Genesis of the Donggushan tungsten polymetallic deposit, central Anhui Province: A clue of diagenetic and metallogenic system of a crustal source

Abstract

• The W mineralization in the Donggushan was caused by the Late Cretaceous magmatism . • Diagenetic and metallogenic system was likely to be originated from a crustal source dominated by the Northern Dabie Terrane . • The REEs of scheelite are mainly controlled by the substitution mechanism Ca 2+ + W 6+ = REE 3+ +Nb 5+ . • The ore-forming fluids were modified by the intense fluid-rock interaction. The newly discovered large-scale Donggushan tungsten polymetallic deposit with resources of 70,000 t WO 3 and 38,000 t Mo, located at the Lujiang county, center of Anhui Province, East China. The deposit is characterized by skarn W-Mo mineralization, which is developed along the external contact zone between the biotite granites and carbonate rocks. Zircon U-Pb dating yields a Late Cretaceous age of 98.3 ± 1.6 Ma for the Donggushan biotite granite. The hidden biotite granites of Donggushan is characterized by high silica and alkali but low Mg, Fe. It is enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs: Rb, K, Th and U), but strongly depleted in heavy REEs, and high field strength elements (HFSEs: Nb, Ta and Ti), and Sr. This high-K granite has medium initial 87 Sr/ 86 Sr ratios (0.706518–0.707116) and low initial Pb isotopic ratios [( 206 Pb/ 204 Pb)i, 16.452–16.533; (207Pb/204Pb)i, 15.449–15.463; ( 208 Pb/ 204 Pb)i, 36.946.335–37.097], and is characterized by low εNd(t) and εHf(t) values (−22.1 to −16.1 and −21.3 to −15.1, respectively). All these data indicate that the Donggushan biotite granite is a high-K calc-alkaline fractionated I-type granitite. This granite may have derived from a crustal source, which is dominated by the Northern Dabie Complex (NDC) mixed with the basement materials of the Taihua Group. The magmatism in the Donggushan polymetallic deposit is quite different from those in the metallogenic belts of the Qinling-Dabie Mo belt (QDMB) and Middle-Lower Yangtze River Belt (MLYB). Based on the geochemical study of REEs of scheelite, it is proposed that the substitution mechanism of Ca2+ + W6+ = REE3+ +Nb5 + occurred during the formation of scheelite. Concentrations of Eu indicate that scheelite precipitated under the oxide conditions. The variations of the Mo concentrations might be caused by the changing of oxide reduction conditions. The Sr of the scheelite and S isotopes of pyrite in the Donggushan deposit reflect a complex magmatic-hydrothermal mineralization process within the intrusion and the country rocks.