The Yauricocha Mine features several mineralized bodies, which have been emplaced along structural trends, with the mineralization itself related to replacement of limestones by hydrothermal fluids related to nearby intrusions. The mineralization varies widely in morphology, from large, relatively wide, tabular manto-style deposits to narrow, sub-vertical chimneys. The mineralization features economic grades of Ag, Cu, Pb and Zn, with local Au to a lesser degree. The majority of the deposits are related to the regional high-angle NW-trending Yauricocha fault or the NE-trending and less well-defined Cachi-Cachi structural trend. The mineralization generally presents as polymetallic sulfides but is locally oxidized to significant depths or related to more Cu-rich bodies.

Goyllarisquizga Formation
The oldest rocks exposed in the area are the lower Cretaceous Goyllarisquizga arenites. This formation is approximately 300 m thick and comprises thick gray and white arenites, locally banded with carbonaceous lutites as well as small mantos of low-quality coal beds and clay. In the vicinity of Chaucha, these arenites have near their base interbedded, red lutite. The arenites crop out in the cores of the anticlines southwest of Yauricocha, as beds dispersed along the Chacras uplift, and isolated outcrops in the Éxito zone.

Jumasha Formation
The mid-Cretaceous Jumasha Formation consists of massive gray limestone, averages 700 m thick, and concordantly overlies the Goyllarisquizga Formation. Intercalations of carbonaceous lutites occur at its base near the contact with the arenites. These layers are succeeded by discontinuous lenses of maroon and grey limestone, occasionally with horizons of lutite and chert about 6 m thick. Also present are pseudo-breccias of probable sedimentary origin and a basaltic sill.

Celendín Formation
The Celendín Formation concordantly overlies the Jumasha Formation and contains finely stratified silicic lutites with intercalations of recrystallized limestone of Santoniana age as well as the France Chert. The average thickness in the Yauricocha area is 400 m.

Casapalca Red Beds
The Casapalca red beds lay concordantly on the Celendín Formation with a gradational contact. It has been assigned an age between upper Cretaceous and lower Tertiary, but because of the absence of fossils its age cannot be precisely determined. It is composed primarily of calcareous red lutites, pure limestones, and reddish arenaceous limestone. Lava flows and tuffaceous beds have been occasionally reported.

Mineralization at the Yauricocha Mine is represented by variably oxidized portions of a multiplephase polymetallic system with at least two stages of mineralization, demonstrated by sulfide veins cutting brecciated polymetallic sulfide mineralized bodies. The mineralized bodies and quartzsulfide veins appear to be intimately related and form a very important structural/mineralogical assemblage in the Yauricocha mineral deposit. Comments made herein regarding the characteristics of the Yauricocha district apply directly to the Yauricocha Mine.

Mineralization in the Yauricocha district is spatially and genetically related to the Yauricocha stock, a composite intrusive body of granodioritic to quartz monzonitic composition that has been radiometrically dated at late Miocene (approximately 7.5 million years old) (Giletti and Day, 1968). The stock intrudes tightly folded beds of the late Cretaceous Jumasha and Celendín Formations and the overlying Casapalca Formation (latest Cretaceous and Paleocene?). Mineralized bodies are dominantly high-temperature polymetallic sulfide bodies that replaced limestone. Metal-bearing solutions of the Yauricocha magmatic-hydrothermal system were highly reactive and intensely attacked the carbonate wall rock of the Jumasha and Celendín Formations, producing the channels in which sulfides were deposited.

The Yauricocha Mine is a producing operation with a long production history. Most of the mining is executed through mechanized sub-level caving with a relatively small portion of the mining using overhand cut and fill. The mine uses well-established, proven mining methods and is planning to increase the production rate to 5,500 tpd (2.0 Mt/y) in 2024.

Mechanized sub-level caving (SLC) and overhand mechanized cut and fill (MCF) mining methods are currently used in the mine to achieve production with most of the production by SLC mining methods.SLC is the primary mining method at Yauricocha, representing 84% of the annual production.

SLC mining areas have historically been established by developing three sub-levels for each 50m main level via ramps. This results in a planned 16.7 m sub-level spacing which are called pisos (floors). Below the 1070L, main level spacing will be increased to 100m, but the sub-level spacing remains the same. One aspect of modernizing the SLC practices will be to work towards increasing the sub-level spacing to 25 m which is typical of modern SLC mines. Geotechnical work and trial mining will be conducted as part of the program to phase in this change. Not all mineralized bodies will necessarily be converted due to geotechnical constraints.

On each sub-level, drawpoints are developed from the footwall to the hangingwall of the mineralized body, typically at 3.5 m wide x 3.0 m high and are spaced 8.0 m apart along the Footwall drift. Steel sets, shotcrete and bolting are used as ground support in the drawpoints and the length of each drawpoint varies with the thickness of the mineralized zone.

As the drawpoint is developed, samples of mineralized material are collected for grade control analysis from the left and right ribs. Upholes are drilled and blasted in stopes to initiate caving. Effective draw control is an important aspect to successfully extracting the expected tonnes and grades for this mining method. Drawpoints are staggered by 4.0 m horizontally between sub-levels.

MCF mining is employed in the smaller mineralized bodies. Typically, the 3.0 m high cuts are mined at a minimum width of 3.0 m in a bottom-up sequence (overhand) where the previous cut is filled with uncemented rock fill (URF) as mining progresses to the next sub-level above. Sill pillars are left between levels as mining comes up underneath the previously mined level. Based on geotechnical constraints, the sill pillars are typically a minimum of 2.0 m in thickness.

Mine trucks deliver polymetallic mineralized material and oxide mineralized material to their respective coarse mineralized material bins. The single crushing plant batches mineralized material that is delivered to dedicated mineralized material bins to each processing line. Each process line includes a grinding stage.

Yauricocha operates a conventional, multi-stage differential flotation plant that includes two parallel processing circuits, one to process polymetallic mineralized material, and the second to process oxide mineralized material. Each processing circuit consists of a crushing stage, grinding, sequential differential flotation, dewatering of the concentrates, thickening and disposal of the flotation tails.

Yauricocha’s original combined capacity of the two processing circuits totals 3,600 tonnes per day. The polymetallic circuits nominal capacity has historically been 3,000 tonnes per day and the oxide circuit 600 tonnes per day, however ongoing improvements to the circuits have been increasing daily throughput.

No oxide mineralized material has been processed since 2018 and current plant production includes only three mineral concentrates: lead sulfides concentrate, copper sulfides concentrate, and zinc concentrate.

Recent improvements to the processing ........