The mineralogy and geochemistry of skarn minerals from the Lalangmai W deposit in the East Kunlun Orogen, China and its comparision with the Baiganhu w-sn deposit: Implication on regional metallogenesis

Abstract

East Kunlun Orogen (EKO) hosts numerous economically important deposits in western China, including the Baiganhu W-Sn deposit in the west and the Lalangmai W-only deposit in the east, which share similar geological characteristics. However, significant differences exist between the two deposits, which include the decoupling of W and Sn mineralisation and the smaller size of the mineralisation at Lalangmai compared to Baiganhu. These differences reflect contrasting magmatic and fluid evolution histories and offer a valuable opportunity to refine models for the W-Sn metallogenesis in the EKO. In this contribution, we present a comprehensive study of the geochemistry and mineralogy of garnet, diopside and scheelite from the Lalangmai W deposit, supplemented by published data on petrology and isotopic geochemistry of monzogranite. The data are further compared with those of Baiganhu to better illustrate nature of the geological bodies. The results suggest that the differences between the two areas can be largely attributed to variations in the nature of the granitic rocks. The Lalangmai granites are characterised by lower temperature of emplacement, the absence of biotite and are relatively enriched Sr-Nd isotopic signature compared to the Baiganhu granites. In addition, the prevalence of Al-rich garnets in the peraluminous, felsic, ilmenite-bearing intrusions at Lalangmai contrasts with the Fe-rich garnets related to alteration in the Baiganhu area. This mineralogical distinction possibly suppresses the deposition of Sn and W mineralisation at Lalangmai, given that Sn substitutes for Fe, which represents the principal mechanism of deposition. Furthermore, a lack of oscillatory zoning in garnet and scheelite, a more uniform REE pattern of scheelite, and the prevalence of Mo-elevated only scheelite indicate a relatively stable redox environment and felsic environment. The single-stage mineralisation during prograde phase, as opposed to fluid circulation and multi-phase interactions, further restrict the scale of the deposit. These findings highlight a spatial and genetic decoupling of W and Sn mineralisation and distinct styles of mineralisation across the orogen and share similar pattern to that of the Nanling region in China. The proposed model contributes to a deeper understanding of the diversified W-Sn mineralisation in the orogen and provides valuable insights for guiding future prospecting endeavours in both W-only and W-Sn systems.