The mineral deposit that comprises the El Roble Project consists of mafic-type volcanogenic massive sulfide (VMS) mineralization for which there are numerous examples in the world.

At El Roble, current geologic thinking is that the basalt and chert-bearing sedimentary host rocks represent a fragment of a Late Cretaceous seafloor that was accreted to the South American plate. The position of the El Roble deposit is believed to be in the chalcopyrite/pyrite/pyrrhotite zone in the central “mound” area of the schematic section, which explains the apparent lack of banded textures commonly found in the distal portions of the deposit model.

Based on the large number of mafic-type VMS deposits (more than 1,000 in total) around the world and the current knowledge of the sizes of these, it is possible to estimate a typical size and metal content for these deposit types. Franklin et al. (2005) cite the statistical mean deposit size for 74 individual, mafic-type VMS deposits is 2.7 million tonnes (Mt) at 1.82% copper, 0.02% lead, 0.84% zinc, 1.4 g/t gold, and 10.62 g/t silver. The El Roble Project concession block covers a strike length of 10 kilometers of prospective ground, allowing substantial room for the discovery of additional clustered VMS deposits.

Other mafic-type VMS deposits in Colombia include Guadalupe (Antioquia), La Equis (25km from El Roble in Choco), Sababablanca (Valle de Cauca), and El Alacran.

The volcanogenic massive sulfide mineralization that comprises the El Roble deposit has been overturned by folding such that it now dips steeply to the east.

The presence of narrow local thicknesses (0.5m) of massive sulfides finely interbedded with gray to black cherts essentially confirms the syngenetic origin for the deposit. VMS mineralization continuity is locally disrupted by Tertiary andesite and latite dikes up to 10 meters in width that intrude both the VMS mineralization and the host rocks.

In hand specimen and in diamond drill core, the massive sulfide mineralization is fine-grained with little internal structure or banding, consisting dominantly of pyrite and chalcopyrite. Pyrite occurs as euhedral and subhedral grains that measure on average approximately 200 microns in diameter, but which can vary from 0.04 to 0.01 millimeters. Colloform pyrite textures and crushed pyrite grains are also common. Chalcopyrite typically fills spaces between pyrite grains, along with minor pyrrhotite and sphalerite, No other sulfide minerals have been identified. Gold occurs as electrum in 10 to 100 micron irregular grains in the spaces between pyrite grains. Minor silver is also present, presumably as a component of the electrum. Gangue minerals include quartz and chlorite along with lesser calcite, dolomite and minor hematite and magnetite.

In addition to massive sulfide mineralization, stockwork-type mineralization consisting of chalcopyrite with subordinate pyrite in massive veins and patches of sulfides occurring in veins dominated by quartz and chlorite recently has been intersected in exploration drill holes between the 2000m and 1980m levels.

The El Roble Mine consists of an underground mine with surface infrastructure and a processing plant with a nominal capacity of processing 850 dry metric tonnes of ore daily using standard flotation technology. Access is by paved primary and secondary highways from Medellin, Antioquia. The mine produces ores that are processed at the local process plant, concentratres are shipped to Buenaventura, Colombia on the Pacific coast for storage and eventual shipping to overseas smelters.

The workings are all underground. The principal mine adit is located within a kilometer of the process plant at the nominal 1,850 Level (1,850-m MASL). The 1880 Level serves as a ventilation intake as well as access for all personnel and materials; additionally, it is the main haulage access to transport ore and waste to the surface. A secondary access is located at the 2000 Level (2,000-m MASL), this access is the primary ventilation exhaust for the mine.

Ore is hauled from underground in highway dump trucks and dumped to covered surface stockpiles, the stockpiles are sampled and the material blended to meet the plant feed grade needs.

Mining Method
Various stoping methods have been used at El Roble successfully. Early in the mine's life blasthole open stoping was done successfully. Large, stable voids were excavated in the massive sulfides with no backfill palced immediately after mining. This method was used from abpve the 2200 Level to the 2000 Level. As large voids were not filled, eventually massive wall failures resulted in collapsed stopes and accesses.

Atico elected to develop a new main access at the 1880 Level to address the newly discovered, deeper deposits. The adit was started in August 2013 and intersected the first deposit in January 2014. Since that time mining has been continuously performed from the 1880 Level, with a declining ramp and raises developed to address the deposit below the 1880 Level horizon.

The drift-and-fill mining method is used in the Zeus deposit. Several other deposits are also mined at El Roble, the company uses variations of sublevel caving and glory-holing to mine these deposits. The work is mostly mining remnants within the other deposits, there is not enough reliable data to be able to estimate a mineral reserve for any deposit other than Zeus at El Roble at present.

Mining in the Zeus Deposit
Zeus is the deepest deposit to be mined at El Roble, approximately 450 meters below the mountain topography. Zeus is accessed via a main ramp (nominal section 4.5m x 4.5m) departing from the 1880 Level at a decline of nominally 12 percent. All equipment access, haulage, fresh air intake and services are placed in the ramp. There are several Alimak raises that connect the ramp at various elevations to the upper workings on the 2000 Level; these raises serve as exhaust raises to remove spent air from the workings and deliver it to the surface through an adit and workings on the 2000 Level.

Zeus Stope Access
The Zeus deposit is accessed at vertical intervals ranging from 45 to 60 meters, using cross-cuts and sub-ramps from the main ramp. These cross-cuts and sub-ramps have a nominal section of 4m X 4m and wide radii of curvature to accommodate large equipment. The main ramp was situated approximately 40-60 meters from the Zeus deposit while the ramp was located in black chert. Basalt was found in the footwall of the deposit and the ramp transitioned to the basalt as it is much more stable than the black chert and requires much less ground support. The ramp in basalt remains a nominal 40 meters from the Zeus contact.

