Texture and trace element geochemistry of quartz in porphyry system: Perspective from the Gaogangshan Mo Deposit, NE China
crossref(2023)
Abstract
<p>The Gaogangshan deposit in the northern Lesser Xing'an Range, NE China, consists of typical collision-type porphyry Mo mineralization related to Permo-Triassic granitic intrusions. Ore-forming process is recorded by multiple generations of quartz, including pre-ore stage quartz with unidirectional solidification texture (UST), early ore-stage quartz-molybdenite veins with K-feldspar alteration halos (Q<sub>1</sub>), late ore-stage quartz-sulfides veins with sericite alteration (Q<sub>2</sub>), and post-ore stage quartz veins (Q<sub>3</sub>) associated with calcite and fluorite. Cathodoluminescent textures, trace elements and fluid inclusions in quartz reveal physicochemical conditions, evolution of ore fluids and the Mo mineralization process. The UST quartz and Q<sub>1</sub> veins are dominated by CL-bright homogenous and/or granular mosaic textures, containing more Ti concentrations (average = 35-42 ppm) than Q<sub>2</sub> and Q<sub>3</sub> veins. The molybdenite-bearing Q<sub>2</sub> veins are dominated by CL-gray granular and zonal textures, displaying less CL intensity and lower Ti concentrations (average = 16 ppm) than early-stage quartz. The Q<sub>3</sub> veins have the lowest CL-intensity and the lowest Ti concentrations (average = 2.5 ppm) among all quartz types. Three types of inclusions are identified in above quartz samples, including liquid-vapor aqueous inclusions, CO<sub>2</sub>-bearing liquid-vapor aqueous inclusions and halite-bearing multiphase aqueous inclusions. The ore-forming fluids in ore-stage Q<sub>1</sub> and Q<sub>2</sub> veins are dominated by large salinity variation (2.3-38.9 wt% NaCl equiv.), CO<sub>2</sub>-bearing (4.2-8.9 mol%) two-phase aqueous inclusions with vapor volumetric proportions of 30-65%. Intersections of fluid inclusion isochores with Ti-in-quartz isopleths yield quartz formation conditions of ~2.2 kbar at ~640°C for UST quartz, ~1.25 kbar at ~510°C for Q<sub>1</sub>, ~1.0 kbar at ~440°C for Q<sub>2</sub>, and ~0.37 kbar at ~220°C for Q<sub>3</sub>. The Gaogangshan porphyry Mo deposit formed at depths of 3.8 to 4.7 km. Fluid decompression and temperature decreasing resulted in molybdenite precipitation.</p>
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