Séminaire Loïc Bouat

Abstract

Topaz is commonly found in environments hosting rare element ores such as Li, Nb, Ta, Sn, and W. This fluoride mineral is ubuquitous in pegmatites and highly evolved peraluminous granites, both during magmatic and hydrothermal stage. Due to its high density and hardness, topaz is used in stream-sediment sampling as a tracer mineral for these rocks (Stendal & Theobald, 1994; McClenaghan, 2005; Gent et al., 2011). However, the topaz-bearing rocks vary significantly in morphology and mineralogy (i.e. resources). New advance is required to fully use topaz as an indicator mineral for exploration program.

This study investigates the potential of using trace element concentrations in topaz to distinguish different rare element ores. Firstly, we present geochemical data obtained via LA-ICP-MS on trace elements in topaz from environments associated with these ores (topaz rhyolites, hydrothermal quartz veins, rare element granites, pegmatites, and greisens), as well as from non-associated sources (topaz granites). Secondly, we evaluate the consistency of trace element signatures in topaz by comparing primary and secondary topaz samples from the vicinity of topaz-bearing rocks.

The results indicate that Ge and Ga are the only two elements consistently present in all analysis. Additionally, Li, Mg, Ti, and W are detected in at least half of the rock groups. The concentrations of these elements enable the differentiation of various rock groups, specifically distinguishing mineralized from non-mineralized rocks, as well as volcanic, plutonic, and hydrothermal environments.

Statistical analysis of the geochemical footprint between primary and secondary topaz prove the efficiency of the topaz as an indicator mineral, and highlight probable new mineralized rocks still unknown today.

This first database demonstrates the potential of topaz to be a good indicator mineral for exploration of rare metal ore deposits.