The Toka Tindung Gold Mine area is located on the eastern margin of the South East Asia Plate within the SulawesiEast Mindanao magmatic arc, a highly mineralised belt of volcanics and high level intrusives of early Miocene to Quaternary age. A series of north-northwest–south-southeast trending faults define structural corridors which host the deposits. The deposits are low-sulfidation epithermal systems.

Low-sulphidation epithermal gold mineralisation within the Project area occurs in shoots that form at dilational sites along quartz vein-hosted structures.

The Toka Tindung deposit lies at the northern end of a series of north-northwest trending faults. These faults define a structural corridor at least 2 km wide and extending for about 15 km south of Toka Tindung Gold Mine. The mineralised system is up to 200 m wide and has been delineated over a 1.2 km strike extent. The gross trend of the stockwork zone and larger veins at Toka show a north strike, with the veins generally near vertical or dipping steeply to either the east or west. Local variations in dip, strike and width occur along individual veins within the stockwork system.

The main structural elements in the Batupangah area are brittle faults and fractures with north, north-northeast and northwest mineralised trends. These structures are interpreted to be block faults and have dips generally steeper than 60°. In summary:
- At Pajajaran, two subvertical, parallel sheeted veins around 2 to 5 m wide and a minor stock occur with a northwestern trend;
- The Blambangan deposit consists of a single vein around 2 to 5 m wide with minor stockwork and a northerly trend;
- The Araren deposit consists of two veins each varying between 1 and 7 m in width with north to northeast trends.

Mineralisation within the concession area is characterised by pervasive silicification and adularia alteration within and around the mineralised vein systems zoning vertically and horizontally. Traces of disseminated pyrite, chlorite, carbonate and hematite accompany this alteration. These rocks are associated with anomalous arsenic, antimony and mercury geochemical signature, with lesser molybdenum and tellurium.

Minor argillic alteration overprints the adularia altered volcanics and comprises variable proportions of smectitite, illite, minor chlorite, carbonate, hematite and pyrite. This overprint is strongest at the contact of the upper andesite.

Haloes around the two mineralisation styles at Toka Tindung Gold Mine provide the basis for a pathfinder alteration model supporting both the Near Mine and Greenfields exploration activities. The two mineralisation styles exhibit similar alteration composition but differ in morphology and spatial distribution of certain trace elements in their haloes. The basic difference between the two mineralisation styles is reflected in the host rocks and how they react to the altering fluids.

In the Toka-style alteration system the volcaniclastic host rocks are permeable, leading to a more extensive alteration halo (with the silica halo at Toka measuring some 3.5 km by 1.3 km).

From an exploration perspective, increasing quartz vein percentages, hydrothermal alteration and elevated gold/silver values, are all interpreted to be indicative of proximal mineralisation.

Weathering and oxidation of the altered volcaniclastics and vein systems is generally weak to moderate and produces mixed assemblages of iron oxides, kaolinite and smectite.

All economic gold and silver mineralisation discovered to date at the Toka Tindung Gold Mine is of low-sulphidation epithermal style comprising quartz–adularia vein and stockwork-hosted gold and silver deposits. This low tonnage, high grade gold mineralisation typically occurs within small shoots that form at dilational sites along the host quartz vein structures. District scale structural controls on mineralisation and include north–south and north-northwest trends.

Within the broader concession area, two broadly northwest-trending structural corridors are interpreted to focus the epithermal mineralisation. Within these interpreted corridors, the shoots are developed at sites of structural complexity where there are strike and/or dip changes, intersecting structures, links and/or jogs developed. Other controls on mineralisation include the stratigraphy, host lithology (volcanics versus volcaniclastics) and proximity to intrusive bodies.

Gold and silver mineralisation occurs within quartz vein structures, which are sulphide and base metal-poor with abundant chalcedonic silica, microcrystalline and fine-grained quartz, adularia and minor calcite. These veins vary from solid vein/lode to breccia, containing both wallrock and quartz vein clasts to stockwork or sheeted veins, to fracture fill, cavity fill or as clasts within a fault. Vein mineralogy includes assemblages of quartz, adularia, gold, clay, carbonate, chalcedony, chlorite, hematite and sulphide. While crystalline quartz is the most common vein phase, other quartz vein textures include bladed, cockade, colloform, comb, drusy, vuggy, crustiform, cryptocrystalline, massive, moss and saccharoidal.

