Camphor is sublimable compound while $CaSO_4$ being ionic is not. Therefore, the two can be separated by the method of sublimation. If a mixture of the two is heated in a China dish covered with a porous paper and an inverted funnel over it, we will find the crystals of camphor forming on the inside walls of the inverted funnel. Thus, pure $CaSO_4$ will be left in the China dish.