Evolution Of The Youjiang Sedimentary Basin And Metallogenesis Of Micro-Disseminated Gold Deposits Abstract

Geotectonically, the Youjiang sedimentary basin was referred as Youjiang Yindosinian folded belt. Triassic turbidites accumulated in the basin were derived from surrounding ancient lands including Yuebei, Jiangnan, and Yunkai. Tectonic setting of the sedimentary basin was in between an active continental margin and a continental island arc. Tectono -sedimentary evolution of the basin may be divided into three stages: continental margin rift, back-arc rift, and depression basin.Northwestern Guangxi Province comprises the main part of the Youjiang basin. In this area, most of micro-disseminated gold deposits are hosted by the Middle Triassic turbidites. The immediate host siliceous rocks of typical deposits (Jinya, Gaolong) are of hydrothermal sedimentary origin. Gold ore bodies are layer-like and generally concordant with their host rocks. Abundant relict synsedimentary fabrics are preserved in the ores. Several lines of evidence, including studies on geochemistry of trace elements and rare earth elements, isotopes (S, C, O, D, and Pb), and fluid inclusions, suggest that the main ore-forming materials were scavenged from the contemporaneous sediments and that the fluids were predominantly derived from deep circulated basin brines, recharged by meteoric water, and ancient seawater. The deposits are syngenetic in origin.Gold mineralization in the studied area is closely related to the evolution of the Youjiang basin. Rift setting, lithofacies and palaeogeography of the basin, physical properties of the sediments, and synsedimentary faulting have played important roles in formation of the deposits.