Abstract: Evaluation of LANDSAT Data in Exploring Evaporite Basins

W. D. Carter

Six LANDSAT images obtained over a period of 5 years show that the Salar of Uyuni, an evaporite basin covering about 10,000 sq km in southern Bolivia, is a highly reflecting but changeable surface feature subjected to rapid seasonal variations. During wet seasons, 80 to 100% of the surface may be covered by water, and in dry seasons water may be absent or cover as little as 10% of the surface. Two images were analyzed experimentally by interactive computer methods to utilize the full dynamic range of the LANDSAT multi-spectral scanner. It was found that salt, which appears to be a uniformly white surface on standard image products, can be subdivided using band 6 (0.7 to 0.8 µm) and band 7 (0.8 to 1.0 µm) on the basis of radiance values into three reflectance cla ses. Field work indicated that the classes correlated best with relative ages of the salt (young, intermediate, old) which, in turn, are related to their degree of surface roughness. Areas of water and moist salt could also be distinguished and separated into several classes based on the relative depth of water.

Surface sampling by Carter and Ballon in April 1976 indicated the presence of high concentrations of lithium and potassium in two shallow, surface-brine pools. Later sampling by Ericksen and Vine, in September 1976, revealed more widespread distributions and that the highest concentrations were in brine and mud below the salt crust in the southeast quadrant of the salar.

While repetitive LANDSAT images do not provide a direct indication of the distribution of lithium and potassium concentrations, it is suggested that repeated observations may assist in developing a strategy for more detailed exploration. Although the Salar of Uyuni currently supplies Bolivia's requirements for salt, additional work is needed to determine the areal extent and volume of commercial values of lithium and potassium, and where they can be best exploited.

AAPG Search and Discovery Article #90967©1977 GCAGS and GC Section SEPM 27th Annual Meeting, Austin, Texas