Preliminary map of limonitic hydrothermal alteration for portions of the Needles 1° x 2° quadrangle, Arizona and California

Portions of the Needles quadrangle have been designated by the Bureau of Land Management as potential wilderness areas and are being evaluated by a multidisciplinary team to determine the mineral-resource potential. As a part of this study Landsat images are being used to map the generalized distribution of limonitic materials as a guide to hydrothermal alteration which, in turn, acts as a guide to mineralized systems. The term limonite, defined by Blanchard (1968) as a general term for hydrous iron oxides, is here modified to include any material with the unique spectral reflectance properties of the ferric oxide minerals such as hematite and goethite, as defined by Hunt (1980).

The map shows areas of limonitic hydrothermal alteration but does not show hydrothermally altered areas lacking limonitic materials. Table 1 lists, for each hydrothermally altered area detected, the type of alteration and the anomalous trace-element geochemical suite found in that area.