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

摘要

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;943 ppm) 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 3Ca(2+) = 2REE(3+) + square 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 delta Eu: 0.45), indicating an oxidizing condition, whereas that from near the porphyry shows positive Eu anomaly (average delta Eu: 3.58), indicating a reducing environment. Scheelite from the sandstone-hosted stratiform orebody shows slight and variable Eu anomalies (delta Eu: 0.66-1.47), indicating possible fluctuating physicochemical conditions. Our data demonstrate an increasing oxygen fugacity (fO(2)) 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. (C) 2016 Elsevier B.V. All rights reserved.