Summary:
At the Bolivar Property, the volcanic rocks strike northwest and dip gently to moderately to the northeast.
Skarn alteration and mineralization at the Bolivar Property is hosted primarily in a package of sedimentary rocks that occur as a layer or lens within the LVS (Reynolds, 2008). All sedimentary units have undergone low grade metamorphism. The lowermost sedimentary horizon observed is a dolostone which ranges from 24 m to 40 m in thickness. The lower part of the dolostone horizon is interlayered with siltstone. To the south, progressively less of the sedimentary sequence is cut out by granodioritic intrusive rocks and the dolostone is observed to be underlain by a siltstone horizon.
The Bolivar deposit is classified as a high-grade Cu-Zn skarn and exhibits many characteristics common to this type of deposit. The term ‘skarn’ refers to coarse-grained calcium or magnesian silicate alteration formed at relatively high temperatures by the replacement of the original rock, which is often carbonate-rich.
The dikes locally cut the granodiorite, have planar, chilled contacts, and are generally finely crystalline. Both their texture and crosscutting relations suggest that the dikes are younger and shallower than the granodiorite. Both granodiorite and andesite dikes have alteration and locally skarn along their contacts. In addition, endoskarns, which are skarns of igneous origin that form within the granite mass itself, affect both the granodiorite and in rare cases, the andesite dikes. Thus, these rocks are older than or at best coeval with alteration/mineralization. The presence of skarn veins cutting an andesite dike is clear evidence that at least some skarn is later than at least some of the andesite dikes. A closer association of granodiorite with skarn alteration and mineralization is suggested by local K-silicate veining of the granodiorite and the zonation of skarn relative to this contact.
Mineralization at the Bolivar Property is hosted by skarn alteration in carbonate rocks adjacent to the Piedras Verde granodiorite. 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 sulfide (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. Zones of breccia follow faults like the Rosario, Fernandez, and Breccia Linda trends as well as nearly vertical breccia pipes such as La Increible.rly vertical breccia pipes.