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

Abstract

• The Gongpoquan porphyry Cu deposit is located in the Beishan Orogen, NW China. • Muscovite 40 Ar/ 39 Ar dating yielded Early Devonian (404.0 ± 2.2 Ma) mineralization age. • Ore fluid was magmatic-sourced with more meteoric water input toward late stage. • Fluid mixing and boiling were likely effective mechanism for Cu ore precipitation. • The Devonian mineralization was likely related to Paleo-Tianshan Ocean sbuduction. 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 220 °C), intermediate-low salinities (peak at 1.5 to 5.5 wt% NaCl eqv.), and belong to a H 2 O–NaCl–CO 2 ± CH 4 ± 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 δ 34 S values of −9.0 to −2.4‰, 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 40 Ar/ 39 Ar 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.