Hydrothermal Quartz Microtextures and Depositional Processes Revealed by SEM-CL Imaging

Abstract

SEM-CL imaging of hydrothermal quartz from the Te Kopia geothermal field (New Zealand), complemented by fluid inclusion analysis, has revealed a complex history of crystal growth, dissolution and overprinting, unseen by other observational techniques. CL-dark quartz (characterised by euhedral growth zones) grew into fluid-filled space, at least 300-320 m below the present ground surface, in a 195 2 25'C reservoir. Movement on the Paeroa Fault provided pathways for fluids to move through the system, which resulted in further quartz precipitation, but SEM-CL evidence also shows that the quartz was partly dissolved, with later overprinting and void-filling by CL-bright quartz.