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/ BMRI -San Luis Pit Ball: Sequential Batch Tests of Gneiss ~ III ~ IIIII~IIIIII III <br />sss <br />t~ ~ R~~EIVED <br />TECHNICAL MEMORANDUM OCT 2 3 1995 <br />DATE: i 8 October, 1995 ~ merals & Geology <br />TO: Mr. Jim Dillie / Dr, Harry Posey(DMG) <br />FROM: Mark J. Logsdon (Geochimica) <br />Through: Dan Robertson/Sally Hayes (BMRI) <br />RE: BACKFILLING THE WEST PIT -SAN LUIS: SEQUENTIAL <br />BATCH LEACH TESTS OF PINK GNEISS <br />CC: A. Baldridge (BMG); B. Lytle (JCHA) <br />Battle Mountain Resources (BMRI), Inc.'s San Luis Mine has proposed bzckfilling the <br />deep portion of the West Pit with waste rock from the "Pink Gneiss" unit (Technical <br />Revision 18). Backfilling the pit will have several beneficial effecu on the Project area <br />at the end of mining. Firstly, backfilling the pit will buttress the high wall between the <br />West Pit and Rito Seco, improving the long-term geotechnical and hydrological <br />performance of the reclaimed mine system. Secondly, backfilling the pit will <br />significantly reduce the amount of waste rock that must be reclaimed above the ground <br />surface (i.e., subject to surficial weathering processes) at the end of mining. Thirdly, <br />backfilling the pit will reduce long-term consumptive water loss due to evaporation <br />compared to the case of a free-lake surface. The Division of Minerals and Geology <br />(Division) raised questions about the geochemical behavior of the backfilled pit that had <br />to be addressed before the Division would authorize backfilling. <br />BMRI agreed to perform additional geochemical test work as a condition to the <br />Division's approval for the back{illing. One portion of the additional tesq work was a <br />set of sequential batch leaching tests of Pink Gneiss samples, using site g{ound water as <br />the lixiviant. The purpose of the tests was to evaluate the likely behavior of the Pink <br />Gneiss backfill after the pit has been re-saturated and the flow system re-established. <br />This memorandum presents the results of the sequential batch leach testing program. <br />Geochimica, Inc. 1 95021/26-Sep~95 <br />