RESOLVING FLUID CHRONOLOGY IN HYDROTHERMAL ORE DEPOSITS USING CATHODOLUMINESCENCE

By their very nature, hydrothermal ore deposits are located in environments characterized by at least transiently enhanced permeability and focused fluid flow. As a consequence, it is the norm for deposits to have experienced multiple flow events making the interpretation of fluid inclusion data and hydrothermal evolution difficult. Cathodoluminescence of quartz using an SEM-mounted CL detector can be used as a powerful tool to help resolve complex fluid histories. The application of SEM-CL can be done over a range of scales, from the growth stage (mm-scale) to the growth zone (100’s of microns) and even down to individual microfractures (a few microns). The establishment of petrographic relationships between precipitation events differentiated by their CL signatures allows temporally-constrained fluid inclusion data to be collected. In the ideal case, all fluid inclusions become “primary” with respect to their host, be it quartz within a growth zone or quartz healing a secondary microfracture. This methodology has been used to resolve a number of processes in vein gold deposits: the transition from homogeneous H₂O-CO₂ fluid to fluid unmixing, the progressive mixing and dilution of H₂O-CO₂ fluids, and low temperature brine overprinting and gold remobilization. The future application of the methodology will provide a powerful way of unravelling the complex chemical evolution of ore-forming solutions that laser ablation microanalysis has the potential to reveal.