1989-10-10_REVISION - M1988112 (12)

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The fine ore from the SAG mill is conveyed to the pump box which supplies feed to the hydrocyclones. The hydrocyclones are cyclones that physically separate the ore according to particle size. Water is added and the ore is processed as a slurry. A particle size of 80 ye passing 100 microns is necessary for the process used in the mill. The larger particles in the slurry are separated centrifugally by the cyclones and fed to the ball mills. The San Luis mill will utilize one or two ball mills to further reduce the particle size and send the ore back through the cyclones until the proper size is reached. The next step i s di 1 uti on of the slurry to 20% so~l ids. An inert flocculent is added to the slurry and the slurry is then pumped to the thickener tank where the slurry is allowed to settle. The settled slurry, at 50% solids, is pumped to the leach tanks. Mater from the thickener tank is decanted from the top of the thie~kener and is recycled to the grinding circuit. • The leach tanks will hold the slurry in a closed system. The gold will be dissolved from the slurry in the leach tanks using a dilute cyanide solution for leaching. The leach tanks will be mechanically agitated and will be sparged with air too elevate the dissolved oxygen content of the slurry. Leach reaction time for this ore is expected to be approximately 40 hours. From the leach tanks, the leach solution is sent to the adsorption tanks where the dissolved gold is removed from solution by adsorption onto activated carbon. Granular coconut shell carbon is used as the adsorption media. The adsorption occurs in agitated vessels similar to the leach tanks. The carbon is advanced through the adsorption stages countercurrently to the slurry. Slurry flows through the adsorption tanks on a continuous basis. Carbon handling after adsorption is a three stage process. In the first step, the gold loaded carbon is washed with an acid in D-14