Los Santos lies within Lower Palaeozoic sediments in the Central Iberian Tectonic Zone, which forms part of a Europe-wide, Variscan age orogenic belt. The stratigraphy comprises a thick sequence of clastic metasediments, ortho- and para-gneisses, with volcanic andcarbonate formations.

The Los Santos deposit is a typical skarn-hosted scheelite deposit, where intrusion of granitoids into carbonate-rich sedimentary rocks has resulted in their replacement by calcsilicateor siliceous minerals, together with mineralisation.

The deposit has been divided into a number of zones, six of which form the basis of the current project. From west to east these are known as Las Cortinas, Sector Central, Capa East and Los Santos Sur. The strike length varies for each zone and zone dips are fairly uniform across the deposit varying between 60o to 90o.

Within each zone, the skarn mineralisation is located within a number of individual beds, separated by barren lithologies. The major skarn beds vary between 2m and 20m in width; there are, however, numerous thinner bands measuring tens of centimetr.

There are several varieties of skarn mineralisation, economically the most important being the fine to medium grained, equigranular pyroxene skarn with scheelite mineralisation. The pyroxene is predominantly a dark green variety of hedenbergite.

Pyroxene skarn occurs in all zones at Los Santos. It forms from impure Fe-rich carbonates and contains pyroxene, scheelite, plagioclase and locally magnetite. The scheelite is generally fine grained, minus 1mm in size, but individual crystals may exceed 1cm.

At the eastern margin of Las Cortinas, sulphide-rich skarns occur. They are up to 5m thick and several metres in strike length, and comprise massive or semi-massive sulphide horizons with scheelite mineralisation. Sulphides comprise pyrite, arsenopyrite (lollingite), pyrrhotite and chalcopyrite as principal minerals and scheelite, sphalerite, native bismuth, bismuthinite and marcasite as accessories. Wolframite also occurs at Las Cortinas: approximately 6% of the tungsten in this area. There are also some higher amounts of wolframite in sulphide zones in Capa Este.

It has been deduced that the scheelite and pyroxene have crystallized simultaneously, within a high temperature phase. Later, remobilisation has led to amphibole, or apatite as in the talc veins at Las Cortinas. In eastern and western ends of Las Cortinas sector, scheelite and wolframite are associated with massive sulphides, with the following minerals:

• Main minerals: Pyrite, arsenopyrite (and/or lollingite), pyrrhotite and chalcopyrite. Pyrite, arsenopyrite (and/or lollingite), pyrrhotite and chalcopyrite.

• Accessory minerals: Scheelite, pseudo galena, bismuth, bismuthinite, and marcasite.

Two metallogenetic stages have been recognized, the first one of As-W in which arsenopyrite, scheelite and pyrite have been deposited. Later, a breccification phase has taken place in which these minerals have been fractured and, through the fissures and hollows, the other minerals of the paragenesis have been introduced: pyrrhotite, chalcopyrite, pseudo galena, bismuth and bismuthinite.

The open pit operations are conventional drill and blast operations, using mining contractors.

Mining operations are based on mining 10m benches in waste, and 5m benches in ore, with 0.5m of sub-drilling. Tamrock CHA1100 rigs are used for blasthole drilling. The blastholes are 3.5 in. in diameter, and drilled on a 3m x 2.5m pattern in Los Santos Sur, and a 3m x 2.5m pattern in the other pits.

Pre-split lines are drilled along the edges of final walls. These pre-split holes are 3 in. in diameter, and are 0.8m apart.

The night following every blasting containing ore, a team of geologists checks with ultra-violet (UV) lighting the real position of the ore after blasting displacement, in order to reduce dilution to the minimum. They also pass the UV lamp by the waste dumps and stockpiles, to check for any kind of error on ore/waste selection. During all ore mucking operations, a grade control geologist is always present, to check and check for any other variations that can be seen in the pit with the blasted skarn material.

The plant is primarily based on gravimetric separation, aimed at recovering scheelite, so as to provide a concentrate containing greater than 65% WO3. Current overall plant recovery of scheelite is approximately 60%.

Run of mine ore (ROM) is dumped in various locations on the ROM pad according to grade range categories and for weathered material. This material is then blended by feeding into a primary jaw crusher, using a front-end loader at a nominal 100 t/h rate. The jaw crusher product is then delivered by conveyor to a primary cone crusher and the product from this crusher is dry-screened on a double-deck vibrating screen.

The top deck oversize (plus 27mm) is returned to the primary cone crusher, while the bottom deck oversize (plus12.5mm) is passed to a secondary cone crusher. The secondary cone crusher product joins the primary cone crusher product and recycles back to the screen, while the bottom deck undersize at minus 12.5 mm size is discharged to a ........