Alunite Characterization with Ultra-High Resolution SWIR

Alunite characteristics and composition are used as a good indicator of gold potential in an epithermal system. Alunite precipitates from fluid that is very acidic and oxidized in hypogene acidic epithermal systems and supergene environments. When Alunite occurs as an alteration of some other mineral, it is difficult to identify and distinguish by eye due to the crystals occurring at sizes too small to see, even with a hand lens. A clue to hypogene alunite is the association with pyrophyllite and occurrence with high temperature kaolinite. Pyrophyllite that occurs with alunite is very difficult to identify by eye as it almost never forms crystals big enough to visually see. Field portable spectrometers have been widely used around the world to focus on the spectral shift in the composition of alunite from potassium rich (K-alunite) to sodium-rich (Na-alunite) to vector the mineralization. In recent years, spectral resolution of these instruments has increased due to demand by correlating data sets from other remote sensing technologies like hyperspectral imaging. This study focuses on the evolution of spectral resolution using ultra-high resolution to characterize K-alunite from Na-alunite and its association with pyrophyllite and high temperature kaolinite by identifying additional features not seen with lower resolution spectrometers, an application that could prove to be useful in the future for better understanding of mineralized zones.