Local geology
The AGM deposits are located within the Kumasi Basin on the Asankrangwa Gold Belt, which was recognised after decades of artisanal mining in gold-bearing, shear zone hosted quartz reefs. The basin is bound to the south by the Ashanti Fault/Shear and the Bibiani shear to the north. The Asankrangwa Belt expresses itself as a complex of northeast trending shear zones situated along the central axis of the Kumasi Basin. Several major northeast trending shears/structures that bisect the Kumasi Basin/Asankrangwa Belt. The Nkran deposit is located on a jog along the regional 35-40° trending Nkran Shear, which is a zone of about 15 km in width and may be traced on a northeast to southwest trend for a distance of some 150 km. The Nkran Shear Corridor also hosts the Asuadai, Dynamite Hill and Akwasiso deposits. The parallel Esaase Shear Corridor hosts the Esaase, Adubiaso and Abore deposits. The Miradani Shear Corridor hosts the Tontokrom, Miradani and Fromenda deposits.

The local geological setting, i.e. the Kumasi Basin, is heavily faulted and consists of an isoclinally folded sequence of metasediments, dominated by turbiditic sequences of greywackes and shales, intercalated with rare andesites and volcanoclastics, previously described as greywackes, phyllites, argillites and shales.

The Asankrangwa Belt straddles two broad domains of distinct magnetic character. The western portion is characterised by the low magnetic relief that is typical of the Kumasi Basin as a whole. In the east, moderately magnetic mafic volcanic rocks results in a high magnetic zone corresponding to the Lower Birimian Supergroup, and the infolded, strongly magnetic rocks of the Ashanti Belt volcano-sedimentary and Tarkwaian sedimentary packages. This domain is in sharp contact with the weakly, to non-magnetic rocks of the upper Birimian metasediments, which dominate the Kumasi Basin in the west. This zone of contrast coincides with the prominent, shear zone which bounds the northwest margin of the Ashanti volcanic belt that plays host to most of the large gold deposits in the area.

A sharp NE trending break separates these two distinct magnetic domains and also truncates the dominant ENE to WSW trends typical of the eastern domain. Evident, dramatic changes in the structural grain in the area indicate the presence of a major shear zone separating the two domains. This interpretation results in the Upper Birimian metasediments of the western domain occurring in the hanging wall of the shear zone, and above Lower Birimian metavolcanics of the eastern domain which occur in the shear zone footwall. This arrangement of ‘younger-over-older’ supports a long and intense thrusting history on the shear zone.

One of the structural setting interpretations of the Asankrangwa Belt that explains these relationships is an inverted half-graben, in which growth faulting-controlled accumulation of the upper Birimian metasediments, above the Lower Birimian metavolcanics in the footwall.

DEPOSIT TYPES
Two broad styles of gold deposits are present in southwest Ghana:
• Structurally controlled lode or orogenic gold deposits
• Paleoplacer disseminated gold deposits in Tarkwaian conglomerates.

The primary controls on mineralisation in the Asankrangwa Belt are structural in origin. Certain sandstone units within the Birimian metasedimentary package provided favourable rheological conditions that optimised gold deposition often close to major lithological contacts with either Birimian metavolcanics, or Tarkwaian metasediments. The deposit type targeted by Asanko Gold is this structurally controlled mesothermal quartz vein style mineralisation. This is the most important type of gold occurrence in West Africa and is commonly referred to as the Ashanti-type. Milesi et al. (1992) recognised that mesothermal quartz vein style deposits are largely confined to tectonic corridors that are often over 50 km long and up to several kilometres wide and usually display complex, multi-phase structural features, which control the mineralisation.

There are at least two separate gold mineralising events that are linked to the structural evolution of the area. Mineralisation is linked to:
• Early isoclinal folding, shearing and/or duplexing of stratigraphy controlling the location of deformation zones and fluid flow
• A late approximate east-west compressional event that generated shallow dipping to flat orientated conjugate vein sets that crosscut the earlier fabric and gold mineralisation.

This brittle style deformation postdates the emplacement of granitic intrusives into the core of the existing deformed and sheared sediments.

Two distinct gold events are recognised in southwest Ghana:
• D2 gold related to regional north-east south-west compression and reverse faulting (ca. 2,110 Ma)
• D4/D5 gold related to regional sinistral strike slip faulting (ca. 2,090 Ma).

Gold mineralisation is associated with major NE striking, 5 m to 40 m wide graphite-chlorite-sericite fault zones. In particular, gold mineralisation is developed where the NE fault zones intersect major ENE striking fault zones, and especially where they are recognised to have influenced granite emplacement, alteration and gold geochemical trends.

