Formation of the Baiyun gold deposit, Liaodong gold province, NE China: Constraints from zircon U–Pb age, fluid inclusion, and C–H–O–Pb–He isotopes

Abstract

The Baiyun gold deposit is located in the Liaodong peninsula in NE China. The gold orebodies are hosted in the Paleoproterozoic Liaohe Group metamorphic rocks. The alteration/mineralization can be divided into three stages: (I) quartz ± pyrite ± K-feldspar veins, (II) quartz-polymetallic sulfide veins, (III) quartz-carbonate veins. New LA–ICP–MS zircon U–Pb dating suggests all the ore-related porphyries, including monzonite porphyry (224.2 ± 1.3 Ma), quartz porphyry (221.4 ± 1.2 Ma) and diorite porphyry (221.8 ± 1.2 Ma), were emplaced in the Late Triassic. Four types of fluid inclusions (FIs) are identified in the ore-related quartz, i.e., liquid-rich two-phase, vapor-rich two-phase, CO2-bearing and pure CO2 FIs. The ore-forming fluids were likely characterized by medium temperature, low salinity, low density, CO2-rich, and belong to the H2O–NaCl–CO2 ± N2 ± C4H6 system. We propose that fluid phase separation likely caused rapid precipitation of the ore minerals. The C–H–O–Pb isotope data indicate that the ore-forming fluids may have had multiple sources, including magmatic, metamorphic and meteoric fluids. The ore-forming materials may have mainly derived from metamorphic rocks of the Proterozoic Gaixian Formation, and minor from the Triassic intermediate-felsic rocks. The He–Ar isotope data indicate that the ore-forming fluids were mainly crust-derived. We conclude that the Baiyun gold deposit is an orogenic-type system formed during the Late Triassic North China-Yangtze continent-continent collision.