Gold-copper skarns have developed mainly along the contact between intrusives and carbonate units. Two different types of skarn have been recognised at El Valle-Boinás. The first is a calcic skarn related to limestone units and the second is a magnesian skarn, called “black skarn”, that is related to dolomite units.

The gold-copper bearing skarns at Carlés are generally calcic skarns. Better grade goldcopper mineralisation is associated with high magnetite and bornite content that is localised in generally continuous, relatively thin (four metres thick) layers of retrograde skarn.

At the El Valle-Boinás deposit, reactivation of fracture zones (along northeast-southwest, eastwest, and northwestsoutheast orientations) produced widespread brecciation and favoured the emplacement of porphyritic dykes. A low temperature alteration and mineralisation event is spatially and genetically associated with the subvolcanic porphyry dykes, which overprint all previous lithologies. Depending on the host rock, there are different styles of hydrothermal alteration and mineralisation, such as: sericite-adularia-carbonates (+py-aspy) in granites and skarns; leaching, enrichment, and silicification in skarns (+ native copper and chalcocite); and silicification (+py) in dolomites.

Highest gold grades occur where the low temperature mineralisation overprints previously mineralised gold-copper skarn, forming jasperoid or semi-jasperoids with native copper and minor chalcocite and cuprite. The associated geochemistry is characterised by an increase in As, Sb, and Hg. This low temperature event is the principal gold mineralising episode at El Valle.

Gold, and in some cases base metal mineralisation, has been found in association with late tectonic breccias related to low angle thrust faults at El Valle-Boinás. The origin of the gold mineralisation in these structures is thought to be due to remobilisation of previous skarn or jasperoid related gold mineralisation. Gold associated with low angle structures is important at El Valle-Boinás where a significant percentage of the open pit minable gold mineralisation extracted from the Boinás East Zone came from this type of structure.

EL VALLE-BOINÁS
Mineralisation at the El Valle-Boinás copper-gold deposit can be grouped into several significant deposits related to the Boinás granitic intrusive and carbonate rocks of the Láncara Formation (Cambrian age).

The gold mineralisation system has a strike length of two kilometres and a width of at least 0.5 km. The intrusive is elongated trending N35°E with a length of 500 m and an average thickness of 300 m. A copper-gold mesothermal skarn was developed mainly along the contact between the igneous rock and the carbonate unit.

Late reactivation of the main northeast trending fracture system was accompanied by two or more phases of epithermal mineralisation as well as the intrusion of porphyry dykes. These events produced hypogene oxidation with further enrichment of gold, arsenic, antimony, and mercury (Martin-Izard et al., 1999). Rhyodacite dykes, which are always sericitised, were emplaced along fractures and breccia zones trending north-northeast. The intense silicification along fractures and breccia zones resulted in the formation of hematitic jasperoid that is characterised by enrichment in gold, arsenic, antimony, and mercury. The presence of cuprite and native copper in the structures and breccias suggests the leaching of chalcocite, which is encountered at a depth of approximately 400 m along the A107 structure. This can be viewed as evidence of two-cycle leaching and enrichment.

CARLÉS
The Carlés deposit is a gold and copper bearing skarn developed predominantly in the Devonian limestones of the lower portion of the Rañeces Formation along the north margin of the Carlés granodiorite. The Carlés intrusion is approximately circular in plan with a diameter of approximately 750 m. The intrusion is located at the intersection of major faults (east-west, northeast-southwest, and southeast-northwest) and it is bisected from west to east by the Río Narcea. The northern part of the granodiorite is in contact with the lower part of Rañeces Formation and the southern part of the intrusion is in contact with the siliciclastic Furada Formation. Several barren Permian porphyritic and diabasic dykes crosscut the existing lithologies.

Mineralisation is continuous for over 1,000 m, ranging in thickness from 1.5 m to over 25 m, dipping 50° to 90° away from the granitic intrusion. The skarn is known over a vertical continuity of 400 m and remains open at depth.

The Carlés skarn is of calcic composition and is an exoskarn although irregular endoskarn has developed locally. It consists of layers of garnet (grossularite-andradite composition) intercalated with layers of pyroxene skarn, mostly of hedenbergite composition. Retrograde phases of the skarn results in the formation of irregular magnetite layers associated with amphibole. Inside these bands is where most of the copper sulphides and gold mineralisation occur. The skarn mineralisation transitions into coarse grained marbles then non-altered limestones away from the intrusive. The latter may show narrow intercalations of distal garnetpyroxene incipient skarn.

