He-Ar isotope geochemistry of the Yaoling-Meiziwo tungsten deposit, North Guangdong Province: Constraints on Yanshanian crust-mantle interaction and metallogenesis in SE China

Abstract

Isotopic abundances and ratios of He and Ar found in inclusion fluids in pyrites formed in the Yaoling-Meiziwo tungsten mineralization epoch show that the concentration of 4He varies widely, from 1.54×10−7 cm3 STP/g to 2609×10−7 cm3 STP/g. 3He is 0.759×10−12 cm3 STP/g-3.463×10−12 cm3 STP/g. 3He/4He is 0.0043–4.362 Ra, varying from crustal to mantle values. The concentration of 40Ar ranges from 0.624×10−7 cm3 STP/g to 8.89×10−7 cm3 STP/g. The 40Ar/36Ar varies extensively, from 330 to 2952, between atmospheric and crustal or mantle radiogenic values. Mantle-derived He is present in ore-forming fluids and the calculated average proportion of the mantle He is 22%; the maximum is 67%. Our research results show that mantle-derived fluids play a significant role in tungsten mineralization. The fractionation of He and Ar indicate that there was 4He-enriched air-saturated water (MSAW) in the ore-forming fluid. The ore-forming fluid was a mixture of mantle fluid, crustal magmatic fluid and MSAW. The occurrence of a mantle component in ore-forming fluid indicates the large-scale W and Sn mineralization, including Yaoling-Meiziwo, in southeastern China was the result of crust and mantle interaction. The underplating or intrusion of voluminous basaltic magma formed by partial melting of the upper mantle provided the necessary heat to cause partial melting of the crust and the generation of voluminous S-type granitic magmas. Crustal magmatic fluid and mantle fluid with high 3He/4He were released from magma crystallization and fractionation, mixed with the circulating modified air-saturated water, and filled the extensional tectonic fractures, leading to the formation of world-class W and Sn deposits in southeastern China.