Summary:
The Ermitaño project gold and silver deposits form as prominent east–west-trending veins and associated breccias in sub-aerial felsic volcanic rocks. The Ermitaño Vein is delineated by drilling along an 1,850 m strike length and vertically over 550 m, starting at surface.
The regional geology and the form, textures, alteration, and mineralization observed to date within the Ermitaño deposit are diagnostic of low-sulphidation epithermal mineralization. The Ermitaño Vein is hosted in a sequence of volcanic lavas and tuffs and displays epithermal minerals and textures.
Exploration programs that use a low-sulphidation epithermal model are considered appropriate for the Santa Elena and Ermitaño areas. First Majestic is using geochemical and geophysical surveys, and field X-ray fluorescence analyzers and spectrometers as part of its ongoing regional exploration program. Mapping, rock chip sampling and drilling of vein outcrops remain the primary exploration tools at Santa Elena and the Ermitaño project.
Mineralizing fluids are interpreted to have used the Ermitaño Fault as a conduit to form the Ermitaño Vein and sub-parallel tertiary veins which drilling has delineated over 1,800 m along strike and 550 m down dip. The vein is best developed where the structure cuts the older brittle volcanic rocks, where the older volcanic rocks are juxtaposed with younger brittle volcanic rocks, and where the structure shows deflection.
A four-stage vein paragenesis is observed for the Ermitaño Vein. Stage 1 consists of grey quartz, normally cementing breccias, well banded white quartz + pyrite, and calcite pseudomorphs. Stage 2 is dominantly banded and crustiform textured green veins and typically hosts the highest grades of gold and silver. Stage 3 consists of several hydrothermal/tectonic breccia facies with some calcite pseudomorphs, tensile veins, and crack and seal textures. Stage 4 is dominated by white quartz fragments in a hematite + silica cement. The vein assemblage also includes minor adularia, and rarely fluorite and barite.
Sulphide abundance within the Ermitaño Vein, stockwork, and surrounding veins is typically <1–2%, dominated by pyrite with minor galena, sphalerite, pyrrhotite, and chalcopyrite. Gold occurs as native gold or electrum, and silver occurs as electrum, acanthite, and argentite.