OPTICAL AND GEOCHEMICAL ANALYSES OF FLUORESCENT HYDROTHERMAL CALCITE FROM THE BATOPILAS MINING DISTRICT, CHIHUAHUA, MEXICO

Photoluminescence (PL) and cathodoluminescence (CL) in hydrothermal calcite is a well-studied field with applications in understanding paragenesis and constraining hydrothermal fluid chemistry. The native silver-bearing calcite veins from the Batopilas mining district in southwestern Chihuahua exhibit PL colors ranging from light orange to reddish purple when exposed to short wave UV (254 nm). Mn²⁺ is the most common cation activator for luminescent calcite; however it has been noted that native silver commonly occurs in the calcite veins with reddish luminescence. This relationship suggests that Ag²⁺ could be affecting the luminescent character of the calcite in these veins. Other cations could have effects as well, as Pb, Zn, and Fe sulfides are also present in some veins. Laser ablation ICP-MS and electron probe microanalysis are used to determine the trace and major element concentrations in these veins. The results of the elemental analysis are correlated with images from optical CL microscopy and SEM-CL to assess the relationships among the colors of luminescence and trace element concentrations.

CL images of the calcite veins are also used to document crystal growth patterns, such as sector zoning overprinting concentric zoning, as a means of helping decipher vein paragenesis. The provenance of the Batopilas mineralizing fluid is not well constrained, and growth patterns visible only with CL can help understand fluid evolution and establish genetic relationships between various veins and their contained metallic components.