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.

The structural history of Haile is complex and is affected by four orogenic episodes.

Four deformation/geological events are observed at Haile; the D1 and D2 events provide the dominant geometric constraints on the Haile ore deposits.

• D1 syn-mineral hydrothermal replacement of sedimentary rocks by silica and pyrite with Au, Ag, As and Mo precipitation along ENE faults and foliation; rocks were likely in a nearly flat position and were intruded by dacite flows and capped by pyroclastic rocks.
• D2 regional Alleghanian metamorphism and deformation (folding, shearing, pervasive foliation, quartz veins) and greenschist facies metamorphism (chlorite, carbonate, coarse pyrite); this is the dominant event that overprints the Haile region. Pervasive foliation strikes east-northeast and dips 40-600 northwest. Foliation intensity increases along sedimentaryvolcanic contacts and is strongly developed in laminated siltstones where gold mineralization is hosted. Rocks were folded into an asymmetric anticlinorium with a steep southeast limb and moderate northwest limb.
• D3 minor brittle reactivation of foliation along NW-dipping normal faults; displaces some ore zones.
• D4 diabase dike intrusion and minor dextral faults down step district from west to east.

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 (Figure 7-6). 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.

Two silicification events are observed in the mineralized zones. Early massive silicification is finely disseminated to diffuse with less than 1% pyrite. This pyrite-poor silicification correlates roughly with the 0.1 g/t Au shell. Phase two silicification is manifested as matrix fill in tectonic and hydrothermal breccias with 1% to 5% pyrite and is associated with grades more than 0.5 g/t Au. High-grade gold zones more than 3 g/t are characterized by intense silicification and more than 1% fine-grained disseminated pyrite. Pyrite grain size is typically less than 20 microns in ore zones. Pre-ore silicapyrite zones are frequently stretched, boudined and sheared. A second phase of barren, coarse, cubic, undeformed pyrite overprints the fine- grained pyrite that formed during regional greenschist metamorphism. Pyrite cubes in chloritic metamorphosed rocks are 0.5 to 1 mm in size but can be as large as 1 to 2 cm. Pyrrhotite occurs in 5 to 25 m thick halos around and on the edges of ore zones. Its ductile nature produces length: width ratios more than 5:1 in foliated rocks. Pyrrhotite formation is interpreted to be coeval with early, fine-grained pyrite precipitation.

Propylitic alteration is characterized by increased chlorite (25% to 50%) and a mottled texture with blebs of 1 to 5 mm calcite/ankerite aggregates (2 to 10%) and stockwork. Late calcite ± quartz veining is often focused along fault zones and along shear zones within strongly deformed rocks. Sigmoidal pods of strained quartz are often observed. Oxidation at Haile extends to depths of 20 to 60 m and is deepest along faults and in volcanic rocks. Hematite and goethite are strongest near surface in the saprolite and decrease at depth as weak joint stains.

Gold spatially correlates with silver, arsenic, molybdenum, and tellurium. Base metals are rare at Haile. Thin section petrography and scanning electron microscopy show that the gold occurs as native gold, gold-pyrite and gold-pyrite-pyrrhotite clusters in fine-grained silicified zones. Smeared molybdenite occurs primarily on foliation surfaces and as fine-grained aggregates in silicified zones. Molybdenite at Haile has been dated by Re-Os isotopes at 553.8 ± 9 Ma (Stein et al., 1997), which is coeval with the zircon crystallization age of 553 ± 2 Ma reported by Ayuso et al. (2005). This age correlation indicates that molybdenite mineralization was concurrent with Persimmon Fork volcanism. Seven ReOs molybdenite ages from Haile (Mobley et al., 2014) yielded ages ranging from 529 to 564 Ma. Four of these samples produced an average age date of 548.7 ± 2 Ma (Mobley et al., 2014).

Haile is currently being mined using conventional open pit methods and OceanaGold plans to continue with current mining methods.

The material encountered at Haile is a combination of soft (Costal Plains Sands [CPS] and saprolite) and hard (metavolcanics and metasediments) rock units.

