Enrichment Regularity And Mechanism Of Dispersed Elements Cd, Ge And Ga Of Typical Lead-Zinc Deposits In The Eastern Edge Of Kangdian Axis

The Eastern edge of Kangdian axis, is located in the combined zone of circum-Pacific tectonic and Tethys tectonic domains. It is a important tectonic cell of the Songpan—Ganzhi in India-China folded zone. The area has gone through a long and complex geologic-tectonic evolutionary history since late Archean. A great quantity of metal mineral resources had been formed in this area. There into, they include lead-zinc deposits of enrichment dispersed elements such as cadmium (Cd), germanium (Ge) and gallium (Ga). Several giant (supergiant) typical lead-zinc deposits (such as Tianbaoshan deposit in Sichuan, Daliangzi deposit in Sichuan and Huize deposit in Yunnan) were studied in this article. Based on systematic field investigations, the article described in detail the geologic and geochemical characteristics of three typical Pb-Zn deposits from Tianbaoshan, Daliangzi and Huize. Study in door, based on common observation of polished sections and thin sections, the author synthesize to use chemical analysis, ICP-MS analysis and electronic microprobe (EMP) analysis to technical means. The thesis has finished systematic research in many aspects such as the major elements, trace elements and lead, sulfur, carbon isotope geochemistry of rocks (ores) and minerals in deposits, the content of dispersed elements cadmium (Cd) and germanium(Ge) and gallium(Ga), the occurrence and characteristics of enrichment of dispersed elements cadmium(Cd) and germanium(Ge) and gallium(Ga). Combined with the evolution of the regional geology and structure, the article has researched the geological and structure conditions and the mineralization of lead-zinc deposits in the eastern edge Kangdian axis, revealed the enrichment occurrence and enrichment mechanism of dispersed elements cadmium (Cd), germanium(Ge) and gallium(Ga) in the lead-zinc deposits, and summed up the enrichment regularity of dispersed elements cadmium(Cd), germanium(Ge) and gallium(Ga). In this paper, to obtain new understanding as following:1. The host rock of occurrence ore are all carbonate rock in typical lead-zinc deposits in the eastern edge of Kangdian axis. There into, deposits of Tianbaoshan and Daliangzi are dolomite of the upper Sinian Dengying group, Huize deposit is dolomite (or gray dolomite) of under Carboniferous Baizuo group. These layers are all rich ore-forming elements Zn and Pb, as well as dispersed elements cadmium (Cd) et al. The contents of Zn in no-alteration host rocks of occurrence ore were obviously higher than Clarke number of similar rocks in the earth's crust. Some of rocks may be higher to over several-ten times of Clarke number. Lead also has a degree of enrichment in various types of rock, but degree of enrichment is below than Zn. The contents of dispersed element cadmium(Cd) is commonly higher upper ten times of Clarke number of similar rocks in the earth's crust. But the contents of dispersed element germanium and gallium are similar to Clarke number of same rocks in the earth's crust. From this we can see, the high based value of zinc,lead and cadmium et al elements in region rocks, supply the matter foundation for the Pb-Zn mineralization and the enrichment of dispersed elements.2. ICP-MS analysis and electronic microprobe (EMP) analysis showed that disposed elements cadmium(Cd), germanium(Ge)and gallium(Ga) are mainly as the form of isomorphism occurrence in the primary sulfide such as sphalerite, galena and pyrite. A small amount of them may be occurrence as ultra-micro independence minerals. Cadmium(Cd) is major occurrence in sphalerite , germanium(Ge) and gallium(Ga) are major occurrence in galena.3. .According to the characteristics of the ore bodies occurrence, combined with the data of lead isotope model age of deposits, the author thought that the forming ore times are later than layers of occurrence ore in the eastern edge of Kangdian axis. They are typical epigenetic deposits. The lead isotope tectonic evolution showed that ore leads of lead- zinc deposits in the eastern edge of Kangdian axis come mainly from the upper crust, especially the orogenic belt.4. The host rocks of occurrence ore, ores and sphalerite have similar geochemistry characteristics of rare earth elements. They showed in total relatively enrichment light rare earth, europium(Eu) and cerium(Ce) were weak negative anomaly, the distribution curve of rare earth elements trended to right. It illustrated that the rare earth elements composition characteristics of ores inherited the characteristics of rare earth elements composition of the host rock of occurrence ore. They reflected that the rare earth elements of ore come from the layers of occurrence ore.5. The sulfur isotope composition of sulfide from typical lead-zinc deposits in the eastern edge of Kangdian axis are totally similar to the sulfur isotope composition of marine sulphate which the layers of occurrence ore form times. They illustrated that sulfur of deposits mainly come from the layers of occurrence ore. Butδ³⁴S value of sulphide from the Tianbaoshan deposit is obviously lower thanδ³⁴S value of sulphide from marine sulphate of Sinian period. It may be caused by bacterial reduction, mineralization was in the environment of relatively reduction.6. For the first time, this article summed up the state of occurrence and distribution laws in space of dispersed elements from the typical lead-zinc deposits in the eastern edge of Kang-Dian axis. Dispersed elements cadmium(Cd), germanium(Ge) and gallium(Ga) are mainly as omorphism and mechanical mixed matters in single minerals of sulfides, especially in sphalerite and galena, but the degrees of enrichment are relatively lower. From west to east, in other words, from Tianbaoshan deposit to Daliangzi deposit to Huize deposit, enrichment of dispersed elements had clearly zoning appearance in space. They showed that deposits had the varying tendency of cadmium and gallium -rich to cadmium - rich to germanium-rich.7. Pb, Zn et al metal elements mainly were activated and moved as complex compound of chloride. Cadmium(Cd), germanium(Ge) and gallium(Ga) et al dispersed elements may be also to form part of a complex compound of chloride or to be adsorbed together by complex compound of Pb, Zn and to move with them. The heat energy brought by ore-bearing hydrothermal caused that the thermal degradation of organic matter in mineralization host rocks produced methane. It resulted reduction of sulphate and deposition of metal sulfides.