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Characteristic And Genesis Of Tongshan Skarn-type Copper Deposit In Anhui Province

Posted on:2012-11-03Degree:DoctorType:Dissertation
Country:ChinaCandidate:Z Y ZhangFull Text:PDF
GTID:1100330332488819Subject:Mineralogy, petrology, ore deposits
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Tongshan skarn copper deposit is located in the Anqing-Guichi ore-clustered district of the Lower Yangtze River metallogenic belt. Ore host strata include the Qixia Formation of the Lower Permian and the Huanglong Formation of the Middle Carboniferous. Folds and faults are important ore control structures. Intrusions formed during the intense magmatism of the Mesozoic Era consist of quartz diorite porphyry, quartz monzonite porphyry and granodiorite porphyry. Copper-bearing skarns on a certain scale occur in the contact zone between the granodiorite porphyry and ore host strata. A detailed study has been carried out on the skarn deposit in this area, with a focus on an analysis of skarn evolution and ore genesis so as to set up a mode of skarn mineralization. The following are major achievements obtained in this dissertation.1.The Tongshan intrusion is dated at 145.1±1.2 Ma, close to the metallogenic age (147.5±2.3Ma). Emplacement of the crust-mantle syntactic magma is responsible for the formation of this intrusion. The crystallization conditions of minerals are estimated to be temperature of 750 to 755℃and pressure of 1.16 to 1.64 kb. The tectonic setting for the formation of the pluton is defined as post collision uplift to late orogeny.2. Skarn in the Tongshan copper deposit indicates an evident temporal and spatial Zoning. Horizontally, garnet is rich in the skarn near the intrusion, but diopside is rich in the skarn far from the intrusion. Hedenbergite skarn occurs near the marble zone, but limestone with stronger silicification exists far away from the marble zone. Vertically, hornfel, calcareous skarn and magnesian skarn occur in order from shallow to deep. Enrichment of Cu exists in the porphyries with quartz veins, skarns far from intrusion, hornfel and marble. The evolution process of skarns includes prograde metasomatic, magnetite, quartz-sulfide, and late retrograde stages. Copper mineralization mainly happened in quartz-sulfide stage.3. Ore-forming material may be mainly from magma, but sulfur occasionally from strata. During the prograde metasomatic stage, ore-forming fluids may be mainly from magmatic water, but carbon generally from marine sedimentary carbonate. In contrast, meteoric water may be gradually increased in the ore-forming fluids and provide a larger part of carbon during the retrograde stage.4. Inclusions includeⅠ-type of polyphase inclusions with daughter crystals,Ⅱ-type of fluid inclusions andⅢ-type of CO2-rich inclusions. From the prograde metasomatic stage to the retrograde stage, addition of meteoric water is responsible for the decrease of temperature and sality of ore-forming fluids.5. The skarn in the tongshan copper deposit is contact metasomatism skarn. Vertical occurrence of skarns and metamorphic rocks may be controlled by the lithologies of strata. The zoning mode of skarns may be controlled by the property of fluids and wall-rocks, redox state and temperature condition in the different locations of geological bodies.
Keywords/Search Tags:skarn copper deposit, zoning of alteration and mineralization, ore-forming fluids, genesis, Tongshan in Anhui province
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