CPS is loosely consolidated sand which can be mined without the need for drilling and blasting. Mineralization is not present in CPS thus drilling for the purposes of ore control and waste classification is not necessary.

Saprolite is mined without blasting where possible. Saprolite is sampled for waste classification to meet the requirements in Haile’s Overburden Management Plan (OMP).

Drilling and blasting are required in all hard rock. Drilling and blasting are performed on 10 m benches. Multiple bit sizes (115 mm, 171 mm, 200 mm) are used depending on material type and application. Blast hole depth is 10 m plus subdrill; subdrill ranges from 1.4 m to 1.9 m.

The number of samples taken per blasthole is material-type dependent. Blastholes in waste are typically sampled twice on 5m intervals (top half and bottom half). Blastholes in ore are typically sampled three times at 3.3 m sample intervals.

Flitch height is variable. Waste is typically mined on a 10 m flitch. Ore is mined on either 3.3 m or 5 m flitches.

Ore is usually mined with hydraulic excavators, while the majority of waste is mined with hydraulic shovels. Front-end loaders may be used in either application in back-up capacity. The haul truck fleet is a mix of 175 t, 140 t and 90 t payload units.

The major design parameters used are as follows:
• Ramp grade = 10%.
• Full ramp width = 32 m (3x operating width for 730E).
• Single ramp width = 20 m for up to 60 m vertical or six benches.
• Minimum mining width = 40 m but targets between 150 m to 300 m.
• Flat switchbacks.
• Bench heights, berm widths and bench face angles in accordance with current site-specific design criteria.

The open pit loading and hauling equipment fleet consists of hydraulic excavators (Komatsu PC3000 and PC4000 models) and rigid frame haul trucks (CAT 777, CAT 785 and Komatsu 730). Blasthole drilling and wall control drilling is performed with a fleet of Sandvik DR410i and Epiroc D65 drills. Typical ancillary equipment, including track dozers, wheel dozers, motor graders and water trucks support the mining operation.

Waste is drilled with either 171 mm or 200 mm diameter holes and ore is drilled with 171 mm diameter holes. Productivity rates vary depending on drill type and rock type, but the average LoM drilling productivity is approximately 26.5 m/hr across the drill fleet.

Five to seven passes of the primary digging units will be used to load the matching trucks. Annual productivity rates have been estimated from equipment specifications, material characteristics, spot and loading times, truck presentation and primary digging unit propel factors, scheduled hours per year, mechanical availability and use of availability. For PC3000 excavators, the estimated productivity is 1,950 tonnes per hour. For PC4000 excavators, the estimated productivity is 3,000 tonnes per hour.

Additional equipment was installed in some areas of the plant between 2018-2020 to achieve the
expanded capacity of 4.0 Mtpa.

The key additions to the process plant for crushing and grinding operations included:
• Upgrade to apron feeder motors for the crusher and emergency feeder.
• Speed upgrade to the SAG feed conveyor to achieve 600 t/h rate.
• Pebble crushing installation on existing SAG mill scats recycle.
• Installation of a Nippon Eirich ETM-1500 tower mill (1.2MW) and 10-inch cyclone pack.
• Installation of an M10000 Isamill (3MW) and six cyclone pack.
• Implementation of the Andritz expert system to cover SAG mill, ball mill, cyclone, thickening and cyanide destruction circuits to maximize throughput.

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.

Selected flotation reagents are added in the grinding circuit. A portion of the grinding circuit ball mill circulating load is treated in a flash flotation cell with the concentrate going to the regrind circuit.

The grinding circuit product passes to a bank of bulk rougher flotation cells to recover the balance of the sulfide mineralization. Thereafter, the combined flash and rougher flotation concentrates are reground in a two-stage circuit utilizing an ETM-1500 tower mill in closed circuit with cyclones to a P80 under 40 microns and then followed by an M10000 Isamill in closed circuit with cyclones to a target P80 of 13 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 ........