Left stepping flexures (10 km to 30 km scale) in the NE striking fault zones (which produce more northerly striking fault sections), are important for the localisation of gold mineralisation. Other local complexities in stratigraphy and fault geometry, associated with major NE striking faults, are also important for example, folds in stratigraphy that may produce saddle reef style mineralisation, or fault duplexes.

The most common host rock is usually fine-grained metasediments, often in close proximity to graphitic, siliceous, or manganiferous chemical sediments. However, in some areas, mafic volcanics and belt intrusions are also known to host significant gold occurrences. Refractory type deposits feature earlystage disseminated sulphides in which pyrite and arsenopyrite host important amounts of gold overprinted by extensive late stage quartz veining in which visible gold is fairly common and accessory polymetallic sulphides are frequently observed. This type includes important lode /vein deposits in Ghana such as at the Obotan and Esaase area. However, a second non-refractory style of gold mineralisation occurs in which gold is not hosted within sulphide minerals either in early, or late stage mineralisation. These deposit types have lower sulphide content in general and often lack the needle-like arsenopyrite that is common in the refractory type deposits.

The Obotan deposits demonstrate a late (second) phase of gold mineralisation hosted in granitoids (Nkran basin type granite), emplaced in regional shear corridors. The deposits are situated within the Birimian metasediments, but the granitoid and mineralisation both occur at contacts between greywacke and carbonaceous phyllite units. The deposits are dominated by D2 regional reverse faulting gold, and only contain quartz vein-hosted free-milling gold lodes.

Mining by conventional open pit methods of drill and blast followed by load and haul will be employed. Drilling and blasting will be performed on 6 m benches. Loading of the blasted material will be performed on two 3 m flitches. Mining is currently undertaken by two separate mining contractors under the direction of Asanko Gold management. The intention is to get the optimum economical solution from a contracting approach through a tender process planned for 2020.

Blending strategy
The mine plan was developed around a 5.4 Mtpa processing throughput, where between 20% and 50% of the feed is oxide. A blending program is followed throughout the LOM that consider grade-bins, oretypes and Bond-work-index (BWI).

Mining operations
Grade control
Grade control (GC) drilling and sampling will be required to determine whether material in a given area is above, or below the cut-off grade. The ore is not anticipated to be visually controlled in the active mining face. GC definition drilling and sampling will be required to delineate the ore zone prior to the blast planning of the ore blocks.

Site preparation
The entire mining area will be cleared of buildings, installations and vegetation to a depth of 0.3 m. All building rubble, trees, bushes and other vegetable matter shall be stockpiled separately at designated locations. Vegetation suitable for use as firewood shall be stockpiled separately to all other cleared vegetation. The actual depth recovered will vary depending on location and based on recommendations from the Environmental department. All areas, where topsoil stripping occurs, will be surveyed before and after topsoil removal. The topsoil will be pushed into piles by a dozer or grader before a loader or excavator is used to load it into trucks. Trucks will then haul the soil to stockpiles for later use on rehabilitation, or directly to active rehabilitation areas. Prior to topsoil deposition, the stockpile areas will be cleared and surveyed.

Drill and blast Ore and waste will be broken using conventional drilling and blasting techniques. Experience gained to date during operation of the mine has shown that it is possible to free dig some of the material using either backhoe excavators or by ripping with a CAT D9 dozer, (or equivalent).

Load and haul
The mining fleet for the major pits (Nkran and Esaase) will include CAT 6030, 300 t hydraulic backhoe excavators with a 17 m3 bucket capacity, or equivalent, and face shovels with a 16.5 m3 bucket and CAT 6015, 140 t hydraulic backhoe excavator with a 6 m3 bucket capacity or equivalent. The primary hauling fleet will be CAT 777D dump trucks with a 94 t capacity. The mining fleet for the Satellite Pits will typical include CAT 390, 90 t hydraulic excavators with a 6 m3 bucket capacity, or equivalent, and CAT 374, 70 t hydraulic excavators with a 4.5 m3 bucket capacity or equivalent. Excavation will be executed from the mining dig plan as provided by the mine planning team to the operations team, with ore being hauled from the pits to the respective ore ROM pad, or directly to the crusher. Ore will be separated in different grade bins and material types outside the pit area, from where it will be transported by road haul trucks over land to the Nkran ROM pad for feeding into the Obotan plant.

Ore blending operations
Ore stockpiles will be used to manage the feed requirements. The configuration and capacity of the ore handling system will have the capability for direct blended ore feed, or alternatively switch-over between Oxide/ Transitional and Fresh material as and when required. Refer to the Section 17 (processing) on the importance of ore blending for process recovery, preg-robbing, BWI and process throughput. The proposed stockpile management will consist of buffer stockpiles which include Oxide, Transitional and Fresh material, located close to the primary crusher. It is estimated that 25% of the plant feed tonnage will be directly tip into the crusher and the remaining 75% will require re-handle using a CAT 992 front end loader (or equivalent) and CAT 777D haul truck. This is managed as per discussion in Section 16.1.2. Although direct tipping will be the preferred option, to minimise double-handling cost, this will be superseded by blending requirements. A longer-term strategic stockpile located approximately 750 m from the ROM pad will be maintained to balance the mining schedule with the plant feed schedule.

