Source and evolution of ore-forming fluids in the Huangtian tungsten deposit in southeastern Yunnan: Constraints from geochemistry characteristics of scheelite

The Huangtian tungsten deposit is located in the northern margin of the Laojunshan polymetallic metallogenic zone in southeastern Yunnan. It is a newly discovered large-scale scheelite deposit in recent years. Scheelite is divided into two stages from early to late: scheelite-fluorite-quartz stage(scheelite Ⅰ), scheelite-carbonate stage(scheelite Ⅱ); Four types: scheelite Ⅰ-a, scheelite Ⅰ-b, scheelite Ⅱ-a, scheelite Ⅱ-b. The scheelite Ⅰ-b and Ⅱ have obvious oscillating rings. In order to determine the source and evolution of its ore-forming fluids, based on the detailed borehole core cataloging and the study of mineral microfabrication, LA-ICP-MS was used to analyze the trace and rare earth elements in scheelite at different stages. Our data show that the rare earth elements in scheelite are mainly controlled by the substitution mechanism of 3Ca²⁺=2REE³⁺+□Ca, the distribution of rare earth elements in scheelite is obviously inhomogeneous, but they are all LREE-enriched types, similar to the chondrite partition pattern of the Laojunshan granite. The LREE-MREE-HREE diagram of scheelite and the Sm/Nd ratio show that it is closely related to the Laojunshan granite. Except for some test points of early scheelite Ⅰ-a, which showed negative Eu anomaly, the rest of the test points showed positive Eu anomaly, Eu also changes from the Eu³⁺ dominated to Eu²⁺ dominated. and the content of Mo in scheelite also changed. It gradually decreases, indicating that the oxygen fugacity of the ore-forming fluid decreases gradually from the early stage to the late stage. In addition, the Sr content(36.6×10^-6~619×10^-6, average 206.25×10^-6)in scheelite is relatively high, and the surrounding rocks of the deposit are mainly marine sedimentary carbonate rocks. It is speculated that the water-rock reaction is as follows: Ore-forming fluids provide a large amount of Sr and Ca.