Genesis of the Gongpoquan porphyry Cu deposit in Beishan Orogen, NW China: Evidence from geochronology, fluid inclusions, H-O-S isotopes, and sulfides trace element

摘要

The Gongpoquan is a representative porphyry Cu deposit in the Beishan Orogen, which is located between the Tarim-North China Craton and South Mongolia. The mineralization is associated with dacite porphyry and granodiorite porphyry, and occurs as veins/veinlets, and disseminations. The mineralization can be divided into three stages: (I) quartz-sericite/muscovite-K-feldspar +/- chalcopyrite/bornite veins associated with phyllic alteration, (II) quartz-K-feldspar-chalcopyrite/bornite/pyrite veins/veinlets associated with propylitic alteration, and (III) quartz-calcite +/- pyrite +/- epidote veins. The mineralizing fluids are characterized by intermediate-low temperatures (peak at 210 to 22 degrees C), intermediate-low salinities (peak at 1.5 to 5.5 wt% NaCl eqv.), and belong to a H2O-NaCl-CO2 +/- CH4 +/- N-2 system. Oxygen and hydrogen isotope data indicate that stage I and II fluids were dominantly magmatic-sourced, with increasing meteoric water input toward stage III. Stage I and IIa-b chalcopyrite, bornite, and sphalerite have in situ delta S-34 values of -9.0 to - 2.4 parts per thousand, indicating a magmatic sulfur origin. The chalcopyrite has largely similar contents of Ti, Ge, As, Sn, Sb, and Se across stage I to III, and the contents are higher than those of bornite and sphalerite. This indicates that sulfide formation are controlled by intermediate-low temperatures with no mineral textural modification or chemical remobilization throughout the mineralization. Muscovite Ar-40/Ar-39 dating of stage I vein in the granodiorite porphyry ore host yielded an Early Devonian age of 404.0 +/- 2.2 Ma (MSWD = 0.40), indicative of the close temporal with the Gongpoquan arc granitoids formed during the Paleo-Tianshan Ocean subduction.