THE ROLE OF FLUID PRESSURE IN THE FORMATION OF BEDDING-PARALLEL, THRUST-HOSTED GOLD DEPOSITS, SABIE-PILGRIMS REST GOLDFIELD, EASTERN TRANSVAAL

Shallowly dipping, thrust-hosted gold veins occur within the Paleoprot erozoic Transvaal Supergroup rocks in the eastern Transvaal of South A frica, Internally, the veins record episodic events of fluid infiltrat ion and subsequent mineral deposition, within discrete local-scale thr ust faults, Evidence also exists for subvertical dilation within the i ndividual veins, and textures which record open-space filling are pres erved. The probable depth of formation suggests lithostatic pressures in excess of 2.2 kbar, and the vein textures indicate numerous reactiv ation events associated with individual thrust faults occurring in a t errain characterised by low levels of preserved strain. Fault reactiva tion may have occurred under conditions of low differential stress in the presence of high pressure fluids, with P-fluid approaching or exce eding lithostatic levels.