New Mexico Geological Society Annual Spring Meeting — Abstracts

Pyrite, like most sulfide minerals, is opaque in thin section to visible light and has traditionally been studied in reflected light. Recent developments in transmitted light infrared microscopy allow the study ofinternal features such as growth banding, crystal intergrowths, solid and fluid inclusions in opaque minerals including pyrite. Doubly polished, 100 -150 µm thick sections of pyrite were prepared from different locations throughout New Mexico. These were examined for internal features using a transmitted infrared microscope coupled with an infrared camera sensitive to wavelengths between 0.8 - 2.2 µm. Transparency ofpyrite varied between analyzed samples as well as within any given sample. Three samples (Ortiz Mine, Nacimiento Mts., and Pinos Altos) were completely opaque to infrared light; the rest of the samples were poorly to well transparent, with mostly patchy transparency. The well transparent samples were from Chino Mine, Kelly Mine, and Groundhog Mine. The initial goal of this research was to find fluid inclusions. Transparent, two phase (liquid and vapor) fluid inclusions, varying in size from 5 -30 µm, were found in the pyrite samples from Kelly Mine. There is abundant fluid inclusions in most of the transparent samples but, the majority of them appear completely black in infrared, without discernible internal details. In addition to fluid inclusions, other interesting internal features observed in the analyzed samples included growth banding (Chino Mine and Kelly Mine) and fiber like solid inclusions (Groundhog Mine). This study indicates the potential for further research on fluid inclusions in New Mexico pyrite, especially from Kelly Mine.