The appearance of part of this area in a natural color aerial photo (somewhat overly red-brown in its printing) is seen in here.

In the field, the same area is seen to consist of gentle rolling terrain covered sporadically by cedar and sagebrush;

in the satellite image this vegetation does not stand out as blotches of red suggesting that cedar has a weak reflectance response in the near-IR.

A published geologic map (Stringham and Brooke, 1962) of this area indicates a wide variety of alteration types have developed here. Their report states that mineralization consists of pyrite and chalcopyrite (copper-bearing), the latter of insufficient grade (amounts) to be minable. Alteration is confined to a group of volcanic rocks called andesites which, after emplacement and cooling, were subjected to volcanic gases and hot solutions that modified some of the lava rocks. One alteration type is kaolinite, a common clay mineral much sought after for ceramics, that is light brownish-white at this location. A second light-gray mineral is alunite, a hydrous potassium aluminum sulphate. The principal alteration mineral is hematite, the anhydrous iron oxide, which is a medium grayish red in color; minor amounts of limonite are present but the yellow-brown color of the space image corresponds mainly to altered hematite rather than the similar gossan. Very white areas of siliceous sinter are scattered about and a few areas actually contain native sulphur derived from the breakdown of the original sulphides. In the ground based photograph above, the light patch coincides with mainly a kaolinite-alunite (k/a) mix and the reddish area is hematitic staining on weathered volcanics. To appreciate their general distribution in this subscene, examine the map below, a simplified version of the published map, itself too detailed to reproduce well on this Web Page. This map can be printed out with your Web Browser for ease of reference in studying the images below.

We will now peruse a set of images prepared to illustrate how remote sensing data can be applied effectively in mineral exploration. Suppose, to start, that you are a modern-day prospector searching for some metal (gold is the obvious choice but copper is often the more likely find). If you had chosen a large region in which to hunt, you would be grateful for Landsat imagery that encompasses many thousands of square miles. Even in a full scene, the anomalous color in the White Mountain area (as this alteration district is known by) would grab your attention because it is typical of a gossan signature. Your first logical step would be to zoom in on your image processor to the immediate area showing this signature in a natural color (bands 1-3) rendition. Dark areas in the subscene relate mainly to the volcanics. On the left side, the map shows these to be basalts (an almost blackish rock typical of Hawaiian volcanism and of the Snake River volcanic plains of Idaho); those at the top and bottom are somewhat lighter (but still dark grayish-brown) andesites (typical of volcanoes in the western U.S. such as Mt. St. Helens). White Mountain stands out on the right in light bluish-gray tones; it contains a radial pattern that corresponds to furrowed gullies draining down from its central peak. The main alteration zones make up a pattern with an E-W branch that meets a N-S segment on the left. Most of this alteration is displayed in the yellow-browns seen in the regional subscene. Other zones are much lighter (sort of tan) in this image. These two principal zonal types broadly match the hematite and k/a areas on the generalized map shown above. Areas on that map identified as alluvium (soil and loose surface debris) show up in several variant colors in the subscene. Those with a color similar to the hematite are alluvial deposits derived from the altered hematitic zones. (An equivalent subscene made from bands 2,3,4 [not reproduced here] contains very little discrete red patches, confirming the sparsity of active, reflectant vegetation.)

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