Geological And Geochemical Characteristics,Metallogenesis Of Hutouya Polymetallic Deposit,Qinghai Province

Abstract:Hutouya polymetallic deposit is situated in the orogenic belt of Western East Kunlun, where Paleo-Asian plate and Paleo-Tethyan tectonic domain converged, and it is assigned to Qimantage metallogenic subzone of East Kunlun metallogenic belt. Based on field survey of the deposit, identification of thin sections and polished blocks, characteristics of fluid inclusions, S and Pb stable isotope, rocks and ores’ geochemistry analysis, etc., the geological and geochemical characteristics, genesis have been studied in this thesis.The orebodies are mainly formed in contact zone of magmatites and wallrocks, or in the carbonate rocks, with Fe-Cu orebodies formed in the margin of magmatites, and Cu-Pb-Zn orebodies in the wallrocks, relied on field geological survey. Metasomatic texture, massive and disseminated structures were observed obviously in the various ores under microscope and in the field.3epochs and6stages have been divided in this research, while orebodies were formed in epochs of skarn and quartz-sulfide. Skarnization, silicification, fluorination and carbonation are the main kinds of wallrock alteration discovered in this research.According to the geochemistry of intrusions and wallrocks, ore-forming intrusions are K-feldspar granite and adamellite in Indosinian epoch, with weak peraluminous, high potassium and calc-alkaline characteristics. Furthermore, intrusions in the district are inferred to the products of crustal materials’evolution, while for intrusions, the evolution sequence is demonstrated to be dioritoid, porphyraceous granodiorite, porphyraceous adamellite, granite porphyry, syenogranite, respectively, from early to late epoch.Three categories of fluid inclusion have been distinguished based on petrographic and microthermometric criteria:daughter mineral-bearing fluid inclusions (A type), liquid-rich aqueous inclusions (B type), and vapor-rich aqueous inclusions (C type). The homogenization temperature of ore-forming fluid which has low density and immiscible characteristics ranges from170℃to550℃, with salinity of0to24.1wt.%equivalent of NaCl. From the early period of mineralization to the late, homogenization temperature and salinity decreased gradually. The depth of metallogenesis was estimated to be1.6～4.7km from surface.It is inferred that metallogenic materials mainly derived from magma which was formed by the mixture of crustal and mantle materials, but with dominant percentage of crustal materials, with a small proportion from wallrocks, while the S abundance from wallrocks gained progressively when orebodies are formed in distal intrusions, in terms of S and Pb isotope characteristics. Granitoid intrusions are received to have the potential to offer metal elements when mineralized by the analyses of ore-controlling factors. It is illustrated that intrusions, wallrocks and orebodies were in the same ore-forming system, in accordance with the REE characteristics.This deposit was formed in settings of post-collision orogenic belt, with manifest control by strata, intrusion, structure, and obvious metasomatism, which can be illustrated to be poly-metallic skarn deposit. Moreover, metallogenic regularities, prospecting criteria have been summarized in this thesis. Furthermore, this research can be utilized to guide exploration in the district.