Ore-forming mechanism and fluid evolution processes of the Xingluokeng tungsten deposit, western Fujian Province; Constraints form in-situ trace elemental and Sr isotopic analyses of scheelite

The Xingluokeng tungsten deposit is located in the middle area of the Wuyishan metallogenic belt, which is the largest tungsten discovered in the belt by now. 'Hie orebody mainly occurs in the roof part of an extensively altered granite stock. Multifile mineralized types have been recognized, including veinlet-disseminated, stockwork and vein-type mineralization, with scheelite/wolframite ratios at 1 : 1 , approximately. The ore genesis of the Xingluokeng deposit is still debated, and ore-forming mechanism and fluid evolution processes remain enigmatic. In this study, we describe the detailed ore-forming stages, and carry on fluid inclusions, H-0 isotope and in-situ LA-1CP-MS trace elements and Sr isotope on multi-generation scheelites from different mineralization stages. The mineralized processes of this deposit could be divided into three stages; veinlet-disseminated scheelite-molybdenite stage (stage I) , K-feldspar-scheelite-wolframite-beryl stage (stage 11) and sulfide-wolframite-scheelite-carbonate stage (stage 111). Microthermometric analyses of fluid inclusions indicate the ore-forming fluids belong to NaCl-1O-CO-, system, with medium-high temperature and low salinity. H-0 and Sr isotopic compositions suggest the ore-forming fluids dominantly originated from magma water, and limited meteoric water involved in late mineralization stage. The scheelites in early stage have higher contents of REE, Mo, Na and Nb, but lower Sr content; whereas REE, Mo, Na and Nb were gradually depleted and Sr was enriched, with the evolution of ore-forming fluids. The scheelites of stage 1 are characterized by euhedral or subhedral crystals, with dense and homogeneous oscillation zonation. In this type of scheelites, the REE substituted into the Ca site by Na- A nd Nd-dominated substitution mechanism. Whereas the scheelites in stage 11 and 111, the incorporation of REE into scheelites can be coupled with [H(a(where 0(-a is a Ca site vacancy). Together with mineralization and alteration features, we propose that the scheelites in stage I crystallized in a low fluid/rock ratio condition, by way of pervasive replacement of primary magmatic fluids along micro fractures. Whereas the scheelites in stage 11 and 111 were precipitated by extensively fluid-rock interaction accompanying by immiscibility of C02. Coupled with the geological characteristics of ore deposit, we consider the Xingluokeng deposit as generalized porphyry tungsten deposit. Hie veinlet-disseminated tungsten mineralization constitutes the metallogenic base, and the superposition of stockwork and vein-type tungsten mineralization is a key process for the Xingluokeng tungsten deposit. © 2021 Science Press. All rights reserved.