Abstract
Reflection spectra of particulate samples of minerals that commonly occur in hydrothermally altered rocks and soils were recorded to display their features at their natural spectral bandwidths in the near-infrared from 1.3 to 2.4 mu m. Atmospheric transmission spectra were recorded over limited wavelength segments in the same region to demonstrate the availability of some of the diagnostic mineral bands that occur close to regions of intense absorption. Changes occur in the appearance of all these spectra caused by instrumental factors such as less than adequate spectral resolution and response time. The features in the mineral spectra are sufficiently characteristic to be used for analytical purposes, especially including those near 1.4 mu m which are unavailable for remote-sensing activities because of atmospheric obscuration. For remote-sensing purposes, the features in the 2.2-mu m region are emphasized as particularly valuable because they are common to alteration minerals and allow discrimination from nonalteration minerals which provide features only as close as 2.4 mu m. Detection of unique features near 1.76 mu m that occur only in alunite and gypsum is possible through the atmosphere and so provides diagnostic potential. The location and shape of mineral spectral features are retained unaltered in the spectra of rocks, and intensity with which they appear is governed by the accessibility of the particular mineral in the rock to the interacting radiation. For remote-sensing purposes, it appears that at least two 0.1-mu m wide filters in the 2.2-mu m region would be necessary to unambiguously identify the presence or absence of alteration minerals, and that judicious selection of the exact location of filters could provide finer discrimination.
