Doebrich and Theodore (1996), Theodore (1998), and Theodore (2000) described the deposits at Marigold as distal disseminated silver–gold deposits. These deposits are disseminated equivalents of polymetallic vein deposits, characterised by a geochemical signature that includes silver, gold, lead, manganese, zinc, copper, antimony, arsenic, mercury, and tellurium (Cox and Singer, 1990). Typically, they contain substantially more silver relative to gold than other types of disseminated gold deposits and may feature supergene enrichment of silver if significantly oxidised.

Gold at Marigold is currently mined from multiple deposits located on a 10 km by 1.5 km area. From north to south, historical and future mineral deposits at Marigold include 32 North (32N), 5 Northeast (5NE), 5 North (5N), 8 North(8N), 8 Deep (8D), Terry Zone North (TZN), 8 South (8S), 8 South Extension (8Sx), Terry Zone (Old Marigold), Top Zone, HideOut, Terry Complex (Battle, Red Rock, East Hill), Red Dot, Mackay, Mud, Target, Valmy, Basalt-Antler, East Basalt, and Battle Cry. The majority of these individual mineralisation zones have coalesced into the Mackay pit.

The gold deposits at Marigold cumulatively define a north-trending alignment of gold mineralised rock more than 8 km long.

Gold mineralizing fluids were primarily controlled by fault structure and lithology, with tertiary influence by fold geometry. Within the Valmy Formation, higher gold grades are observed in the hinge zones of open folds that trend west–north-west and plunge gently. When viewed down plunge, the undulation of these folds is mimicked by gold mineralised horizons. The deposition of gold was restricted to fault zones and quartzite dominant horizons within the Valmy Formation and high permeability units within the Antler sequence.

In unoxidised rocks, gold occurs in arsenic-enriched overgrowths on pre-ore pyrite. Arsenopyrite is also present on pre-ore pyrite grains but is not auriferous. Geochemically, the gold mineralisation event is characterised by elevated arsenic, barium, antimony, and mercury, among others. Gangue minerals include quartz, arsenopyrite, stibnite, calcite, clay, and barite. Hypogene sulfide minerals do not occur in ore as these gold-bearing phases are not amenable to heap leaching.

In oxidised rocks, gold occurs natively in fractures associated with iron oxide. Rocks within the Marigold mine area are oxidised to a maximum depth of approximately 450 m. The redox boundary is not consistent throughout the property and is substantially influenced by lithology. Shale, argillite, and siltstone units are frequently unoxidised adjacent to pervasively oxidised quartzite horizons.

A silver and base metal mineralizing event at Marigold includes a mineral association of chalcopyrite, argentiferous tennantite, galena, and sphalerite. The absolute age of this event is unclear, although it may be related to late Cretaceous magmatism in the district.

Alteration of rocks includes silicification along mineralizing structures and decalcification of carbonate horizons (primarily in the Antler sequence). Argillic alteration of quartz monzonite intrusive bodies occurs in fault zones and areas of high hydrothermal fluid flow (Fithian, 2015). The intensity of alteration decreases towards the core of the intrusions.

Studies have demonstrated a spatial correlation between gold mineralised rock and increased white mica crystallinity index (Kester, 2015). There is evidence for large volumes of quartz precipitation within and outboard of gold mineralised zones, including jasperoid bodies, cryptic silicification, and quartz vein breccias.

Marigold uses standard open pit mining methods at a LOM sustained mining rate of approximately 250,000 tpd. The mine conducts conventional drilling and blasting activities with a free face trim row blast to ensure stable wall rock conditions. Electronic detonators are used to control the timing of the blasthole detonation.

Drilling and blasting occurs on 15.2 m benches. One grade control sample is taken from each blasthole with the sub-drilling excluded. Mining occurs on 15.2 m benches when prestripping waste or mining ore areas with the P&H electric shovel. 7.6 m benches are mined using the smaller hydraulic shovels to minimise the dilution that would otherwise occur from dozing a 15.2 m high face to these smaller shovels Blasting is done with an ammonium nitrate and fuel oil (ANFO) blend and a sensitised ANFO emulsion. The ore control mark-out procedure includes blast movement analysis for 90% of ore production blasts.

The Marigold geotechnical management plan (GMP) includes highwall monitoring using three radar systems which provide full coverage for the (largest) Mackay pit, or can be deployed in smaller pits, if required. Routine monitoring of waste dumps, leach pads and inactive pits using INSAR data is performed by a third party on a monthly basis.

Loading operations are currently performed using one electric shovel and three hydraulic shovels. Waste and ore haulage is performed with a fleet of 300 t primary haul trucks.

Historically, Marigold pits have been designed with inter-ramp angles (IRAs) at 48° to 50°. The primary rock, a quartzite in the Valmy Formation, dips in a westerly direction at 40° to 70°. The east highwall, which has rock dipping out of the face, is designed at 48° to 50°. The west highwall, which has rock dipping favourably into the face, is designed at 50°. Achieved IRAs range between 48° and 50°. Because many of the interim and final pit walls are within the Valmy Formation, the steeper 50° angle is thought to be achievable for pit designs within the same rock unit (Knight Piésold, 2014). Call & Nicholas, Inc. (CNI) consultants perform an annual audit of activities and provide guidance if any issues arise with slope stability. A 2019 CNI Slope Stability Study of the Red Dot design based on the results of a 2018 geotechnical core drilling program recommended flattening the slope of the west wall of Red Dot to 47° to 49° and the east wall to 45°. The results of this study were used to inform the ultimate pit design for Mackay / Red Dot pit.

The Marigold geotechnical management plan (GMP) was implemented in 2011. The GMP is continually updated with information as mining progresses.

Mining is scheduled 24 hours per day, 363 days per year on a rotation of two 12-hour shifts. The current mine plan provides 17 years of operational life, including 11 years of active mining followed by 6 years of processing the heap leach pad.

In order to meet near-term LOM production rates, the existing shovel fleet of four units will be maintained by deferring retirement of the smaller EX5500 hydraulic shovel to 2023. The haul fleet averages 25 x 300 t class units and will peak at 28 trucks. Short term variations in mine fleet requirements are managed by delaying retirement of older units when they are scheduled to be replaced. The average sustained mining rate is 90.4 Mtpa over the first 10 years of the remaining 11 year mining life while ore delivery to the ROM leach pad is at an average annual rate of 19.7 Mt. Average payable gold production over the 10 years of full production is approximately 222,000 ounces per year. In general, ore will be mined on 15.2 m benches.

The mineralised zones are structurally controlled and strike in a generally northern direction. They vary in width throughout the Property from one metre or less up to 40 m long and 49 m wide. In the LOM model, there is no dilution or mining loss added to the Mineral Reserves for planning and scheduling.

The Marigold processing facilities combine industry standard run-of-mine (ROM) heap leaching, carbon adsorption, carbon desorption and electro-winning circuits to produce a final precious metal (doré) product.

The Marigold heap leach and gold recovery circuit is typical in the industry for treating solutions containing gold cyanide.

Ore processing is undertaken via stacking and leaching on a ROM heap leach pad. ROM ore is delivered to the leach pad by haulage truck and stacked in 6.1 to 12.2 m lifts. Pebble lime is added to the haulage trucks from a storage silo to control pH prior to dumping. Fresh ore is ripped and cross-ripped prior to commencement of leaching. The available pad area is divided into manageable cells for inventory and irrigation control. These cells provide control of irrigation duration and time between lifts to manage future ore placement.

A series of header and sub header lines distribute the barren solution to the pad with applic ........