The Study On Minerogenic Series Of Epithermal Deposits In Mid-southern Segment Of The Sanjiang Orogenic Belt, Southwest China

Comprehensive analysis of the regional metallogenic background in the MSOB including stratigraphy, tectonic settings, geological feature and geochemical characteristics of typical ore deposits and chronology in the different tectonic units. Based on those works and tectonic evolution of the Sanjiang orogenic belt, I try to divide the MSOB into three metallogenic subseries:(1) Hot spring type Au metallogenic subseries in the Tengchong which form in the volcanic arcs causing by the India-Asia continental collision.(2) Epithermal Pb-Zn metallogenic subseries hosted in the late Paleozoic Carbonate in the Baoshan block which occur in the extension environment after the close of Middle Tethys ocean.(3) Weishan porphyry-epithermal polymetallic metallogenic subseries in the Lanping-Simao strike-slip and pull-apart basin which form under continental collision during Himalayan.Regional structure and orefield structure reveal that the spatial distribution of metallogenic subseries and associated intrusions controlled by regional deep fault belt and orefield structure controlled ore bodies emplacement and styles. On the insight of field work and observation of thin sections, it is recognized that ore mineralization characterized by open space and cavity filling in the MSOB. The ore mineral assemblage and walk-rock alteration are very simple but ore mineral assemblages are difference in each metallogenic subseries. On the basis of the former data and the data of trace elements in the sphalerite by LA-ICPMS, ore-forming temperatures of the MSOB are below300℃. The study of hydrogen-oxygen isotope display that the metallogenic fluid at least has two sources:(1) ore-forming fluid migration along the faults including brine in the stratigraphy and meteoric waters.(2) magmatic hydrothermal fluids. The δ34S values of sulfide in the MSOB are between-16.0‰～6.O%o which mainly concentrated on-6.0‰～6.0‰suggesting that sulfur mainly derived from magma, with minor other sources. The source of mineralization multiple members in the MSOB which is associated with background value of stratigraphy in each metallogenic subseries. Pre-enrichment of metallogenetic elements in the whole rocks are extracted by deep fluid and down circulating fluid.Systematic Chronology study demonstrate that the formation age of epithermal deposits in the MSOB is closely related to tectonic evolution of the Sanjiang orogenic belt. The Tengchong and Weishan metallogenic subseries form during post-collision (25Ma-now) and late-collision (～34.11±0.36Ma) in Himalayan, respectively. The formation age of Baoshan Pb-Zn metallogenic subseries may be related to the close of Middle Tethys ocean. Through the comprehensive analysis of all data, a metallogenic model is proposed for epithermal metallogenic series in the MSOB. Based on the model, the prospecting direction is pointed out in adjacent regions under the guidance of theory of minerogenic series.