Gold mineralisation at Carlés is closely associated with copper sulphides, which consist of disseminated and patchy chalcopyrite and bornite that precipitated mainly in the magnetite zone. Other minerals common in the skarn are arsenopyrite, löellingite, pyrrhotite, and latestage pyrite. Mineralisation at Carlés is divided into four areas: Carlés East, Carlés North, Carlés Northwest, and Carlés West.

The Orovalle Operation consists of underground mines at Boinás and Carlés and an open pit at Carlés. Currently the Boinás underground mine is the only producing asset, with a nominal mining rate of 2,000 tpd. Both Carlés mines are currently on care and maintenance with underground production planned to recommence in the near future.

The current mining methods used at Boinás underground mine are overhand D&F and transverse and longitudinal longhole SLS. The D&F mining method is utilised in oxides and some transitional areas of the Boinás mine. Longitudinal SLS is used exclusively in the more competent skarns. The Carlés mine is planned to utilise both SLS methods underground, where the orebody dip is suitable, and D&F where the orebody dip is too shallow for SLS mining. Should the open pit at Carlés recommence production, then a conventional drill and blast, truck and shovel method will be used.

Access is typical for SLS methods, with an upper drill drift and lower mucking drift. Cable bolting is carried out to support the hanging wall and help reduce dilution. In Boinás there are primary and secondary stopes. Primary stopes are backfilled with cemented rock fill (CRF) and secondary stopes are backfilled with uncemented rock fill (URF). In Carlés all the stopes will be backfilled with URF. Waste suitable for CRF production will be hauled to surface where it is screened and mixed with 4% cement before being transported back underground in trucks for placement.

SLS stopes vary in size depending upon their location and whether they are transverse stopes in the Black Skarn zone of the Boinás mine, or longitudinal stopes in the High Angle zone or underground at Carlés northwest. Stope sizes also vary depending on whether they are primary or secondary stopes. Primary stopes are smaller by design in order to optimise the usage of CRF.

D&F mining of oxide ore is also driven by the ground conditions. The oxides form a very weak rock mass consisting of a silicified gravel type material. Mining is completed using a rock breaker mounted on an excavator. Muck is moved using a load-haul-dump (LHD) unit and trucks. CRF is used in the primary drifts and URF is used in secondary drifts. Ground support used in the oxides consists of shotcrete, swellex, and wire mesh if the drift will be open for an extended period of time. The main ramps and hauling drifts in weak rock are also supported with arches positioned every five meters.

Mining of oxide ore has been designed so that multiple panels can be worked concurrently in each zone. No sill pillars are left between successive panels, maximising extraction, and ensuring no high stress concentrations are created within a single mining horizon.

A 75 m crown pillar has been demarcated between the El Valle TSF and the upper level workings, which mainly constrains extraction from the A107, and El Valle fault zones. Also, a 42 m crown pillar has been demarcated between the Boinás East pit and the upper level workings, which mainly constrains extraction from Boinás East, and High Angle zones. Existing ramps and ramp designs have a maximum gradient of 15%.

PRODUCTIVITIES
Productivities used for long term planning were based on the recent Orovalle Operation operating history. Development in fresh rock is by conventional twin and single boom jumbos mucked out by scoop trams. Development rates are scheduled to reach a maximum of 3.0 metres per day (m/d) in a single heading with cross sections of 5.0 m wide x 4.8 m high, or 4.5 m wide x 4.8 m high in the declines, and 4.5m x 4.5 m in horizontal drives. For oxide development using a rock breaker mounted on an excavator, the maximum advance rate is 3.0 m/d with standard drift sizes of 5.0 m wide x 4.5 m high.Maximum advance in the oxides is 1.5 m cuts before support is required. The advance rate for ventilation raises is 4.0 m/d with a 5.0 m x 2.3 m raise as the standard size.

Long term planning production rates for SLS range from 700 tpd to 1,000 tpd, with 900 tpd being the common rate used to achieve the tonnages required to meet production targets. The schedule is sensitive to equipment availability, utilisation, and the backfill placement rate. The cyclic nature of the D&F operation is such that interruptions in that cycle can have a significant knock-on effect and lead to a drop in productivity. To achieve the production profile, backfill placement rates of 280 m3/d for CRF and 560 m3/d for URF will be required, for an average total of 840 m3/d.

