Fluorescence of Silver Bearing Hydrothermal Calcite Veins
My project focused on the luminescence of silver-bearing hydrothermal calcite veins from Batopilas, Mexico, which is in southwestern Chihuahua. Luminescence is when an external energy source excites electrons in a mineral to a higher energy state, and then as they return to ground state they emit the extra energy as visible light. I used photoluminescence (stimulus from a UV light) and cathodoluminescence (stimulus from an electron beam). There were a variety of photoluminescent colors in the calcites ranging from red-violet to pink to orange. The red-violet and pink photoluminescent samples also contained metallic minerals such as galena, sphalerite, and native silver whereas the orange samples were barren. This makes photoluminescent color a useful indicator in the field for finding metallic mineral-bearing veins.
The colors also correlate to an increase in Ce and Mn trace metal concentrations, as determined with Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). With cathodoluminescence there was no color variation or relationship with metallic mineral assemblages. There was a relationship between increasing cathodoluminescence intensity and Zn trace-metal concentrations. The implications of these relationships to the mining district are still being investigated.