VANCOUVER (miningweekly.com) – Toronto- and Lima-listed Sierra Metals has updated the compliant resources and reserves for its Bolívar and Cusi copper mines, in Mexico’s Chihuahua state.

At Bolivar, the Toronto-based miner reported a new probable reserve of 4.3-million tonnes grading 1.18% copper equivalent comprising 0.31 g/t gold, 0.85% copper, and 17.5 g/t silver. The indicated resource now stands at 9.3-million tonnes grading 1.23% copper equivalent, made up of 0.3 g/t gold, 0.9% copper and 18.1 g/t silver.

In the inferred category, Bolivar has 9.1-million tonnes grading 1.2% copper equivalent, comprising 0.33 g/t gold, 0.86% copper and 17.9 g/t silver.

The updated resource and reserve estimates are based on drilling programmes completed between January 2013 and September 2016, as well as production data of September 2016. After the cut-off date of September 2016, the updated resource estimate does not include about 20 000 m of drilling, some of which is in the process of being drilled, with the aim of further expanding the resources and reserves at the Bolivar mine.

Sierra could further refine the orebody thanks in part to new exploration drilling, lower commodity price assumptions, sampling, face mapping information and geologic interpretations, as well as grade estimates.

Small-scale mining was conducted in the Piedras Verdes district during the Spanish Colonial days, but historical records of production were not maintained and production values are unknown. An estimated 300 000 t of ore was reportedly mined from 1998 to 2000, while the Bolívar mine was under the control of Bencomo family, but production records are not available for this period either.

Sierra on Thursday also announced a resource update for the Cusi mine, incorporating results of drilling programmes completed between January 2014 and January 2017.

The total indicated resources comprise two-million tonnes grading 283 g/t silver equivalent, comprising 237 g/t silver, 0.53% lead, 0.53% zinc and 0.16 g/t gold. The inferred resource stands at 1.2-million tonnes averaging 354 g/t silver equivalent, or 305 g/t silver, 0.51% lead, 0.64% zinc or 0.14 g/t gold.

Sierra noted that the review did not include any data from the 15 000 m drilling programme that was focused on the high-grade Santa Rosa de Lima zone. Drilling in this area is based on a new conceptual interpretation of the Santa Rosa de Lima structure.

Gold and silver were first discovered in the Cusi project area within the San Miguel and La Candelaria zones in 1687.

Sierra continues to grow its mineral resources with several brownfield opportunities such as the Esperanza zone, at the Yauricocha mine, in Peru, which went from first discovery to mining in less than one year.

The TSX-listed stock has gained nearly 60% since the start of the year.