Sierra Metals, through its wholly owned subsidiary Dia Bras Mexicana S.A. de C.V. (“DBM”), owns and operates the Bolivar Mine owns and operates the Bolivar Mine and Piedras Verdes processing plant.
On May 12, 2025, Alpayana S.A.C. announced the successful all-cash offer (the "Offer") to purchase the issued and outstanding common shares of Sierra Metals Inc. Once the Offeror has taken up the Sierra Shares tendered, Alpayana will own 70.74% of the issued and outstanding Sierra Shares.
Following the Expiry Time, Alpayana Canada intends to pursue a subsequent acquisition transaction to complete the privatization of Sierra and acquire all Sierra Shares not acquired pursuant to the Offer.
- subscription is required.
Summary:
The Bolivar deposit is classified as a high-grade Cu-Zn skarn.
The deposit is located within the Guerrero composite terrane, which makes up the bulk of western Mexico and is one of the largest accreted terranes in the North American Cordillera. The Guerrero terrane, proposed to have accreted to the margin of nuclear Mexico in the Late Cretaceous, consists of submarine and lesser subaerial volcanic and sedimentary sequences ranging from Upper Jurassic to middle Upper Cretaceous in age. These sequences rest unconformably on deformed and partially metamorphosed early Mesozoic oceanic sequences.
The Piedras Verdes district is made up of Cretaceous andesitic to basaltic flows and tuffs intercalated with greywacke, limestone, and shale beds. Cu-Zn skarn mineralization is in carbonate rocks adjacent to the Piedras Verde granodiorite. Mineralization exhibits strong stratigraphic control, and two stratigraphic horizons host the bulk of the mineralization: an upper calcic horizon, which predominantly hosts Zn-rich mineralization, and a lower dolomitic horizon, which predominantly hosts Cu-rich mineralization. In both cases, the highest grades are developed where structures and associated breccia zones cross these favorable horizons near skarn-marble contacts.
Mineralization
Mineralization at the Bolivar Property is hosted by skarn alteration in carbonate rocks adjacent to the Piedras Verde granodiorite (Meinert, 2007). Orientations of the skarn vary dramatically, although the majority are gently-dipping. Thicknesses vary from 2 m to over 20 m.
Skarn mineralization is strongly zoned, with proximal Cu-rich garnet skarn in the South Bolivar area, close to igneous contacts, and more distal Zn-rich garnet+pyroxene skarn in the northern Bolivar and southern skarn zones near El Val. The presence of chalcopyrite+bornite dominant skarn (lacking sphalerite) in the South Bolivar area, along with K-silicate veins in the adjacent granodiorite suggests that this zone is close to a center of hydrothermal fluid activity.
In contrast, the main Bolivar Mine is characterized by Zn>Cu and more distal skarn mineralogy such as pyroxene>garnet and pale green and brown garnets. Alteration is zoned relative to fluid flow channels. From proximal to distal, the observed sequence is red-brown garnet to brown garnet with chalcopyrite ± bornite ± magnetite to green garnet ± pyroxene with chalcopyrite + sphalerite to massive sulphide (sphalerite ± chalcopyrite ± galena) to marble with stylolites and other fluid escape structures.
Mineralization exhibits strong stratigraphic control, and two stratigraphic horizons host the majority: an upper calcic horizon, which predominantly hosts Zn-rich mineralization, and a lower dolomitic horizon, which predominantly hosts Cu-rich mineralization.
In both cases, the highest grades are developed where fault or vein structures and associated breccia zones cross these favorable horizons near skarn-marble contacts. Meinert (2007) suggested that hydrothermal fluids moved up along the Piedras Verde granodiorite contact, forming skarn and periodically undergoing phase separation that caused brecciation. Zones of breccia follow faults like the Rosario, Fernandez, and Breccia Linda trends as well as nearly vertical breccia pipes such as La Increíble.
Dulce Deposit
In contrast with the main Bolivar Mine, whose orebodies have a general trend NW-SE, Dulce Vetiform type skarn body is oriented northeast to southwest with dip 60°. The principal economic minerals are massive chalcopyrite, disseminate bornite and minor presence of sphalerite. The actual known area delimitated by drillholes covers a volume of 400 m in length by 450m in depth and an average of 12 m in width. Stratigraphic controls of this structure at hangingwall are andesitic flows and at the footwall by marble.