Summary:
The San Martín mine is considered to be a typical example of a low sulfidation epithermal deposit, and the geological model used for exploration as well as the mineral resource estimation is that of a low sulfidation vein type deposit. Epithermal deposits form at shallow depths in volcanic-hydrothermal and geothermal environments, typically at temperatures between 160°C and 300°C (White and Hedenquist, 1995). They define a spectrum with two end members, low and high sulfidation (Hedenquist et al., 1998).
Fluid inclusion microthermometry carried out in sphalerite, quartz and fluorite for the Zuloaga vein indicates average homogenization temperatures and salinities of 297°C and 4.1 wt% NaCl eq (Albinson et al., 2001). The homogenization temperatures and low salinities (diluted fluids) in the Zuloaga vein and the alteration-mineral assemblage (interstratified illite/smectite in Zuloaga and Rosario) are consistent with low sulfidation vein-type deposits described by White and Hedenquist (1995) and Hedenquist et al. (1998). The presence of epidote in Zuloaga, Rosario and Other Veins is also consistent with the homogenization temperatures around 300°C determined for Zuloaga by Albinson et al (2001).
In the opinion of the QP, the deposits in the San Martín mine area are considered to be examples of low sulfidation epithermal deposits. The Miocene age of the mineralization and its association with volcanic rocks of the Upper Volcanic Series is also found for other low sulfidation deposits in Mexico. Additionally, structural-textural features, such as hydrothermal breccias cemented by quartz-calcite, stockworks and cymoid loops, are also common in other low sulfidation epithermal vein-type deposits in Mexico.
Mineralization in the San Martín mine occurs in east–west, northwest–southeast, northeast southwest and north–south fault structures in the form of stockworks, sheeted veinlets, veins, and breccias. The veins in the San Martín mine can be described as fault veins or mineralized faults, given that the amount of gangue minerals such as quartz, calcite, fluorite, epidote, ankerite and adularia are very limited, i.e., they do not form massive or banded veins typical of open space-filling veins.