黔西南、桂北地区微细浸染型金矿床砷、锑、汞、铊元素及矿物组合特征

FEATURES OF As,Sb,Hg,Tl AND THEIR MINERAL ASSEMBLAGES OF SOME DISSEMINATED GOLD DEPOSITS IN GUIZHOU AND GUANGXI PROVINCES

本文结合野外地质调查和有关的低温硫化物相平衡实验结果，对黔西南、桂北地区的浅成低温热液浸染型金矿床中与金共（伴）生的硫化物矿物组合、地球化学特征及其成矿作用机制进行了综合分析研究。研究表明，与金矿化共（伴）生的砷、锑、汞和铊等地球化学指示元素及其矿物组合不仅具有成生方面的联系，而且可以作为寻找金的一种特征的标型标志。

A systematic study on characteristics of As, Sb, Hg, TI and their assemblages of some sediment-hosted disseminated gold deposits in southwestern Guizhou and northern Guangxi has been carried out based on the field geological investigation and experimental mineralogy.The gold deposits involved are situated in the southwestern margin of the Yangzi Paraplateform and bordered on the Southern China fold belt which is controlled structurally and stratigraphically. They occur mainly in the Upper Permian and Middle-lower Triassic siltstone, claystone, sandstone, black shale and marl which are important ore-bearing formations of polymetals for they have rather high contents of An.As, Sb, Hg, and TI. The wall rock alteration related to gold mineralization is generally silicification, pyritization, arsenopyritization and argillic alteration. Among them the silicification is very common in these areas. The gold deposits are usually composed of pyrite, marcasite, arsenopyrite, stibnite, realgar, optment, cinnabar, quartz, hydromica group, carbonates etc. It is suggested that pyrite and arsenopyrite are the most important An-bearing minerals in all these gold deposits. The majority of An in the ores are present invisible grains (usually less than 0. 0n mm). It is obvious that the gold mineralization in these areas is accompanied a special indicative element assmeblage and definite zonally distributed mineral intergrowths. Enrichment of gold is promoted by multistaged mineralization. Five types of mineral paragenesis can be classified according to the features of geochemical elements and mineral associations in these gold deposits= 1 ) native gold-stibnite-pyrite; 2) native gold-cinnabar-stibnitepyrite;3) native gold-arsenopyrite-realgar-orpiment;4) native gold-cinnabar-realgar-orpiment-stibnite-pyrite; 5) native gold-realgar-orpiment-cinnabar-arsenopyrite-Tl minerals. The genetic interpretation of the As, Sb, Hg, TI element associations with An is also discussed in this study based on the results of experimental mineralogy. The stable phase relations of the pseudoternary As2S3-HgS-Tl2S system and the ternary An-Tl-S system are successfully used to estimate the formation conditions of the element associations and mineral assemblages of the gold deposits. It is noteworthy that the tectonic activity of the faults also play an important role in the mineralization process of these low-temperature, low-pressure disseminated gold deposits. Both macroscopic and microscopic studies show that gold mineralization usually presents in strongly alternated tectonic belts in which not only pyrite and arsenopyrite but also orpiment, realgar, stibnite or cinnabar and TI-bearing minerals can be observed.It is suggested that the characteristics of the indicative element associations, such as As, Sb,Hg and TI, and the corresponding mineral assemblages are of typomorphic significance forsearching and evaluating the disseminated gold deposits.