Relationships between SEM-cathodoluminescence response and trace-element composition of hydrothermal vein quartz

Abstract

Laser-ablation ICP-MS data of hydrothermal vein quartz with zonation in scanning electron microscope cathodoluminescence reveal two groups of trace elements, one that co-varies in concentration with luminosity and another that remains uniform throughout. Bright luminosity correlates with a high total abundance of trace elements in early quartz, including Al (up to 410 μg/g), Ti (up to 240 μg/g), K (up to 330 μg/g), Li (up to 8 μg/g), Na (up to 36 μg/g), and Fe (up to 20 μg/g). Up to 20 times lower concentrations of these elements are associated with dark luminosity in late quartz. Concentrations of P (~21 μg/g), Ga (~0.3 μg/g), Ge (~1.3 μg/g), Sn (~1.5 μg/g), Cu (~0.3 μg/g), and Ag (~0.1 μg/g) demonstrate no relationship with luminosity. Charge balance cannot be achieved for bright luminescent quartz unless the presence of up to 6 μg/g H+ (not analyzed by LA-ICPMS) or interstitial Al3+ is invoked. Interestingly, the inferred ~6 μg/g H+ remains constant for quartz containing more than 10 μmol total trace elements and might represent the solubility of H+ in hydrothermal quartz at temperatures between 450 and 700 °C.