Mineralization and gossans in the Wadi Wassat-Wadi Qatan region, Kingdom of Saudi Arabia

Very large bodies of stratabound iron sulfides in volcanic rocks of the Wadi Wassat-Wadi Qatan region of Saudi Arabia are capped at surface by numerous iron oxide-rich gossan outcrops. The gossan at Hadbah overlies a low-grade nickel-bearing sulfide body, but most of the sulfide lenses are almost devoid of base metals. Supergene alteration of pyrrhotite-pentlandite has given rise, in profile, to a narrow (<5 m thick) zone of violarite-pyrite (or marcasite) beneath an oxide zone (<35 m deep) of goethite-hematite-silica. Geochemical data show that, despite intensive leaching in the upper parts of the profile, the gossans over the nickeliferous sulfides have higher contents of trace metals than do the gossans overlying pyritic bodies. Both hypogene and supergene textures are well preserved in the gossans; in particular, the presence of very fine-grained pentlandite in the primary sulfide assemblage is precisely recorded by diagnostic replica textures in the gossans.