Structurally- controlled deep leaching processes have removed vast quantities of carbonate from a substantial portion of the "silica-dolomite" enclosing the 500 copper orebody. Mine drainage subsequently allowed free access of air to the porous environment created and oxidation of sulphides commenced. During the mIne development stage the exothermic and temperature-dependent nature of these hydrolysis reactions resulted in a slow general elevation of ground temperatures. and levels of 90 - lOOC were attained in restricted moist sulphide-rich areas.With the advent of production and extensive use of explosives, the oxidation processes were locally raised to new levels of activity. Direct interaction of explosives and sulphides in favourable conditions caused temperature rises to above 260 C. Above this point the dry oxidation of sulphides in air was initiated and rapid escalation to the vicinity of 800 C has been known to occur in isolated cases.Ground reactivity is a function of the complex interrelationship of several controlling factors and no simple index exists.Control techniques are presently aimed at prevention of temperature rises in the range 100 -260 C. Inhibition of the rapid dry oxidation processes above 260 C is difllcult and current efforts have met with only partial success.