The San Andres deposit is classified as an epithermal gold deposit associated with extension structures within tectonic rift settings.  Gold occurs in quartz veins predominantly comprised of colloform banded quartz (generally chalcedony with lesser amounts of fine comb quartz, adularia, dark carbonate, and sulfide material). The gold mineralization is deposited as a result of cooling and the interaction of hydrothermal fluids with groundwater and the host rocks. The hydrothermal fluids may have migrated some distance from the source; however, there is no clear evidence at the San Andres Mine that the fluids or portions of the fluids have been derived from magmatic intrusions. Minor silver is present in the mineralization.  A recently completed exploration program, using reverse circulation and diamond drilling, mapping, and sampling of rock exposures in road cuts, has been carried out to better define the pit boundaries, test areas between the pits, and assess potential extensions of the mineralization in other areas of the mining lease.

The core drilling in particular has generated new insight into the deposit geology and controls, as well as extent of mineralization. Previous exploration was focused on three principal pit areas: Water Tank Hill, which is depleted; Twin Hills, currently being mined; and East Ledge, where additional mining will take place as part of the expansion plan. However, recent drilling indicates that the gold mineralization system is much more extensive than previously recognized. Economically extractable gold mineralization is continuous between the East Ledge pit and the Twin Hills deposit and extends to the east, west, and south of these deposits.

Exploration drilling is continuing at the mine to better define the existing mineral resource and increase the resource and test new targets.