AREA-SELECTION IN GOLD EXPLORATION, WESTERN SAUDI ARABIA

Upper Proterozoic rocks are exposed over 680,000 sq km of western Saudi Arabia, and contain 786 known occurrences of gold. Computer-statistical modeling has been used within a geographic information system (GIS) to select areas where follow-up exploration may be warranted. Data in the GIS were used (Shujoon, 2001) as input to a Boolean Logic Model (BLM), and two Index Overlay Models: one using binary evidence maps (IOM-BEM), and a second using multi-class maps (IOM-MCM). The BLM identified 6691 sq km of rocks with high potential for gold, the IOM-BEM 11,903 sq km, and the IOM-MCM 14,215 sq km of high gold potential. These numbers represent 0.98, 1.74, and 2.09 % of the Shield within Saudi Arabia.

Localities with high gold potential are associated with felsic to intermediate intrusive rocks, felsic to mafic volcanics, and epiclastic sedimentary rocks, and they often are concentrated in linear and what appear to be fold "trends". Rocks identified by all three models lie almost exclusively within the Zalm sub-terrane of the Afif lithotectonic terrane, in the east-central Shield. When known occurrences are overlain with the result maps, significant areas are identified by all three models that contain no known gold, making them particularly attractive targets for follow-up study. This is especially true in the northwest Zalm, although much larger areas of high potential are present in the center of the Zalm sub-terrane.

The area to be examined for gold within the Saudi Shield has been reduced by more than 98 percent using the Index Overlay Models, and more than 99 percent using the BLM. The IOM-BEM may be the most suitable model overall, as it is less restrictive than the BLM, yet uses the same reliable binary input grids as the BLM. The IOM-MCM by contrast enlarges the area of exploration to a level that may not be supportable.