Characteristics And Genessis Of The Hucunnan Polygenetic Compound Cu-Mo Deposit, Tongling, Anhui Province

Tongling area in Anhui province is a part of Middle-Lower Yangtze metallogenic belt. It is a typical area for studying skarn-type deposit, and attracts much attention in the last decade. The Hucunnan deposit is a new discovered typical porphyry- skarn Cu-Mo deposit in the Tongling area, through two period of mineralization.This study carried out systematic analysis on alteration charateristics, molybdenite Re-Os isotope, bulk-rock major and trace element composition, LA-ICP-MS zircon U-Pb isotope, S isotope. Integrating these datasets with the regional tectonic evolution and current ore petrogenesis theories, we achieved the conclusions bellow:Based on the general understanding of the regional geological background and mineral deposits of Hucunnan ore field, the alteration type, alteration zoning and minerogenetic stage of the field were researched. The alteration belt, from wall rock to the center of the porphyry, can be divided into marble intercalated with hornfels, silication alteration, skarn, prophylitic zone, quartz-sericite zone, and K-silicate zone. Two types of ore are present in the Hucunnan deposit: skarn- and porphyry-type ores, which are associated with Cu and Cu-Mo mineralization, respectively. Mineralization process of skarn type is divided into the skarn and quartz-sulfide stages. Cu-sulfide precipitated mainly in the quartz–sulfide stage. Mineralization process of porphyry type is divided into the high temperature pneumatolytic, middle to high temperature hydrothermal and low temperature hydrothermal stages. Cu-Mo sulfide precipitated mainly in middle to high temperature hydrothermal stage.The granodiorite and quartz diorite in the Hucunnan deposit belong to the High-K calc-alkaline series. The U-Pb isotopic ages of the granodiorite and quartz diorite are 137±1.2 Ma and 125±1.5 Ma, respectively, corresponding to the two episodes of post-collisional to postorogenic magmatic activities in the Middle-Lower Yangtze metallogenic belt. The Re-Os isotopic dating of 7 molybdenite samples gave an isochron age of 139.5±1.1 Ma, reasonably consistent with the age of the granodiorite. Based on the evidenc mentioned above, we conclude that the granodiorite contributes to the Cu-Mo mineralization, while the quartz diorite may lead to further enrichment of Cu.The Mo content in magma increases with increasing magma evolution grade, namely, high evolved magma has more Mo concentration, which is more prone to generate Mo deposit than low evolved magma of which the Mo content is similar to that of mantle in East China. S isotopic analysis indicates that magma mainly sourced from mantle with little contamination from wall rock, i.e, wall rock contamination is unimportant to the Mo mineralization.