STRUCTURE MAPPING ON ENHANCED LANDSAT IMAGES OF SOUTHERN BRAZIL: TECTONIC CONTROL OF MINERALIZATION AND SPECULATIONS ON METALLOGENY

Abstract

Computer enhancement, particularly contrast‐stretching, reveals a previously unnoticed east‐west structural zone across a Landsat image of the southern Brazilian Precambrian shield. In this zone occur the only known economic or near‐economic deposits of gold, tin, and copper. Such deposits are typically localized by small east‐west structural elements. Non‐economic copper occurrences elsewhere in the region appear to be related to major northeast‐ and northwest‐trending lineaments mapped on Landsat images. Mineral exploration should be primarily directed at the main east‐west lineament, but two other possible east‐west zones might be worthwhile targets also. The major east‐west lineament projects through a break in the continental shelf, across the Atlantic along a large transoceanic fracture zone and into the African continent along a mapped tectonic trend that goes through an area that produces copper, gold, and tin. Global geophysical data suggest that the mapped east‐west trend in South America is a surface reflection of structures that developed in the tectosphere in Precambrian time and that have persisted until the present.