The Tropicana Gold Project area lies east of a northeast trending magnetic feature, interpreted to be the major tectonic suture between the Yilgarn Craton and the Proterozoic Albany-Fraser Orogen that extends over 700km. The gold deposit is hosted in Archaean gneissic metamorphic rocks (ca. 2,640Ma) with cover sequences generally 10 to 30m thick resulting in the mineral deposit not being exposed at surface.

Together, the Tropicana, Havana, Havana South and Boston Shaker deposits define a northeast trending mineralised corridor, approximately 1.2km wide and 5km long that has been tested to a vertical depth of more than 1,200m. The Mineral Resource remains open down-dip from the Tropicana, Havana and Boston Shaker deposits and has the potential to be extended to the north and south. Neither the immediate metamorphic host rocks nor the mineralised zones are exposed at surface due to the presence of widespread younger cover sequences.

The Tropicana deposit comprises a mineralised zone up to 50m thick, hosted predominantly in quartzo feldspathic gneiss with a garnet-gneiss dominated hangingwall package. The mineralisation is comprised of subordinate thin (3 to 5m), discontinuous mineralised lenses that typically return intercepts of >0.5g/t gold. The Havana deposit comprises a lower, laterally continuous, higher-grade lode up to 50m thick that is overlain, in the central and southern parts of the pit, by stacked, typically lower-grade and thinner (up to 25m thick) mineralised zones. Havana is also dominantly hosted in quartzo-feldspathic gneiss, again with a garnet gneiss dominated hangingwall.

Mineralisation is accompanied by pyrite (2% to 8%) with accessory pyrrhotite, chalcopyrite and other minor sulphides and tellurides. The gold mineralisation is related to shear planes that postdate the main gneissic fabric developed during peak granulite-facies metamorphism.

Open pit mining activities are undertaken by Macmahon in an alliance partnership with AngloGold Ashanti. Mining is conventional open cut, drill and blast, followed by truck and excavator operation to develop the deposits (Havana, Havana South and Boston Shaker). The total annual movement of ore and waste is approximately 95Mtpa. Underground mining utilises mechanised jumbo development and open stoping methods. At peak production, annual production from underground is planned to reach 1.1Mt of ore.

Development of the Boston Shaker underground mine was approved in March 2019, and the mine transitioned into commercial production september 2020 on schedule.

Access to the mineralisation will be via a decline with a portal at the base of the Tropicana Open Pit. A second portal will be established later in the completed Boston Shaker Open pit. As disclosed in the Prefeasibility Study (PFS)1, underground conditions at Boston Shaker are good and conventional ground support systems and practices will be used for the underground development. The underground mine design is based on the use of conventional mechanised mining and underhand sublevel stoping.

The Joint Venture has awarded the underground mining contract to Macmahon, a leading surface and underground mining services business.

The Tropicana, Havana, Havana South and Boston Shaker open pits have been mined as a series of cutbacks, sequenced and scheduled to maximize value at a mining rate that delivers the best mining unit cost for the scale of the operation. Up until June 2020 ore production from the open pits exceeded the plant capacity, allowing higher grade ore to be preferentially treated (grade streaming) while lower grade ore was accumulated on stockpiles.

Over the course of H2 2019 and H1 2020 the Tropicana pit and Havana pit were completed, in line with the mine plan. As a result, grade streaming came to an end and stockpiled ore is currently being used to supplement the mill feed from the Havana South and Boston Shaker pits.

A decision was made in the June 2020 quarter to invest in the next cutback of the Havana pit (Stage 2) which will allow access to the deeper Havana open pit ore from 2022 onwards. While this cutback is being completed, mill feed will be sourced from the Boston Shaker open pit, supplemented by approximately 4 Mtpa of low grade (0.85 – 1.05 g/t) stockpiled ore, resulting in a lower milled grade over the period.

The lower grade will be partially offset by the Boston Shaker underground mine, which is ramping up and will be contributing at full capacity by the second half of calendar 2021.

