Assessment of shear zone‑derived quartz from the Etam area, southwest Cameroon as potential high‑purity quartz resource: petrography, geochemistry and technological studies

摘要

This study focuses on the evaluation of the high-purity quartz (HPQ) potential of a shear zone-hosted hydrothermaland metamorphic quartz deposit in Etam, southwest Cameroon. The shear zone quartz-rich rock is monomineralic andconsists of both milky and translucent varieties. The combination of ICP-MS and LA-ICP-MS analytical techniques wasused to assess the chemical purity of both quartz varieties. These compositional analyses show that all quartz sampleshave SiO_2content of 98.46–99.75 wt% with very low concentrations of all the other elements. Translucent quartz whencompared to the milky quartz variety shows low concentration of most of the elements including the following principalimpurities: Al (mean 107 μg g~(−1)), Ca (mean 27.85 μg g~(−1)) and Fe (mean 26.05 μg g~(−1)). Bubble generation in the samplesafter flame fusion over a silica plate was assessed to test the suitability of the quartz in industrial uses. The results obtainedfrom the chemical analyses and bubble formation tests indicate that all the samples investigated do not meet the HPQrequirement. However, the translucent quartz shows characteristics of medium-purity quartz and can produce silica glassfor some industrial manufacturing even without further purification. In this study, the fluid inclusions in the sampleswere examined as this bears information on the economic viability of the deposit and provides clues on the genesis ofthe quartz vein. Also tiny mineral inclusions within individual quartz grains were identified by SEM–EDS. The results ofthese studies show that the deposit is probably of metamorphic origin marked by crystal-plastic deformation in quartzgrains. The veins were later modified by hydrothermal fluid input. The results also indicate that the majority of impuritiesare likely hosted by fluid inclusions and thus the quartz can be upgraded to HPQ after purification by suitable methods.