The Geology, Geochemistry And Metallogenesis Of The Typical Lead-zinc Deposits, Southern Tianshan Orogeny

The South Tianshan Orogeny is located on the northwestern margin of the Tarim Basin, which is one of the important lead-zinc metallogenic belts in China. Although many researches have been carried on there, there are still many controversies, such as the metallogenesis and the metallogenic model of the deposits. Based on the former researches, we choose three typical lead-zinc deposits, Shalitashi, Wulagen and Hushibulake, for study. The thesis is focusing on the geological characteristics, metallogenesis, source of the metal, geochronology and metallogenic model. The host rocks of the lead-zinc deposits in South Tianshan Orogeny are mainly carbonat and sandstone. Controlled by the strata and the fault, the deposits consisting of lens, nested and tubular orebodies are typical epigenetic. The sulfate minerals in the ore are of simple assemblage. The alterations in the wall rocks are weakly developed. The similar rare earth elements and trace elements normalized patterns suggests that the metals in the ores are likely derived from the sediments in the basin of high metal content. The research on the lead isotopie in the sulfates also supports the conclusion. The characteristics of the sulfur isotope (δ³⁴S=-27.9-27.2) imply that the sources of the reduced sulfur are derived form a varity of crustal sources. Based on the analysis of the geological characteristics and the isotopic geochronology, we conclude that the lead-zinc deposits in the South Tianshan Orogeny dominantly formed in the late Paleozoic and the Cenozoic, which probably have some genetic relations with the continent-continent collision caused by the closure of the South Tianshan Ocean and the compression caused by the convergency of the India Plate and the Eurasian Plate. The typical lead-zinc deposits in South Tianshan Orogeny can be classificated into the Mississipi-Valley type lead-zinc deposits which has genetic relations with the brine in the basin. Based on the geological and geochemical charactersitcs of deposits, we divide the lead-zinc metallogeny into three stages: the formation of the potential metal source, the formation of the basin brine and the deposition of the metal.