Geochronology and Geochemistry of Metallogenetic Porphyry Bodies from the Nongping Au-Cu Deposit in the Eastern Yanbian Area, NE China: Implications for Metallogenic Environment

The metallogenetic porphyry bodies in the Nongping Au-Cu deposit, in the eastern Yanbian area, mainly include porphyritic granodiorite and biotite granodiorite porphyry. They are featured with high silicon and enrichment in sodium, and classified into sodic rocks of low-K tholeiitic basalt series. Except slightly low Sr content, the rock basically has the geochemical characteristics of the adakite： relatively high A12O3 content, relatively low MgO content, depletion in Y and Yb; relative enrichment in large ion lithophile elements （LILEs） and light rare-earth elements （LREEs）, relatively low content of high field strength elements （HFSEs）; positive Eu anomaly or weak negative Eu anomaly. In situ zircon dating technology LA-MC-ICP-MS was used to conduct single-grain zircon dating of biotite granodiorite porphyry, and the results show that the age of metallogenetic porphyry body is 100.04±0.88 Ma, indicating that the porphyry bodies were emplaced in the late Cretaceous period. According to the regional tectonic setting and the comparison with the same kind of deposits, we think that the metallogenetic porphyry bodies in the Nongping Au-Cu deposit have a close genetic connection with the subduction of the Pacific plate in the late Yanshanian period. The adakitic magma generated from partial melting of the subducting plate has high formation temperature, high oxygen fugacity, and volatile constituents＇ enrichment, so it is helpful for enrichment of metallogenetic elements and plays an important role in the formation of porphyry Au-Cu deposits in this region.

A new type of Mo-bearing quartz vein by acid leaching:evidence from Dahu-Qinnan Mine,northern belt of the Xiaoqinling gold province,central China

Dahu-Qinnan molybdenum deposit,located in the northern part of the Xiaoqinling gold province,belongs to the Xiaoqinling-Waifangshan sub-zone of the eastern Qinling Mo-W metallogenic belt,central China.Molybdenite mineralization is associated with Au-bearing quartz veins.This paper is based on field observations and PIMA analytical data on the occurrences,and details textures and alteration patterns of Mo-bearing quartz veins in Dahu-Qinnan region.The Mo-bearing quartz veins exhibit friable with cream colored,vuggy,infilling texture and brecciated texture.The breccia clasts within Mo-bearing quartz veins are dominated by gneissic rocks of the Taihua Supergroup,and Mesozoic porphyritic granite dyke with stockwork and disseminated molybdenite mineralization.The breccias are replaced by clay minerals.Alteration associated with molybdenite-bearing quartz veins is characterized by K-feldspar(only in the breccias),sericite,sillicification(residual silica),kaolinite,smectite and anhydrite.Molybdenite with other sulfide minerals infills fissures and pore spaces in the quartz veins.As the results of above,and according to the observed geological events in the area and taking into account the geological setting,molybdenite-bearing quartz veins are likely to have been affected by late acid leaching.The precursor porphyry Mo ore,associated with porphyry granite dyke formed probably at ca.245--211 Ma during the continent-continenl collision of Qinling orogeny.