Hermosa’s capacity is expected to be 13,700 tons per day (tpd) or 5.0 million tons per annum (tpa). The plant will accommodate the two major types of ore present in the Hermosa open pit: Manto Oxide and Upper Silver. Average throughput is expected to be 4.3 million tpa for the first ten years when Manto Oxide ores are primarily being processed and 1.9 million tpa for the remainder of the mine life when the Upper Silver ore is processed.
The Manto Oxide ore, which represents approximately 73% of the total ore reserve, will be fine crushed, passed through magnetic separation, calcined and then leached. The leached filtrate will proceed to the Merrill Crowe process for the recovery of silver and gold to produce a silver/gold doré on site. The Hardshell ore type, which is a subset of the Manto Oxide ore, makes up 4.2% of the total ore and will be processed the same as the Manto Oxide ores except that it will not be passed through magnetic separation. Silver recoveries for the Manto Oxide ore average 79%, including Hardshell ore at 59%, while gold recoveries average 90% for both types of ore. The use of magnetic separation for the Manto Oxide ores at the front end of the process enables the non-magnetic fraction, which has a very low metal content and represents approximately 44% by weight of the ROM ore, to go directly to the tailings facility. This allows for a greater throughput rate at relatively lower capital and operating costs.
Zinc in solution after the Merrill Crowe process will be recovered using existing SX/EW technology producing zinc cathodes on site. Copper in solution after the Merrill Crowe process will be recovered using SART technology and precipitated as a high grade copper concentrate (79% Cu). Overall, approximately 8% of the contained zinc and 61% of the contained copper is expected to be recovered.
The tails will be processed through a Wet High Intensity Magnetic Separator (WHIMS) to produce a manganese concentrate averaging approximately 35% Mn. These concentrates will be further processed through the onsite stand-alone 55,000 tpa EMM facility. The EMM facility is expected to produce high grade manganese flake metal for sale in the North American marketplace. The balance of the manganese concentrate recovered in excess of that required to produce 55,000 tons of EMM will be stored on site for future processing. The stand-alone nature of the EMM facility provides the Company greater flexibility as it could be financed separately or deferred and phased in and funded through cash flow from production.
Upper Silver ores make up the remaining 27% of the total ore tons. These ores will be processed by fine crushing, leaching and recovery of silver and gold in the Merrill Crowe circuit to produce a silver/gold doré on site. These ores contain no appreciable zinc, copper or manganese. Recoveries of silver and gold average 46% and 90%, respectively.
The bench and pilot plant test-work incorporated in this pre-feasibility was performed by Hazen Research Inc. in Golden, Colorado and included the processing of approximately 14 tons of Manto Oxide and Upper Silver Zone material. Metallurgical development work will continue, with the focus on advancing it to feasibility level.
Wildcat’s next step for Hermosa is to advance the project into feasibility stage. Work on the feasibility study will include continued metallurgical testing to optimize plan operating efficiency and metal recoveries.
Hermosa Process Flow Sheet http://www.wildcatsilver.com/files/PROCESS FLOW SHEET.pdf