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REE fractionation between scheelite and apatite in hydrothermal conditions
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1993
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Geochemical analysis of hydrothermal apatite and scheelite pairs from W ore deposits reveals insights into REE partitioning between the two minerals. The study aims to use REE determinations in coexisting scheelite and apatite to identify successive ore‑bearing fluids. Among 18 scheelite–apatite pairs, only five equilibrated, ten deviated, and the rest displayed distinct REE patterns; both minerals concentrate REE with similar HREE/LREE behavior, scheelite slightly richer in HREE, while variations in lanthanide ratios and Eu behavior reflect fluid composition and redox differences between vein and skarn environments.
The geochemical analysis of hydrothermal apatite and scheelite pairs from various types of W ore deposits (skarns, disseminated scheelite, and quartz veins) provides an insight into REE partitioning between the two minerals. Among the 18 analyzed pairs, only five appear to have grown in equilibrium conditions. Ten other pairs show more or less important departures from equilibrium. The remaining apatite and scheelite pairs have quite different REE patterns, indicating crystallization from different fluids. Both minerals concentrate REE. The relative behavior of HREE and LREE is quite similar in the two minerals. Scheelite is only slightly more enriched in HREE relative to LREE than apatite, with K(ap-sch)La-Yb = 0.86 +/- 0.22. Beside these regularities, some dispersion in the lanthanide content ratios of apatite and scheelite, ranging from 0.6 to 5, may be related to fluid composition. The behavior of Eu can be related to redox conditions, which appear to be more oxidizing in vein associations than in skarn environments. Determination of REE in coexisting scheelite and apatite seems an efficient tool for identification of successive ore-bearing fluids.