Florida Canyon was a large tonnage low grade Neogene aged epithermal gold system adjacent to an active geothermal system. The close spatial association with the geothermal system has led to a general belief that Florida Canyon is a hot springs-type epithermal gold deposit. Hydrothermal alteration assemblages and the mineralogy of both oxidized and unoxidized gold mineralization at Florida Canyon have been characterized as having formed in a low-sulfidation epithermal environment.

Mineralization
The location and geometry of the mineralized bodies at Florida Canyon are a result of structure; the presence of favorable silty argillite, quartzite, and limestone host rocks; and the position of the host rocks relative to structural conduits. The higher-grade zones of mineralization tend, in general, to follow the high-angle, northeast- and northwest-trending fault and shear zones. The more moderate- or lower-grade zones are controlled by favorable host rocks more distal to feeder structures.

Rock units that are more favorable hosts to mineralization include silty argillite, hornfels contact zones with mafic sills, karsted limestone, and platy, silty limestone with interbeds of calcareous shale. Local factors that influence the occurrence and geometry of mineralized bodies include variations in folds, foliation, and bedding in favorable units, intersecting structural fabrics, and proximity to low-angle structures (Taylor 2001). Hypogene mineralization at Florida Canyon consists of native gold and electrum associated with quartz, iron oxides, pyrite, marcasite, and arsenopyrite (Hastings et al., 1987). Quartz is the major gangue material. Secondary minerals identified in the Florida Canyon deposits to date include gypsum (likely remobilized from the Grass Valley Formation), alunite, barite, native sulfur, calcite, dolomite, fluorite, anhydrite, pyrargyrite, pyrrhotite, and stibnite. There are two types of hydrothermal, epithermal quartz veins at Florida Canyon (Hastings et al., 1987). The most important are vein swarms and stockworks that contain most of the gold mineralization. These veins generally follow a north-northeast trend (Hastings et al., 1987) and are characterized by colorless, euhedral to subhedral quartz, or banded chalcedonic white to colorless quartz that contains limonite after pyrite (Taylor, 2001).

The second type of hydrothermal quartz veining occurs as large, through-going, banded fissure veins that follow the original north-northeast structural fabric (Hastings et al., 1987). These veins are interpreted to represent a late hydrothermal event that overprinted the earlier episode of gold-bearing quartz veining and stockworks. These veins are characterized by bands of coarse, prismatic quartz alternating with bands of cherty chalcedony and only occasionally contain economic gold grades. Milky white bull-quartz veins, considered to be metamorphic in origin, may also be present in the mineralized zones, but they are not gold bearing (Taylor, 2001). Locally, pervasive silicification is generally associated with areas of high-density quartz veining and/or intense hydrothermal brecciation (Taylor, 2001). Sericite, adularia, clay, and chlorite occur locally in quartz veins, breccia matrix, and on fracture surfaces. There is extensive argillization and bleaching throughout the deposit area, with pervasive hematization that is largely confined to silty units marginal to the bleached areas (Hastings et al., 1987).

A different style of mineralization has been recognized in the more recently discovered deposits east of the original Florida Canyon Main. At Radio Tower, karsted surfaces in Natchez Pass Limestone are replaced by cryptocrystalline silica forming jasperoid and hornfelsed contact zones between mafic sill and limestone are strongly quartz-veined and pyritized. These ore zones represent a likely older event relative to the younger, hot-spring style mineralization in the Main Pit and Madre areas.

Florida Canyon is a conventional open pit hard rock mining operation. Typical of other mines in Nevada, bench heights are 20 ft and the loading and haulage fleet are 13 to 14 cu yd front loaders matched to 100-ton rigid frame haul trucks. Most of the loading and hauling equipment have been leased from Caterpillar and include Maintenance and Repair contracts on the leased units (MARC).

The mining plan that defined the Mineral Reserve was developed by the staff of IMC working on site with the team at FCMI. It should be noted that this mine plan and schedule is practical and IMC check calculations confirm it to be economic at the design prices and at current spot prices. However, there is room for optimization and improvement going forward.

A mine production schedule was developed from the phases that would supply 750 tons per month (9,000 ktons/yr) of feed to the crusher. Total loading capacity at the mine is limited to about 70,000 to 75,000 tpd which on an annual basis is 25,550 to 27,375 kton/yr of total mining capacity.

The mine schedule was developed from a set of mine phase or pushback designs. Phase designs are practical expansions of the pit that included all necessary access roads and working room for equipment. FCMI often utilizes pushbacks that are as narrow as 120 to 140 ft. Although not optimal for equipment productivity, many of the current operating conditions at FCMI were retained in the phase designs.

Some of the phase designs were in existence at FCMI prior to this effort. They were adjusted by the IMC team to conform to the new final reserve pit. Other phases were developed during this work to incorporate proper access roads. Earlier mine plans and mineral reserves published previously did not necessarily include appropriate and practical haul road designs. Interramp Slope angles for phase design were provided by FCMI based on earlier geotechnical recommendations by Golder and Barr Engineering.

Interramp Slope angles were: 45 degrees in hard rock, 37 degrees in fill, and 35 degrees for NW Facing pits in the Central Pit.

Haul roads were 90 ft wide at 10% maximum grade. If single lane access was incorporated in the last few benches of a pit, they were 65 ft wide. There were 14 phases utilized for the FCMI production schedule.

The schedule starts with a 0.005 oz/ton cutoff for 3 years which is the internal cutoff for the material in the early phases. A higher cutoff grade cannot be utilized with the current loading capacity at the mine. If the cutoff grade were higher during the first 3 years, substantially more waste would have to be removed to assure ore release. That level of ore and waste production exceeds the loading capacity of the equipment at Florida Canyon. Once the required total material movement reduces after year 3, the cutoff grade is increased to 0.006 oz/ton which is the breakeven level for everywhere except Radio Tower where 0.006 reflects the internal cutoff. IMC limited the vertical development rate to a maximum of 12 benches per year for each pushback when preparing the schedule. FCMI regularly exceeds that figure in operations.

Florida Canyon is a conventional gold/silver heap leach operation where ore passes through two stages of open circuit crushing. Final product runs 80% minus 1½ inch. Historically material was run through a closed circuit crusher and the final product was reduced to ¾ inch. The crushed ore is agglomerated with a polymer binding agent and stacked in 20 foot lifts. Solution is applied through drip tubes at a rate of 0.0028 gpm/ft2 . Discharge (pregnant solution) from the bottom of the pad is sent to carbon columns, a conversion from the original Merrill Crowe process. There is no intermediate or recycled solution. Loaded carbon is pressure stripped, gold is recovered by electrowinning and precipitate is melted into dore’ bars. The gold to silver ratio is about 1:1. Stripped carbon is reactivated, acid washed and returned to service. The volume of carbon being stripped exceeds the capacity of the reactivation kiln so only about 25 percent of the carbon is reactivated per cycle.