Overview

Deposit type

• Hydrothermal
• Vein / narrow vein
• Paleoplacer

Summary:

Two epigenetic gold forming events are identified in Ghana. A pre-Tarkwaian event which provided the protolith of the world class Tarkwaian palaeoplacer deposits, and a post-Tarkwaian deformation event which, led to the formation of orogenic hydrothermal gold deposits in Ghana and other West African countries.

Damang exploits oxide and primary zone orogenic style hydrothermal mineralisation in addition to palaeoplacer mineralisation. The post-Tarkwaian phase of hydrothermal mineralisation overprints the lower grade Tarkwaian palaeoplacer conglomerates.

Palaeoplacer mineralisation
Three main gold-bearing conglomerate horizons are recognized on the limbs of the Damang Anticline within the Banket Series of the Tarkwaian Group. From footwall to hanging-wall (i.e., oldest to youngest), these are the Star/Composite, Malta/Breccia, and Gulder Reefs on the west limb and the Lima, Kwesie-K1 and Kwesie-K2 Reefs on the east limb. The conglomerate horizons on both limbs are separated by poorly mineralized sandstone units. The reefs are usually characterized by an upward fining sequence of poor to moderately sorted, clast supported polymictic conglomerates. However, local variations are observed where the conglomerate domain is interbedded with fine to coarse-grained sandstones. The conglomerates host gold grades that range from 1.3 g/t Au to 1.5 g/t Au whereas the sandstone units usually contain grades of between 0.1 g/t Au to 0.2 g/t Au.

Hydrothermal mineralisation
A significant portion of the gold mineralisation at the Damang pit is associated with hydrothermal mineralisation, with veins being the principal sources of ore. The mineralisation at Damang formed in response to progressive Dz (NNWW-SSE) shortening and compression, with mineralisation occurring after peak regional metamorphism at around 2058 Ma (Tunks et al., 2004). Gold mineralisation is associated with hydrothermal alteration halos around auriferous quartz veins.

Two main controls on the distribution of the alteration signature have been identified. Structural fracturing controls the distribution of veins and therefore the distribution of localized alteration, and primary lithology, which concentrates alteration along bedding foresets in the Banket Footwall, particularly in the heavy mineral foresets of the Banket Series sandstones.

Compressional deformation controlled the development of the structures that provided fluid pathways for the localization of hydrothermal fluids. Veins occur in two general styles which are gradational with one another, extension veins and shear veins - with their associated alteration envelopes.

Extensional veins comprise en-échelon arrays of sigmoidal vein arrays that form stacked sub-horizontal vein sets between shear veins (fault-fracture mesh) or at shear vein tips (Rhys, 2019). They vary from 0.5 to 20 cm thick white to glassy clear quartz veins that have simple blocky quartz fill and sharp contacts with the wall rock. These veins are lenticular in cross section and lack foliation or banding. They vary to carbonate rich in areas outside of ore zones, where they lack alteration and gold-mineralisation.

Shear veins are generally sub-parallel to bedding and vary in thickness from <2 cm to 0.7 m and have a more banded or complex fill of white quartz with wall rock slivers and layers, trails, bands and stylolites of sulphides, tourmaline and sericite-Fe-carbonate. Gold occurs as free grains, typically associated with sulphides and as a refractory component in pyrite. Discontinuity of mineralisation is inherent, due to the én-echelon arrangement of the veins within the shear zone as well as the highly sheared and disrupted nature of such zones.

The veins are cross-cut lithologies and are mainly confined to the silicified Banket Series units as well as in the Tarkwa Phyllites, Intrusives and to a lesser extent the Huni Sandstone units.

Since reddish albite was observed to occur in vein selvages and envelopes in many areas, at least some of this alteration is associated with syn-ore hydrothermal fluid flow. Broader areas could represent more distributed, earlier hydrothermal activity that is a precursor to the areas of vein development, but still indicative of hydrothermal corridors, as is commonly present in other orogenic gold systems.

