The Magistral tailings deposit consists of the deposition of rejects from historical mill workings from the mid-1900s. These tailings were deposited within a natural low relief valley to the west of the historical mill and made up of relatively unconsolidated clay/silt particles. The provenance of the reject material was from treating gold bearing granodiorites and quartz veins. The primary sources were from the nearby mines: Colorados, Recompensa, Los Angeles, and Santa Ana. Thickness varies within the tailings up to 16 m.

The Magistral tailings is host to gold, copper and silver mineralization. The longest axes of the tailings deposit are approximately 550m north–south and approximately 575 m east–west.

A portion of the tailings, reportedly 750,000 tonnes, was removed from the deposit for secondary processing between 1992 and 1996. There are a few minor workings observed on the surface of the tailings deposit from artisanal miners (gambusinos), but these are not considered to have a significant impact on the estimated mineral resources.

Mining of the tailings by small scale open pit mining methods made the most sense based on the size of the resource, grade tenor, grade distribution and location on top of topography of the deposit. AGP’s opinion is that with current metal pricing levels and knowledge of the mineralization, open pit mining offers the most reasonable approach for development.

The mine plan includes sending mineralized material to mill located adjacent to the tailings. The mine plan is based on Measured, Indicated and Inferred Mineral Resources. Any waste material encountered will be placed back within the footprint of the existing tailings facility being mined.

The mining method is excavation of the tailings by excavator or front-end loader, followed by haulage to the plant and tailings screening to remove coarse clumps, vegetation and other unwanted material, before processing. Two 20-t haul trucks are required to maintain the plant production due to the proximity of the feed material to the process plant. Some dilution along the original topographic contact is expected but should not be significant as the use of the excavator can help minimize this. Support equipment includes a track dozer, grader and water truck. No drilling and blasting is required.

The pit design was based on the revenue factor (RF) =1 pit shell. This design mined the blocks contained within the shell. Waste associated with the basal blocks, while included in the design, would be left in the pit at the time of mining. The dilution was manually added to the production schedule to reflect the corresponding change in tonnage and grades.

Ramps within the pit are only needed within the sinking cuts and are sized at 15 metres wide. The pit has access to topography along the edges and the existing roads present work for the haulroads. It is anticipated that due to the shallow nature of the mining small ramps connecting the levels will be pulled in by the excavators or dozed in with the available loose material. Access along the levels will be maintained for haulage to the main road leading to the mill.

The mine schedule delivers 1.1 Mt of material grading 1.87 gpt gold, 3.04 g/t silver, 0.16% copper, 1,400 ppm As and 15.8 ppm mercury to the mill over a 3.25-year mine life. No prestripping is required as the material is present on the surface at grades sufficient for processing. No waste is mined other than dilution which is accounted for. Separation of waste material at the contact of the pit is not expected to be hauled but rather placed to the side when encountered. Therefore, there is no stripping ratio to report.

Grinding
An existing ball mill, arranged in closed circuit with a cyclone cluster, was selected to reduce the mineralized material from a nominal F80 of 130 µm to P80 of 90 µm. The ball mill will serve as lump material breaking, repulping and polish grinding.

The grinding circuit will include:
• One ball mill, 2.1 m diameter by 4.5 m length, powered by a 300 kW motor;
• Two slurry pumps to pump ball mill discharge to cyclones, with one pump in operation and one in standby;
• One cyclone cluster; and
• Associated material handling and storage systems (sump pumps, pump box).

The process plant feed material will be reclaimed from a hopper onto a trash screen. The trash screen undersize will report to a ball mill feed conveyor and discharge into the feed chute of the ball mill. The trash screen oversize will report to a trash bin. Process water will be added to the ball mill feed chute and cyclone feed pump box to maintain a target mill discharge slurry solids density. Ball mill discharge will be discharged into the cyclone feed pump box and will be pumped to the cyclone clusters. The cyclone underflow will return to the ball mill feed. The cyclone overflow will report to a leach circuit.

The project has an existing processing plant consisting of a ball mill, trash screen, four agitated leach tanks, three CCD thickeners, Merrill-Crowe circuit, cyanide destruction agitated tank, various reagent tanks, and material handling equipment. The condition of the equipment was inspected by a local Mexican contractor from SEM-PENTA which is the basis of the equipment identified in this flowsheet. Equipment refurbishment costs have been considered in the estimate based on the assessment report.

Metallurgical test work was conducted to validate the performance of the existing flowsheet and identify the addition of any new equipment to maximize the plant recovery. The modification to the plant considers the throughout of the existing plant and metallurgical test results.

Based on the metallurgical testing results a SART plant will be added to treat the Magistral tailings deposit.

Cyanide Leaching Circuit
The cyclone overflow slurry at a solids ........