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 stack-out conveyor which forms a conical open stockpile ahead of the main process plant.

Crushed ore from the stockpile is delivered via variable-speed belt feeders and conveyors at 65t/h to a 2.9m diameter x 4.8m long rod mill which wet grinds the ore in open circuit to approximately 50% passing 250 µm.

From the rod mill, the ground ore passes to a Derrick Stacksizer where it is wet-screened at 1000 µm. The Stacksizer oversize (plus 1000 µm) is fed to a regrind mill. This regrind mill is a 2.1m diameter x 3.7m long ball mill. The re-milled product from the ball mill, is then sent to the gravity circuit. Since the beginning of 2011, the hole-size of the panels used in the Derrick screen has been progressively increased from the initial 325 microns to 1 mm. This modification has been motivated by the observation that the majority of the losses were in the -38 microns size range. Even grinding at just 1 mm, it was verified that less than 5% of the losses are in the +500 microns.

The ground ore is first classified into separate coarse (minus 1000 µm, nominally plus 150 µm), and fine (nominally minus 150, plus 30 µm) fractions using banks of hydrocyclones. The final cyclone overflow, nominally minus 30 µm in size, is not processed in the gravity circuits and goes direct to the tailings thickener. The first separation step is the removal of strongly magnetic particles, mainly mill steel and pyrrhotite, using one-off, wet low intensity magnetic drum separator in each of the two gravity circuits.

The non-magnetics in the coarse circuit pass to a bank of coarse rougher spirals (36 starts), the concentrate from these spirals going to a bank of cleaner spirals (12 starts) and the middlings going to a bank of middlings-cleaner spirals (12 starts). The tailings from the rougher and middlings-cleaner spirals go to final tailings (as does the middlings from this last bank), while the tails from the cleaner bank go back to the regrind ball mill, and the middlings are recycled back to the feed.

In the fines circuit, the rougher spirals comprise one bank of 48 starts. The concentrate from these fines rougher spirals goes to a bank of fines cleaner spirals (12 starts) and the middlings, from both banks, recirculate back to the rougher bank. The tails from both banks of spirals go to the new fines scavenging circuit.

The new fines scavenging circuit comprises a bank of rougher spirals (36 starts) and a bank of cleaner spirals (12 starts). The middlings from each bank recirculate over the respective feed, and the tailings are discarded as final tailings. The concentrate from the cleaner spirals is sent to the hydrosizer (table circuit). The overflow from the cyclones that control the pulp dilution in the rougher bank is thickened in a second group of cyclones, being the underflow fed to another set of fine spirals (12 starts). The middlings from these spirals recirculate over the feed, and the tailings are discarded as final tailings. The concentrate is sent directly to the ultra-fine group of tables (table circuit).

The concentrate from the coarse and fine cleaner spirals, the concentrate from the middlings- cleaner spirals, and the concentrate from the fine scavenging spirals are collected in a sump and pumped to the continuous flotation circuit.

This circuit comprises one bank of four Denver DR cells of 1.4 m³ each. In the froth, are recovered the sulphides, being mainly composed of arsenopyrite and loellingite. These sulphides are discarded as final tailings. The flotation is performed at neutral pH and PAX is used as collector. Copper sulphate is used to help in the activation of the sulphides and pine oil is used as frother. The product that remains in the pulp is collected in a sump and pumped to the hydrosizer (table circuit).

The hydrosizer comprises nine chambers, and feeds four separate tabling circuits. All the circuits are structured in rougher and cleaner steps, with the exception of the fine and ultrafine circuit, which only has rougher tables. The tailings from the rougher step of the coarse and intermediate tabling circuits are sent to regrinding. The tailings from the rougher fine tables are sent to the fine rougher spirals, while the tailings from the ultra-fine tables are considered final tailings.

The tailings from the cleaner step of all tabling circuits are recycled back to the hydrosizer. Finally, the concentrate from all the cleaner tables and from the ultra-fine rougher tables forms the gravity preconcentrate.

The combined concentrates from the gravity circuits (the so-called “pre-concentrate”) is fed into a round screen (via a dewatering cyclone). The oversize (+500µm) is reground in a 900x1200mm rod mill, in close circuit with the screen. The undersize is stored and semidewatered in a settling cone, which feeds a 3m3 batch flotation cell where flotation of the sulphides takes place. Recently, a second cell of 3m³ has been installed. Typical flotation reagents are dosed to the cell and flotation takes place over about 120 minutes at pH <4.3 to remove sulphides as a froth concentrate. These sulphidesrecirculate to the continuous flotation circuit. The non-floating material, which is principally scheelite and calc- silicates, is discharged from the batch cell into a dewatering / settling cone and hence transferred to Area 60 for drying and final processing. A filter press has also been recently installed ahead from the dryer, in order to avoid the losses of fines that would occur if the material was stored and dewatered in bulk bags.

The semi-dewatered non-float product from the filter press is directly fed into a 20t-capacity surge hopper, from which is extracted at nominally 1t/h rate by a variable-speed belt feeder, and hence by conveyor into a rotary kiln drier. The bone-dry material is then subjected to high intensity, dry, magnetic separation in a three- stage, rare earth roll (RER) magnetic separator. More than 90% of the material collected by the separator comes out in the first roll. The mineralogical composition of this product is mainly magnetic pyroxene (hedenbergite). Due to the presence of scheelite and wolframite, the WO3 content can be as high as 3%. The product that comes out in the second and third rolls is progressively less rich in magnetic pyroxene and with a higher content in WO3.

The intermediate products from the RER magnetic separator are now dressed on a doubledeck table, from which it is possible to obtain a low-grade concentrate, of about 45% WO3. It is important to notice that in this way it is possible not only to recover scheelite but also wolframite.