The Atacocha property is situated in the Pasco region of the Western Cordillera of the Andes mountain range in central Peru, within the Eocene-Miocene Polymetallic, and Miocene Au-Ag Epithermal Belts.

Within the property area the stratigraphic units of primary interest are the Chambara´ Aramachay and Condorsinga formations, as well as other undifferentiated limestone units of the Pucara´ Group, the Goyllarisquizga formation, and stratigraphically overlying basalt layers. Intrusive rocks within the property are variably porphyritic dacite to quartz diorite with hornblende and biotite phenocrysts. Dacitic dikes are sub-divided into 2 units: porphyritic with feldspar phenocrysts and little quartz restricted to the groundmass; and porphyritic with abundant quartz phenocrysts, with minor biotite and hornblende. These dacitic dikes generally trend north-south, and are observed in 3 areas: Santa Ba´rbara/central, south along/parallel to the Atacocha Fault, and south of Section 3. The intrusive suite is part of the Milpo-Atacocha-Vinchos, age dated to 29-26 Ma. The Santa Ba´rbara and San Gerardo stocks are two principal intrusive units within the property.

At Atacocha, mineralization is characterized as either a skarn-, replacement- or hydrothermal vein/brecciastyle mineralization. Skarn-related mineralization generally spatially associated with either the Santa Barbara stock or San Gerardo stock is paragenetically earlier, followed by the hydrothermal mineralization. Garnet-skarn related mineralization is associated with Zn, Pb, Ag, and Bi occurring within the Pucara Group sediments around the Santa Ba´rbara stock. Replacement-style mineralization as well as low-temperature hydrothermal veins and polymitic breccias comprising a Ag, Pb, Zn mineral assemblage, occurs between the San Gerardo stock and Fault (or Falla) 1, which are also characterized by Mn-skarn, and silica-sericite-halloysite alteration.

Skarn-related mineralization is characterized by pyrite, chalcopyrite, sphalerite, galena, with lesser bismuthinite and a variety of sulfosalts (Bi-bearing) and pyrrhotite, bornite, and covellite at lower elevation. Molybdenite may occur proximal to the skarn-related mineralization. Elevated Bi and Au are reported to be associated with skarn-related mineralization. Veins and veinlets with pyrite, chalcopyrite, sphalerite, galena, with quartz and carbonate occur within marble units, and are spatially associated with skarn bodies. Replacement bodies comprising of pyrite, sphalerite, galena, chalcopyrite, and possibly other fine undistinguished sulfides occur within garnet-skarn, marble, and silicified zones. Breccias have been grouped in to either Ag-Pb-Zn hydrothermal breccias or siliceous breccias based on their mineralogical assemblages, and textural characteristics.

Three types of mineral deposits are recognized at Atacocha, described as either: Skarn (Exo and Endo Skarn); Replacement (Lithological and structurally controlled); or Hydrothermal veins (and collapse breccias).

Atacocha operates two mines: the Atacocha underground mine and the San Gerardo open pit mine. The underground mine is currently suspended, but mining continues in the San Gerardo open pit mine.

San Gerardo is an open pit operation located at the top of mineralized zone, and is mined by 6 m high benches. Since the temporally suspension of Atacocha underground mine, the open pit production is responsible by the metallurgical plant feed. Operations are carried out by contractor with a mining fleet that allows selectivity in the loading process.

The Atacocha underground mine is mined by the overhand Cut & Fill (C&F) and sublevel stoping (SLS) mining methods. C&F stopes are 20 m high consisting of 4 m high cuts and a minimum mining width of 4 m. C&F stopes are located 55 m from the main ramps and accessed by stope access ramps with grades varying from -15% to +15%. Production is achieved by horizontal drill and blast, and backfilled using unconsolidated waste fill or hydraulic backfill. The SLS mining method has demonstrated increased productivities and reduced unit costs as compared to the C&F mining method. SLS stopes are located a minimum of 40m from infrastructure, are 20 m high, 30 m long and have a minimum mining width of 4 m. Production is achieved by vertical blastholes, and backfilled using unconsolidated waste fill.

Both underground and open pit mines deliver ROM to the crushing plant. The three-stage crushing plant consist of a primary jaw crusher operating in open circuit followed by a secondary stage in open circuit with pre-classification, and the third stage operating in closed-circuit with vibrating screens to produce a particle size of approximately 3/8”.

A grinding plant using conventional ball mill receive the crushed product and target a final particle size of 51% - 200#. A primary grinding stage operates six parallel ball mills, each one operating in closedcircuit with hydrocyclones. The product from the grinding stage feeds the multi-stage differential flotation circuit.

The Atacocha concentrator utilizes a conventional crushing, grinding, and sequential flotation scheme to produce lead and zinc concentrates with an average daily processing rate of approximately 4,300 tonnes. A flashflotation step is included in the grinding circuit that recovers lead at a grade sufficiently high to report directly to the final lead concentrate. The majority of gold and silver report are into the lead concentrate. Despite the plant having capacity to produce copper concentrate, the circuit of the plant has been disabled and the Atacocha metallurgical plant produces only zinc and lead concentrates.

Description (2017)
The first flotation circuit collects a bulk lead/copper concentrate that is then subject to differential flotation to collect lead minerals as concentrate and copper minerals as tails, finally each stream is individually cleaned in multiple flotation stages to produce final concentrates that are stored in their respective thickeners.
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