1. IN A HEAVY MEDIUM MINERALS SEPARATION PROCESS IN WHICH MINERAL PARTICLES ARE INTRODUCED TO A WATER SUSPENSION OF MAGNETIC PARTICLES, HEAVIER MINERAL PARTICLES SINK IN THE SUSPENSION WHILE LIGHTER MINERAL PARTICLES FLOAT, THE RESULTING SINK AND FLOAT PRODUCTS ARE SUCCESSIVELY DRAINED OF SUSPENSION AND WASHED WITH WATER, BOTH THE WASH WATER AND A VARIABLE FRACTION OF THE DRAINED SUSPENSION ARE TREATED TO REMOVE NONMAGNETIC CONTAMINANTS AND WATER AND THEREBY PRODUCE A DENSIFIED SUSPENSION, SAID DENSIFIED SUSPENSION TOGETHER WITH THE REMAINDER OF THE DRAINED SUSPENSION IS TRANSFERRED TO A PUMP BOX, AND THE SUSPENSION FEEDS FROM THE PUMP BOX TO A VESSEL WHERE THE MINERAL PARTICLES ARE INTRODUCED, THE COMBINATION THEREWITH OF A METHOD OF CONTROLLING THE SPECIFIC GRAVITY OF THE SUSPENSION IN THE VESSEL TO A SET VALUE COMPRISING MEASURING A SPECIFIC GRAVITY REPRESENTATIVE OF THE SUSPENSION IN THE VESSEL, MEASURING CHANGES IN THE LEVEL OF THE SUSPENSION IN THE PUMP BOX FROM A SET LEVEL, AND ADJUSTING BOTH THE MAGNITUDE OF THE TREATED FRACTION OF THE DRAINED SUSPENSION AND THE RATE AT WHICH SAID DENSIFIED SUSPENSION IS TRANSFERRED TO THE PUMP BOX IN RESPONSE TO THESE MEASUREMENTS TO TREAT A LARGER FRACTION AND TRANSFER MORE OF SAID DENSIFIED SUSPENSION AS THE SPECIFIC GRAVITY GOES DOWN FROM SAID SET VALUE AND THE REVERSE AS THE SPECIFIC GRAVITY GOES UP, WITH ONE OF THE ADJUSTING STEPS FOLLOWING THE OTHER.