At the Toka deposit, the banded and brecciated quartz-adularia veins range in thickness from <1 up to 10 m and are associated with a zone of pervasive quartz–adularia alteration. In excess of 60 veins have been defined within the deposit, typically grading between 3 and 5 g/t Au, and locally up to 30 g/t Au. Silver grades are generally low, with an Ag:Au ratio in mined ores of 2.3:1. Quartz vein stockwork zones are found between the main veins and have a bulk grade ranging between 0.2and 3 g/t Au. Weathering and oxidation to depths of up to 80 m is localised along the main veins and structures.

The southern pits (i.e. Pajajaran, Blambangan, Kopra, Araren and Alaskar deposits) are much simpler ore systems than at Toka and range from single veins to dual and multiple splayed veins and vein stockworks, with vein widths typically between 1 and 10 m.

The majority of the gold delineated to date (from all deposits including those of the Western Corridor) exists as fine, 5–20 micron (µm), grains of ‘free’ gold or associated with the silver–gold alloy electrum.

Toka Tindung Gold Mine commenced overburden mining in 2009 and production mining operations in January 2011.

The Toka Tindung Gold Mine open pit mining complex consists of several open pits within an area spanning approximately 10 km2. These include the active producing open pits; Toka, Araren, and Kopra, as well as the Alaskar and Marawuwung open pits, which are in pre-production and due to commence production in 2021 and 2024, respectively. The Pajajaran and Blambangan open pits have been mined out (completed) and are being backfilled with waste rock from other operating open pits. This area also includes the Toka, Batupangah, Pajajaran and Kopra WRDs.

Since mining inception, Archi has successfully transitioned the Project to a multi-open pit operation with initial mining commencing at Toka (2011), Pajajaran (2011), Kopra (2012), Blambangan (2013) and Araren (2015).

The geotechnical design parameters are bench heights either 15 m or 20 m, berm widths varied between 5 m and 10.5 m, and batter angles between 34° and 70°, dependent on the open pit depth and rock type (oxidised, transitional and fresh). The general open pit design parameters are ramp widths of 15 m (single lane) and 25 m (dual lane) and ramp gradients of 10%.

Final designed open pit depths are:
No Open Pit Name Design Depth(m)
1 Toka - 170;
2 Marawuwung - 105;
3 Alaskar - 165;
4 Kopra - 195;
5 Araren - 280;
6 Talawaan - 100 .

Waste rock from the southern open pits is currently transported to the Batupangah, Pajajaran and Kopra WRDs, as well as backfilling of the Pajajaran and Blambangan open pits, while waste rock material from the Toka open pit is used for tailings dam construction or dumped at the Toka WRD (Toka Stage 3).

Conventional open pit mining methods are applied at the Toka Tindung Gold Mine to extract gold– silver ores from multiple open pits. Both selective and bulk mining methods are implemented utilising conventional hydraulic excavators and articulated haulage trucks depending on the geology of the vein systems within each of the open pits. Mining activities typically consist of drilling, blasting, excavation, loading/haulage of rocks and dewatering of the open pits.

Archi operates a traditional CIL plant with a jaw crusher of 600t/hr feeding a SAG mill which has tertiary and secondary ball mills in parallel.

From ore stockpiles, ore is reclaimed by front end loader (FEL) and fed to a single stage gyratory crusher and crushed ore stockpile with one apron feeder and two vibrating reclaim feeders. Material is fed into the primary crusher at a certain ore blend designed to achieve optimum metal content. Ores are crushed to a size of <120 mm and then conveyed to the crushed ore stockpile.

Crushed ores are then fed by conveyor to the grinding circuit comprising a 4.1 MW SAG mill in closed circuit with a pebble crusher, and two stages of ball milling, a 6.75 MW secondary ball milling and 2.6 MW tertiary ball milling circuit, both of which are in closed circuit with hydrocyclones classifying to an ultimate target grind size of approximately P75 of 75 µm.

The Toka Tindung Gold Mine processing plant flowsheet is conventional and well suited to the continued processing of the Toka Tindung gold ores.

The predominantly oxide-based ore is processed on site at a centralised processing facility using comminution processes (crushing/grinding) followed by conventional carbon-in-leach (CIL) extraction, elution and smelting to produce gold and silver doré.

The Toka Tindung Gold Mine plant has been operating continuously since April 2011. It has undergone a number of debottlenecking projects, upgrades and expansions in the ensuing years to arrive at its current flowsheet configuration and plant capacity, most notably the installation of a scats/pebble crusher, a third ball mill and three additional CIL tanks.

The Toka Tindung Gold Mine processing facility is a conventional CIL circuit. Mined ore from each pit is hauled and stockpiled at three stockpile pads, locally termed the TTN ROM, MSM ROM and Low-grade ore s ........