The Cretaceous Huangdaoshan Cu-bearing intrusion in Chuzhou: Petrogenesis and implications for the Cu mineralization in the Middle Lower Yangtze River Valley Metallogenic Belt, eastern China

摘要

The Huangdaoshan mineral deposit in the Middle-Lower Yangtze River Valley Metallogenic Belt, is located on the northern margin of the Yangtze Craton, eastern China. It is hosted by the high-K calc-alkaline quartz-monzonite porphyry and quartz-diorite porphyry of Huangdaoshan intrusion. The molybdenite Re-Os age for the mineral deposit suggests that mineralization occurred at 128.9 +/- 2.3 Ma and was coeval with the ore bearing intrusion (130 +/- 1 Ma). Both porphyries are enriched in light rare earth elements (LREE) and large-ion lithophile elements (LILE), depleted in heavy rare earth elements (HREE) and high field-strength elements (HFSE), and have positive Eu anomalies. They also show adakitic affinities with high Sr (914-1227 ppm) and Sr/Y ratios (125-212), and low Y (5.40-9.00 ppm) and Yb (0.46-0.75 ppm) contents. Petrography, micro-fabric features, and Sr-Nd-Hf isotopic results suggest that these adakite-like magmas were derived from magma mixing between mantle- and crustal-derived materials. The strong REE fractionations as well as the high La/Sm (6.0-7.1) and intermediate Sm/Yb (4.5-5.6) ratios, suggest that hornblende crystallization was the dominant control on fractionation. Apparent temperatures based on Ti-in-zircon thermometry show that the mineralization-related porphyries crystallized at 711 degrees C-790 degrees C. The oxygen fugacity (fO(2)) estimated from hornblende Mg contents and biotite Fe3+, Fe2+ and Mg contents indicates that the mineralized magma possessed a high oxidation state (NNO + 0.15 to NNO + 1.62). The geochemical characteristics of the intrusions (enrichment in LILEs, depletion in HFSEs, and Nb-Ta anomalies) indicate that the mafic magma was derived from partial melting of the enriched lithosphere mantle, which had been metasomatized by slab-derived fluids from a sub-ducted oceanic plate. Therefore, the parental magma contained high contents of H2O and metal (e.g., Cu), with high fO(2). The extensive contemporaneous magmatism, metallogenic events, and volcanic basins in the region suggest an extensional tectonic setting. We further correlated this extension regime with slab roll-back of the Paleo-Pacific Plate.