Geology and Mineralization
The Zacatecas Mining District is located within the physiographical provinces of the Western Sierra Madre and the Central Plateau.
The basement rock units in the area include the metamorphic rocks of the Zacatecas Formation of Upper Triassic age. Overlying these rocks are the volcano-sedimentary units of the Chilitos Formation of Upper Jurassic-Lower Cretaceous age. During the Tertiary, a polymictic conglomerate known as the "Red Zacatecas Conglomerate" was discordantly deposited, and overlying this, andesitic to rhyolitic flows and tuffs were deposited. All units are intruded by small stocks and plugs of rhyolitic to andesitic composition.
The Zacatecas Formation is composed of a sequence of sericitized phyllites and metamorphosed shales, sandstones, conglomerates and limestones. These rocks are host to some veins such as those of the El Bote vein system and the deeper portions of the Mala Noche vein system.
The Chilitos Formation of Upper Jurassic-Lower Cretaceous age is a volcano-sedimentary sequence made up of massive and pillowed lavas of basaltic-andesitic composition with intercalations of sedimentary, volcaniclastic and calcareous rocks, metamorphosed to greenschist facies. This sequence is locally thrust over the Zacatecas Formation and is the main host rock for mineral systems in several mining districts in the region, including Zacatecas and Fresnillo.
During the Oligocene-Miocene period, extensive deformation occurred that produced normal faulting, forming grabens and horsts bearing generally north-northeast/south-southwest. It was during this phase of deformation that most of the epigenetic mineral deposits were formed.
Cautionary Note regarding Estimates of Measured, Indicated and Inferred Resources: The United States Securities and Exchange Commission permits mining companies, in their filings with the SEC, to disclose only those mineral deposits that a company can economically and legally extract or produce. We use certain terms in this presentation, such as “indicated” and “inferred resources” that the SEC guidelines strictly prohibit us from including in our filings with the SEC. US investors are cautioned not to assume that any or all of measured, indicated or inferred resources are economically or legally mineable or that these resources will ever be converted into reserves. US investors are urged to consider closely the disclosure in our Form 10-K and other SEC filings. You can review and obtain copies of these filings from the SEC’s website at http://www.sec.gov/edgar.shtml.