Abstract:Although of skarn type, the Fengsandong copper deposit of Hubei Province shows mineralization and alteration features of porphyry copper ore. In this paper, main-characteristics of the Fengsandong igneous body have been described in detail, alteration zoning has been defined around this body, and parametric data available through the determination of fluid inclusions have been examined. On such a basis, an attempt is made to probe into the genetic relations of the igneous mass to mineralization. The Fengsandong intrusion is a small Yenshanian intermediate- acidic body composed chiefly of granodionite porphyry of normal calc-alkaline series. Its exposure measures 0.73 km2 and its main petrochemical parameters are: SiO2, 63.51-64.90%; Na2O+K2O, 7.15-7.81%; δ= (Na2O+K2O)/(SiO2 - 43), 2.25-3.10; DI (Differ6ntial Index), 62.31-73.13. During the period of ore-forming activity, the igneous body suffered intense alteration and metasomatism, forming around it alteration zoning in outward order of potassium feldsparbiotite-potassium feldspar→quartz-sericite→skarn→marble. Copper ore bodies occur mostly in skarn zone; though formed at different stage of magmatic evolution and deposited at different sites, porphyry copper mineralization and copper ore bodies in skarn are likely products of identical magmatic source; skarn, therefore, is the favorable wall rock for ore deposition. Inclusion data indicate that ore-forming fluids are enriched in alkali metals and volatiles, belonging to NaCl-KCl-H2O system, twice. These fluids probably migrated in outward and within the igneous body and have boiled upward directions. It is presumed that alteration-mineralization proceeded through pneumato-high temperature stage, median temperature stage (main ore forming stage) and low temperature stage. The major agents affecting mineralization seem to be temperature, acidity-alkalinity and chemical composition of ore-forming fluids, characters of wall rocks and small igneous body itself, the last factor being decisively important. Ore-forming materials came from the depth of the earth-s crust. The mineralization for the most part occurred at the transitional stage when high pressure was converted into low pressure, alkali-metasomatism into hydrogen metasomatism and high salinity into low salinity. A thorough investigation of alteration pattern and fluid inclusions enables us to understand the variation in physico-chemical parameters of ore-forming fluids as well as the ore-forming mechanism, thus having great significance in search for ores.
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张洪涛.1984.封三洞铜矿床成因探讨[J].矿床地质,3(3):57~66.1984.Genesis Of The Fengsandong Copper Deposit: A Preliminary Study[J].Mineral Deposits3(3):57~66
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