Cross-cuts and sub-ramps are driven with mechanized equipment following normal mechanized development cycles of drilling, blasting, scaling, mucking, mapping (geology and/or geotechnical), installation of ground support and then repeated. Ramps and cross-cuts have a nominal 4.5m x 4.5m cross-section with a graded road bed. Since there is little water present in the mine there is no significant ditch but this does not affect the quality of the road bed surface. Headings are ventilated with ventilation fans taking fresh air from the main ramp and forcing the air into the heading to be ventilated with standard plasticized canvas, flexible ventilation tubing. Vent tube diameter depends upon the active heading and associated equipment fleet; diameters range from 30 inches to 36 inches.

Cross-cuts and sub-ramps are driven from the main ramp to access the Zeus deposit as per the mine design. The deposit is amorphous; the accesses may be located at any reasonable access point depending upon the design needs. The sub-ramps and cross-cuts are designed to swing or pivot, providing one access point from the main ramp for each nest of sub-ramps or combination of cross-cut and sub-ramps. The sub-ramp or cross-cut intersects the deposit at the required elevation, stope development and stoping commence. When the lift is completed and the primary stopes have been backfilled the back of the access is brought down as required to provide access to the next lift upward. The broken rock from the back provides the fill for the roadway, extra swell is hauled to the surface as waste. Once the contact has been reached the normal stope development and mining plan resumes.

As the stope access nears the contact a cut-out is slashed and excavated. The cut-out becomes the access for an ore pass system on that level. The orepass system consists of vertical raises with nominal 3-m x 3-m dimensions, either driven conventionally or using longhole raising techniques. At the bottom of the ore pass system chutes have been installed for loading ore from the ore pas into haul trucks and delivered to the surface stockpiles.

Backfill
All stope backfill at El Roble is cemented rockfill, with the exception of final fills in some lifts where the central stope access drift is filled with uncemented rockfill. Cemented rockfill is produced on surface and delivered underground in underground cement mixer trucks. The use of uncemented rockfill is limited to areas where no further work adjacent to, under or (in some cases) over the uncemented rockfill is planned. This percentage of the backfill is not large compared to the cemented rockfill.

Crushing
Run-of-Mine (ROM) material is passed through a grizzly to a coarse ore bin, bar spacing on the grizzly is fixed to pass minus 10-inch material. The material in the coarse ore bin reports to an Otsuka 20-inch x 30-inch, 60-HP, single-toggle type jaw crusher via a 3-foot x 10-foot apron feeder. After jaw crushing the material reports to a conveyor system and then a two deck (3/4-inch and %-inch screen openings respectively), 5-foot by 12-foot vibrating screen.

The oversize from the vibrating screen reports to a 3-foot diameter, 100-HP cone crusher, this crushed material joins the middling product and reports to a single-deck vibrating screen (1/4-inch openings), the undersize reports to the fine ore bin and the oversize reports to a 4.25-foot diameter, 150-HP short head cone crusher. Crushed material from the secondary and tertiary crushers (cone crusher and short-head conce crusher respectively) reports back through the screen system for resizing and eventually reports to the fine ore bin.

Grinding
Material from the fine ore bin reports by apron feeder to a derrick screen where the material is wetted and screened using a 2.5-millimeter by 2.0-millimeter aperture high frequency vibrating screen. The undersize material reports to the ball mill discharge pulp, screen oversize reports to an Otsuka 2.1-meter by 2.1-meter, 250-HP ball mill. Ball mill discharge reports to the pulp slurry line without further classification. The pulp is then piped by gravity down a steep gradient with an approximate vertical drop of 150-meters to the main process plant.

The ground material reports to the 2.7-meter by 2.7-meter, 308-HP Otsuka ball mill discharge sump, from the sump the amterial is pumped to an SK-240-type flotation cell. The flotation overflow reports to the concentrate thickener, underflow reports to a cyclone nest where the material is classified, with the cyclone overflow reporting to flotation and the cyclone underflow reporting to the second ball mill for further size reduction. The ball mill discharge reports to the same ball mill sump where the pulp from the first stage of milling reports.

Minera El Roble S.A. is in the process of installing a SAG mill at the site to replace the present first stage ball mill. The existing circuit will be kept and maintained on a stand-by basis. No change in recovery or other process results is expected, the metallurgical results in the process plant expected to remain the same. No adjustments in the plant performance used to estimate the mineral reserve has been made to recognize the change in the first stage of milling.

The processing methods consist of conventional crushing, grinding, and flotation to produce a copper-gold concentrate. Grinding is to 80 percent passing 200 mesh before reporting to flotation cells. Four banks of six flotation cells each generate concentrates which are subsequently thickened, filtered and stored on site for shipping via highway truck to the Pacific coast port of Buenaventura. Process tailings are deposited in an impoundment facility situated along the banks of the Rio Atrato located downstream of the processing plant. Process waste water is decanted in a tailings dam and then released (at a pH between 7.48 to 8.45) into the Rio Atrato.

Flotation
The flotation circuit begins with one OK-20-style flotation cell fed by the secondary ball mill cyclone overflow. The OK-30-style cell overflow reports to the concentrate thickener, the underflow reports to a bank of two, OK-8-style flotation cells. The flotation overflow from these cells reports to the concentr ........