Initial Silver Cyanide Leach Results Positive at Sierra Mojada
Twenty three composite samples representing one hundred twenty four sample intervals from drill core into the deposit area were selected for triplicate head grade analyses prior to cyanide leach analyses at a commercial laboratory. These samples were selected to test the western, central, and eastern portions of the Northside silver zone, and two distinct and unique mineralogical zones that form part of the Northside silver zone: the Silver Sulfide area to the east and an area on the west, termed the “Lead Manto composites” that mixed some samples from the upper Northside with some from the upper Southside zones.
Overall cyanide leach solubility’s were very high. Fourteen of the composites containing silver grades ranging from 37 gpt Ag (1.08 opt Ag) to 810 gpt Ag (23.6 opt Ag) representing the main Northside silver zone and had cyanide solubility averaging 208.7% of total silver content as determined by triplicate Aqua Regia digestions. Eliminating the high and low analyses from this sample set only reduces the overall solubility to 155% of total contained silver. Clearly there is a coarse silver aspect to the sample suite that is resulting in cyanide extractions over 100% of contained silver, but the indications are positive that whatever silver is present in the majority of the Northside silver zone is soluble with cyanide.
Silver in the Northside silver zone occurs primarily as native silver, acanthite, and a variety of halide minerals including cerargyrite, embolite, and iodargyrite, and others, based upon mineralogical studies completed to date. All of these minerals are soluble in cyanide, which explains the excellent cyanide leach results to date.
Five composites from the “Lead Manto area” of the deposit containing silver values of 48 gpt Ag (1.4 opt Ag) to 977 gpt Ag (28.5 opt Ag) demonstrated average cyanide solubility of 79% of total silver content, which is still very encouraging.
Only the four composite samples from the restricted silver sulfide area within the Northside silver zone demonstrated poor cyanide leach characteristics. Four composites representing grades of 40 gpt Ag (1.2 opt Ag) to 450 gpt Ag (13.1 opt Ag) returned an average cyanide solubility of 23.3%. Further metallurgical work will be done on samples from this area to determine whether higher cyanide strengths will liberate more of the silver in the presence of sulfide minerals, or whether flotation of the sulfides followed by cyanidation would liberate the silver from this area.
These initial cyanide leach characterization results demonstrate that the majority of the Northside silver zone is amenable to cyanide leach processing, and provide guidance to the Company on further advancing the Northside silver zone. The entire drill hole sample suite will be subject to cyanide analyses in the future to fully characterize the cyanide leach characteristics of the Northside silver zone. The “Lead Manto” area composites will be reformulated and retested so that their leaching characteristics better represent differences in style of mineralization. The Silver Sulfide area and other areas of distinct leaching behavior will be modeled separately from the balance of the Northside silver zone going forward, so these areas can be handled separately in further processing and engineering evaluations of the deposit.
There is no correlation between silver solubility in cyanide and the base metal content of the samples tested. Zinc content ranged from 0.02 – 14.35% Zn, lead content ranged between 0.01 – 7.41% Pb, and copper content ranged from 0.01 – 13.45% Cu. This observation leaves open the possibility of recovering the base metals after extraction of the silver by cyanidation
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SOURCE Metalline Mining Company