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 ........

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 pla ........

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