Damang is a world class gold mineralisation system where drilling has only tested to relatively shallow depths along known ore-bearing corridors in the Tarkwaian sediments on the margins of the Damang Anticline. Within this corridor and in the adjacent Birimian rocks there may be additional potential for new orebodies in both a near-mine setting and at a brown fields district scale in the following general areas:

- Stacked mineralisation potential
Potential exists for additional stacked areas of mineralisation to be identified, which could form deep pit or underground exploration targets below the currently mined and drilled levels. Given the presence of continuous higher grade zones apparent in the resource definition drilling assays, there is potential for underground selective mining of concentrated vein arrays and shear veins if additional zones either below, down plunge of or between the pit areas can be identified. Stacked zones of mineralisation may locally have vertical gaps, so even if gold grades and vein intensity diminish immediately under currently mined areas, these could pick up at depth, especially if additional folds or shear zones are present. Further to this, if additional reverse faults like the West Birimian Fault underlie, and control the positions of folds west of Amoanda, these could be prospective targets for shallow plunging zones where veins have developed adjacent to or above the faults.

- Birimian mineralisation potential
Current mining and exploration at Damang has primarily concentrated on the Tarkwaian sequence. Given the potential for Birimian hosted ore implied by other deposits in the region, there may be potential for mineralisation in this sequence, especially where competent units such as intrusions or mafic flows occur in weaker rocks, forming a rheological contrast that could focus shear zones and vein arrays. This potential is exemplified by the presence of mineralisation in a small intrusive body which was mined in the Birimian rocks in the eastern portion of the Amoanda pit.

Mining Methods

• Truck & Shovel / Loader

Summary:

Mining operations are carried out by contractor miners using open-pit, conventional drill and blast with truck and shovel methods. Since December 2022, mining is focused on the Huni pit. Gold mineralisation is mined to a selective COG and segregated into grade ranges to balance ore production and processing capacities. The pit walls are monitored by radar to mitigate geotechnical challenges, with additional controls implemented to ensure safe operations.

Damang has one open pit constituting the Mineral Reserves, seven open pits comprising the Mineral Resources, one ore stockpile.

In open pit mining, access to the orebody is achieved by stripping the overburden in benches of fixed height to expose the ore below. This is most typically achieved by drilling and blasting an area, loading the broken rock with excavators into dump trucks and hauling the rock and/or soil to dumps. The overburden material is placed on designated waste rock dumps.

Extraction of the orebody involves a similar activity as in stripping the overburden. Lines are established on the pit floor demarcating ore from waste material and the rock is then drilled and blasted. Post blasting, the ore is loaded into dump trucks, based on a defined ‘dig plan’ demarcating the position of the ore and waste boundaries post the heave and throw movement caused by the blasting, and hauled to interim stockpiles or directly to the crusher at the process plant, while the waste is hauled to waste rock dumps.

Mining at Damang is carried out using conventional open pit methods. This has been the preferred mining method since the commencement of the mine in 1997 due to the characteristics of the ore deposit. The outcome of a scoping study undertaken in 2020 on the future of Damang supported the economic and technical viability of the open pit mining methods under prevailing conditions due to the modelled underground low tonnages of the sparsely distributed ore domains above estimated underground cut-off grades in the major reefs of the Damang pit.

Damang’s life of mine plan is based on a contractor mining model. Mining is planned to end in 2023 with processing of stockpiles until 2025. Grade control drilling precedes production drilling and blasting. Fresh rock and transitional zones are drilled and blasted as 9 m benches that are excavated in 3 m flitches. Oxide material which cannot be “freedug” is blasted using lower powder factors. Conventionally, Nonel detonators and emulsion are used in both fresh and oxide material. However, electronic detonators are used to control the impact of blasting on the pit walls in areas where there are geotechnical challenges. Presplit wall control methods and trim blasting are also used in the fresh zones to ensure stability of the pit walls. CAT 777 trucks haul the ore to the run-of-mine pad and waste to the respective planned dumps.

