The Loulo and Gounkoto deposits can be classified as a typical shear hosted Birimian style mesothermal gold deposits.

The Loulo project area is characterised by a sequence of sandstone, limestones and greywackes which are truncated by three major north to NE trending shear zones. Two major mineralised bodies have been discovered within the Project area, Gara and Yalea. Several other satellite deposits are also present.

Yalea is located in a north-south striking, steeply dipping package of metasedimentary rocks. Host lithologies at Yalea (from west to east) comprise of quartzite/grey in the hanging wall, with tectonic breccias in the north. Immediately above the main body of mineralisation is thin (0 m to 5 m) sequence of banded schistose greyish limestone, with alternating white and grey calcitic layers and dark grey to black phyllite units. The main mineralised body is a hydrothermally brecciated argillaceous pink quartzite that becomes more argillaceous (and less altered) towards the footwall. A higher grade ‘Purple Patch’ zone is observed in a dilatational strain transfer zone formed as the dip of the mineralised package steepens forming hydraulic breccias. The footwall package is a thick sequence of argillaceous quartzite and black sandstone. This sedimentary package is intruded locally by thin (0.1 m to 2 m) acid intrusives of mostly granitic composition. The country rocks are also cross cut by a late EW dolerite dyke that is generally sub-horizontal, with a gentle southward plunge.

Economic levels of gold mineralisation are almost exclusively associated with paragenetically late sulphide veins, breccias and zones of massive sulphides. Higher grade material commonly contains sulphide veins which cut the various generations of albite ± carbonate alteration. There is a strong correlation between sulphide intensity and gold mineralisation with the dominant sulphide phases consisting of pyrite (abundant), arsenopyrite and minor chalcopyrite. The sulphides can be disseminated or massive along fabric.

Yalea mineralisation, remains open at depth and to the south with potential for significant highgrade extensions. To the south of the ‘Purple Patch’ zone the Yalea Shear forms a subhorizontally plunging transfer zone where the competency contrast of the footwall argillaceous quartzites (SQR) contact causes a transfer of strain associated with normal movement. Consequently, this transfer creates dilatational hydraulic breccias with the potential to host significant high-grade extensions.

The Yalea and Gara underground mines are currently operating and are accessed via portals located in open pits and a box cut. The declines were originally developed as twin declines. One decline containing a conveyor and the second decline is used for mobile equipment access. The lower part of the mines has been developed as single declines with truck haulage up to crushers which feed ore and waste onto the conveyors.

Three mining methods are used at the Yalea and Gara underground mines. They are long hole transverse open stoping; long hole longitudinal retreat open stoping; and stoping under rock fill (SURF). SURF mining is planned to be introduced in the weathered areas of Yalea South Upper.

Previous longitudinal stoping in the upper areas of the mines uses a panel and pillar method, where approximately 10 m long pillars were left between 50 m long panels. In 2014 paste fill plants were commissioned at both mines. The paste fill plants at each of the mines produce a mixed paste/ aggregate fill. With the introduction of paste fill the lower areas of the mines are being mined using an underhand (top down) long hole stoping method which retreats to central accesses in an echelon format. Panels are 50 m long, mined as single level stopes (25 m high) and filled with cemented paste fill. The paste fill is exposed by the mining of both the panel below and the next panel on the same level. Transverse long hole open stoping is used in the wider (>15 m wide) parts of Yalea North. Transverse stopes are 15 m to 30 m along strike and mined from hanging wall to footwall.

The SURF method is planned for the portion of Yalea South Upper that has weathered transition or saprolite present in the mineralised zone, or the immediate hanging wall. The method will be used is expected to provide a more consistent production in the less competent ground.

From an operational perspective SURF is very similar to longitudinal sub level caving (SLC). The exception is that in SURF waste rock is tipped into the stope to fill mined voids and prevent caving of the hanging wall. In contrast SLC works by the hanging wall caving to fill the mined void.

A diesel trackless fleet is used for production comprising of 11 LHD’s and trucks, in addition to production drills and development drills.

The Loulo processing plant uses a conventional carbon in leach (CIL) gold extraction process with a budget throughput in 2017 of 4.8 Mt, which is in line with the plant design capacity.

Since 2014 multiple optimisation projects have been undertaken, resulting in increased throughput and improved recoveries. It is expected that the improvement initiatives will continue but are considered part of operations and not necessarily confined to capital projects. The expected throughputs and recoveries are based on historical metallurgical testwork and the actual operational performance.

The upgraded process plant remains a conventional crushing, milling, gravity, CIL, and tailings disposal circuit. It will process an average of 580 tph using the following circuits:

• Crushing – three stage crushing for the hard rock sulphide ores and a single stage roll toothed crusher for the soft weathered oxide ores.
• Milling – one primary mill (7 MW); two identi ........