General Study On The Stable Isotope Geochemistry Of The Daliangzi Pb-Zn Deposit In Huidong, Sichuan

The Daliangzi Pb-Zn deposit, located in Huidong County, Sichuan Province, is one of the famous large Pb-Zn deposits in the contiguous region of Sichuan-Yunnan-Guizhou. Its geotectonic position is on the Kangdian basement complex belt under the secondary upper Yangtze landmass tectonic unit, belonging to the first-order Yangtze landmass tectonic unit. This area has undergone multiphase and multistage magmatic-hydrothermal events and metamorphic-deformative effects, roughly experienced the basal formation stage, caprock formation stage, intracontinental rift stage, foreland basin and orogenic belt formation stage. The Daliangzi Pb-Zn deposit in the Sichuan-Yunnan-Guizhou Pb-Zn metallogenic province is within the triangle area of the Anninghe-Lvzhijiang fracture, the Mile-Shizong fracture and the Kangding-Shuicheng fracture. Almost all the formations from each time are distributed in this region, lacking of individual formation.The Sinian is the first stable epeiric sea sedimentary strata in the Yangtze block, and its lithology is mainly carbonate rocks mixed with clastic rocks. The tectonic attribute and regional geological features all above had laid favorable metallogenic conditions for forming the Daliangzi Pb-Zn deposit.Exposed strata in the Daliangzi mining area include the Sinian Dengying Formation and the Cambrian Qiongzhusi Formation, and the Dengying Formation is the main ore-bearing strata of ore bodies. Geological structures in the mining area include folds, joints and fractures.Fracture structures are especially developed, mainly including NWW, NW, EW and NE faults which are the main ore-controlling and ore-bearing structural systems. Exposed magmatic rocks and metamorphic rocks are not found in the mining area. The Daliangzi Pb-Zn ore bodies consist of the No.1 and No.2 orebody, the former is the main ore body and the latter orebody scale is small which had already been picked. The ore body shape is irregular lenticular, cystic, veined and net veined. Ore mineral components are simple, mainly composed of sulfide minerals, oxide minerals and non-metallic minerals. Sulfide minerals include sphalerite, galena, pyrite, chalcopyrite, and a few arsenopyrite, silver tetrahedrite, pyrargyrite and marcasite. Oxide minerals include smithsonite, cerussite, limonite, hydrozincite, anglesite, hemimorphite, etc. Non-metallic minerals include calcite, dolomite and quartz. In addition, they are also associated with silver, cadmium, sulfur, germanium, gallium and other useful components. The most common ore structures are brecciated structure, block structure, veined-net veined structure and disseminated structure, etc. The main ore textures are granular texture, metasomatic corrosion texture and surface texture. Wall rock alteration in the mining area is not strong, mainly including carbonatization, carbonization, siliconization, pyritization, limonitization and malachite mineralization.The alteration types are often not separately output, overlapping on the space and having a close relationship with mineralization.In this paper, on the basis of detailed field geological survey, collecting ore rocks which can represent main orebody main metallogenic phase formation of the ore mining area as the research objects, to mainly carry out the stable isotope tests and analyses of the ore minerals. C, O isotope test and analysis results show that the ore-hosting rock(dolomite) of the Daliangzi Pb-Zn deposit were formed in the marine sedimentary environment, mainly derived from the dissolution of marine carbonate, hydrothermal calcite fluid was also mainly from the dissolution of carbonate rocks, thus the carbon in the metallogenic fluid mainly derived from the dissolved marine carbonate. The carbon isotopic composition can be affected by the organic carbon, atmospheric precipitation and the external environment. H, O isotope test and analysis results show that the water source of ore-forming fluid of the Daliangzi Pb-Zn deposit was mainly from the mixture of evaporated basin brine and atmospheric precipitation, organic matter might be involved in the mineralization. S isotope test results show that the sulfur has obvious characteristics of crust source, mostly come from the thermochemical reduction of seawater sulfate in the marine sedimentary strata of the same period, while some sulfur might come from the bacterial sulfate reduction in the sedimentary diagenetic process. Pb isotope variation range is wide, having the nature of mixed leads.Ore rocks and Huili group metamorphic rocks of the basement provided the major lead source for the ore deposit, but the join of a small amount of mantle-derived lead and(or) lower crust lead could not be ruled out.The extensional “minus flower structure” strike-slip system, “black crushed zone” and the carbonate rocks constitute the three-level ore-controlling elements of the Daliangzi Pb-Zn deposit. From indosinian to yanshanian period, the gravity gradient and the tectonic compression stress from the Longmenshan orogeny drove the ore-forming fluid migrating with large-scale and long distance, leaching ore-forming materials from the basement and surrounding rocks, and gathering inside the “minus flower structure”. The organic fluid of the upper Cambrian reducing formation penetrated along the fracture, and mixed the ore-forming fluid, prompting metal minerals to enrich and form the deposit due to changes of chemical and physical conditions for pressure drop and reduction of the organic matter. At the same time, clastics riched in organic matter formed the “black crushed zone” in the fault zones or formed carbonaceous cement in cataclastic rock fissures, further providing a good space for ore-transimitting, ore-blending and ore-containing. The Daliangzi Pb-Zn deposit has the deep and periphery ore prospecting potential, both existing concealed ore bodies, and is divided into 6 predicting workspaces.To sum up, the author of this paper thinks that the Daliangzi Pb-Zn deposit is a typical Mississippi Valley-type(MVT) Pb-Zn deposit, and it can absolutely compare to the Tianbaoshan Pb-Zn deposit of Huili, Huize(Qilinchang ore deposit, Kuangshanchang ore deposit) ore deposit of Yunnan, and the American Mississippi Valley Pb-Zn ore deposit.