The Bolivar deposit is a Cu-Zn skarn and is one of many precious and base metal deposits of the Sierra Madre belt, which trends north-northwest across the states of Chihuahua, Durango and Sonora in northwestern Mexico (Meinert, 2007). 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. The Bolivar deposit is classified as a high-grade Cu-Zn s ........

The Bolivar Mine is currently mined by the sub-level stoping and room and pillar methods and the specific method applied to a particular area of the mine is determined by geotechnical constraints, mineralization trends, dimensions and mine production targets.

Current production at Bolivar comes from the El Gallo Inferior, Chimenea 1 and 2 and the Bolivar West mineralized zones. Mineralized material is currently hauled to the surface using one of several adits or declines accessing the mineralized zones and is then dumped onto small pads outside the portals. The mineralized material is then loaded into rigid-frame, over-the-road trucks and hauled on a gravel road approximately 5.1 km south to the Piedras Verdes Mill. As explained in more detail in Section 18, the mine is constructing an underground tunnel that will enable mineralized material to be delivered via underground truck transport to a portal adjacent to the Mill.

Sub-Level Stoping - Bolivar West
The longhole method is applied in the shallow dipping mineralized bodies in Bolivar West. Excavation for longholes with openings of 9.0 m and pillars of 7.0 m x 7.0 m for stope heights between 12.0 m and 15.0 m. From the access ramp, access to the mineralized material is established in the central part of the chamber and the mineral cut begins. A drive is developed within the mineralized material, then the drilling of long holes is carried out and extraction begins. Ramps are established in some cas ........

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