The Cozamin mine is an underground mine with a surface milling facility. The underground area of the mine is accessed by either a shaft from the surface, or one of two ramps from the surface down to the lower workings.
Mining of the Mala Noche vein is by either long hole stoping, or cut and fill mining. Cut and fill mining is utilized to extract veins that are characterized with a shallow dipand/or narrow (less that 4 m). When the vein is wider (4-10 meters) long hole stoping is used that at this time does not require passive fill support. Those areas where the vein is wider than 10 meters generally rely on an Avoca Mining method where development waste rock is utilized as fill that provides passive support to the excavation which minimizes hanging wall dilution. Levels are excavated every 20 vertical meters, whereupon long hole drills are utilized to bore holes between levels which are then loaded with explosives and blasted. Blasting of a stope is sequenced to ensure good fragmentation and productivity in a safe manner. This bulk mining method is relatively inexpensive and highly productive, however, due diligence is required to ensure that dilution is minimized and extraction of the ore is not compromised if the vein has large undulations over the vertical distance.
Cut and fill mining is normally used in areas where the vein is less than 4 meters wide, or where the vein is very sinuous. Mining is done in 2.5-3.0 meter lifts along strike, with material blasted and excavated, and then the area partially filled (leaving enough height for equipment to restart the cycle). This method is more expensive but allows better control of dilution and increased recovery of the ore.
Mined ore is brought to surface via either a shaft or the two production ramps that are collared from surface (currently 60% via the shaft). The ore is trucked to the crusher and fed directly to the primary crusher feed bin or to the crusher stockpile. Ore is processed through a three stage crushing plant to produce a 9.5 millimeter product size which is stored in the fine ore (24 hour storage capacity) bins ahead of the grinding circuit.
Material fed to the grinding circuit is reduced in size to 55% minus 200 mesh and then sent to flotation. The flotation steps involve flotation of lead and copper first, followed by zinc. All products go through multiple stages of upgrading (or cleaning) in the flotation circuit ending with a silver-rich copper concentrate, a silver-rich lead concentrate and a zinc concentrate.