Metallogenesis Of The Hamaling Cu-Au-Mo Deposit,Tongling,Anhui Province

The Hamaling Cu-Au-Mo deposit is a typical composite deposit of porphyry-skarn-breccia-hydrothermal vein types newly discovered in Tongling ore district,Anhui province.Detailed field geological investigation combined with petrographical,mineralogical,ore deposit geochemical,and isotopic chronological studies has been carried out on this deposit,with focuses on analysis of magmatic hydrothermal mineralization process and establishment of a metallogenic model for the formation of the Hamaling composite deposit.There exist porphyry Cu-Au(-Mo),skarn Cu-Au,breccia Mo,and hydrothermal vein Au orebodies in the Hamaling deposit.The porphyry Cu-Au(-Mo)orebodies with disseminated and veinlet-disseminated Cu-Au ores occur in the middle to upper part of the quartz diorite pluton,and the skarn Cu-Au orebodies with taxitic and vein Cu-Au ores exist in the contact belt of the pluton with Ordovician limestone.The breccia Mo orebodies with Mo-bearing breccia ores are distributed in the interlayer fracture zone between the Wufeng Formation of Upper Ordovician Series and the Baota Formation of Middle Ordovician Series,and the hydrothermal vein Au orebodies with vein pyrite ores occur in the fracture or interlayer stripping structure of periphery Silurian System sandstone of the pluton.High temperature,middle to high temperature,and middle to low temperature alterations with mineralization occur in the porphyry Cu-Au(-Mo)and skarn Cu-Au orebodies,while only middle to high temperature and middle to low temperature alterations with mineralization exist in the breccia Mo and hydrothermal vein Au orebodies.Molybdenite samples yield Re-Os isochron age of 138.4±1.9 Ma,indicating that mineralization in the Hamaling deposit took place in Early Cretaceous,which was closely associated with Early Cretaceous quartz dioritic magmatic intrusion.The EPMA and sulfur isotopic data of pyrite samples show gradual decreasing in mineralization temperature from the porphyry Cu-Au-(Mo)orebody to the peripheral hydrothermal vein Au orebody and derivation of sulfur in ores mainly from magma,and partly from the strata.All of the obtained data support the formation of the four type orebodies of the Hamaling deposit by a complicated metallogenic process in a same set of magmatic-hydrothermal system.In Early Cretaceous,emplacement and cooling of magma with mixing source of crust with mantle is responsible for the formation of the Hamaling quartz diorite.Postmagmatic high temperature hydrothermal replacement of the quartz diorite led to the formation of the porphyry Cu-Au(-Mo)orebodies in the porphyry.The contact metasomatism reaction between high temperature hydrothermal fluids and Ordovician limestone formed the skarn Cu-Au orebodies.After this,hydrothermal replacement and filling resulted in the formation of the breccia Mo orebodies during movement of the middle to high temperature ore-forming fluids into the interlayer fracture zones between the Upper Ordovician Wufeng Formation and the Middle Ordovician Baota Formation.The hydrothermal vein Au orebodies were formed by hydrothermal filling when the middle to high temperature fluids mixed with meteoric water moved into the peripheral Silurian sandstone fractures and detachment structures.