The Fresnillo mine ore deposits consist of replacement chimney and manto bodies, disseminated sulfide bodies, and vein deposits hosted mainly in Cretaceous marine sedimentary and volcanic rocks.

The base metal-silver deposits are zoned to the southeast away from a small quartz monzonite stock, with increasing silver content and decreasing base metal values with distance from the stock. Wall rocks adjacent to the stock exhibit silicification and calc-silicate alteration that has been partially replaced by the sulfide minerals. Vein wall rocks exhibit potassic, phyllic, argillic, and propylitic alteration with increasing distance from the veins.Chimney and manto bodies contain pyrite, pyrrhotite, sphalerite, chalcopyrite, galena, tetrahedrite, marcasite, arsenopyrite, and silver minerals. Chimney and manto bodies predate or are contemporaneous with base metal veins containing a similar mineralogy. Younger silver-rich veins consist primarily of pyrargyrite with lesser acanthite, proustite, miargyrite, polybasite, tetrahedrite, galena, sphalerite, and chalcopyrite. Individual veins exhibit increasing silver and decreasing base metal concentrations with increasing elevation.

Fresnillo one of the world’s oldest continuously operated underground mines. There are three types of veins Wide (> 3 mts), Medium (2-3 mts) and Narrow (< 2 mts) in Fresnillo. Bench & FIll and Cut & Fill methods are used for mining operations.

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