The Wassa property lies within the southern portion of the Ashanti Greenstone Belt along the eastern margin of the belt within a volcano-sedimentary assemblage located at proximity to the Tarkwaian basin contact. The eastern contact between the Tarkwaian basin and the volcanosedimentary rocks of the Sefwi group is faulted, but the fault is discrete as opposed to the western contact of the Ashanti belt where the Ashanti fault zone can be several hundred meters wide. Deposition of the Tarkwaian sediments was followed by a period of dilation and the intrusion of late mafic dykes and sills.

The Wassa deposit is located on the eastern flank of the northeast trending Ashanti Belt, a Paleoproterozoic greenstone belt which was formed and deformed, along with the dividing Birimian and Tarkwaian sedimentary basins during the Eoeburnean and Eburnean orogeny. Most deposits found within the Ashanti belt can be classified as lode gold deposits or orogenic mesothermal gold deposits, with the exception of the Tarkwaian paleoplacer deposits which have a sedimentary origin.

The Wassa lithological sequence is characterized by lithologies belonging to the Sefwi Group and consisting of intercalated meta-mafic volcanic and meta-diorite dykes with altered meta-mafic volcanic and meta-sediments which are locally characterized as magnetite rich, banded iron formation like horizons

The Wassa mineralization is subdivided into a number of domains, namely; F Shoot, B Shoot, 242, South East, Starter, 419, Mid East and Dead Man’s Hill. Each of these represents discontinuous segments of the main mineralized system which extends for approximately 3.5 km along strike from surface and is still open at depth. The SAK deposits are located approximately 2 km to the southwest of the Wassa Main deposit on the northern end of a well-defined mineralized trend parallel to the Wassa Main trend. The mineralization is hosted in highly altered multi-phased greenstone-hosted quartz-carbonate veins interlaced with sedimentary pelitic units.

Mineralization within the Wassa Mine is structurally controlled and related to vein densities and sulphide contents. In detail, the mineralization generally consists of broadly tabular zones containing dismembered and folded ribbon-like bodies of narrow quartz vein material, zones are typically 10 m to 50 m wide within a 900 m mineralized corridor.

Three vein generations have been distinguished on the basis of structural evidence, vein mineralogy, textures and associated gold grades. Evidence further relates the majority of gold mineralization to the earliest recognized vein generation which is believed to be syn-Eoeburnean. Gold grades broadly correlate with the presence of quartz-dolomite/ankerite-tourmaline bearing quartz veins and the presence of sulphide minerals (predominantly pyrite) within and around the quartz veins. Gold grades appear to be spatially restricted to the quartz veins, vein selvages and the immediate wall rocks. The alteration haloes developed around the veins and pervasively developed within the core of the Wassa Fold contain lower grade mineralization.

HWINI-BUTRE
The Hwini-Butre deposits can be characterized as mafic intrusive hosted, orogenic shear zones. The deposits are hosted within diorite and granodiorite intrusive rocks of the Mpohor complex.

The Hwini-Butre concession is underlain by three deposits: Adoikrom, Dabokrom and Father Brown, which are all characterized by different styles of mineralization. The Hwini-Butre deposits are hosted within the Mpohor mafic complex, which consists mainly of gabbroic and gabbrodioritic intrusive horizons. . At Father Brown and Dabokrom, mineralization is associated with quartz vein systems which are locally surrounded by extensive, lower grade, disseminated quartz stockwork bodies, especially at Dabokrom. The Father Brown deposit is characterized by well-developed fault-filled quartz veins which are, as is the case for Dabokrom, light grey with carbonate and mica accessory minerals and minor tourmaline and feldspar.

BENSO
The Benso deposits can also be characterized as mafic intrusive hosted, orogenic shear zones deposits, which are hosted by Birimian metavolcanics into which coarse plagioclase porphyry units have intruded and are generally conformable with the volcaniclastic units.

The Benso concession is underlain by four main deposits: Subriso East, Subriso West, G Zone and I Zone. All the deposits are characterized by similar style of mineralization. As with Hwini-Butre, the Benso deposits are hosted within mafic intrusive rocks of gabbroic to dioritic composition, which intrude a thick volcano-sedimentary sequence mainly composed of mafic volcanic flows. Mineralization at Benso is associated with late deformational stages of the Eburnean orogeny and deposits are shear hosted along subsidiary structures.

CHICHIWELLI
The Chichiwelli deposits can also be characterized as mafic intrusive hosted, orogenic shear zones, the deposits are hosted within diorite and granodiorite intrusive rocks

The Chichiwelli deposit consists of two sub-parallel mineralized trends which hosts two distinct types of mineralization. The Chichiwelli West trend is a shear zone hosted deposit with a quartz, carbonate, sericite and potassic alteration assemblage, the mineralization is associated with pyrite. The Chichiwelli East trend is a quartz vein associated deposit with an ankerite and sericite alteration assemblage. Mineralization is also associated with pyrite along vein selvages and in the wall rocks.

