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.

A mill and concentrator at the Fresnillo mine process the ore extracted from the mine. The mine produces (i) a lead concentrate which is high in silver content, and (ii) a zinc concentrate, and has milling capacity of 8,000tpd of ore. Crushed ore from the mine is fed into two SAG mills, where it is ground further, and then passed into ball mills to further process the ore prior to it passing to the flotation stage. Flotation consists of two circuits: first a lead concentrate circuit that recovers the majority of the silver, then a zinc concentrate circuit that processes the tailings from the lead circuit.

In the lead circuit, sodium cyanide and zinc sulfite solution is added to the ore prior to flotation. It is then moved on to a lead thickener before being filtered to recover the thickened lead concentrate. Tailings from the lead circuit are then passed through the zinc circuit, where copper sulphate, xanthate and di-thiophosphate solution are added to aid zinc flotation. ........