Abstract:
The northern margin of the West Tianshan in Xinjiang is well endowed with epithermal gold deposits. These deposits are primarily hosted in the continental volcanic rocks of the Late Devonian-Early Carboniferous Dahalajunshan Formation and are concentrated in the Tulasu and Yelimodun volcanic fault-depression basins and the Wusunshan area. Based on a systematic review of the geological and geochemical characteristics of typical gold deposits such as Axi, Jingxi-Yermand, and Tawuerbieke in the region, this paper analyzes the relationship between gold mineralization and regional tectonic-magmatic evolution, and discusses the post-mineralization modification and preservation processes as well as their implications for mineral exploration. The epithermal gold deposits in the northern margin of the West Tianshan include various types such as low-sulfidation, high-sulfidation, and porphyry-epithermal transitional types, which exhibit significant differences in ore body occurrence, ore texture, mineral assemblages, and alteration characteristics. The ore-forming materials are mainly derived from the host volcanic-subvolcanic rocks, and the ore-forming fluids consist primarily of magmatic hydrothermal fluids (high-sulfidation type), meteoric water (low-sulfidation type), or a mixture of these two fluids (porphyry-epithermal transitional type). Gold precipitation mechanisms include fluid boiling, water-rock interaction, and fluid mixing. The mineralization age is mainly concentrated in the Late Devonian-Early Carboniferous, formed in a back-arc extensional environment during the peak subduction of the North Tianshan and South Tianshan oceans. After their formation, the deposits underwent a complex modification and preservation history. The epithermal gold deposits in the Tulasu and Yelimodun basins have been preserved due to relatively weak erosion, and their deep sections hold potential for the discovery of porphyry-skarn-type Cu-Au polymetallic deposits. In contrast, the peripheral areas of the basins have experienced higher degrees of erosion, leading to the destruction of most epithermal deposits, but the prospects for porphyry- and skarn-type deposits remain favorable.