QUANTITATIVE REFLECTANCE SPECTROSCOPY OF BUDDINGTONITE FROM THE CUPRITE MINING DISTRICT, NEVADA

Buddingtonite, an ammonium-bearing feldspar diagnostic of volcanic-hos ted alteration, can be identified and, in some cases, quantitatively m easured using short-wave infrared (SWIR) reflectance spectroscopy. In this study over 200 samples from Cuprite, Nevada, were evaluated by X ray diffraction, chemical analysis, scanning electron microscopy, and SWIR reflectance spectroscopy with the objective of developing a quant itative remote-sensing technique for rapid determination of the amount of ammonium or buddingtonite present, and its distribution across the site. Based upon the Hapke theory of radiative transfer from particul ate surfaces, spectra from quantitative, physical mixtures were compar ed with computed mixture spectra. We hypothesized that the concentrati on of ammonium in each sample is related to the size and shape of the ammonium absorption bands and tested this hypothesis for samples of re latively pure buddingtonite. We found that the band depth of the 2.12- mum NH4 feature is linearly related to the NH4 concentration for the C uprite buddingtonite, and that the relationship is approximately expon ential for a larger range of NH4 concentrations. Associated minerals s uch as smectite and jarosite suppress the depth of the 2.12-mum NH4 ab sorption band. Quantitative reflectance spectroscopy is possible when the effects of these associated minerals are also considered.