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Big Pit/Pique Amarillas area

The Canasta Dorada property lies within the Mojave-Sonora megashear, which is a significant regional control observed at other bulk mineable gold deposits in northwestern Sonora. The Canasta Dorada property covers portions of three mountain ranges and the primary controlling structures that host mineralization appear to be low-angle thrust faults, possible detachment faults, structures which are parallel to sub-parallel to bedding, and NW-striking structural zones and faults. Projections of the W-NW San Jose fault zone that hosts mineralization at the adjacent El Chanate mine appear to extend into the Chanate North target area.

Detailed studies in the Big Pit area show that low-angle structural fabric and mineralization with introduced silica and iron are associated with the gold mineralization. The area of gold mineralization appears to be bound on the north by a high-angle east-west striking normal fault or structural zone which exhibits less than 40 m of vertical displacement. The structure hosting mineralization appears to have locally controlled emplacement of felsic dikes, which are altered and are spatially associated with higher grades of gold mineralization. To the south of the Big Pit, the gold system and the thrust fault may be displaced by what appears to be a low angle detachment structure striking east-west and dipping south at approximately 20° degrees.


View of the Big Pit area, looking south from the Caballos area, showing the trenches and drill roads that expose the altered and mineralized rock, the Pique Viejo and Placer areas are behind the large hill in the middle center of the photo.

The areas surround the Big Pit is largely covered by pediment and colluvium with sparse outcrops that commonly occur as discrete small exposures along the arroyos. Mineralization is hosted by a low-angle structural zone that underlies the area and occurs at the contact between siltstone/phyllites and overlying sandstone and intrusive rocks. This structural zone appears to be the same intersected during drilling at the Big Pit and Amarillas area (Pique Viejo and Placer areas). In the Big Pit area, this structural zone is the host for significant gold mineralization with an average thickness of 10.5 metres.

There are two sedimentary units identified within the Big Pit area that host gold mineralization along a low-angle structure that dips to the S-SW. The uppermost stratigraphic unit is a Jurassic 31 sandstone unit (upper plate), which consists of poorly-sorted, lithic-rich sandstones containing variable amounts of coarse clasts and are oxidized to an orange-yellow color. The unit has been moderately deformed with original bedding commonly preserved. This upper stratigraphic unit structurally overlies a lower sedimentary unit that is “highly deformed” and sheared (lower plate). The lower sedimentary unit consists of calcareous, fine-grained sandstone, siltstones, phyllite, and thin intercalated fine-grained mafic flows or sills that are emplaced along structural shear zones. The matrix of the sheared rocks commonly consists of black carbonaceous clay, graphitic material, and silt. The origin of this package of rocks is unclear and is dominated by a strong structural fabric. When relict bedding is observed in this unit it is chaotic and discordant with the adjacent overlying “upper plate” sandstone unit. Surrounding the Big Pit area, the sedimentary rocks are exposed in “outcrop windows” that rise above the surrounding pediment cover. These rocks generally consist of the “upper plate” sandstones and “lower plate” phyllite and weakly mylonitic sandstone, and the low angle fault contact is rarely exposed but contact is often associated with dikes and sills, as described below.


View of the Chanate North area looking SW, Cerro El Alamo in the distant background, andesite flows in foreground, showing low undulating topography in the valley along projections of the NW structures extending from the El Chanate mine.



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