McEwen Mining recently put together a new district-scale prospecting model, which largely ties together all the known deposits in the area.
The deposits at Palmarito, El Gallo Mine and El Gallo Silver are characterized by being proximal to a large, outcropping granodiorite intrusive body, shown in light pink in the geological map of Figure 1. From an airborne geophysical study done in 2011, we know that this intrusion is partly surrounded by areas of variably intense potassic alteration, with the more intense alteration represented in dark pink patches in Figure 1. The expectation is that the next prospective areas in the district are likely to be found in these areas of stronger potassic alteration in between the two ellipses shown on the map.
The map highlights the locations of the known resource areas at El Gallo, Palmarito and El Gallo Silver and the exploration areas of the El Encuentro and Texcalama projects to the northwest.
Outside of this area, the known Mina Grande project in the northeast is close to the same intrusive body, however in this location the intrusion is buried, but the area is still characterised by similar alteration patterns and lends itself to a high degree of prospectivity.
The mineralized bodies previously identified at the El Gallo Silver and Mina Grande areas are not the traditionally steeply dipping veins characteristic of the low-sulfidation epithermal deposits found elsewhere in Mexico, but are relatively shallow dipping (approximately 20⁰) breccia sheets. As well as the deposits being related to the intrusive body, they also show characteristics of typical IOCG (iron-oxide-copper-gold) deposits, which can be very large and very high in grade. Similarities include the very strong potassium alteration seen in the airborne radiometric surveys that is also seen in our drill cores, the fact that the principal ore mineral at the El Gallo Mine is specular hematite (an iron oxide mineral), and the fact that at El Gallo Silver and Mina Grande we see these sheet-like breccia bodies, which are relatively parallel to the underlying intrusions.