Dewatering in the Damang and Huni pits, as well as the surface drains and sumps, is undertaken by a combination of diesel and electric pumps. The current annual discharge capacity is about 4 Mm3. The water is discharged into the Lima, Kwesie and Tomento pits and later pumped to the Adjaye dam to serve as raw water source for the processing plant or for dust suppression. Alternatively, when the water quality meets regulatory standards, the water is discharged into the environment.

Equipment and labour requirements
Primary loading is completed by Liebherr R9250 (250 t) and Hitachi 1900-6 (190 t) excavators. Primary haulage is completed with Cat 777F/G (90 t). Major equipment is modelled with an availability of 84 % to 86 % and use of availability of 85 %.

Mining is a continuous operation with 3 crews on 2 X 12-hour shifts.

Mine design
The west wall of the Damang pit includes 80 ° batters at a height of 18 m separated by 6 m wide berms. This geometry produces a 63 ° crest-to-crest inter ramp slope angle. The highest uninterrupted inter-ramp slope (126 m high) is located at 26,000 N. The current life of mine design includes ramp switchbacks and other slope decoupling step-outs that create a nominal overall slope angle of 52 ° (a slope section located at 26,000 N has a design crest-to-toe angle of 53 ° at a height of 337 m) in the hard rock zone.

The configuration of the east wall of the Damang pit includes 65 ° batters at a height of 18 m separated by 6 m wide berms. This geometry produces a 52 ° crest-to-crest inter ramp slope angle and nominal overall slope of 46 ° at a slope section located at 25,900 N at a height of 360 m.

The Huni pit includes 75 ° and 65 ° batters at the west and east walls respectively. The highest uninterrupted interramp slope produces 57° crest-to-crest inter ramp slope angle at 26,630 N at a height of 108 m and overall slope angle of 51 ° at 26,920 N at a height of 141 m on the west wall. The configuration of the east wall produces an overall slope angle of 44 ° at 26,980 N at a height of 142 m.

Mining in the Damang main pit was completed in 2022. Mining in the Huni pit was completed in 2023.

Damang completes mining at the Huni and Lima Kwesi Gap (LKG) pits and increases the processing of low-grade stockpiles.

Comminution

Crushers and Mills

Summary:

The crusher is fed by a front-end loader or by rear dump trucks. The crushing circuit comprises a primary 2,000 t/hour gyratory crusher followed by a secondary crushing circuit, which is comprised of sizing screens, two secondary crushers, five tertiary crushers, five feeders and conveyors. The primary circuit contains a 750 t/hour single-toggle jaw crusher that can provide consistent feed when the gyratory crusher is down for maintenance. The Pg 19 mm product reports to the coarse ore stockpile, which has a live capacity of 10,000 t and static capacity of 80,000 t.

The milling section produces leach feed at approximately Pg 106 pm and consists of a semi-autogenous grinding (SAG) mill (8 m high by 5.1 m long) and a ball mill (6.1 m high by 9 m long). Both mills have an installed power rating of 5.8 MW.

Processing

• Gravity separation
• Centrifugal concentrator
• Smelting
• Carbon re-activation kiln
• Crush & Screen plant
• Concentrate leach
• Inline Leach Reactor (ILR)
• Agitated tank (VAT) leaching
• Carbon in leach (CIL)
• Carbon adsorption-desorption-recovery (ADR)
• Elution
• Solvent Extraction & Electrowinning
• Filter press
• Cyanide (reagent)

Summary:

The processing plant treats predominantly fresh ore, comprising a three-stage crushing circuit, SAG/ball mill with a pebble crushing circuit, a gravity recovery circuit and a CIL gold recovery circuit. The plant has been optimised to process 4.6Mtpa.

The gravity circuit comprises two XD48" Knelson concentrators with dedicated InLine Leach Reactor for intensive cyanidation of the gravity concentrate. The gravity circuit recovers approximately 30 % of the gold. The leached tails from the ILR reports to the Ball Mill for regrinding after the clarified pregnant solution has been transferred to the electrowinning circuit and the remaining solids have been subjected to several wash cycles using raw water.

