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The Geological Characteristics And Deposit Genesis Of Sandstone Copper Deposit In Guihua Dacun Of Chuxiong Basin

Posted on:2017-04-15Degree:MasterType:Thesis
Country:ChinaCandidate:T Y HuFull Text:PDF
GTID:2180330488971087Subject:Mineralogy, petrology of ore deposits
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Chuxiong basin and its adjacent regions in Yunnan province are China’s famous sandstone copper deposit enrichment region in Mesozoic-Cenozoic, which is situated in the southwest of the Yangtze platform. Predecessors made an extensive research of Chuxiong basin and its adjacent regions sandstone copper deposit. Through the research based on the sedimentary formation of Chuxiong basin, ancient geography, ancient climate, etc. predecessors put forward the metallogenic geological background and the differences of basin evolution. Because of factors about the numerous seam of ore deposit, structure controlling ore pattern, the characteristics of ore-bearing rock series stratum and the sedimentary environment. There are many divergences in predecessors research work, it is difficult to sum up the ore-controlling factors of whole area sandstone copper deposit, metallogenic process and development mechanism completely.Used the Dacun copper mine as the research object, systematically analyzed the ore-bearing rock series stratum characteristics and sedimentary environment. Studying of syncline internal different elevation on the three middle level section of in Pacun, using XRD and electron probe method, analyzed the crystal structure of main ore mineral and the changing rule of the mineral composition. Used the C, H, O, S isotopic data, explained its genesis of mineral deposit.This research mainly achieved the following results:1. Systematically found out the strata, structure and characteristics of ore-bearing rock series stratum and analyzed its sedimentary environment.(1) A new understanding of lithological features of ore-bearing rock series, predecessors thought, the Matoushan formation sandstone is purple or green feldspar quartz sandstone, the conglomeratic on top of it; At the Jiangdihe formation tuffaceous green colored mudstone layer of carbonaceous shale and marl of mixed rock series. After this paper studies, we knew that the Matoushan formation sandstone containing tuffaceous fine in sandstone. On the basis of predecessor’s work, we found in lower cretaceous the Puchanghe formation has andesite thin level of output. That shows before the sedimentation of the ore-bearing rock series having been volcanic activity in the area.(2) Analyzed the sedimentary environment of mineral-bearing system. When Matoushan began to deposit, the foot would deposit the sandstone.2. Systematically detected the mineralization types of copper deposits in this area and its geological characteristics, established ore tumble belt model.(1) There are three kinds of sandstone copper deposit mineralization types in area, breccia type, mudstone type mineralization is the main mineralized types of copper deposits in this area. For the profile, conglomerate type sand 'sandstone type (including gravel) ' mudstone type is combined output from bottom to top, continuous ore tumble belt.(2) Analysis the mineralization zonation characteristics of the Dacun copper. In the Dacun copper, there is no obvious mineralization zonation in the horizontal direction, but in the vertical zonation it is obvious ore tumble belt phenomenon, that is from chalcocite & bornite zonation'bornite zonation' bornite &chalcopyrite zonation'chalcopyrite zonation from bottom to top.(3) The Dacun area is located on the sedimentary transform zone, which is from meandering river to delta, the Matoushan formation of top conglomerate layer pinch out disappeared in the region, who makes the upper Jiangdihe formation set low calcareous mudstone cover directly on the underlying sandstone of the Matoushan.3. Using powder XRD diffraction and electron probe analysis, found out the main ore mineral crystal structure, chemical composition characteristics and transformation law. Especially Dacun copper deposit. We used the C-H-O-S isotope traced the fluid characteristics and source.(1) The main minerals were ore minerals chalcocite、bornite and chalcopyrite, which cell parameter is different to the standard mineral.The XRD analysis and electron probe analysis data can’t carry out match analysis, Therefore, it’s impossible to accurately determine the main reason for the change parameters of the unit cell parameter.(2) Cu deposit contain a penetrating mineral、bornite、chalcopyrite、trace element. And the trend is gradually decreasing from the bottom to the top.(3) δ34S of ore mineral in the area are mainly distributed in around-27.1%o~-10.1‰, displayed biogenic sulfur in mineralization.4. Explained the cause of the sandstone copper deposit comprehensively.Copper deposits in the area mainly are the products of the same sedimentary rock deformation effect. Copper deposits are mainly divided into two metallogenic stages:(1) Synsedimentary ore-forming stages:In ore-bearing sedimentary process, deep-water lake basin formed by the rift subsidence or relatively static water environment facing delta in the areas, the minerals which are transported by adsorption form in solution, suspended particles and clay mineral, happened chemical differentiation of sediment deposition along with the ore-bearing rock series mechanical settlement. Finally, due to the large number of precipitation of iron, the copper concentration is relatively higher, the replacement of early Eh high seam lower pyrite, chalcopyrite, bornite forms chalcocite.(2) The late hydrothermal fluidization stages:The stage is characterized by typical sand liquefaction, under the action of strong power of the tectonic deformate, the former stage formation of mineral is upward into the upper mudstone layer together. At the same time, with the mineral and fluid activation of sedimentary mineralization stages, including bedding or wear layer upward migration of ore fluid, filling in structure or wear layers of cleavage and bedding or wear layer is formed in the geode vein or miarolitic and sandstone veins star point of mineralization.(3)The supergene reformation stage:Sichuan movement, in Paleocene-Eocene, made the Mesozoic strata in the area generation large-scale fold and fracture. The ore-bearing bed of this suffered from groundwater leaching, formed the malachite, limonite supergene mineralization.
Keywords/Search Tags:ore-bearing rock formation, geological character, Ore deposit genesis, sandstone copper deposit, Chuxiong basin Dacun
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