These results were achieved at primary grinds of 80% passing 70 to 75 microns and Pb and Zn regrinds of 10 and 15 microns, respectively. It is expected that with further work these variables could be optimized to provide both improved recoveries and lower grinding requirements. In addition, closing the circuit in a locked cycle test generally improves overall recovery. Cyanidation test work completed on finely ground zinc rougher flotation tails showed that silver recovery from Marta Este and Marta Centro was 52% and 49%, respectively. Tailings cyanidation gold recovery was low at 26% and 11%, respectively.
Preliminary Leach Testing
Preliminary heap leach column test work on the oxide samples was encouraging. Marta Norte and Tranquilo samples were crushed to minus half inch and leached in seven-inch columns. Silver recoveries for the two veins were 70% after 30 days and 81% after 45 days, respectively. Gold recoveries returned were 63% and 69%, respectively. Both silver and gold were still leaching when the tests were terminated, suggesting the recoveries may increase with longer leaching periods.
Bottle roll test work by ALS on oxide samples ground to minus 75 micron indicated 48-hour recoveries ranging from 34% to 95% for silver and 76% to 94% for gold. G&T completed bottle roll testing on drill core oxide composites from five of the veins. These indicated good recoveries from 4 of the veins for both precious metals.
---------------------------------------------------------------------------- Au Ag NaCN CaO ------------------ -------------------- ---------- Feed Res. 48 Hr Feed Res. 48 Hr ---------------------------------------------------- g/t g/t Ext. g/t g/t Ext. kg/t kg/t ----------------------------------------------------Vein/Material % %----------------------------------------------------------------------------Marta Este - Oxide(i) 4.24 0.51 87.98% 1,588 1,110 30% 1.92 0.88----------------------------------------------------------------------------Marta Centro - Oxide 2.90 0.19 93.44% 140 26 81.59% 0.92 1.10----------------------------------------------------------------------------Marta Norte - Oxide 0.27 0.02 92.58% 624 17 97.21% 1.64 1.06----------------------------------------------------------------------------IVN e IVO - Oxide 2.60 0.48 81.57% 23 10 55.30% 0.96 1.70----------------------------------------------------------------------------Tranquilo - Oxide 0.09 0.02 78.39% 64 10 85.11% 0.96 1.70----------------------------------------------------------------------------(i) As a result of the low silver recovery from the high-grade Marta Este Oxide composite, it was later retested under more aggressive leach conditions and this resulted in gold and silver recoveries of 96% and 98%, respectively. Mineralogical work is currently underway to identify the high grade silver mineral in this material and future testing will involve optimization of recoveries and reagent requirements related to its presence.
Results from similar bottle roll tests on sulphide zone samples were generally poor. Further work on representative composites from sulphide veins is recommended to fully evaluate the potential for leaching sulphide material. The Company intends to conduct ongoing metallurgical test work in order to evaluate recoveries and costs of various process alternatives.
