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.