Minera Tres Valles mining complex (MTV) is a Cu-Ag stratabound, manto-type deposit.

The MTV Project consists of two main deposit areas about 5km apart. The Don Gabriel area hosts the Don Gabriel Manto and Don Gabriel Vein deposits. The Papomono (“PPM”) area consists of seven known deposits: Massivo, Cumbre, Mantos Connection, PPM South, Mantos North, PPM North, and Epithermal.

Papomono
The dominant sulphides in the deposit are in decreasing order: chalcocite-covelite (~85%), bornite (~6%), enargite (~5%) and chalcopyrite (~4%). It is important to mention that the bulk of the chalcocite at MTV is hypogene. Very few parts were observed with supergene chalcocite. In places where intense fracturing and faulting occurs, the action of oxidizing agents generates oxide copper minerals: chrysocolla, malachite, brochantite and atacamite. For this reason, the traditional vertical zonation of oxides on top and sulphides in deeper parts are not identified in Papomono and the main oxide zones are related to more fractured zones, sometimes deeper than preserved sulphides.

The most common deposit geometry is the manto-type (stratiform). The individual “mantos” have a thickness that ranges from 2 to 50m, up to 500m strike extension and length along dip reaching 600m. Examples of this type of deposit geometry are the PPM South, Mantos Connection, and the Mantos North deposit. The other common geometry is vein-type, with a thickness between 2 and 15m, strike length from 100 to 420m and 100 to 250m deep. Dip angle is generally steep, between 80° and 90° to the west. There are also sets of tens of cm-thick N-S veins dipping 55° to the east. These sets of veins occur in clusters of 10 to 30 narrow, around 50m long, massive chalcocite veins.

One specific and important geometry is observed in only one deposit, PPM Massivo. It is a complex geometry which resulted from the intersection of at least three different mineralization controls in the same area: the Papomono Fault system, the favorable strata (mantos) and the N-S set of small veins dipping east. The resulting geometry is roughly an inverse triangle or a truncated rhomb shape, which has 440m strike, up to 190m wide and 190m high.

Finally, there is a cylinder-shape geometry related to the intrusive plug of Cumbre. This deposit is vertical, with at least 400m deep (310m from the bottom of exploited Cumbre pit) and an average diameter of 180m. A near surface oxide mineralized zone was hosted in the upper part of intrusive as well in the contact zones with volcanic to volcanoclastic rocks of the Quebrada Marquesa Formation and was already exploited by open pit. Deeper zones in Cumbre present disseminated chalcocite and bornite mineralization.

Don Gabriel
The mineral deposit of Don Gabriel is formed of two main zones:
- An upper deposit of “manto” type, medium copper grade, with a set of stratabound disseminated, fine chalcocite, mineralization approximately 100m thick, dipping 30° SSW.
- A lower deposit, vein-shaped (straight-tabular), sub-vertically oriented N45°W, with intense strong to spotty mineralization or veinlets type (stockwork or sheeted veinlets), high copper grade, with chalcocite, digenite and some bornite.

Whereas the first type is hosted mainly in andesite amygdaloidal levels, the second type has medium to coarse porphyritic andesite and/or dioritic to microdioritic dikes as host rock, which underlies the level of coarse sandstone. The layers of sandstone serve as a guide-level separating the two main units. It is used as a sharp limit between the two geological models, Don Gabriel Mantos and Don Gabriel Veins.

The vertical-tabular mineralization seems to be intimately linked to the presence of dioritic dikes, which, in turn, are related to an intrusive stock to the W and SW, and outcrops at the bottom of the ravine near the mineral deposit. Such stock was also intercepted by several drill holes a little further to the east. Those dikes found in such drill holes may also be observed in the mine’s roads cut, as a 2 to 10m-thick dike swarm, which follows the same N45-50°W direction of the mineralization.

Considering the clear relationship between the vein shape mineralization and such dikes, it is possible to speculate the presence of a metasomatic component in its genesis, despite no distinctive skarn mineral being observed, only epidote and chlorite. Another possibility is that the dioritic magma emplaced areas of structural weakness, also employed by the mineralizing fluids immediately after the igneous siting (tardi- magmatic event). In some areas, mineralization zones are also observed, with similar characteristics to the “mantos”, chalcocite disseminated mineralization with pervasive albite, which makes it possible to glimpse the potential presence of stratabound deposits, but not stratiforms, as a set of parallel veins restricted to favorable stratigraphic levels (e.g. mineral deposits El Soldado or El Espino). Another aspect worth mentioning is the common presence of veins or disseminated hematite surrounding the best mineral grade sectors.

PPM North and Cumbre are amenable to continued open pit mining. There is also a portion of Cumbre below the resource cone shell that might be amenable to underground mining. It would need to be a fairly low cost method such as block caving, or maybe sub-level caving.

The geometry of the Massivo deposit is also amenable to bulk mining methods such as block caving or sub-level caving. Block caving is currently the method of choice for MTV personnel.

Papomono Masivo uses a combination of front caving and inclined block caving mining methods, based on financial considerations, deposit geometry and geotechnical characteristics.

The Epithermal Vein and also the Don Gabriel Veins are narrow, steeply dipping structures. They are amenable to a method such as sub-level stoping.

The relatively flat lying nature of PPM South, Mantos Connection, and North Mantos makes them amenable to methods such as room and pillar (or post pillar), cut and fill, or front caving. However, the post pillar and cut and fill methods are relatively expensive. Front caving is a less expensive method, though it will probably result in higher dilution.

Don Gabriel Manto commenced the exploitation in 2012 using open pit method and, after a period of suspension from 2014 to 2016, it is currently in the ramp-up phase reaching its maximum production capacity (about 2.4 kt/d) at the beginning of 2019.

The base case mine plan is based on Mineral Reserves of 5.168 million tonnes at 0.81% total copper (TCu) and is expected to produce approximately 14 million pounds of copper per year over a six-year reserve life.

The Papomono Masivo is designed to be exploited using the inclined block caving method (IBC) and its underground operation is planned to start in September 2019. A sector of Papomono Masivo is under exploitation using front caving method (FC) and is planned to continue until before the start-up of the inclined block caving operation. The mine plan considers reserves of 3.07 million tonnes at 1.5% TCu and during its useful life of about 5 years will produce the order of 12.5 million pounds of copper per year.

MTV currently produces high grade copper cathodes using a heap-leach and SX-EW process. Ore is stockpiled above the crusher, and is loaded into a primary jaw crusher, secondary cone crusher, tertiary and quaternary crushers; reducing the rock to fragments to a final granularity of the mineralized material with a target size is 80% < 6.4mm (1/4”).

The crushed material is agglomerated and water and acid is added to commence the leaching process. The agglomerated material is trucked to the heap leach area and stacked by front-end loaders. A grid of hoses with drippers is placed over the heaped material and the first phase of intensive leaching to recover the oxide ore during the first 3-month period by constant and high acid- concentration irrigation. The product of this first leaching stage is the “oxide-pregnant leach solution” (oxide-PLS), which has high copper content and is accumulated in a pond at the bottom of the leach pads. For the subsequent 6 months the material ........