Zinc-lead-silver mineralization of economic interest at El Mochito occurs in association with calc-silicate bearing skarn intervals hosted by limestone and calcareous shale of the Upper and Lower Atima Formation, in calcareous units of the Atima Formation’s main subunit, the Mochito Shale, in calcareous siltstone and shale of the Cantarannas Formation and in quartz rich sandstones and siltstones of the siliciclastic-dominated Todos Santos Formation, which underlies the Cantarannas Formation. The stratigraphic section within which economic mineralization occurs at El Mochito slightly exceeds 1,250 m in true thickness.

Mineralization consisting of sphalerite, galena, argentite, tetrahedrite, acanthite, pyrrhotite and magnetite is associated with garnet and pyroxene skarn zones that are both structurally and stratigraphically controlled. The distribution of skarn directly reflects the geometry of the complex graben-related fault systems that channeled hot hydrothermal fluids through graben fill sequences to sites where they selectively reacted with calcareous wall rock to create siliceous, garnet and pyroxene dominated skarn. Introduction of zinc-lead-silver mineralization on existing skarn zones reflects continued capacity of the graben’s fault systems to conduct the large volumes of hydrothermal fluid necessary to create this district’s high metal endowment.

Two main styles of zinc-lead-silver mineralization are present at El Mochito, these being mantos a ........

The El Mochito mine is in its 70th year of operation and the mining infrastructure is expansive. The existing underground workings at the El Mochito mine covers approximately 3,000 m in the east-west direction, 1,200 m north-south and vertically from surface to a depth of up to 1,300 m (-1,000 m below the shaft collar).

The mine employs a combination of long hole, cut & fill and conventional mining methods to exploit the mineral from mineralized zones of different shapes and sizes. A predominately trackless mining fleet is used in mining and hauling the mineral to the vertical shafts through multiple ramp systems that are essentially a result of a series of stope access development that have been linked together, creating a complicated, inefficient and tight transport network of tunnels.

Mining operational costs are consequently relatively high and reflect this deep mining environment with long hauling distances, coupled with high pumping and pump maintenance costs. As the mine grows deeper, transport distances will further increase. As expected, this would result in increasing the size of the trucking fleet and manpower and increasing maintenance cost and mechanical parts inventory. There would also be negative impact on the ventilation circuit, and the water pumping system is old, very extended and inefficient.

The Expansion Project proposes to address these challenges through the upgrade of infrastructure and mining and mineral processing ........

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