LIFE OF MINE PLAN
The schedule includes oxide and skarn ore mined from both the Boinás and Carlés underground mines at an average rate of 686,000 tpa for a period of five years. The total production schedule shows 3,431,000 t of ore, mined from both Boinás and Carlés, containing an estimated 307,000 oz Au, 756,240 oz Ag, and 27.6 Mlb Cu.

Underground mining at Carlés is planned to re-commence in the near future subject to evaluation of the results from the current drilling campaign. In the LOMP, proposed Carlés skarn production averages 45,000 tpa over the last three years of the schedule producing 11,200 oz Au, 20,600 oz Ag and 0.6 Mlb Cu.

Infrastructure at the Boinás mine consists of ramp access and a rock hoist shaft. Intake ventilation is provided via the main access declines and return air raises connected to a surface fan via a shaft draw fresh air through the mine to the various work areas via a series of regulators. A 420 m deep shaft equipped with rock skips is used to hoist most of the skarn ore and waste rock to the surface. Some skarn ore and waste, and all oxide material, is transported to the surface by truck via the main access ramp.

While the rock hoist can handle the Boinás skarn ore and waste more efficiently than truck haulage, due to the sticky nature of the oxide material, oxide material is not hoisted and instead is truck hauled to surface. CRF is prepared on surface and hauled back underground by returning trucks to be placed into stopes and primary D&F drifts, which increases the overall truck productivity. Development mining outside the oxide zones uses jumbos to advance the face using drill and blast. Inside the oxide zones a rock breaker mounted on an excavator frame is used to advance the face.

CRUSHING
A front end loader feeds the ore blend to the primary crusher tip which is equipped with a 600 mm grizzly. Minus 600 mm ore is fed by apron feeder at a controlled rate to a 110 kW jaw crusher which reduces the rock size to < 153 mm. Original Dragon MR-10 jaw crusher was replaced by a new Sandvik CJ411 jaw crusher in 2018. Crushed ore is conveyed to a 100 tonne capacity level controlled mill feed bin after passing under a tramp iron magnet. The crushing circuit can operate at up to 200 tph.

Ore is withdrawn from the mill feed bin via apron feeder and conveyed to the SAG mill. The mill feed conveyor also receives recycled crushed pebbles. The mass of the new feed plus the recycled pebbles is continuously recorded as the belt passes over an in-line weightometer. Recycled crushed pebbles are also weighed by a belt weightometer prior to joining the feed to the mill.

SAG MILL AND PEBBLE CRUSHER
The mill feed conveyor discharges ore into the SAG mill feed hopper at a typical feed rate of 90 tph to 100 tph (new feed 80 tph to 100 tph + recycled pebbles 20 tph to 30 tph). The mill feed rate is controlled electronically to maintain load and power draw targets. Water is also added to the mill feed hopper to maintain a desired in-mill pulp density.

The 700 kW SAG mill dimensions are 5.5 m internal diameter and 2.3 m effective grinding length. The SAG mill discharges through an end grate slotted with 70 mm pebble ports. A discharge trommel screen with 12 mm apertures separates the pebbles from the slurry. Pebbles are conveyed to a 132 kW cone crusher for crushing down to <12 mm. The crusher is protected from tramp metal in the feed by an overhead magnet and metal detector on the feed conveyor belt. The crusher product particle top size is 10 mm.

BALL MILL
SAG mill trommel screen underflow and ball mill discharge are collected in a common pump box,. The slurry is pumped to a cyclone cluster for classification, with fine overflow (P80 75 µm) reporting to the flotation section. The coarse underflow is split into two streams, a bleed stream which undergoes gravity concentration, and the main stream which is directed to the ball mill feed spout.

The El Valle processing plant consists of the following process stages:
• Single stage crushing
• SAG and pebble crushing
• Ball milling
• Gravity circuit
• Flotation circuit
• CIL circuit
• Desorption and regeneration circuit
• Electrowinning and smelting
• Tailings detox and disposal

A gravity-flotation-leach processing plant, located at Boinás, produces doré bars and copper concentrate with gold and silver credits.

Ore is delivered to the El Valle processing plant receiving pad and stockpiled according to source and ore type to enable blending of the plant feed to achieve target gold, copper, and arsenic grades into the plant.

Based on the gold mineralogy in the oxide and sulphide ores, it is anticipated that gold in oxide ore will generally be recovered as doré product from gravity and CIL circuits, while gold in sulphide skarn ore will be recovered into flotation concentrate.

GRAVITY CONCEN ........