SEM-CL imaging of hydrothermal quartz – lessons and applications

Abstract

Scanning electron microscopy-cathodoluminescence (SEM-CL) is an effective tool for deciphering quartz deposition processes in ancient (fossil) hydrothermal systems, explored for their ore-mineral potential, and in active geothermal systems, which are potential energy resources. SEM-CL imaging may reveal chronological relationships between secondary (hydrothermal) quartz and primary rock-forming minerals, or aid the differentiation of unique hydrothermal events (e.g. at Te Kopia (New Zealand), where CL-dark quartz grew into open space in a 215 ± 15°C reservoir, was dissolved and overprinted by CL-bright quartz). SEM-CL integrated with fluid-inclusion data may enable quartz from specific alteration events to be "fingerprinted", constraining the timing of fluid-inclusion trapping and nature of fluid migration. Flow-reactor autoclave experiments, and SEM-CL examination of laboratory “grown” quartz, are used to model reservoir dynamics in enhanced geothermal systems that depend on fracture surfaces as areas for heat exchange, because quartz precipitation can ‘plug’ these systems.