Scheelite geochemistry constrains the origin of W mineralization in the Laojunshan district, Southeast Yunnnan, China: Comparative studies from the Nanyangtian, Changtian and Saxi deposits

• The oxygen fugacity evolution of the ore-forming fluids at Nanyangtian followed a decrease–increase–decrease trend, with a predominantly reducing fluid environment. • The Nanyangtian, Saxi, and Changtian tungsten deposits consistently exhibit reduced mineralization characteristics, indicating a generally low oxygen fugacity condition of W mineralization across the Laojunshan district. • The Nanyangtian and Saxi deposits share a common deep-seated source with the Laojunshan granite, while the Changtian deposit is directly originated from the Laojunshan granite. The Laojunshan district in southeastern Yunnan is a critical Sn-W metallogenic district in China, with multi-episode and multi-type W mineralization. However, the comparative studies were lacking to reveal the genetic relationship among these W deposits. In this study, scheelites from three representative W deposits (Nanyangtian, Saxi and Changtian) in this district were collected for in situ trace element and Sr Nd isotopic analyses, with the aim of constraining differences in material sources and ore forming physicochemical conditions. In the Nanyangtian deposit, six scheelite types (Sch A-1, Sch A-2, Sch B, Sch C, Sch D-1 and Sch D-2) were identified, corresponding to distinct mineralization stages including prograde skarn stage, retrograde skarn stage, quartz-sulfide stage and quartz-scheelite vein stage. Cathodoluminescence (CL) imaging shows two substages within the Sch A (Sch A-1 and Sch A-2) and rim overgrowths of Sch D-1 on Sch C. The diverse REE patterns and Eu anomalies imply that the oxygen fugacity evolution of the ore-forming fluids at Nanyangtian followed a decrease–increase–decrease trend, with a predominantly reducing fluid environment. This result is further confirmed by the low Mo contents and the lack of positive δCe–δEu correlations. Similarly, scheelite from Saxi (Sch SX) and Changtian (Sch CT) display positive Eu anomalies and low Mo concentrations, indicating a generally low oxygen fugacity condition of W mineralization across the Laojunshan district. The variations in initial 87 Sr/ 86 Sr ratios among different scheelite types at Nanyangtian likely resulted from different levels of wall rock contamination, and the linear isotopic trend excluded the superimposition of multi-episode mineralization events. All ( 87 Sr/ 86 Sr) i values of scheelite (0.71465–0.72956 at Nanyangtian, 0.71261–0.72227 at Saxi and 0.72505–0.72710 at Changtian) overlap with the field of the Early Cretaceous Laojunshan granite (0.71301–0.74172). Integrating Y/Ho ratios, ε Nd (t) values of scheelite, and recent geochronological data, we infer that although formed at different ages, the Nanyangtian and Saxi deposits share a common deep seated source with the Laojunshan granite, whereas the Changtian deposit was derived directly from the granite.