113-10 Assessing the Suitability of Natural Scheelites for In Situ REE Analysis and Ore Geochemistry

Session: Mineralogical Characterization of Economic Resources: From Critical Minerals to Gemstones (Posters)

Presenting Author:

Authors:

Abstract:

Scheelite, CaWO₄, is a rare-earth-element (REE)-enriched accessory mineral found in ore deposits with the capacity to incorporate REEs, molybdenum, and uranium, making it a valuable geochemical proxy for understanding mineralization and critical mineral potential.   Despite advances in in-situ trace element analysis, the absence of a well-characterized, widely available scheelite reference material (RM) hinders interlaboratory reproducibility and method validation of in situ trace element analyses.   Five natural scheelite samples from four geologically distinct localities:  Stibnite Yellow Pine (NMNH-4, Idaho, USA), Victory South–McLeay (Australia), Yaogangxian (South China), and Xuebaoding (Sichuan, China) were assessed for REE and U concentrations along with homogeneity and precision, both within and between discrete crystals.  Laser Ablation – Inductively Coupled Plasma – Mass Spectrometry analysis reveals distinct REE and trace element patterns that differentiate the scheelites by deposit type: Four distinct REE profiles were observed: (1) bell-shaped with a positive Eu anomaly and MREE enrichment, (2) LREE enriched and HREE depletion with a negative Eu anomaly, (3) HREE-enriched with a positive Eu anomaly, La enrichment and Ce depletion, and (4) flat with a positive Eu anomaly, La enrichment and Ce depletion in the rim, and the inverse pattern in the core. Scheelite NMNH-4, a primary RM for in situ U-Pb dating, has high U (~21 ppm) but poor spot reproducibility for U (119% RSD) and REEs (300–400% RSD), low REE content (e.g., 2.9 ppm La, 7.0 ppm Ce, 1.4 ppm Yb, 0.14 ppm Lu), and strong core-rim zonation, limiting its use for trace element calibration. In contrast, natural scheelites, Xueboading 5 (0.14 ppm U, 87.0 La, 241.5 Ce, 19.8 Yb, 2.02 Lu, 20–60% RSD), Xueboading 6 (0.59 U, 17.8 La, 43.5 Ce, 45.0 Yb, 7.22 Lu, 50–150% RSD), and Yaogangxian (0.36 U, 14.3 La, 39.0 Ce, 124.05 Yb, 18.1 Lu, 20–100% RSD), exhibit lower U,  improved analytical precision and minimal core to rim zoning. With further screening of specific grains, they are possible candidates for REE and U RMs.  In particular they may be suitable as secondary RMs for interlaboratory reproducibility and method validation in conjunction with synthetic scheelites (Zhang et al., 2023 doi: 10.1111/ggr.12523), used as primary RMs, which are more homogeneous (0.5-5.6% RSD for REE) but have more limited supplies.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8345

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.