In-situ LA-ICP-MS trace elements analysis of scheelites from the giant Beiya gold–polymetallic deposit in Yunnan Province, Southwest China and its metallogenic implications

Abstract

The Beiya gold–polymetallic deposit, located in the middle of the Jinshajiang–Ailaoshan alkaline porphyry metallogenic belt, is the largest skarn gold deposit in China. Scheelite is a typical hydrothermal mineral which can serve as mineralization process tracer and is significant for the hydrothermal deposit study. In this paper, we present in-situ LA-ICP-MS scheelite geochemical data from the different parts of the skarn mineralization in the Beiya deposit. The data indicate that the Beiya scheelite has high Mo (average: 38,943ppm) and high LREE/HREE (average: 29.6), resembling typical skarn-type scheelite. The mechanism of REE substitution of Ca in the Beiya scheelite was probably 3Ca2+=2REE3++□Ca, which implies that the scheelite inherited its REE composition from magma-derived ore-forming fluids. The scheelite from near the marble shows negative Eu anomaly (average δEu: 0.45), indicating an oxidizing condition, whereas that from near the porphyry shows positive Eu anomaly (average δEu: 3.58), indicating a reducing environment. Scheelite from the sandstone-hosted stratiform orebody shows slight and variable Eu anomalies (δEu: 0.66–1.47), indicating possible fluctuating physicochemical conditions. Our data demonstrate an increasing oxygen fugacity (fO2) trend from the ore-related intrusion to the surrounding carbonates at Beiya. The Rb/Sr, Nb/Ta and Zr/Hf ratios of the Beiya scheelite suggest an addition of mantle-derived components to the ore-forming materials of the Beiya deposit.