Hundreds of gold deposits in the southeast USA are located along a 700 km long SW-NE trend that extends from Alabama to Virginia (McCauley and Butler, 1966, Butler and Secor, 1991). Most of these deposits are small prospects worked and explored along narrow quartz veins. The larger gold deposits are located at or near the contact between volcanic and sedimentary rocks, including the Haile, Brewer, Barite Hill and Ridgeway mines. Brewer is unique in the region and is classified as a highsulfidation epithermal gold system with volcanic and breccia-hosted gold accompanied by quartz, pyrite, topaz, enargite and chalcopyrite. Gold mineralization at Barite Hill contains the assemblage of pyrite-chalcopyrite-galena-sphalerite and is characteristic of a submarine, high-sulfidation volcanogenic massive sulfide deposit. Haile and Ridgeway are similar in that sediment-hosted gold mineralization is hosted by silicified, sheared and foliated siltstone.

Haile gold mineralization occurs as en echelon clusters of moderately to steeply dipping ore lenses within a 4 km x 1 km area. Nine named gold deposits are recognized at Haile. From west to east, these deposits include Champion, Small, Mill Zone, Haile, Ledbetter, Red Hill, Palomino, Snake and Horseshoe that often show ‘pearls on a string’ alignment. Ledbetter is by far the largest orebody (approximately 1M oz) and includes the shallow Chase and deep Mustang deposits. Orebody geometry, depth, size, grade, mineralogy, and alteration are variable. Orebody geometry is partly controlled by orientation of volcanic-sediment contacts and location of barren dacite sills. Ore lenses are typically 50 to 300 m long, 20 to 100 m wide, and 5 to 30 m thick. Ore zones are separated by barren siltstone, dacite sills and diabase dikes. The Mv/Ms contact and gold mineralization gradually deepen from west to east across the Haile district. The Mv/Ms contact at Champion has been partly removed by erosion in the west portion of the district and is over 500 m deep at the Horseshoe deposit, 4 km east of Champion. Depth and position of the contact are complicated by faulting and folding. Drilling in southeast areas around Palomino has encountered gold mineralization up to 1 km deep.

Gold mineralization at Haile is mostly hosted by laminated siltstone in the Upper Persimmon Fork Formation and is capped by less permeable coherent dacite. Mineralization is typically within 100 m of the dacite-siltstone contacts. Gold mineralization is disseminated in silicified and fine-grained, pyritic siltstone with local K-feldspar and molybdenite. Small mineralized zones at Ledbetter, Red Hill and Snake are hosted in dacite along fault zones within 15 m of the Mv/Ms contact. Gold grades in mineralized dacite are typically weaker than in the underlying siltstone and sericite alteration is stronger in the dacite. Hydrothermal brecciation is common in portions of the Ledbetter, Horseshoe, Small and Champion deposits where milled, silicified siltstone clasts occur in a fine-grained quartzpyrite matrix intruded by fingers of quartz feldspar porphyry with quartz stockwork veinlets.

The Haile gold mine is located 5 km northeast of Kershaw in southern Lancaster County, South Carolina. The Project is currently being mined as an open pit mine. Mineralization extends down at depth and outside of the pit extents. This mineralization, not mined by the open pit, is assessed as an underground mine and is referred to as the Horseshoe deposit.

The underground mine is accessed via a decline from the surface. The decline portal is located on an open pit bench approximately 80 m below the natural surface. Two ventilation drift portals are also located on an open pit bench.

Transverse longhole mining has been selected as the mining method for the entire orebody. This method requires upper and lower access drifts to be developed from the footwall haulages with a proposed 25 m vertical spacing between levels. The total open stope height in 25 m with the overdrive drift above the open stope. The overall open stope dimensions are 20 m wide x 25 m high x 25 m long (maximum length).

Each stope has a 4.5 m x 5 m access located at the bottom of the stope. Top accesses (also 4.5 m x 5 m) are designed to give access to stopes on the next level and to allow for backfilling. The stopes are drilled from the top and rings are blasted from the end of a stope toward the footwall access. The blasted material is remotely mucked from the stope access. A primary/secondary stoping sequence will be used. The stope accesses are connected to a level access located in waste material. The level accesses connect to the main ramp which is located in the footwall. Each level access is connected to the ventilation system. Ore will be remotely mucked from the bottom stope access using a 14.9-t LHD and loaded into 51-t trucks for haulage to surface.

The Horseshoe underground mine production schedule is based on the productivity rates developed from first principles which were adjusted based on benchmarking and the experience of OceanaGold personnel. The schedule was completed using Deswik scheduling software and is based on mining operations occurring 365 days/year, 7 days/week, with two 12 hour shifts each day. A production rate of approximately 2,000 t/d was targeted with ramp-up to full production as quickly as possible.

The mining method employs primary/secondary stoping sequence. The primary stopes will be backfilled prior to mining the adjacent secondary stopes. The required strength of cemented rockfill (CRF) placed in primary stopes has been checked for stability under the critical conditions of mining the adjacent secondary stopes. The secondary stopes must remain stable so remote equipment can safely muck the ore without being buried by ground fall.

A relatively compact Run of Mine (ROM) area is provided for storage and re-handling of ore allowing blending to minimize variation of head grade (sulfur and gold) and rock type, into the crusher. Ore is rehandled into the crusher dump pocket by Front End Loader (FEL).

Ore is reclaimed by an apron feeder onto a vibrating grizzly that delivers scalped oversize to the primary jaw crusher to reduce the ore size from RoM to minus 150 mm. Crushed ore is conveyed for surge and storage of the recombined grizzly undersize fines and primary crushed ore in a coarse ore surge bin or diverted on to an open conical emergency stockpile for later reclaim by Front End Loader (FEL) into a reclaim bin.

Ore is reclaimed from either the surge or reclaim bins, separately or simultaneously, using apron feeders onto a SAG mill feed conveyor belt delivering into the SAG mill feed chute. Ore is milled in the SAG–Ball Mill-Pebble Crusher (SABC) circuit. The SAG mill operates in closed circuit with a vibrating discharge screen and a pebble return circuit incorporating a surge bin and Sandvik CH-440 cone crusher. The ball mill operates in closed circuit with hydrocyclones to produce the desired grinding product size of 75 microns.

Progressive debottlenecking and upgrades to the processing plant proceeded following successful commissioning of the process plant. The flowsheet and unit operations did not change as part of the upgrades with the target of 4,000,000 t/a capacity increase achieved with a reduced scope than that expected during the optimization study completed in 2016.

The process plant consists of the following major components:
• Crushing and conveying.
• Storage and stockpiling of ore and reclaim.
• Grinding.
• Flotation.
• Fine grinding of concentrate.
• Carbon in leach (CIL) recovery of precious metal values from reground flotation concentrate and flotation tailings.
• Acid washing and elution of precious metal values from CIL loaded carbon.
• Electrowinning and refining of precious metal value.
• Thermal regeneration of eluted carbon and recycle to CIL.
• CIL tailing thickening, cyanide recovery, detoxification and pumping of slurry to s ........