Copper mineralization at Robinson occurs in monzonite porphyry intrusive rocks and associated marginal garnet skarns with varying quantities of pyroxene, magnetite and sulfide which formed in the surrounding upper Paleozoic wall rocks. Early stage potassium silicate alteration in porphyry and skarn mineralization in the wall rocks are typically overprinted by a widespread and commonly intensive high acid alteration event which altered porphyry and some host units to quartz-sericite-pyrite or even advanced argillic assemblages locally. Carbonate host rocks were altered to pyritic marbles or silica pyrite rock containing up to 20 volume percent pyrite locally during this late stage alteration event. Early stage potassium silicate mineralization and skarn was dominated by pyrite and chalcopyrite and is generally low in sulfide with average values ranging from trace to 3%. The high acid alteration event is dominated by up to 10% or 20% pyrite with pyrite:chalcopyrite ratios typically ranging from 10:1 to more than 1,000:1. Where present in the late stage alteration zones, the chalcopyrite may be relict from earlier stage alteration events. Chalcopyrite appears to be the sole hypogene copper mineral, with a few possible exceptions.

Skarn and porphyry ores form much of the current resource and reserve with grades ranging from cutoff (and below) to greater than 1.0%. Metallurgical recoveries in this material are generally good, but are complicated where weathering has partially altered the sulfides or silicate gangue.

Mid-Tertiary extension and normal faulting dissected and rotated the hypogene copper deposits to their current configuration and they have been extensively oxidized, leached and enriched. The oxidation and enrichment is extensive, generally pervasive and intense. Faults and fracture zones locally modify the morphology of the leached and enriched zones, but in many places the upper surface of the original enrichment blankets parallel the surface. In light of this, it seems likely that much of the weathering and enrichment took place after the mid-Tertiary faulting.

Mining is conducted by conventional open-pit methods. It comprises extraction using blasting materials and dump trucks, loading and ore transport to a processing plant.

The mining equipment fleet consists of five large loading units: a BE-495 shovel, a P&H 2300 shovel, a Hitachi EX-5500 shovel, a Hitachi EX-3500 shovel and a LeTourneau L-1850 front end loader. There is a smaller front end loader, a CAT 992 that is used for utility and clean-up operations.

The haulage fleet consists of sixteen CAT 793D (240 ton class) trucks and six CAT 785 (150 ton class) trucks. Haulage requirements vary by year, driven mostly by the haulage profile. When requirements diminish, the 785 trucks are idled first.

The Robinson mill consists of a crushing circuit with one 60' x 89' gyratory crusher with a nominal capacity of 2,500 TPH, crushing to minus 6” material. The grinding circuit consists of one 32' x 14.75' (9.75 m x 4.50 m), 10,000 horsepower (HP) variable speed semi autogenous grinding (SAG) mill followed by two 20' x 30.5' (6.1 m x 9.3 m) 8750 horsepower closed circuit ball mills. The rougher flotation circuit consists of two parallel rows of ten 3,000 cubic feet flotation cells followed by cleaning in six 10' x 38' (3.05 m x 11.58 m) column flotation cells in a parallel configuration. No regrinding is currently being performed. The concentrates are thickened and filtered prior to shipment. The tailings are thickened and are transported by gravity flow to the tailings impoundment.