科研之友
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摘要
Garnet is one of the definition minerals of skarn deposit, its textural and compositional characteristics have proven useful in tracking the features of ore-forming fluids at early stage. However, the relationship between garnet growth and the enrichment process of economic metal remains unclear. In this paper, texture and geochemistry of garnet from the Tongshankou Cu-Mo-W deposit, Edong district, were studied by electron probe microanalysis and LA-ICP-MS. Results show that the majority of garnet grains belong to andradite-grossular series with a certain amount of W, especially in garnets with high proportions of andradite (up to 3898 × 10-6 ). Tungsten has strong positive correlations with Mo and As, as well as a certain negative correlation with Ti, indicating that W was incorporated into the garnet lattice by isomorphic substitution. Garnet can either includes scheelite grains with simple texture or be replaced by scheelite grains with complex textures, suggesting garnet recorded the evolution of hydrothermal fluids features (e. g., fo2 and W contents) from pre- to co-precipitation of scheelite. The deposit of massive andradite at Tongshankou is expected to widely dispersion of W in the early stage of mineralization, resulting in low grade and small scale of W deposit. The W host by garnet is likely to release and improve the grade of the ore to a certain extent only when these garnets experience extensive replacement during retrograde alteration, which is probably the critical reason that why oxidized W skarn commonly has lower grade and smaller scale than reduced W skarn. This research highlights that the compositional features (e. g., W, Sn contents or W/Sn, W/Mo and W/As ratios) of garnet can be used as indicators for the redox properties of skarn and the grade and scale of W deposits. Garnet also serves as a potential prospecting and exploration indicator mineral for W, Mo, and Sn deposits. ? 2023 Science Press.
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