INSIGHTS INTO HYDROTHERMAL PROCESSES FROM CATHODOLUMINESCENCE AND TRACE ELEMENTS IN QUARTZ

Scanning electron microscope-cathodoluminescent (SEM-CL) textures reveal textures in quartz that are not observable using any other technique. SEM-CL textures show that veins that appear simple optically actually formed during multiple episodes of fluid flow, precipitation, and dissolution. These textures and the trace elements that cause them result from the specific physical and chemical conditions of quartz precipitation. However the specific conditions reflected by different trace element compositions and CL textures remain largely unknown. Here, we present SEM-CL images and trace elements in quartz from hydrothermal quartz from several types of hydrothermal ore deposits. This data enables fingerprinting of ore deposit types and insight into the physical and chemical histories of hydrothermal systems and ore deposit formation.

Porphyry copper deposits are distinguished by a wide range of complex CL textures with abundant evidence for superposition of multiple fluid flow events. Porphyry copper quartz contains more Ti than quartz from any other deposit type, consistent with higher formation temperatures. Epithermal deposits and Mississippi Valley Type (MVT) deposits are characterized by quartz with oscillatory euhedral growth zones. Epithermal quartz is typically more complex than MVT quartz with variations in crystal sizes and CL intensities as opposed to the consistent zoning observed in MVT quartz. Epithermal and MVT quartz are similar to one another in composition; however, quartz from epithermal deposits typically contains a few tens of ppm of Sb, whereas MVT quartz contains a few tens of ppb Sb. Quartz from these deposits is characterized by low Ti concentrations and bimodal distribution of Al concentrations between a few tens of ppm and a few thousands of ppm. Iron oxide copper-gold (IOCG) quartz and orogenic Au quartz are difficult to distinguish from one another based on trace elements alone, however their CL textures are quite distinctive. Orogenic Au quartz has homogenous CL textures with little observable variation in intensity. IOCG quartz has more complex textures including euhedrally zoned crystals. These two deposit types contain fewer total trace elements than any other deposit type analysed.