Study On Occurrence And Distribution Of Au In The Coals And Its Enrichment Mechanism In Western Guizhou Province, China

This paper uses the theories of coal geochemistry, trace element geochemistry, coal petrology, coal geology, mineralogy and petrology to systematically investigate the geochemical behavior of Au and other associated elements of Upper Permian coal-bearing formation in Western Guizhou Province, find out the main distribution characteristics of Au in coals and reveal the geological controlling factors of Au geochemical anomaly. On the basis of the mathematical statistical analysis and the data from the sequential chemical extraction , the occurrence of gold in coals and the main gold-bearing mineral are analyzed .It reveals the complexity of the occurrence of gold in coals that exists mainly in inorganic forms, and the pyrite in coals may be the main carrier mineral of gold. Further more, this paper discusses the material sources and the processes of transportation deposition and enrichment of gold in coals, establishes the geological and geochemical mechanism for the migration enrichment of gold in coals. The results of the study have theoretical and realistic significance to improve the theory of geochemical behavior and scientifically predict the mineral resource potentials of scattered metals.The research comes to the results:①The concentration of gold in Upper Permian coal in southwest Guizhou Province is generally higher than the crust abundance and the average concentration of gold in America or the other coal-accumulating periods in China. The anomalous concentration of gold in shale comes to be highest. Areas where the anomalous concentration of gold is really high are mainly distributed in the"triangle"area including NW-trending Ziyun—Yadu deep fault, NE-trending Shizong—Guiyang deep fault and EW-trending Kaiyuan--Pingtang fault.②There are many reasons for instability of the Upper Yangtze platform: the intense activity of Emei mantle plume in Late Permian, many fault zones and sedimentary fracture. It is not only the main factors of coal metamorphism, but also providing the conditions of deep magmatic activities and low-temperature hydrothermal. Further more, it is considered to be the main geological factors of anomalous concentration of gold in coals of Western Guizhou, Province.③Though the occurrence state of gold in coals in research area is complicated, the inorganic affinity is stronger than the organic affinity according to the mathematical statistics analysis and the results from the sequential chemical extraction.The gold in coals exists mainly in inorganic forms, that is , nano-gold is the form of existence in coal. The pyrite in coals may be the main carrier mineral of gold.④The gold in coals comes from multiple sources, but the endophytic source of gold (magmatic activity and epithermal fluid) is the main material source of the gold in coals in Western Guizhou Province based on the relation among gold, Emei mantle plume and epithermal fluid. The fault belt not only provides paleo-geotherm for epithermal fluid, but also becomes the channel for the gold contained in the epithermal fluid.⑤Tectonic movements, epithermal fluid and lithofacies paleogeography have significant effect on the activation, transportation and precipitation of the gold in coals. The enrichment process of the gold in coals in Western Guizhou Province is actually the activation→transportation→enrichment process of the gold along with the epithermal fluid that is resulted from Emei mantle plume activity coming from mantle to crust. In accordance with the distribution characteristics, enrichment regularities and occurrence modes of gold in coals, the enrichment type of gold in coals is from deep faulted zone to low temperature hydrothermal activation.There are 55 figures, 33 tables and 286 references in the dissertation.