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. 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.

Mineral zonation grades outward from quartz-pyrite ± K-feldspar + gold (QS) to quartz-sericite- pyrite ± gold (QSP) to sericite + pyrite ± pyrrhotite to chlorite-calcite ± epidote (propylitic). QS and QSP mineralized zones are tens of meters thick. Sericite envelopes range in thickness from tens to hundreds of meters and are controlled by protolith, permeability, and weathering. Within the mineralized zones, quartz is dominant (60% to 80%), pyrite is moderate (1% to 10%), and sericite is variable at 5% to 40%. Semi-massive pyrite zones are locally observed over thicknesses of 0.5 to 5 m, especially in the Mill Zone, Red Hill and Haile pits.

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).

Open Pit mining
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.

Underground mining
The Project is currently being mined as an open pit mine. Economic mineralization extends below and outside of the pit extents. Mineralization is concentrated in two main zones based on vertical position which form a “horseshoe” geometry over a vertical distance of 350 m. This mineralization will be mined as an underground mine and is referred to as Horseshoe.

Based on the orientation, depth, and geotechnical characteristics of the mineralization, a transverse sublevel open stoping method (longhole) with has been selected. The stopes will be 20 m wide and stope length will vary based on mineralization grade and geotechnical considerations. A spacing of 25 m between levels is used. Cemented rock fill (CRF) will be used to backfill the stopes. There will be an opportunity for some non-cemented waste rock to be used in select stopes based on the mining sequence. The CRF will have sufficient strength to allow for mining adjacent to backfilled stopes. Paste backfill could be used instead of CRF and there is ongoing work investigating this possible change.

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 ........