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<p>Scheelite is the principal ore mineral in skarn‑type W deposits, with its texture and geochemical signatures directly recording the metal source, mineralization conditions, and fluid evolution. The Maka W–Pb–Zn–Sn–Be polymetallic deposit in southeastern Yunnan has been studied primarily for its Pb–Zn or Be mineralization, whereas W mineralization has received limited attention, hindering a systematic understanding of regional W potential and ore‑forming processes. Based on integrated field and petrographic analyses, four texturally and compositionally distinct scheelite types (Sch I–Sch IV) have been identified. In-situ textural, geochemical, and Sr‑isotopic analyses of these scheelite varieties were performed using scanning electron microscopy-cathodoluminescence (SEM‑CL) and LA‑(MC)‑ICP‑MS to constrain the W source and mineralization conditions at Maka. Results indicate that Sch I, disseminated within epidote–diopside skarn, exhibits uniform CL brightness, low ΣREE (average 18&#xa0;ppm), low <sup>87</sup>Sr/<sup>86</sup>Sr (0.71279–0.71482), moderate Mo (average 206&#xa0;ppm), Y/Ho ratios of 14–50, and LREE‑enriched patterns. Sch II, occurring in fluorite–quartz veins, displays oscillatory zoning, higher ΣREE (average 96&#xa0;ppm), elevated <sup>87</sup>Sr/<sup>86</sup>Sr (0.72662–0.73025), Mo content (average 720&#xa0;ppm), and Y/Ho ratios (19–101). Sch III, hosted in fluorite–feldspar–quartz veins, shows moderately lower ΣREE (average 65&#xa0;ppm), further increased <sup>87</sup>Sr/<sup>86</sup>Sr (0.73137–0.73643), equivalent Mo (average 556&#xa0;ppm), and reduced Y/Ho ratios (2–29). Sch IV forms fine grains in chalcedony veins, with ΣREE near 79&#xa0;ppm, a distinctive “wing‑shaped” MREE‑enriched pattern, lower <sup>87</sup>Sr/<sup>86</sup>Sr (0.71761–0.71841), sharply reduced Mo (average 2.7&#xa0;ppm), and Y/Ho ratios of 12–40. Systematic shifts in Eu anomalies across the scheelite generations trace an evolving redox trajectory: from high <i>f</i>O<sub>2</sub> (Sch I) to low <i>f</i>O<sub>2</sub> (Sch II) and back to high <i>f</i>O<sub>2</sub> (Sch III and Sch IV). Sch I–III exhibit LREE‑enriched profiles, Y/Ho ratios, and Sr‑isotope compositions consistent with a magmatic‑fluid origin exsolved from the Yanshanian Laojunshan granite. In contrast, Sch IV shows a metamorphic‑fluid affinity, indicated by its MREE‑enriched “wing‑shaped” pattern, low Mo content, high Y and Ho concentration, and elevated Sr/Mo ratios. Integrated with regional tungsten metallogeny, this study proposes that Yanshanian Laojunshan‑related W systems typically comprise "inner quartz-wolframite-vein-type + middle skarn-type + outer fluorite-scheelite-vein-type" mineralization. Scheelite that occurs in fluorite‑bearing veins and exhibits high Sr isotopic ratios with well‑developed oscillatory zoning can serve as a key macro‑ to microscopic indicator for W exploration in late Yanshanian granite.</p>

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In-situ texture and geochemistry of scheelite from the Maka W polymetallic deposit: Implications for late Yanshanian W metallogeny in Southeastern Yunnan Province, China

  • 期刊论文

  • 发表日期：

    2026年4月10日

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  • Jihuang Lai,
  • Yinghua Chen,
  • Mingguo Deng,
  • Wenchang Li,
  • Tao Wang,
  • Xiaoyu Zhao,
  • Die Wang,
  • Wenye Li

摘要

Scheelite is the principal ore mineral in skarn‑type W deposits, with its texture and geochemical signatures directly recording the metal source, mineralization conditions, and fluid evolution. The Maka W–Pb–Zn–Sn–Be polymetallic deposit in southeastern Yunnan has been studied primarily for its Pb–Zn or Be mineralization, whereas W mineralization has received limited attention, hindering a systematic understanding of regional W potential and ore‑forming processes. Based on integrated field and petrographic analyses, four texturally and compositionally distinct scheelite types (Sch I–Sch IV) have been identified. In-situ textural, geochemical, and Sr‑isotopic analyses of these scheelite varieties were performed using scanning electron microscopy-cathodoluminescence (SEM‑CL) and LA‑(MC)‑ICP‑MS to constrain the W source and mineralization conditions at Maka. Results indicate that Sch I, disseminated within epidote–diopside skarn, exhibits uniform CL brightness, low ΣREE (average 18 ppm), low 87Sr/86Sr (0.71279–0.71482), moderate Mo (average 206 ppm), Y/Ho ratios of 14–50, and LREE‑enriched patterns. Sch II, occurring in fluorite–quartz veins, displays oscillatory zoning, higher ΣREE (average 96 ppm), elevated 87Sr/86Sr (0.72662–0.73025), Mo content (average 720 ppm), and Y/Ho ratios (19–101). Sch III, hosted in fluorite–feldspar–quartz veins, shows moderately lower ΣREE (average 65 ppm), further increased 87Sr/86Sr (0.73137–0.73643), equivalent Mo (average 556 ppm), and reduced Y/Ho ratios (2–29). Sch IV forms fine grains in chalcedony veins, with ΣREE near 79 ppm, a distinctive “wing‑shaped” MREE‑enriched pattern, lower 87Sr/86Sr (0.71761–0.71841), sharply reduced Mo (average 2.7 ppm), and Y/Ho ratios of 12–40. Systematic shifts in Eu anomalies across the scheelite generations trace an evolving redox trajectory: from high fO2 (Sch I) to low fO2 (Sch II) and back to high fO2 (Sch III and Sch IV). Sch I–III exhibit LREE‑enriched profiles, Y/Ho ratios, and Sr‑isotope compositions consistent with a magmatic‑fluid origin exsolved from the Yanshanian Laojunshan granite. In contrast, Sch IV shows a metamorphic‑fluid affinity, indicated by its MREE‑enriched “wing‑shaped” pattern, low Mo content, high Y and Ho concentration, and elevated Sr/Mo ratios. Integrated with regional tungsten metallogeny, this study proposes that Yanshanian Laojunshan‑related W systems typically comprise "inner quartz-wolframite-vein-type + middle skarn-type + outer fluorite-scheelite-vein-type" mineralization. Scheelite that occurs in fluorite‑bearing veins and exhibits high Sr isotopic ratios with well‑developed oscillatory zoning can serve as a key macro‑ to microscopic indicator for W exploration in late Yanshanian granite.