ECONOMIC-POTENTIAL OF THE ROOIBERG GROUP - VOLCANIC-ROCKS IN THE FLOOR AND ROOF OF THE BUSHVELD COMPLEX

Volcanic rocks of the Rooiberg Group are preserved in the floor and ro of of the mafic Rustenburg Layered Suite of the Bushveld Complex. Fiel d and geochemical characteristics of these volcanic rocks imply that t hey are genetically related to the Rustenburg Layered Suite. Four majo r ore-forming events are identified in the Rooiberg Group. The first p hase was accompanied by volcanic hosted, fault controlled, hydrotherma l copper mineralisation, which is found in the lowermost portion of th e Rooiberg Group, underlying the Rustenburg Layered Suite. This type o f mineralisation is tentatively linked to initial Rustenburg Layered S uite intrusions. Stratabound arsenic mineralisation that possibly form ed in response to contact metamorphism, characterises the second phase , and occurred after extrusion of the Damwal Formation, possibly due t o shallow granophyric intrusion. The third mineralising event occurred in response to contact metamorphism during the final stages of the Ru stenburg Layered Suite, where especially Pb and Zn were introduced int o the felsite roof rocks. This type of mineralisation affected the maj ority of the Rooiberg Group, but is most pronounced towards the contac t with the Rustenburg Layered Suite. The fourth phase is restricted to the Rooiberg Group in the Nylstroom area and is linked to the granite intrusions of the Lebowa Granite Suite, from which Sn and F were intr oduced into the uppermost felsite succession. Mineralisation in the Ro oiberg Group appears to be controlled by the character and intrusion l evel of the associated Bushveld magmas. Different styles of mineralisa tion in Rooiberg Group volcanic rocks are encountered at various strat igraphic levels. Major primary volcanogenic ore deposits appear to be absent.