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Exploration Properties :: San Anton >> Geology
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Mineralized Stockwork, Cerro del Gallo

GEOLOGY

The San Anton Property is located within the Mesozoic Sierra Madre Oriental terrain and 80 km north of the west northwest trending Late Miocene Trans-Mexico Neovolcanic Belt. The Sierra Madre Oriental terrain is a thin skinned fold-thrust belt of Laramide age (Late Cretaceous-Early Tertiary). High level felsic intrusions emplaced into the western two thirds of the terrain provided the mechanism for hydrothermal activity and mineral deposition.

The San Anton Property is known to host a variety of styles of mineral deposits, including porphyry gold-rich copper deposits, intrusion-related gold deposits, epithermal silver-gold deposits, and gold-copper skarn deposits. All of these styles of mineralization are known to occur within the property concessions held by SAM. Historic mining within the San Anton de las Minas area was concentrated on epithermal veins. However, the main area of present interest is the large low grade bulk mineable gold-silver-copper deposit at Cerro del Gallo where a significant mineral resource has been identified.

The Cerro del Gallo gold-silver-copper deposit lies within an inlier of deformed clastic sediments and volcanic rocks of probable Triassic-Jurassic age. At Cerro del Gallo, an ash-flow tuff sequence has been intruded by a small elongated upright felsic stock of dacitic to tonalitic composition. The enclosing host rocks have undergone strong pervasive hydrothermal alteration generating a new potassic fine grained replacement assemblage of quartz, K-feldspar, sericite, biotite, pyrite, pyrrhotite, and chalcopyrite. Gold mineralization is concentrated within a gold-rich annulus within wallrock proximal to the felsic intrusion. A gold-bearing skarn has been intersected in drilling south of Cerro del Gallo. Other targets peripheral to the Cerro del Gallo hydrothermal alteration zone remain to be tested. These include coincident magnetic and 3D-induced polarization anomalies on the flanks of the alteration system.
 
 
Deposit Types
 
Stockwork Quartz Veining, Cerro del GalloThe Cerro del Gallo gold-silver-copper deposit at San Antón de las Minas shares characteristics with both intrusion-related gold systems and porphyry gold-rich copper deposits. At Cerro del Gallo most of the gold is hosted by intensely silicified and quartz-sulphide veined wallrock proximal to a small upright fractionated felsic intrusion in what would have been traditionally classed as a “wallrock” porphyry deposit using porphyry copper nomenclature. The recent discovery of a number of intrusion-related gold deposits sharing similar characteristics in the Tintina Gold Belt extending from Alaska to the Yukon over the past decade has been the catalyst for research and subsequent development of the Intrusion-Related Gold System (“IRGS”) model for exploration. Cerro del Gallo shares many characteristics of this new IRGS model.

Peripheral mineralization to Cerro del Gallo consists of epithermal low sulphidation silver-gold vein-breccia deposits occurring dominantly in north northwest trending structures (Carmen-Providencia), but also east northeast (Ave de Gracia) and west northwest (La Paz) trending structures. These structures were the focus of historic mining and prospecting activities. These epithermal vein-type deposits are common in the Mexican silver-rich metallogenic belt and have been the major source of Mexican silver production. The Valenciana mine on the Veta Madre (Mother Vein), located 23 km west of the San Anton Property, was arguably one of the richest epithermal vein systems in the world.

The epithermal silver-gold deposits are characterized by multiple alteration-mineralization events manifested as several phases of silica veining ranging from chalcedonic to comb quartz to milky quartz, tectonic and hydrothermal breccias, bladed carbonate replacement, and two stages of sulphide mineralization.

Gold skarns have been intersected on the southern flank of Cerro del Gallo. The intersections were encountered during systematic exploration to test a zone of magnetic depletion within the alteration halo associated with the porphyry system. The gold zone remains open to the south in an area of strong hydrothermal alteration but no previous drilling or old workings. The gold skarn description of these rocks bears many similarities to other highly productive gold skarn deposits known from other parts of the world.
 
 
Mineralisation
 
At Cerro del Gallo higher grade gold mineralisation is found within a wallrock “annulus” proximal to the felsic intrusion. On the western side of Cerro del Gallo the gold-rich zone appears to be controlled in part by a specific stratigraphic unit 60-80m thick above, and partly overlapping a contact with a shallow dipping shoulder of the felsic intrusion. On the eastern side of Cerro del Gallo the gold-rich zone is 20-30m wide and closely associated with the sub-vertical wallrockfelsic intrusion contact. Peripheral to the gold zone, the copper grade of the mineralisation appears to increase while the gold grade decreases.