In situ LA ICP-MS analysis of trace elements in scheelite from the Xuefeng Uplift Belt, South China and its metallogenic implications

Abstract

Abstract The Xuefeng Uplift Belt (XUB), in the western part of the Jiannan Orogenic Belt (JOB) South China, hosts numerous low-temperature W-Sb-Au deposits, including the Woxi W-Sb-Au deposit, the Zhazixi Sb-W deposit and the Darongxi W deposit. In order to understand the origin of these low-temperature W deposits and the difference from other moderate-high temperature tungsten deposits in the South China Block, Cathodoluminescene (CL) and LA-ICP-MS are employed to investigate the detailed texture of scheelite , and to identify trace element composition and distribution in scheelite, especially rare earth elements (REEs). LA-ICP-MS results show that the most abundant trace elements in scheelite in this study were Sr, Y, Nb, Mo, Zr, Hf, Ta and REEs. Six types of scheelite can be classified according to variations of REEs pattern. Type I and II scheelites from the Zhazixi Sb-W deposit and the Woxi W-Sb-Au deposit have elevated concentration of Sr, low concentrations of Nb, Mo and variable Nb/Ta ratio, reflecting low temperature ( skarn deposit, Type IV scheelite from the Dabaoshan polymetallic deposit, Type V scheelite from the Niutangjie skarn W deposit and Type VI scheelite from the Daping W deposit have relatively higher Nb, Mo and relatively constant Nb/Ta ratios, and lower Sr concentration, consistent with the feature of moderate to high temperature oxidizing environments. Type I scheelite from the Zhazixi Sb-W deposit can be subdivided into Ia, Ib and Ic, which cover a wide range from MREE-rich to MREE-depleted, indicating a complete dynamic evolution process. Type II scheelite from the Woxi W-Sb-Au deposit has uniform patterns with significant depletion of LREE and enrichment of MREE, revealing that the substitutions of MREE into scheelite lattices are dominated by crystallographic factors, especially the Ca-site size in scheelite crystals rather than the REE concentrations and REE complex stability in hydrothermal fluids . Type III scheelite from the Darongxi W deposit shows two distinctive REE patterns, types IIIa and IIIb, which are likely to be two end members, suggesting that successive precipitation results in changes in REE concentrations and Eu anomalies. Type IV scheelite from the Dabaoshan polymetallic deposit inherited the signature of the granitic porphyry . Type IV b and IVc are similar to those Type V scheelites from Niutangjie, both showing the characteristics of skarn type scheelite mineralization. Trace element variations suggest the predominant control factors differ according to temperature. Trace element concentrations and distribution of scheelite formed at low temperature were mainly controlled by crystallographic factors, which contrasted with fluid-controlled feature of the medium–high temperature scheelite mineralization.