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' BMW <br />L <br />S <br />i <br /> - <br />an <br />u <br />s 1998 Bac <br />~', Geochemistry <br />' TECHNICAL MEMORANDUM <br /> <br /> DATE: 16 November, 1998 <br />' <br /> TO: Battle Mountain Resources, Inc. -San Luis Mice <br />' FROM: Mark J. Logsdon (Geochimica} <br />' SUBJECT: GEOCHEMICAL INTERPRETATION OF OCTOBER 1998 PIT- <br />BACKFILL WATER QUALITY <br /> <br /> cc: A. Baldrige (BMGC); B. Lyle, D. Robertson, R. Zumwalt (BMRI); B. <br />' Lytle (JCHA); D. Massey (Parcel Mauro) <br />' - -- <br /> BACKGROUND <br /> <br /> Water samples collected in early October 1998 from monitor wells in and downgradient <br /> of the backfilled West Pit at the San Luis property show total dissolved solids (TDS) <br />' and sulfate (SOa) concentrations that now are elevated compared to pre-mining water <br /> quality in the area. The waters are neutral to slightly alkaline in pH and have <br /> substantial concentrations of bicarbonate alkalinity. The dissolved metals <br />concentrations are very low. <br />' !n the O1 October 1998 sampling, the highest observed concentration of sulfate is <br />1369.5 mg/L in monitor well BF-2, located within the backfill of the West Pit. The <br />TDS of this sample was 2293 mg/L. The sulfate (1369.5 mg/L = 28.5 meq/L) and <br />' bicarbonate (HC03; 290 mg/L = 4.75 meq/L) are balanced by calcium (Ca; 643 mg/L <br />= 32.1 meq/1) plus small amount of magnesium (11.42 mg/L = 0.44 meglL}. The pH <br />of the sample was 6.97 su. Compared to baseline values, the potassium (K) <br />' concentration also is elevated at 19.0 mg/L. <br />INTERPRETATION <br />1 The elevated sulfate and potassium concentrations represent the dissolution of soluble, <br />secondary salts on the surfaces of the backfill solids as the ground water rose through <br />the backfill to its equilibrium elevation. The elevated Ca and HCO; concentrations at <br />' pH 7 represent the buffering of the stored acidity in the secondary phases by the readily <br />available acid-neutralization potential of calcium cazbonate in the system. Leaching of <br />secondary phases was described in Logsdon (1995, p. 6): <br />' Ceochimrca, Inc. I(~Nov-98 <br />1 <br />