In early 2018 Wassa transitioned into an underground-focused operation.

Mining is by underground with trackless access by decline (1:7 gradient), operated by GSWL personnel. The method is long hole open stoping (LHOS), mostly with transverse uphole stopes, in 25 m lifts, mined topdown, in primary/secondary sequence. Stable unsupported stope heights are up to 100 m and stopes are mined to full orebody width. The mine is divided into Panels, which reflect progressive stages of capital development. The Mineral Reserve includes Panels 1, 2 and 3, which lie between 150-650 m depth.

Panels 1 and 3
• Stope length is 25 m along strike with 6-10 m pillars between.
• Stope width is full width of the orebody which can be up to 35 m but is usually 15-25 m.
• Stopes are mined with uphole blastholes drilled from below. The stope lifts are extracted in a topdown sequence; each stope lift is extracted below the open stope void above. Up to four stope lifts are extracted to create a continuous excavation up to 100 m high.
• In Panels 1 and 3, the 100 m height limit usually enables full extraction of the orebody without the need for sill pillars. Where this is not the case, a sill pillar is left in the level between the sets of stopes.
• Mined voids are generally left open with some loose rock fill to dispose of waste or for opportunistic pillar recovery.
• Narrower ore zones (<15 m) are mined as longitudinal stopes with progressive placement of rock fill to minimize ore loss in pillars.
• Stopes at the south end of Panel 1 will utilize paste backfill within approximately 100 m of the panel boundary. Use of paste further north is limited by distribution pressures.

Panel 2
• The introduction of paste backfill permits a change to increase the extraction ratio.
• Primary stope length is 20 m with 20 m pillars left between, which will then be mined as secondary stopes after filling and curing of the primaries.
• Stope width is full width of the orebody which can approach 50 m but is usually 15-25 m.
• Primary stopes are mined with uphole blastholes drilled from below. The stope lifts are extracted in a top-down sequence; each stope lift is extracted below the open stope void above. Up to four stope lifts are extracted to create a continuous excavation up to 100 m high, which are filled with paste fill as a single fill mass.
• Secondary stopes are mined with blastholes drilled from below with each stope lift extracted in a bottom-up sequence, shown in Figure 16-7. To minimize paste exposure in the side-walls, each stope lift is planned to be filled before extracting the lift above. As experience with paste fill increases, there is an opportunity that the secondary stopes could be extracted in multiple lifts before filling. This would deliver a more productive mine schedule but this plan assumes the more conservative approach.
• Combined stope excavations up to 100 m high are planned before a sill pillar is introduced. The first sill pillar in Panel 2 lies between the 520 and 545 mRL levels.
• Sill pillars can be extracted after the secondary stopes are backfilled and sill pillar extraction assumes 60% recovery of the full stope.

In Panel 2, extraction of the first pass of primary stopes is well progressed. Paste backfilling and subsequent mining of the first secondary stopes is planned in 2021.

Panels 1 and 2 are accessed via the Daniel Owiredu Portal (formerly Portal 1), located in the Starter Pit. The Main decline is positioned east of B-Shoot which has variable dip. Maximum ramp grade is 1:7 and follows the plunge of the deposit south toward the deeper levels of Panel 2. Levels are accessed every 25 metres through level access drives connecting the ramp to each level’s footwall drive.

The upper zones will be mined as Panel 3 with two new decline accesses due to their spatial distance from the Main decline:
• Upper B-Shoot decline portal will be in the southern end of the Main pit and connects the Main decline at the 760 mRL. Duplicating the main decline enables the B-Shoot Upper material to be extracted in parallel with Panels 1 and 2, plus also forms part of a haulage loop system.
• 242 decline will be mined in the footwall of the 242 shoot which is north of the mineralized zone. It is remote from any B-Shoot infrastructure and will be an independent ramp.

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The Wassa processing plant is a conventional CIL plant with a four stage crushing circuit (p80 <8 mm) feeding two independent ball mills of 3 MW each.

From 2005 to the end of 2017, the plant processed at a rate 7,400 t/d primarily from oxide and fresh open pit feed. The earlier part of this period was characterized by high availability of oxide material and, from mid-2016, by the feeding of higher average grade underground material.

The plant flowsheet has transitioned from the historical HL processing and currently consists of the following operations:

• Two separate gravity gold recovery circuits using 48” Knelson centrifugal concentrators process a portion of the classifying cyclone feed in each mill circuit.

• The gravity concentrate from the Knelson concentrators is retreated using a Gemini shaking table to produce a HG gold concentrate for direct smelting, while the tails from the centrifugal concentrators and shaking table are return ........