Summary:
The San Matias Property consists of El Alacrán Deposit and Satellite Deposits (The Montiel East, Montiel West, and Costa Azul deposits).
The Project area comprises three primary lithological domains: intrusive rocks (including porphyries) in the El Alacrán, Montiel East, and Costa Azul deposits, volcanic rocks in the Montiel West deposit, and volcaniclastic rocks in the El Alacrán deposit. Volcaniclastic rocks are also present in the El Alacrán Norte and William Prospect areas. The volcanic rocks correspond to aphyric andesite and basalt with variations to andesite porphyry, composed mostly of phenocrysts of plagioclase and augite.
The Montiel East, Montiel West, and Costa Azul deposits can all be broadly classified as Cu-Au porphyry systems. Cu-Au porphyries are typically associated with I-type magnetite-series intrusive rocks and typically contain significant hydrothermal magnetite, indicating the host intrusions are highly oxidized and sulphur-poor members of this series of magmas. The porphyry stocks in these types of rocks span a range of compositions from diorites, quartz diorite, and tonalite through to quartz monzonite, monzonite, and syenite. The porphyry deposits of the Project area are of low-potassium, calc-alkaline dioritic, and tonalitic composition.
El Alacrán deposit
The El Alacrán deposit comprises a replacement style of mineralization that trends northerly for about 1 km and has a vertical extent of >200 m.
The hydrothermal alteration assemblages of the El Alacrán deposit are zoned from early high temperature calc-silicate alteration to a subsequent calc-potassic, sericitic, and CBM alteration. The mineral paragenesis indicates at least three different Au precipitation events:
1) associated with pyrite – mushketovite in the calc-silicate alteration;
2) precipitation of Au electrum with chalcopyrite, traces of the pyrrhotite and molybdenite in the calc-potassic and sericitic alteration;
3) as visible grains in the carbonate base metal-related alteration.
Montiel East Deposit
The shallow parts of the Montiel East deposit display surface dimensions of approximately 100 m x 70 m and a vertical extent of 100 m. Montiel East deposit is porphyry Cu-Au-Ag mineralization associated with a series of tonalite porphyry stocks and sills that intrude basaltic andesitic volcanic rocks and host a strong stockwork of quartz-magnetite-chalcopyrite-bornite veins. Based on cross-cutting relationships, alteration assemblages, and compositions, four different phases have been identified within the Montiel East porphyry suite, three of which are hornblende porphyries and one of which is a quartz feldspar porphyry.
Montiel West Deposit
Diamond drill holes intersected high-density zones of both sheeted and multi-directional quartz-magnetite- chalcopyrite-bornite veining that are hosted in mafic and intermediate volcanic rocks, but no intrusive rocks. This style of wall rock Cu-Au-Ag mineralization is interpreted to be porphyry-related, as seen at both the Montiel East and Costa Azul prospects. The veinlets are generally narrower than those observed at Montiel East, possibly suggesting that there is no direct relationship between the two prospects. Alteration appears to be sodic-calcic, defined by albite, actinolite, and possible diopside.
The Costa Azul Deposit
The Costa Azul porphyry is a shallow dipping, holocrystalline, Cretaceous porphyry diorite intrusion dominated by phenocrysts (approximately 70%) comprising medium-grained (< 2.0 mm), euhedral plagioclase (21%) and anhedral to subhedral hornblende (6%), intergrown with primary magnetite, and biotite. Quartz (27%) occurs either as fine-grained (<.5 mm), anhedral phenocrysts or as very fine-grained (< 0.05 mm) groundmass. Mineralization here is porphyry-style Cu-Au associated with sheeted quartzmagnetite-chalcopyrite-pyrite-bornite veinlets within altered diorite porphyry and unmineralized, mafic volcanic footwall rocks.
Mineralization
Mineralization in the San Matías porphyry deposits is associated with a quartz-sulphide (chalcopyrite+pyrite±bornite) stockwork typically within hydrothermal biotite (potassic) altered rocks.
The El Alacrán deposit Cu-Au-Ag mineralization is hosted by a west-dipping Cretaceous succession comprising mafic volcanic rocks overlain by a calcareous volcaniclastic sequence and capped by pre- to syn-mineral, sill-like diorite, and felsic sub-volcanic bodies. The sequence is approximately 550 m thick, and the diorites are about 200 m thick. Cu-Au-Ag mineralization occurs throughout the volcaniclastic package at El Alacrán, except within the lower mafic units. It is most strongly developed in the calcareous volcaniclastic sequence. Several different deposit models have been proposed for the El Alacrán deposit, including Volcanogenic Massive Sulphide (VMS), Skarn, Carbonate Replacement Deposit (CRD), and Iron Oxide Copper-Gold (IOCG).
El Alacrán Cu-Au mineralization comprises veins and dissemination of chalcopyrite-pyrite ± pyrrhotite with quartz and carbonate and locally forms massive sulphides, and apatite is common. Au correlates with Cu and Mo, Ni, Co, Cr, P and the light rare earth elements are typically enriched in the sulphide-mineralized zones.