The Las Cruces deposit is located within the Iberian Pyrite Belt and classed as a Volcanogenic Massive Sulphide (VHMS) deposit. VHMS mineralisation results from precipitation of metals associated with circulating hydrothermal fluids in volcanically active sub-marine areas. The metals precipitate as sulphides (pyrite/phyrrohtite with variable base metal sulphides such as chalcopyrite, sphalerite and galena) and are inter-layered to varying degrees with volcanic sediments.

The Las Cruces deposit, as per many other VHMS deposits, is characterised by a dipping massive sulphide horizon underlain by a stockwork vein system which are both hosted within shales and felsic volcanics. However, at Las Cruces, post deposition tectonism uplifted the deposit, exposing it to erosion and weathering with partial oxidation of some of the primary sulphides. This resulted in a copper leached gossan, which retained the relatively immobile gold and silver and overly the secondary sulphide horizons. The zones of primary sulphide mineralisation are the source of the current gossan and secondary sulphide zones and are key horizons for defining continuous volumes of similar geology and metal tenor. The zones of gossan, secondary sulphide, primary sulphide and stockwork are used as key domains for Mineral Resource estimation.

Mineralisation is characterised by a notable iron oxide gossan which occurs directly above a welldeveloped, flat lying secondary sulphide zone followed by an underlying north dipping (40 degrees) primary massive sulphide zone. The economically important secondary sulphide (HC) zone is about 150 m below surface.

The Gossan Zone is a 10 m to 20 m thick sub-horizontal iron stained oxide zone, leached of copper and sulphur, but contains relatively high levels of gold, silver and lead. While the contained Gossan metals are not recoverable from the current copper leaching and electro winning processing facilities at Las Cruces there is nevertheless a reasonable expectation that they are economic.

A thin (less than 5 m thick) Depleted Zone (DZ), containing variable but moderate copper mineralisation, represents a transition between the overlying Gossan Zone and the underlying secondary sulphide mineralisation. The DZ consists of a layer of sandy, pyritic material.

The underlying secondary sulphide mineralisation, known as the High Copper Main Zone (HC), has high copper grades due to supergene alteration of primary copper sulphides to secondary copper sulphides as well as from leaching copper from sulphides originally located in the overlying oxidised Gossan Zone. The HC zone has mostly chalcocite with minor bornite and covellite. Mineralisation strikes approximately 1,000 m east west and ranges from 40 m to 300 m wide in the north south direction with an average thickness of 40 m. Cobre Las Cruces Mineral Resources is comprised mostly of HC mineralisation.

A small secondary sulphide zone, known as the High Copper Small Zone (HC4), measures 200 m east west, 100 m north south and is on average 20 m thick. The HC4 mineralisation dips at 40 degrees west- north-west and is located directly below HC and PMS. HC4 orientation is due to remobilisation of copper along a structural fault zone having a similar orientation. While HC4 has similar copper grades to HC, it has been interpreted as a separate domain due to its distinct shape and orientation. Copper mineralisation is comprised mainly of covellite with chalcocite and digenite filling veins and gaps.

The Primary Massive Sulphide (PMS) zone underlies the HC zone and dips to the north at 40 degrees. PMS is approximately 1,000 m along strike and while still not completely delineated (open at depth), is approximately 500 m down dip. The primary massive sulphide is on average 30 m to 40 m thick and is characterised by pyrite intergrown with sphalerite, galena, chalcopyrite as well as minor enargite, tennanite and tetrahedrite. Weakly fractured, faulted or jointed zones of PMS have provided traps for precipitation of thin chalcocite and bornite-covellite occurrences from infiltrating copper rich fluids associated with the secondary supergene process.

The lowermost zone of mineralisation underlies the PMS, HC and HC4 zones as an irregular Stockwork (STWK) of inter-connnected pyrite veins and veinlets with locally high copper and zinc grades.

Cobre Las Cruces uses conventional open pit mining methods, based upon hydraulic shovels and trucks, with drilling and blasting in the lower marls and ore zones. The project has a relatively high stripping ratio supported by the high grade ore. Las Cruces uses contract miners for all mine production.

Ore at Cobre Las Cruces is mined from an open pit excavated into marl. Overall pit slopes are shallow (28 degrees) in accordance with requirements of the Mining Authority. Once exposed the marls weather quickly and pit slopes tend to conform to a natural rill slope.

Mining Fleet [2015 TR, p.88]
The mining fleet is basically made up of hydraulic shovels and 90-t haul trucks. The hydraulic shovels in use are Liebherr 984’s with a 7 cubic meter bucket.

The truck fleet will vary in quantity depending on need. The current configuration with concurrent ore mining and Marl stripping requires 43 units. The contractor supplies both Cat-777 and Komatsu785 trucks.

The current primary earthmoving fleet at Cobre Las Cruces comprises the following:
• 7x Liebherr 984 diesel/hydraulic – 100 tonne excavators
• 13 x Caterpillar 777 D rigid bodied haul trucks - 95 tonne capacity
• 30 x Komatsu 785 rigid bodied haul trucks - 90 tonne capacity

The secondary fleet (ROM blending/rehandle and Tailings placement) comprises:
• 2 x Caterpillar 988 D front end loaders
• 19 x Volvo ADT A40D haul trucks – 40 tonne capacity

The support fleet consists of the conventional equipment such as graders (G-14s), tractor dozers (D8 and D-10 sizes), RTDs and FELs (Cat 984 and 988 sizes), service and lube trucks, etc. The contractor also supplies a CAT825 sheep’s-foot when compacted fill is required.

Drilling is performed by an Atlas Copco L6H drill rig while dust suppression on haul roads is performed with four water tankers. It should be noted that even though the contractor supplies surveyors, the mine plan and pit design is generated by CLC. CLC also supports a surveying team for checks on monthly movement figures.

The ore processing facility is designed to operate 365 days per year, 24 hours per day and process 1.5 Mtpa of ore to produce 72,000 tpa of cathode copper. The ore from the open pit mine ranges in grade from 5% to 10% copper and the design grade is 6.02% Cu. The copper in the ore is primarily found in chalcocite with some minor amounts found in chalcopyrite, tennantite-tetrahedrite complex, and enargite.

The metallurgical plant relies on an atmospheric leaching process to recover copper from the rich secondary sulphide chalcocite mineralisation. A unique feature of the plant is the use of eight OKTOP agitated reactor tanks to dissolve the copper under conditions of high temperature and high acidity. Oxygen is also added into the reactors to complete the reaction. The feed to the leaching reactor tanks is mined ore that has passed through three stages of crushing, a single stage of grinding and has then been thickened to eliminate as much process water as possible and three m ........