥盆统棋梓桥组等特定层位、岩相和岩性组合严格控制,矿体多呈似层状、透镜状等整合矿体,矿石品位一般较贫,矿物成分与围岩蚀变简单:黄铁矿中Co/Ni<1,S/Se比值较高,矿石δS^(34)‰离差大,在较大正、负值范围具多峰式分布,均一化程度低;矿床硫源,为古海水硫酸盐硫和生物成因硫等的混合硫。

The pyrite resources in Hunan province is quite abundant, more than 50 economic deposits having been demonstrated. They can be genetically classified into magmatic hydrothermal type, stratabound type and sedimentary type, Which can be further divided into 6 subtypes, among Which the former two types are the most important ones. The magmatic hydrothermal type pyrite deposits are mainly distributed in eastern and southern Hunan, closely related to Yanshanian small acidic intrusions.The shape of the orebodies iscomplicated and ore grade is relatively rich, with diversified mine-ral composition and wall rock alteration. Co/Ni ratio of pyrite is greater than 1 and S/Se ratio is relatively low. The sulfur isotope composition of the ore shows tower distribution, indicating that the magmatic sulfur source is dominant, also with some sulfur from the sedimentary strata. The stratabound pyrite deposits are centralized in northwestern Hunan and central Hunan, showing no genetic connection with magmatic bodies, controlled by specific stratigraphic horizons (such as Upper Sinian Doushantu Formation and Middle Devonian Qiziqiao Formation), lithofacies and li-thological assemblages strictly. The orebodies often take conformable shapes such as bed-like, lenticular shapes. The ore grade is generally poor, with simple mineral composition and wall rock alteration. The Co/Ni ration of pyrite is less than 1, and S/Se rati is relatively high. δS^(34)‰ of the ore is of large dispersion, showing multipeak distribution in a wide range from negative to positive values, indicating poor homogenization and sulfur source from palaeoseawater sulfides and biogenic sulfur or their mixture.