Summary:
The primary deposit type of interest at the San Ignacio Property is low sulphidation epithermal silvergold mineralization.
San Ignacio is underlain by a monotonous package of basalt (Kbas) and andesite (Kanlf) volcanic rocks belonging to the lower Cretaceous La Luz andesite (Randall et al., 1994; Stewart, 2006; Baker, 2011). The basalt generally has subtle to well-developed pillow structures that are locally flattened. In a few localities, inter-pillow hyaloclastite is present and is characterized by a fine breccia composed of devitrified glass shards in a fine groundmass.
Andesite is generally massive to locally feldspar-phyric to laminated (very rarely) and was probably formed by accumulation of a series of extrusive flows and ash falls.
Locally, these volcanic rocks have interbeds composed of sandstone, siltstone, or fine, pale ash layers (generally sericite-quartz). A more coarse-grained felsic (possibly dacite) unit is exposed northwest of the San Jose mine in the southern part of the property. Where observed, bedding is generally shallowly dipping.
Two types of dykes are present on the San Ignacio Property, and both are quite rare. In the northern part of San Ignacio, a few fine-grained mafic dykes are exposed and preserve foliation and fractures like the host volcanic rocks, so these dykes are probably quite early. Fine-grained felsic dykes occur locally near the Veta Nombre de Dios structure and are generally moderately silicified with minor fine-grained pyrite.
Mineralization
Mineralization at San Ignacio is closely associated with the structural history of the region.
The most important phase of mineralization in the Guanajuato district consists of epithermal Ag-Au veins contained within northwest-trending, Cenozoic-age faults. The La Luz structure consists of numerous mineralized fractures in a north-westerly trending orientation, which extends for a known strike of approximately 8 km long. Historically productive veins at San Ignacio include Veta Melladito and Veta Purisima. Veins identified at San Ignacio include the Melladito, Melladito Bo, Melladito South, Melladito S3, Intermediate, Intermediate 2, Nombre de Dios (NDD), Nombre de Dios 1.5, Nombre de Dios 2N, Nombre de Dios 2S, Nombre de Dios 3, Purisima, Purisima W5, Purisima HW, Purisima FW, Purisima Int., Purisima Bo, Purisima Bo 2, and Santo Niño veins (Figure 7.4).
Mineralization at San Ignacio is contained within tabular veins, vein stockwork and breccias. The eighteen veins with structural continuity inferred from surface mapping and diamond drilling from surface, and now with extensive underground development, have been defined up to 2,200 m along strike and 150 m down dip. The five Melladito and Intermediate veins are very steeply dipping, the five Nombre de Dios veins are shallowly dipping (45-50° west) and are likely off-shoots of the Intermediate veins, and the eight Purisima veins are shallowly dipping at 45-50° to the west. The veins are accompanied by hydrothermal alteration, consisting of argillic, phyllic, silicic and propylitic facies.
The primary commodities of San Ignacio are silver and gold with approximately equal contributions, by value, of each. Mineralization consists of fine-grained disseminations of acanthite and pyrargyrite (silver minerals), electrum (gold-silver mineral), with accessory pyrite, as well as very minor sphalerite and chalcopyrite. Mineral textures in this zone are typically fracture filling, drusy and coliform masses.
Average grades of the eighteen San Ignacio veins range from 58 to 237 g/t Ag and 1.65 to 3.84 g/t Au.
Melladito Veins
The Melladito vein dips steeply to the east, with a true width ranging from 0.25 to 19.5 m. The vein has been delineated to a maximum of 1,450 m along strike and to a depth of 350 m. The structure is open at depth and along strike; however, the strongest mineralization has been observed in a core zone 550 m in strike length and from surface to 150 m down dip.
The Melladito Bo vein is a sigmoidal loop on the footwall side of the Melladito vein between 200 to 500N. It dips steeply to the east and has an average width of 2.5 m. Silver-gold grades in the thicker sections are often on the footwall side.
The Melladito South vein, dips steeply to the east and has an average width of 1 to 2 m. It is noted from 0S to ~650S where it traces off the property and plunges below the Purisima vein.
Intermediate Veins
The Intermediate vein is steeply dipping and narrow with a true width ranging from 0.25 to 8.5 m. It has been delineated for 400 m along strike and 350 m below surface. It is a splay of the Melladito vein and merges into the Melladito vein at approximately 475N. Further south, the structure continues as the Melladito vein.
The Intermediate 2 vein is positioned east of the Intermediate vein. It is a near vertically dipping relatively narrow (approximately 1.0 m in width) vein.
Nombre de Dios Veins
The Nombre de Dios (“NDD”) vein is narrow, ranging from 0.25 to 4 m in width, and shallowly dipping at 45 to 60° to the southwest. It has been delineated for 600 m along strike and 180 m down dip. The vein is open to the south. At depth, the Nombre de Dios vein appears to intersect the Intermediate and Melladito veins and is therefore limited in its potential down dip extent. To the north, it terminates at line 850N where it may continue in Nombre de Dios 2N with a 40 m offset to the east.
The Nombre de Dios 2S runs parallel to the Nombre de Dios and Nombre de Dios 1.5 structures. It has been delineated for 300 m from 150 to 450N. The vein dips 70° to the southwest. The average width of this vein is 1.5 m.
The Nombre de Dios 2N is narrow, ranging in width from 0.25 to 4 m, and shallowly dipping at 45° to the southwest. It has been delineated for 400 m along strike and 100 m down dip. The vein is open to the north. To the south, it terminates at line 850N where it may continue in Nombre de Dios 1 with a 40 m offset to the west.
The Nombre de Dios 1.5 is a parallel vein located between the Nombre de Dios and Nombre de Dios 2S veins. It has been delineated for 400 m from 150 to 550N. The vein dips 60° to the southwest. The average width of this vein is 1 m.
The Nombre de Dios 3 vein is a small segment which is near vertical dipping. It could be a fault offset of the Intermediate 2 vein.
Purisima Veins
The Purisima vein dips at 45 to 50° to the southwest, and ranges in width from 0.5 to 3 me. It strikes to the north-northwest, north of the old San Ignacio mine shaft, but at the shaft the vein swings to a northwest orientation, then merges with the Melladito South vein at 400S where it bends back to a north-northwest orientation.
The Purisima Bo is a footwall splay to Purisima dipping at 75° to the southwest. It includes a 10 m wide bulge in the northern part, but generally averages 1 to 2 m in thickness. Both the Purisima and Purisima Bo were sites of mining from the 17th to early 20th centuries (the historical San Pedro and Mexiamora shafts).
The Purisima Int vein occurs between the Purisima Bo and Purisima vein, in a complex area where the Purisima veins merge with the Melladito vein system.
The Purisima HW vein is ~20 m above the Purisima vein. Most of the Purisima HW vein, typically 0.5 to 2 m thick, seems to be mostly in-situ; however, some historical mining has occurred along the structure. Recent development by Great Panther has noted the Purisima HW veins (Purisima W5 and Purisima Bo 2) to be steeper dipping splays of the Purisima structure.
The Santo Niño vein is the northern continuation of the Purisima structure in the old Santo Niño shaft area. The Santo Niño vein is approximately 20 m into the footwall of the Purisima vein in the old San Ignacio shaft area. Some mining has occurred along the Santo Niño vein, where width is typically 0.5 to 1.5 m.