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Study On The Ore-Forming Fluid Of Nihe Iron Deposit In Lujiang County,Anhui Province

Posted on:2012-07-12Degree:MasterType:Thesis
Country:ChinaCandidate:L HaoFull Text:PDF
GTID:2230330395956117Subject:Mineralogy, petrology, ore deposits
Abstract/Summary:PDF Full Text Request
The Nihe deposit is a new discovered large scale iron-sulfur-anhydrite deposit in the Luzong basin. Some work has been done on the deposit geology so far. In the Nihe iron deposit occurs multiple stages and different types anhydrite, formed anhydrite-pyroxene-magnetite assemblage, a special mineral assemblage. From the study of the fluid inclusions in anhydrite, we can constrain the precise physical chemical conditions of the different hydrothermal stages. This contribution is not only gained some evidence for understand the genetic and establish the metallogenic model of the Nihe iron deposit, but also have the significances for research and the exploration.This paper taking the Nihe iron deposit as the subject described the mineralization types, the geology characteristics and determined the stages of mineralization and the minerals assemblage. The study started with the microscope work and the laboratory analyses work, accompanied with the fluid inclusions microthermal analyses, aims to determine the fluids characteristics and to infer the process of fluid evolution and the ore-forming mechanism, establish the metallogenic model.The volcanic rocks of the Zhuanqiao formation and Shuangmiao Formation in the Nihe district are shoshonitic series rocks. The main intrusions in the mining district are syenite and diorite porphyry. The orebodies are controlled by the diorite porphyry dome. The main ore minerals are magnetite, and pyrite. The main gangue minerals are anhydrite, pyroxene quartz, apatite and garnet. The iron ore structures mainly include massive structure, disseminated structure and vein structure. The ore texture includes euhedral-subhedral granular texture, anhedral granular texture, metasomatic pseudomor-phic texture, and metasomatic relict texture. The alteration of the Nihe iron deposit can be divided into pyroxene (garnet)-anhydrite-magnetite alteration zone, chlorite-epidote-carbonate alteration zone and argillation-siliceous alteration zone. The major hydrothermal epoch of the Nihe iron deposit can be divided into five stages, pyroxene (garnet)-anhydrite-magnetite stage, pyrite-anhydrite-magnetite stage, chlorite-epidote-carbonate stage, kaolinite-anhydrite-quartz-pyrite stage and barite-calcite-anhydrite stage. The fluid inclusions in the gangue minerals anhydrite, apatite and calcite from different stages are mainly NaCl-H2O fluids, no pure CO2fluid inclusions in these minerals. Microthermetric data shows that the early stage fluids are high temperature, moderate salinity and moderate densities. With the ore-forming progresses, the fluid temperature and salinity were gradually reduced, however the density of fluid increasing. The homogeneous temperatures of the early stage fluids were concentrated in460.0-380.0℃, formed anhydrite-pyroxene-magnetite assemblage, and then with the temperature decrease to350.0~270.0℃, formed magnetite-anhydrite-pyrite vein, the temperature of the later stage is250.0~190.0℃, formed anhydrite, quartz and pyrite. Their homogeneous temperatures of the last stage were concentrated in190.0~150.0℃.From early stage to later stage, the average salinity changes from14.11wt%NaCleq, with average density0.72g/cm3, to3.26wt%NaCleq with average density0.93g/cm3.The Nihe iron deposit is a replacement infill deposit, with the fluids temperature from high to moderate-low. The physical chemistry parameters of temperature, pressure, components, pH values and fo2、fs2controls the alteration, minerals assemblage and the deposition of ore minerals. According to the microthermetric data of the different stages, this study determined the evolution and deposition of the ore-forming fluids. The Nihe iron deposit has closely relationships with the subvolcanic magmatic (diorite porphyry) thermal fluids activity, which belongs to the generalized porphyry iron deposit.
Keywords/Search Tags:Luzong basin, Nihe iron deposit, Fluid inclusion, Ore-FormingFluid, Physical and chemical conditions, metallogenic model
PDF Full Text Request
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