Tungsten Scavenging by Garnet and Its Implications for Low Metal Grades in Oxidised Skarn Systems

ABSTRACT Silicate phases coexisting with ore minerals are often overlooked when constraining ore‐forming processes, even when they host significant concentrations of commodity metals and may subsequently release these metals to form discrete mineral phases. Relationships between garnet growth and tungsten mineralisation are studied using W‐rich garnets (up to 3542 ppm) from the oxidised Fujiashan W(‐Cu‐Mo) skarn, China. Compositional heterogeneity in garnet, expressed as core‐to‐rim texture, relates to successive two‐stage fluid infiltration. Tungsten shows strong positive correlations with As, Mo and In, with all four elements appearing to be structurally bound. Scheelite is expected to form during the replacement of W‐rich garnet by retrograde minerals. Scavenging large quantities of W by andradite garnet and the lack of intense retrograde alteration may be critical factors contributing to low W grades observed in oxidised skarns. Our findings underscore the importance of gangue mineral growth and breakdown in influencing the distribution of certain ore metals.