The leach circuit comprises eight tanks in series, each with a nominal capacity of 3,000 m3 providing a retention time of 3.7 hours per tank. Each tank is fitted with two cylindrical inter tank screens (Kemix MPS 750P type 1 mm apertures) with mechanical wiper blades to keep carbon away from the screen surface and dual open impellers. The loaded carbon is recovered from CIL tank 1 into the acid wash column and acid washed using 3 % strength hydrochloric acid followed by water flushing.

The rinsed carbon is transferred to the elution column where a hot caustic solution (3 % concentration) is circulated through the column via heat exchangers to elute the gold absorbed on the carbon. Elution is carried out at 120 °C at an operating pressure of 350 kPa in the column. The dissolved gold is then electro-deposited onto stainless steel wool cathodes. Barren carbon from the elution circuit is regenerated in a carbon regeneration kiln.

Gold sludge from both the gravity and electrowinning circuits is washed and filtered. The sludge is further refined through smelting and crude doré is poured. Gravity doré bars are approximately 90 % to 95 % gold whereas doré bars from the CIL circuit are dependent on ore feed characteristics and can vary between 65 % and 90 % gold. Doré is dispatched to a refinery for further processing into gold bullion.

Water Supply

Summary:

AGL holds water use permits AGLID118/19, AGLID294/19 and AGLID295/19 dated 1 January 2019 and AGLIDA439/20 dated 1 December 2019. The permits allow the mine to abstract raw water from the Tamang Dam, a tributary of Bonsa River, groundwater from boreholes at the plant site and the West Damang townsite for mining and domestic purposes as well as to dewater the Adjaye pond, Damang Cutback Complex, Rex, Lima, Kwesie South, Amoanda and the Tomento pits. In pursuance of the Water Resources Commission (WRC) ACT 522 (1996) and L11692, AGL promptly submits applications for water use permit renewal, quarterly reports and complies with all other issues relating to water use, abstraction, discharges and storage.

Damang Mine has a positive water balance. Over 77 % of the mine’s water use is from recycling return water from the FETSF. Fresh water top up is from the Adjaye Dam which receives water from the active pits or from the mine’s water reservoirs. Inactive pits like the Lima, Kwesie and Tomento pits have been adopted as water reservoirs for storage of excess water from active pits and from runoffs in the wet season. The adoption of the inactive pits as reservoirs has eliminated the need to abstract water from rivers and streams in and around the mine. The approach also ensures adequate availability of water for processing in the dry seasons.

Potable water supply is mainly from groundwater boreholes. Water from boreholes located at various points on the mine are pumped through treatment systems to all areas of the mine including the camp, offices, workshops and the process plant for portable purposes. The mine’s water balance model is currently being reviewed and updated by Golder Associate Consultants.

All pit water recovered is stored in inactive pits (Lima, Tomento 1 and Kwesie North pits) and routed to the Adjaye dam for use in the process plant and workshops for washing heavy maintenance equipment and for dust suppression. Though AGL has a permit to abstract raw water from the Tamang dam, no water had been abstracted from the dam since July 2013.

The ore processing operations recover most of the water from the TSF. Effluent from ore processing (tails slurry) containing ground and rock particles together with large volumes of water are pumped to the FETSF. The supernatant decant is pumped back to the process plant for reuse. This process will continue in 2021 and beyond to reduce raw water abstraction and increase reuse of process water.

Potable water for the mine and residential areas is abstracted from boreholes located at the plant site and the residential area (townsite).

Production

Operational metrics

Personnel

Job Title	Name	Profile	Ref. Date
Metallurgical Manager	Catherine Kuupol Kuutor		Apr 22, 2024
Mine Planning Manager	John Ankomah		Apr 22, 2024
Mining Manager	Charles Kofi Nti		Apr 22, 2024
Project Superintendent	Caleb Dzasa		Apr 22, 2024
Supply Chain Manager	Emmanuel Kingsley Arthur		Apr 22, 2024