Haile is situated within the northeast-trending Carolina Terrane, also known as the Carolina Slate Belt, which hosts the past-producing Ridgeway, Brewer and Barite Hill gold mines in South Carolina. Haile is the largest gold deposit in the eastern USA. The Haile district consists of nine gold deposits within a 3.5 km by 1 km area. Haile occurs within a variably deformed ENE-trending structural zone at or near the contact between metamorphosed Neoproterozoic volcanic and sedimentary rocks. Haile is hosted in laminated siltstones and minor volcanic rocks of the Upper Persimmon Fork Formation and is dissected by barren NNW-striking diabase dikes. Deformation includes brittle and ductile styles with ENE-trending foliation, faults, brecciation, and isoclinal folds. Sedimentary rocks are folded within an ENE-trending anticlinorium with a steep SE limb and a gentle NW limb. Gold mineralization is assumed at ~549 Ma based on closely associated molybdenite dated using Re-Os (Mobley et al., 2014), which postdates peak volcanism and predates the Alleghanian greenschist facies metamorphic deformation. Pressure shadows around pyrite grains, stretched pyrite and pyrrhotite grains, and flattened hydrothermal breccia clasts indicate that there has been deformation subsequent to sulphide mineralization. These observations are consistent with either pre- or syn-tectonic gold mineralization. Interpreted timing of gold mineralization coincides with a major tectonostratigraphic change from intermediate volcanism and tuffaceous to epiclastic sedimentation to basinal turbiditic sedimentation. Quartz-sericite-pyrite alteration is overprinted by regional greenschist facies metamorphism with carbonate-chlorite-pyrite alteration. Haile is currently interpreted as a low-sulfidation, sediment-hosted, disseminated, epithermal gold deposit. Mineralization and Alteration 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 1 Moz) and includes the shallow Chase and deep Mustang deposits. Orebody geometry, depth, size, grade, mineralogy, and alteration are variable. The orientation of gold mineralization generally parallels the regional NW dipping foliation but is concentrated along the metavolcanic-metasediment contact. Orebody geometry is partly controlled by orientation of volcanicsediment 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. 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. Deposit Type 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 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 and ore is typically mined on a 3.3 m flitch. Ore is usually mined with hydraulic backhoe 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 and 140 t payload units. Pit Design 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 to 300 m • Flat switchbacks • Bench heights, berm widths and bench face angles in accordance with current site-specific design criteria Underground Mining Methods 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. Both zones strike NE adjacent to the siltstone-dacite contact, however, the upper zone dips about 400NW and the lower zone is nearvertical. The upper zone NW-dipping high-grade lenses of mineralization are focused along beddingparallel foliation with intense silicification. The Horseshoe fault (NE strike, 400NW dip) juxtaposes the hanging wall of upper Horseshoe against barren dacite with a sill-like geometry. This geometry extends southwestward into the nearby Snake pit. The steeply dipping Lower Zone is adjacent to the subvertical contact with barren dacite. This mineralization will be mined as an underground mine and is referred to as Horseshoe. Figure 16-12 shows the Horseshoe upper and lower mineralized zones. 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. Mine Design Parameters 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). The mine coordinate system has been rotated by 30° from true north to simplify the underground workings such that Horseshoe Underground grid north (HUG grid north) is the hangingwall of the deposit and HUG grid south is the footwall of the deposit. The orientation of the stopes is the same as the 2017 design, so the same geotechnical domains apply to the new design. The mining infrastructure (i.e., ramps, declines, ventilation raises, shops, etc.) are in the footwall offset from the stopes to minimize mining-induces stress damage. Figure 16-18 shows the same plan view, but without the pit outline and with the identified dikes as they traverse the orebody and planned mining. The ventilation system raises are in the low-stress stress shadow of stope mining to minimize potential of mining-induced damage. Backfill 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 numerical model was used to assess the minimum backfill strength requirements. The model results indicate that a minimum UCS strength of 0.7 MPa is required after 14 days of curing to accommodate the mining cycle. Laboratory tests results on batches of cemented rockfill indicate that this required strength can be achieved using 4% cement by mass and a water-to-cement ratio of 2.0 with aggregate from waste rock currently available. The CRF mix designs at Haile will be based on two cement contents: 3.8% and 4.8% GP cement by dry mass. The aggregate will consist of NAF waste that is crushed and screened to -80 mm. It will also have a sufficient amount of fines to eliminate vuggy backfill and create a relatively low rill/beach angle for CFR (i.e., less than 20° will be required to achieve ‘tight-fill’ conditions in the ‘stope wings’ located below the upper ore drive. Technically, this is cut and fill (CAF) backfill. The 4.8% CRF might have a 28-day UCS ranging from about 1.7 to 3 MPa if the placed mix is relatively free of vugs. For the sill pillar recovery, the curing time will be much longer than 28-days and will likely be even stronger than the 28-day UCS.

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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 3,800,000 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 ........