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~ III IIIIIIIIIIIIIIII • <br />To: Ron Zumwalt <br />From: Richard Neu <br />Subject: February Metallurgical Report <br />Date: March 10, 1992 <br />Grinding <br />Monthly mill tonnage was 135,315 tons or 4,666 tons/day. Mill <br />availability was 90.2$. Operating tonnage averaged 216 tons/hr. <br />The 80$ passing size (p80) of the sag mill product was finer at <br />586 microns. The increased ball charge of 12$ most likely was <br />responsible for the finer product. The p80 of the ball mill <br />product remained about the same at 123 microns. Bond work index <br />of the ore remained high at 19.1 kw-hr/ton. Ball mill ball <br />consumption was low due to mill power limits. Ball charge remains <br />limited by power draft. Cyclone u'flow return to the Saq Mill <br />should reduce the ball mill load and improve throughput and grind. <br />A grind study by Armco has indicated that optimum ball mill ball <br />make-up is 40$ - 3" and 60$ - 2" balls. Trash screen opening size <br />reduction from .70 mm to .60 mm should be considered to minimize <br />downstream sand, wood, and flow problems. <br />Recently, the sag mill was re-lined. The first set of liners <br />got 546,520 tons while the second set got 723,302 tons. The first <br />set of 2" grates got 696,169 tons while the second set of 5/8" <br />grates got 516,524 tons. Hopefully, with good operator control, <br />liner life can be extended to exceed 1,000,000 tons. Ball mill <br />liners are still in good shape. Greatest wear is on the lifter <br />bars towards the ends and outer periphery of the mill. Future <br />measurements will indicate when relining is necessary. <br />Thickening <br />Flocculent consumption was reasonable at .19 #/ton. <br />Flocculent feed points remain to be optimized. Thickener underflow <br />density improved some. Current target level is 55$ solids. Most <br />important to maintaining thickener underflow density is constant <br />feed and water balancing. Sag mill water addition ratioing to tons <br />has improved the water balance. <br />Leaching aad Carbon-in-Leaching <br />All grades listed below are expressed in oz/ton solids. <br /> <br />- Au <br />------- Ag <br />-------- <br />Mill Report Grade .041 .084 <br />Production Report Grade .041 .080 <br />Mill Report Solid Tail .009 .051 <br />Mill Report Solid Recovery 77.6 39.6 <br />Production Report Solid Recovery 77.8 36.9 <br />Mill Report Solution Grade .0026 .007 <br />Mill Report Total Recovery 72.8 37.2 <br />Production Report Total Recovery 73.0 34.6 <br />