Remote-sensing studies using Landsat Multispectral Scanner (MSS) and Thematic Mapper (TM) data and side-looking radar images acquired from aircraft were used as field mapping aids throughout this project. Deciduous forests in core-zone areas of intense high-silica hydrothermal alteration were found to have distinctive spectral reflectances on digitally enhanced MSS and TM images. Aided by the enhanced images, we were able to field check and greatly extend the areas of several of the zones found during field mapping, more clearly outline them, and identify previously unknown occurrences in lowland areas having poor outcrops (Anton-Pacheco and others, 1987; Schmidt and Koslow, 1986; Payás and others, 1988, 1993; and Rowan and others, 2000).