Ore-controlling Factors And Metallogenic Model Of Stratabound Skarn Deposits In Tongling Area, Anhui Province

Skarn mineralizaion is one of important research issues in regional metallogeny.Stratabound skarn deposit is a key object for the prospecting and study of the skarndeposits. A detailed study on this type of deposits would give a clue to understand theprocess of regional metallogeny, and provide new evidence for enrichment of themetallogenic theroy of skarn deposits and further exploration for skarn depostis. TheTongling ore cluster is an important district along the Middle-Lower Yangtze RiverValley metallogenic belt (MYRB), and stratabound skarn-type Fe-Cu-Au polymetallicdeposits are widely distributed in this district. These deposits are typical representatives inMYRB, even in the eastern China, making this district an excellent natural laboratory forstudying the ore-forming mechanism of the stratabound skarn deposits.A detailed geological, mineralogical, geochemical and fluid inclusion study hasbeen carried out on the Dongguashan and Datuanshan deposits in Tongling area, AnhuiProvince, with a focus on an analysis of the ore-controlling factors and metallogenicmodel of stratabound skarn deposits.The formation of stratabound skarn deposits in the Tongling area was controlled bysource beds, magmatism, lithological associations, organic materials and gypsumevaporites, etc. The lithological association and magmatism were the main factors, whilesource beds pre-concentrated ore-forming elements for some deposits, and organicmaterials and gypsum evaporites provided part of sulfur, absorbed ore-forming elements,and reduced sulfate to sulfides in some of the deposits. Ore deposit geology, mineralogy,geochemistry and fluid inclusion studies suggested that the Dongguashan strataboundskarn copper deposit was a product related to the Paleozoic syn-sedimentarymineralization and the Mesozoic magma hydrothermal superposition, while theDatuanshan copper deposit was one closely related to Mesozoic magmatic-hydrothermalactivity. These results contributed to develop the following model for the formation ofstratabound skarn mineralization in the Tongling district. During the middle Carbonfierousperiod, massvie sulfide deposits or source beds were formed by exhalative sedimentary,with major ore compositions mainly consisted of sulphur and iron; during the Indosinianstructural movement, especially folding, interlayer detachments occurred betweencarbonate rocks and siliceous sediments/siltstones; during the Yanshanian period,regional extension and crust-mantle interaction caused massvie magama-hydrothermalactivites. On one hand, magmatic hydrothermal moved along interlayer detachmentsbetween Devonian Wutong sandstones and Carboniferouis Huanglong carbonates, and superimposed and reworked the massvie sulfides or source bed developed earlier, whichcontributed to enrich Cu and developed large-sized stratabound skarn deposits (e.g.,Dongguashan copper deposit). On the other hand, hydrothermal fluids filled along theinterlayer detachments without the source beds, and formed mid-sized stratabound skarndeposits (e.g., Datuanshan copper deposit).