Previous investigations have successfully used the 1·65/2·22μm ratio to map the concentration of hydroxyl-bearing minerals in imagery of sparsely vegetated terrain. However, difficulties arise in applying this ratio to semiarid regions where there is a wide variation in vegetation density. Besides mapping the mineralogic features of interest, the 1·65/2·22μm ratio also maps the density of vegetation by responding to leaf water content. A technique has been developed to estimate the vegetation contribution to this ratio based on the near-IR/red ratio. The technique has proved useful in mapping supergene alteration in the Virginia Range, Nevada