Abstract: The invention relates to a method of thermal calcination of minerals wherein mineral matter is calcined in a calcination system comprising an optional pretreatment zone and a kiln directly fired by a fuel which must exceed a predetermined calorific value but must not exceed a predetermined ash content, and wherein combustible matter which need not satisfy said calorific value and ash content requirements is burned in separate combustion apparatus external to the calcination system and heat transferred from said separate combustion apparatus to the calcination system in at least one gaseous medium is employed to replace part of said fuel.