Petrography And Mineralogy Of Skarn From Dongguashan Copper Deposit In Tongling Area, Anhui Province

Tongling area is an important part of the Middle-lower Yangtze Riverpoly-metallogenic belt, Anhui province. As one of the most important types ofdeposits, skarn-type deposits are widely distributed in this area. Dongguashan copperdeposit is the largest and deepest skarn-type deposit in this area, with representativeand typical geological features. A detailed petrographical and mineralogical study hasbeen carried out on the major skarn minerals(including garnet and pyroxene) in theDongguashan copper deposit,with a focus on the genesis of the skarn and associateddeposit. The following are major achievements obtained in this thesis:1. Petrographic observation supports dividing of formation process of garnet intotwo periods based on mineral intersection and metasomatism. The first period garnetis dark brown in color and has a zonal texture. While the second period garnet is lightyellow in color and has an optical anomaly, and occurs as veins intruding into the firstperiod garnet or outer zone surrounding the first period garnet.2. The skarn in the Dongguashan copper deposit is mainly composed of garnetand clinopyroxene. The garnet formed in the two period belongs to anandradite-grossular series, however, the first period garnet is higher in andraditecomponent, but the second period garnet is higher in grossular component. Pyroxenebelongs to a hedenbergite-diopside series, with more diopside component up to92%.3. Rare earth elements analysis result shows the REE partition pattern of firstperiod garnet is rich in LREE, positive Eu abnormal. The REE partition pattern ofsecond period garnet is slightly rich in HREE, negative Eu abnormal. The REEpartition pattern of pyroxene is slightly rich in LREE, negative Eu abnormal. Acomprehensive analysis is consistent with formation of the first period garnet bycooling and crystallization of the skarn magma in oxidize environment; and supportsformation of the second period garnet and pyroxene by metasomatized hydrothermalfluid and carbonate in reduction environment.4. Trace elements analysis result shows all the garnets and pyroxene arecharacterized by a general of Lithophile elements (Th、U. etc) and Siderophileelements (Ga、Mo especially W) enrichment and chalcophile elements depletion(except Sn). These characteristics are similar with elements distribution features ofrelated magmatic rocks in the ore field, indicating the formation of skarn probablyclosely correlation with magmatic rocks. R-system cluster analysis of metallogenic elements and associatied elements suggests that Zn and Pb are closely correlation withCu in garnets, while Ga in pyroxene. These characteristics as one of the symbol ofdeep prospecting.