The Santa Elena Mining Complex, owned and operated by First Majestic's wholly owned indirect subsidiary, Nusantara de México, S.A. de C.V.
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Summary:
Deposit Type
The Santa Elena and Ermitano deposits are examples of epithermal low to intermediate sulphidation gold– silver vein deposits.
The Santa Elena mine and Ermitano project gold and silver depositsform as prominent east–west-trending veins and associated breccias in sub-aerial felsic volcanic rocks. The Santa Elena Main Vein is delineated by drilling along a 1,950 m strike length and 750 m down dip. The Ermitano Vein is delineated by drilling along an 1,850 m strike length and vertically over 550 m, starting at surface.
Mineralization Santa Elena
Silver and gold mineralization at the Santa Elena mine is hosted in quartz veins and stockworks displaying typical epithermal textures, including banded quartz, vuggy quartz, and brown–black bladed calcite (pseudomorph to quartz) with many of these textures intermixed with hydrothermal breccia.
Other gangue minerals include calcite, adularia, chlorite, and fluorite. Rhodonite has been noted at approximately 530 m vertical depth.
Bonanza ore shoots appear to be locally present but have not been delineated in detail. A trend of higher grades and thicker veining is apparent with a plunge of approximately 25° to the east. Up to 200 m of a pyrite and calcite matrix breccia in the hanging wall andesite proximal to the Main Vein has been intersected.
Sulphide abundance is generally low within the veins but can be as much as 5–30%. The sulphides are dominantly pyrite and pyrrhotite with minor galena, sphalerite, and chalcopyrite. Gold occurs typically as native gold, electrum, and silver occurs as electrum, minor acanthite, and rare native silver.
Alteration within the Santa Elena mine deposit is widespread. The volcanic units in the immediate vicinity of the veins exhibit pervasive propylitic to silicic alteration. Widespread argillic alteration and silicification proximal to quartz veining is common. Chloritic alteration increases away from the mineralized zones.
The permeable nature of the fractured zones has allowed partial oxidation to occur to depths of 400 m below the surface in selective fractured zones. Limonite within the oxide zone is brick-red in colour and is associated with brown goethite and local yellow jarosite. Manganese occurs locally as pyrolusite and minor psilomelane near the surface. Kaolin and alunite occur primarily along deeply weathered and oxidized structures and along the fractured contacts.
Mineralization Ermitano
Mineralizing fluids are interpreted to have used the Ermitano Fault as a conduit to form the Ermitano 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 Ermitano 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 Ermitano 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.
Sericite is common in host rocks immediately surrounding the Ermitano Vein and stockwork veins. Carbonate veins are present but are typically minor and late.