SEM-CL Study of Quartz Containing Fluid Inclusions in Wangjiazhuang Porphyry Copper (-Molybdenum) Deposit, Western Shandong, China

Abstract

The Wangjiazhuang porphyry copper (-molybdenum) deposit is located at Zouping volcanic basin in Shandong Province, East China and hosted in the Wangjiazhuang intrusive complex emplaced along a late volcanic conduit. There are two types of ores in this deposit: early disseminated and stockwork ores in the ore-bearing intrusion, and late massive sulfide-quartz veins above brecciated quartz monzonite. The ore minerals are mainly pyrite, chalcopyrite, and subordinately magnetite, tennantite, molybdenite with minor bornite, enargite, galena and sphalerite, etc., and gangue minerals including K-feldspar, biotite, quartz, muscovite-sericite, chlorite and calcite. Combined with fluid inclusion study, the scanning electron microscope-cathodoluminescence (SEM-CL) study of quartz in the deposit and wall rocks shows significant differences between the two types of quartz in the ores. In addition, four types of primary-pseudosecondary fluid inclusions in the quartz have been recognized. They are one- or two-phase aqueous inclusions with vapor/liquid ratios less than 30% to 40% (type I); gas-rich inclusions with vapor/ liquid ratios more than 50% (type II), some of which contain some small opaque minerals, probably chalcopyrite; multiphase fluid inclusions with daughter minerals of halite±anhydrite±opaque (chalcopyrite)± sylvite±hematite±unknown crystal (type III); and mica-bearing fluid inclusions (type IV). Quartz containing abundant muscovite-bearing and halite-bearing fluid inclusions in the mineralized quartz monzonite with potassic-silicic alteration, have better oscillatory growth zoning with CL-colors from bright in the core to darker in the rim, indicating variations of element concentrations in the fluid media from which quartz grew during the later period of magmatic-hydrothermal process. In contrast, the quartz in the sulfide-quartz veins contains mainly fluid inclusions of low-to-medium salinities and does not show oscillatory zoning, indicating that there was less fluctuation in composition and element concentrations of the hydrothermal fluids. However, the quartz containing halite-bearing fluid inclusions and being associated with copper-molybdenum mineralization in the sulfide-quartz veins shows zoning in its rims, indicating variations in composition and element concentrations of the hydrothermal fluids.