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prepared by first agglomerating the ore with Type 3 Portland <br />cement. The ore was then placed in a three inch diameter <br />column. A dilute sodium cyanide solution containing 1.0 pounds <br />of sodium cyanide per ton of solution was circulated through <br />' the ore at an application rate between 0.005 and 0.01 gallons <br />per minute per square ft. The solubilized precious metals were <br />' removed form the solution by activated carbon. Circulation of <br />the solution continued until recovery of the precious metals <br />diminished to an uneconomical rate. At the conclusion of <br />leaching, the solution flow was stopped and the column was <br />allowed to drain for 16 to 24 hours. The column was rinsed with <br />one to four bed volumes of fresh water. Rinse sc+lutions were <br />submitted for analysis and column ore material was sent to the <br />` ~ engineering consultant's laboratory. <br />' D.7.3.1 Geotechnical Characteristics <br />The engineering properties of the native soils in the <br />' area of the heap leach facilities have been estimated based <br />on materials classification using correlations mailable from <br />' ' engineering literature for similar soils. <br />Correlations obtained from NAVFAC (1982) indicate that <br />loose to medium dense silt and silty sand soils, such as <br />encountered in the upper 5 to 10 ft of the heop leach site, <br />are capable of developing internal effective stress friction <br />angles ranging from 26 to 35 degrees. For analytical purposes, <br />an average friction angle of 30 degrees has been assumed for <br />these materials. The associated cohesion intercNpt has been <br />1 assumed to be zero. When amended with powdered bentonite and <br />placed as a compacted soil liner, these materials are <br />anticipated to develop some cohesion and show a slightly lower <br />effective stress friction angle. Correlations obtained from <br />Bureau of Reclamation (1977) indicate that *.he average <br />effective stress friction angle for the amended materials will <br /> <br />D-41 (Revised 4/20/89) <br />