Mantos Blancos is a copper stratabound deposit with subordinate content of silver mineralization hosted by Jurassic volcanic sequences. Mantos Blancos has the typical rock, mineralization, alteration and structural setting of the Jurassic deposits, in spite of its bigger size in comparison with other Chilean stratabound copper deposits. The area has been the subject of geological studies and interpretation since 1917 and the deposit geology has been extensively studied by Ramirez (2006) and Maksaev (2002).

Mantos Blancos is associated with the La Negra Formation. A volcanic arc is recognized in the La Negra Formation in the Coastal Range of northern Chile. This formation comprises mainly thin flows of calc-alkaline basalts, basaltic andesites and high-K basaltic andesites, as well as some volcaniclastic intercalations with a total thickness of 7 km to 10 km. The beginning of the volcanism of the La Negra Formation has been determined to be of Lower Jurassic age. A comparable volcanic belt is also recognized in the Lower Cretaceous in several areas of northern Chile.

The deposit is mainly characterized by pyroclastic and intrusive host rock units. The pyroclastic and intrusive units are from the Permo-Triassic and Early Jurassic age. Andesite belonging to the La Negra Formation (Middle-Late Jurassic), tonalite, granodiorite, aplite and dacite porphyry belonging to the El Ancla and Alibaud plutons of Middle to Late Jurassic age also outcrop along the deposit. Rock types in Mantos Blancos consist of a rhyolitic dome and magmatic–hydrothermal breccias which are intruded by dioritic and granodioritic stocks and sills. The dioritic and granodioritic stockwork locally grade upwards into magmatic–hydrothermal breccias that are mineralized to different degrees. Late mafic dikes cross all the previously mentioned rock units and are essentially of no economic value.

The sulphide mineralization consists of chalcocite (and/or digenite), covellite, bornite, chalcopyrite, pyrite, specularite, magnetite, galena and low sphalerite, occurring in disseminated form, with varying thicknesses. The oxidized copper minerals are atacamite, chrysocolla and minor malachite, antlerite, tenorite, cuprite and almagres occurring as dissemination and fracture filling. Silver occurs in the crystal structure of the copper sulphides and occasionally as native silver. The geometries of the mineralized bodies are irregular lenses and oxidized copper sulphides are arranged in tabular form with a 100 m to 200 m thick interval (Boric et al., 1990) that is strongly controlled by structures.

The mineralization has a distinct vertical zonation (Infanta, 2002), with specularite at the top (porphyritic andesite and upper andesite), followed by an oxidized copper (atacamite with minor chrysocolla) that migrates in depth to a high-grade sulphide (chalcocite-bornite). The latter corresponds to irregular chalcocite rich centre lenses which decrease towards the edge to predominant bornite. Surrounding these lenses is a zone of lower grade with chalcopyrite and bornite, ending at depth with a pyritic zone, occasionally in some sectors associated with chalcopyrite. The areas with secondary enrichment are of small extent, predominantly with covellite over chalcocite and located near major faults. The oxidized copper would have developed by the in situ oxidation of primary sulphides.

The open pit operation includes one large open pit (Santa Barbara) which provides most of the sulphides for the concentrator and oxides for dump leaching.

Other sources of material are:
• Flotation: Sulphide stockpile (Cancha 90);
• Dump leach process: Oxide stockpile (Mercedes Stockpile).

Variable slope angles were used for the detail mine design, with inter-ramp slope values varying between 50° and 59°. A slope angle of 36° (natural slope angle for broken materials) is used on areas with existing underground stopes and for waste dumps.

The pit design was developed considering the following:
• Minimum expansions width: 30 m for front end loaders;
• Minimum road width: 30 m;
• Maximum gradient on ramps: 10%;
• Operating bench height: 12 m (24 m in final pit walls with pre-split blasting).

The selected final pit was divided into operational phases, resulting in a total of eight phases to define the LOM 2020.

Mine movements considered historical KPIs for loaders, operational ramps and maximum quantity of equipment for each phase. The production plan was developed considering a maximum mining rate of 66 Mt per year and the operation of 4 to 5 phases simultaneously.

The resulting plan considers a total mining rate (mineral and waste) which decreases from approximately 66 Mt in 2022 to 60.0 Mt in 2025, staying at this level up to 2030 when production starts to decrease through to 2037.

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Ore processing at Mantos Blancos currently comprises two plants: the oxide plant where the oxide ore is leached using sulphuric acid to produce copper cathodes, and the copper concentrator where the sulphide ore is treated to produce a copper concentrate.

The current sulphide concentrator has a capacity of 4.2 million tonnes of sulphide ore per year, with three stage crushing followed by ball milling and flotation plant. The oxide run-of-mine ore is leached on dumps, and the solution sent to an SX-EW plant with a production capacity of 60 thousand tonnes per year of high purity copper cathodes.

Current mining plans indicate that oxide reserves will be completely depleted by 2023 and only sulphides will be processed after that time.

Flotation and Concentrate Regrinding
The current flotation plant consists of thirteen 42.5 m3 rougher cells, one regrind ball mill, one 3 m x 12 m cleaner column cell and three 28 m3 plus twenty 14 m3 cells operating as ........