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FEATURES OF As, Sb, Hg, TI AND THEIR MINERAL ASSEMBLAGES OF SOME DISSEMINATED GOLD DEPOSITS IN GUIZH0U AND GUANGXI PROVINCES

Qian Handong, Chen Wu, Hu Yong   

  1. Department of Earth Sciences, Nanjing University
  • Received:1995-06-20 Revised:1995-06-20 Online:1995-12-20 Published:1995-12-20

Abstract: A systematic study on characteristics of As, Sb, Hg, T1 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 oil 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 Au, 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, opiment, cinnabar, quartz, hydromica group, carbonates etc.. It is suggested that pyrite and arsenopyrite are the most im portant Au-bearing minerals in all these gold deposits.The majority of Au in the ores are present in visible 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-stibnite-pyrite; 3) native gold-arsenopyrite-realgar-orpiment-stibnite; 4) native gold-cinnabar-realgar-orpiment-stibnite-pyrite; 5) native gold realgar – orplment – cinnaba r- arsenopyrite-TI minerals. The genetic interpretation of the As, Sb, Hg, TI element associations with Au is also discussed in this study based on the results of experimental mineralogy. The stable phase relations of the pseudoternary As2S3-HgS-TI2S system and the ternary Au-TI-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-beating 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 for searching and evaluating the disseminated gold deposits.