Geochemistry, and zircon U-Pb and molybdenite Re-Os geochronology of Jilongshan Cu-Au deposit, southeastern Hubei Province, China

摘要

The Jilongshan skarn Cu-Au deposit is located at the Jiurui ore cluster region in the southwestern part of the Middle-Lower Yangtze River valley metallogenic belt. The region is characterized by NW-, NNW-and EW-trending faults and the mineralization occurs at the contact of lower Triassic carbonate rocks and Jurassic granodiorite porphyry intrusions. The intrusives are characterized by SiO_2, K_2O, and Na_2O concentrations ranging from 61.66 to 67.8 wt.%, 3.29 to 5.65 wt.%, and 2.83 to 3.9 wt.%, respectively. Their A/CNK (A/CNK = n(Al_2O_3)/ [n(CaO) + n(Na_2O) + n(K_2O)]) ratio, dEu, and dCe vary from 0.77 to 1.17, 0.86 to 1, and 0.88 to 0.96, respectively. The rocks show enrichment in light rare earth elements ((La/Yb)_N = 7.61-12.94) and large ion lithophile elements (LILE), and depletion in high field strength elements (HFSE), such as Zr, Ti. They also display a peraluminous, high-K calc-alkaline signature typical of intrusives associated with skarn and porphyry Cu-Au-Mo polymetallic deposits. Laser ablation inductively coupled plasma spectrometry (LA-ICP-MS) zircon U-Pb age indicates that the granodiorite porphyry formed at 151.75±0.70 Ma. A few inherited zircons with older ages (677±10 Ma, 848±11 Ma, 2645±38 Ma, and 3411±36 Ma) suggest the existence of an Archaean basement beneath the Middle-Lower Yangtze River region. The temperature of crystallization of the porphyry estimated from zircon thermometer ranges from 744.3±C to 751.5±C, and 634.04 ±C to 823.8 ±C. Molybdenite Re-Os dating shows that the Jilongshan deposit formed at 150.79±0.82 Ma. The metallogeny and magmatism are correlated to mantle-crust interaction, associated with the subduction of the Pacific Plate from the east.