Graphite deposits occur in three forms: flake graphite, vein graphite, and amorphous graphite.

Landis (1971) tentatively concluded that graphite formation is primarily dependent on metamorphic temperature and forms above 400°C, with pressure and variation in starting material constituting secondary controls.

The Coosa graphite deposits are flake graphite deposits in high grade metamorphic rocks. They are associated with anomalous vanadium, including the vanadium-mica roscoellite, and nickel, as well as other elements.

Geological mapping of the Coosa resource grid was carried out by Alabama Graphite geologists based on stream sections, road cuts, drill pads, and trenches. The main graphite schist trends northeast and to the south changes to north-south, and joins with another unit of graphite schist to the east. There is garnet schist on the east side of the graphite schist, which dies out to the south. These features may be interpreted as an anticline plunging at a low angle to the south with a core of garnet schist overlain structurally by graphite schist. The graphite schist is underlain structurally on the west side by quartz-muscovite-biotite-graphite schist.

Open pit mining was selected as the mining method to examine the Coosa deposit based on the decision to restrict mining to the shallow oxidized horizon as well as the very low strip ratio of the deposit. As there is very little waste rock, and mining would not occur in competent rock, underground bulk mining was not considered to be a practical mining method for this deposit.

Due to the decision to only mine the oxidized mill feed initially, all waste and overburden material was to be hauled outside of potential mining areas. Therefore, no backfilling of pits was to be planned for so that future potential mining below the oxidized horizon could be preserved.

Pit designs were generally very shallow with depths up to approximately 100 feet. Four starter phases were identified in the northern area of the project, followed by six small lower grade pits to the south. Some mining areas were standalone pits and while others were pushbacks of other phases.

Mining will not include blasting, so a simple, small conventional loading and hauling fleet will be used. It will consist of loading with a 6.0 cubic yard excavator in the pit and 45 ton articulated trucks. Assistance to the excavator will be with a 400+ horsepower dozer to loosen and push material to the excavator for loading. Additional support to the mine and plant will be provided by graders and smaller dozers to dress roads and waste/overburden storage facilities.

The proposed method of graphite recovery from the Coosa deposit consists of conventional crushing and milling, followed by rougher and cleaner froth flotation.

Crushing
Ore will be delivered to the primary tip by 20t haul trucks at a frequency averaging two trucks per hour. Peak delivery rate is assumed to be 60 stph. Feed is discharged directly into a rail-lined, 30-ton surge bin.

A vibrating grizzly feeder at the bottom of the surge bin discharges +60 mm oversize into the primary crusher feed chute. Grizzly undersize drops onto the classification screen feed conveyor. The primary crusher consists of a 15” x 24” jaw crusher with a closed side setting of 50 mm, and can accept a top size of 400 mm. Crushed feed discharges onto a sacrificial conveyor, which in turn discharges onto the classification screen feed conveyor. The screen feed conveyor is equipped with an overhead magnet for removing tramp metal ahead of the secondary crusher.

A 4 ft. x 8 ft. vibrating inclined screen is used to classify the primary crushed feed and close the circuit around the secondary crusher. The screen deck consists of 19 mm slots with the screen undersize chute feeding the fine feed bin conveyor. The fine feed bin conveyor is equipped with a weight-o-meter for recording crushing circuit production. Oversize from the classification screen is fed by a lined chute into the secondary crusher.

The secondary crusher consists of a standard roll crusher with a closed side setting of 15 mm. Crushed product discharges via a chute onto the recycle conveyor which returns the material to the classification screen feed conveyor.

The crushing circuit is expected to run at 86% availability, seven days per week. A dust
collection system is included in the classification screen and secondary crushing area.

Grinding
The milling circuit and all subsequent areas of the plant operate at 92% availability on a 24/7 schedule. Crushed run of mine material is stored in a 150-ton fine feed bin with approximately six hours operating capacity. An overflow chute at the top of the bin allows overflow to a stockpile with an additional six hours of capacity. The stockpile material can be reclaimed to the fine feed bin conveyor by front end loader, as needed.

A vibrating pan feeder draws material from the bottom of the fine feed bin onto the mill feed conveyor. The conveyor is equipped with a weight-o-meter to measure mass flow and allow for control of the mill feed rate.

The primary grinding mill consists of a 6 ft. diameter by 10 ft. long overflow discharge rod mill with a 120 kW, single pinion drive. The discharge end of the mill is fitted with a trommel screen with 10 mm openings. Oversize tramp material, woodchips, etc. drop through a chute into a drum or skip. The material passing through the trommel is collected in a chute and fed to the screen pump feed box.

The mill discharge is diluted with process water and is then pumped to a vibrating, inclined classification screen with 10# (1.68mm) openings. The screen oversize is returned to the rod mill feed chute, whereas the undersize is pumped forward to the flash flotation step.

The secondary grinding stage consists of a 5 ft. diameter by 8 ft. long overflow discharge ball mill with a 60 kW, single pinion drive. The discharge end of the mill is fitted with a trommel screen with 6 mm openings. Oversize tramp material, woodchips, etc. drop through a chute into a drum or skip. The material passing through the trommel is collected in a chute and fed to the screen pump feed box.

Ball mill discharge and flash tailings are pumped to an inclined, 6 ft. x 10 ft., classification screen with 595µm (30#) openings. The oversize gravitates to the feed chute of the ball mill, whereas the undersize is pumped to the feed box in the rougher flotation circuit.

The proposed method of graphite recovery from the Coosa deposit consists of conventional crushing and milling, followed by rougher and cleaner froth flotation. The cleaner flotation concentrate is then transported to a purification plant that includes micronization and spheronization prior to upgrading by thermal purification to produce the final product.

The Coosa concentrator is designed for a nominal 16,500 tons per month run of mine feed.

Mine haul trucks will tip into a surge bin feeding a primary jaw crusher designed for 86% availability.

The rougher flotation stage consists of six conventional (“trough”) cells in series. The rougher concentrate is combined with the flash concentrate and pumped to a pre-cleaner flotation circuit consisting of five trough cells in series.

The pre-cleaner concentrate is dewatered at 230 mesh, with the oversize reporting to the first of two polishing scrubbers.

First cleaner flotation concent ........