The plan remains for gold production (at 100%) in 2020 and 2021, to be between 400,000 and 450,000 oz, compared to 513,785 oz last year. From 2022 onwards, annual gold production will normalize at between 450,000 – 500,000 oz as the low grade stockpile ore in the mill feed is displaced by a larger proportion of Boston Shaker underground ore and an increasing contribution of higher grade ore from the Havana pit, as the cutback progresses.

The comminution circuit is based around a HPGR. The circuit was commissioned in September 2013 and comprises two stages of crushing closed with a dry screen, followed by an HPGR closed with a wet screen and the screen undersize reports to a reverse closed-circuit ball mill. The cyclone overflow is thickened prior to a carbon-in-leach (CIL) circuit and gold refining.

Primary crushing is conducted in a single 1400 x 2100 gyratory crusher with 600 kW installed power. The coarse ore is reclaimed from the stockpile via two apron feeders and conveyed to the secondary screen feed bins. The secondary screens are two parallel 3.0 m x 6.1 m double deck banana screens (for duty and standby) operating with 90 mm top deck apertures and 45 mm bottom deck apertures. The oversize from both decks combines to feed the secondary cone crushers while the -45 mm reports to the HPGR circuit. The secondary crushing stage comprises two cone crushers (duty and standby) which operate in closed circuit with the secondary screens.

The secondary crushed product reports to the HPGR feed bin, which has 18 minutes live capacity. A belt feeder is used to maintain choke feed conditions to the HPGR. A single 2.0 m x 1.85 m HPGR is used for the tertiary crushing stage. This is fitted with two 2200 kW variable speed motors. The HPGR operates in closed circuit with wet screens. The design includes the ability to continuously divert a fraction from the HPGR discharge to create a HPGR fines emergency stockpile. This stockpile is then reclaimed using a front-end loader to feed the wet screens when the HPGR or secondary crushing plant is off-line. This stream is dry screened at 4 mm prior to stockpiling, with +4 mm material returned to the HPGR screen feed conveyor.

There are two parallel wet screens that classify the HPGR discharge. The screen pulping boxes deagglomerate the flake ahead of the screens. The wet screens are 4.2 m x 8.5 m double deck banana screens which were originally fitted with 8 mm top deck and 4 mm bottom deck apertures. The combined screen oversize is conveyed back to the HPGR, with the ability to bypass the HPGR via actuation of a flop gate during metal detect events and periods of overly wet feed to protect the HPGR.

The -4 mm screen undersize reports to the ball mill discharge hopper along with the ball mill discharge stream. This is pumped to the cyclone cluster, which is fitted with 26 inch hydrocyclones. The cyclone overflow exits the grinding circuit, reporting to the trash screens and leach feed thickener, while the cyclone underflow returns to the 7.32 m x 13.12 m overflow discharge ball mill for further size reduction. The ball mill is equipped with two 7.0 MW Slip Energy Recovery (SER) drives, allowing variable speed operation and an over-rated total power of 15 MW at maximum speed. The final P80 target for the cyclone overflow is 75 µm.

In FY18, the Tropicana Joint Venture partners announced the construction of a second 6 megawatt ball mill. Installation and commissioning of the mill was completed in December 2018. Installation and commissioning of the mill was completed on time and on budget in December 2018, increasing throughput capacity to 8.2 million tonnes per annum in FY19.

The processing plant, utilising conventional crushing, grinding and CIL (carbon-in-leach) recovery technology, was originally designed with a nameplate capacity of 5.8 million tonnes per annum and this was achieved in March 2014.

In 2016 and 2017, an optimisation project increased the throughput capacity to 7.5 million tonnes per annum by the second half of FY17. In FY18, the Tropicana Joint Venture partners announced the construction of a second 6 megawatt ball mill. In FY18, the Tropicana Joint Venture partners announced the construction of a second 6 megawatt ball mill. Installation and commissioning of the mill was completed in December 2018, increasing throughput capacity to 8.2 million tonnes per annum in FY19.