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Characteristics And Genesis Of The Fenghuangshan Skarn Copper Deposit, Tongling, Anhui Province

Posted on:2016-03-18Degree:DoctorType:Dissertation
Country:ChinaCandidate:A P ZhangFull Text:PDF
GTID:1220330461995857Subject:Mineralogy, petrology, ore deposits
Abstract/Summary:PDF Full Text Request
The Fenghuangshan copper deposit is one of the typical skarn deposits in the Tongling ore district of the Middle-Lower Yangtze River metallogenic belt. It is representative in crust-mantle metallogeny. A detailed geological, petrological, mineralogical and geochemical study has been carried out on the Fenghuangshan deposit, with a focus on the discrimination of the coupling relationship between the crust-mantle interaction and metallogeny and analysis of its genesis.Field investigation and petrographic observation indicate the occurrence of a series of microscopic mafic enclaves in the Fenghuangshan intrusion, which consists mainly of granodiorite and quartz monzodiorite. The mineralogical and geochemical analyses suggest that the Fenghuangshan intrusive rocks belong to a high-K, calc-alkaline, and metaluminous series with mixing source of crust with mantle. The various magmatic disequilibrium textures observed under a microscopy display the existence of magma mixing in a deep magma chamber during the formation of the pluton. Based on mineral assemblage and texture and structure, ores are divided into copper-bearing skarn and quartz-sulfide vein types. The former is characterized by massive, disseminated, veinlet-disseminated, and mottled structures, and the latter by vein structure. There occur early granular and late vein types of garnet. The granular garnet is dominated by andradite, while the vein garnet by grossular.Underground section investigation and measurement show the occurrence of orebodies in the contact zones between the intrusion and carbonate strata and their nearby wall rocks and the compound controlling of them by the contact zones and fractures. There are two types of alteration and mineralization zones in the orefield. From intrusion to wall rock occur in order intrusion, skarn, orebody, and carbonate wall rock in the first type of zone, and intrusion, orebody 1(fracture), skarn, orebody 2, and carbonate wall rock in the second type of zone. The difference between the two zones is the existence of another orebody near the side of the intrusion in the second zone under the influence of the fracture. The vein cutting with mineral assemblage and texture and structure are consistent with the contributions of five stages of hydrothermal activities, including prograde skarn, retrograde skarn, oxide, quartz sulfide(the main mineralization stage), and carbonate stages, to the formation of the Fenghuangshan copper deposit. There are three types of fluid inclusions in minerals, including liquid-rich, vapor-rich, and three-phase fluid inclusions. The gas and liquid phases in them are dominated by H2 O. The ore-forming fluids were originated mainly from magmatic water, and mixed with increasing amounts of meteoric water during the process of fluid evolution. From the early stage to the late stage, there is an evolution from high-temperature, high-salinity ore-forming fluids to low-temperature, low-salinity fluids.On the basis of this study, it is suggested that the genesis of Fenghuangshan copper deposit has close ties with crust-mantle magmatic-hydrothermal mineralization. A large amount of ore-forming material such as Cu, Fe and S could be carried from lower crust and upper mantle by the magma with mixing source of crust with mantle. The contact metasomatism would be responsible for the formation of the skarns during emplacement of this magma upto the Mesozoic carbonate strata. The copper-bearing skarn ores were formed by hydrothermal metasomatism, and the quartz-sulfide vein ores by hydrothermal filling.
Keywords/Search Tags:deposit geology, geochemistry, skarn copper deposit, crust-mantle interaction, ore deposit genesis, Fenghuangshan in Anhui province
PDF Full Text Request
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