Crushing
Obotan sourced ore
The primary crushing circuit consists of a single tip with a dedicated ROM bin and a single jaw crusher in open circuit. Primary crusher product reports to the crushed ore stockpile (COS). The ROM ore (F100 800 mm, F80 500 mm) is loaded into a 100 t ROM bin by means of a front-end loader (FEL), or by direct tipping by haul trucks.

The ROM ore is drawn from the ROM bin at a controlled rate by a single, variable speed apron feeder, and fed directly to the jaw crusher. The speed of the apron feeder is controlled to maintain crusher throughput. Fine material spillage from the apron feeder reports to the primary crushing conveyor, where it is combined with the primary crusher product (P100 300 mm, P80 125 mm). The primary crushing conveyor is fitted with a belt magnet to remove any tramp iron material. The primary crushing conveyor discharges the crushed material onto the COS.

A mobile crushing array is used to assist with crushing of the ROM material, to optimise fragmentation and maintain throughput in the crushing circuit. Dust suppression, for dust control, is used at the crushing circuit.

Esaase sourced ore
ROM Esaase ore P100 of 800 mm is loaded onto haul trucks which transport the ore approximately 28 km to Obotan, where it is crushed in the Obotan crushing plant and thereafter joins the Obotan crushed ore ahead of feeding to the milling circuit.

Milling
The milling circuit is configured as a SAG milling, ball milling, crushing circuit (SABC circuit) comprising a primary SAG mill, a secondary Ball mill and a pebble crushing circuit. Ore is withdrawn from the 1,550 t COS by apron feeders feeding onto the SAG mill feed conveyor. A weightometer indicates the instantaneous and totalised crushed ore mill feed tonnage and is used to control the SAG mill feed rate via the apron feeders as well as the supplementation rate of the feed with the Esaase oxide material. The SAG mill feed conveyor discharges directly into the SAG mill feed hopper. The SAG mill discharge is screened via a 12 mm x 30 mm aperture trommel screen before gravitating to the mill discharge tank. Screen oversize is conveyed to a single pebble crusher, where it is crushed to below 12 mm prior to recycling back to mill feed conveyor. The pebble crusher feed conveyor is fitted with a weightometer for control purposes. A SAG mill pebble bunker is installed, in which any pebble overflow is stored for further handling.

The SAG mill (slurry discharge) operates in reverse open circuit, discharging directly into the Ball Mill discharge sump, and in closed circuit with the pebble crusher. The ball mill discharges into a sump from where the slurry is pumped to the cyclone classification circuit. A portion of the cyclone underflow (84% target) is diverted to the three gravity concentration units, each with its own scalping screen, removing the oversize fraction and diverting this back to the ball mill discharge sump. The remaining cyclone underflow portion reports back to the ball mill discharge sump for further grinding. Gravity recovered gold concentrate reports to an intensive leaching reactor circuit (ILR) while the gravity tailings fraction reports back to the ball mill discharge sump.

Cyclone overflow gravitates to the pre-leach thickening circuit, comprising a single high rate thickener, where it is thickened to approximately 50% solids ahead of leaching and gold adsorption in the CIL circuit. Supernatant solution overflowing the thickener is recycled back to the process plant.

Quicklime is stored in a 100 t silo and is metered onto the mill feed conveyor using a variable speed screw feeder. Quicklime is delivered to site by tanker and pneumatically transferred to the lime silo using an off-loading blower.

A ball loading system is used for loading of grinding media into the SAG mill (via the mill feed conveyor).

Dust control is by way of a water dust suppression system at the stockpile area.

Gravity gold recovery
Gravity concentrate originating from the three milling gravity recovery concentrators is treated in two ILRs. These reactors contain elevated levels of cyanide, caustic soda and oxygen to enable maximum leaching of the precious metals in the concentrate. Leach residence time is approximately 18 hours. At the end of the leach cycle the pregnant solution is treated for Au recovery in two dedicated electrowinning cells to facilitate separate metallurgical accounting. ILR residue is pumped to the mill discharge sump. Overall gravity recovery is approximately 50%.

Pre-leach thickening
The secondary ball mill classification cyclone overflow stream gravitates to a horizontal vibrating trash removal screen, to remove any coarse ore particles, wood fragments, organic material and plastics that would otherwise become locked up with the circuit carbon and block the CIL inter-tank screens. The trash screen oversize reports directly to a trash ........