Fimiston Open Pit
The mineralising event at the Golden Mile led to geochemical enrichment of silica, carbonate, sulphur, potassium, arsenic, tellurium, mercury, lead, vanadium and boron. This enrichment is concentrated on the main gold bearing lode systems with decreasing levels of enrichment occurring further from the ore system. Approximately 80% of the rock mined from the Fimiston Open Pit is Golden Mile Dolerite, with the remaining rock composed of Paringa Basalt (14%) and sediments belonging to the Black Flag Beds (4%) (Also referred to as Black Flag or Black Flag Shale).

Mt Percy
The main rock types at Mt Percy are the Hannans Lake Serpentinite, Devon Consols Basalt, Kapai Slate, and Williamstown Dolerite. The Hannans Lake Serpentinite is the major rock type in the Sir John and Mystery Open Pits and is a minor rock type in the Union Club Open Pit. All four lithologies are well exposed in the Union Club and Sir John (now backfilled) Open Pits and are intruded by felsic porphyries. Mineralisation is associated with quartz veining (Mt Charlotte style mineralisation) and brecciated lodes with disseminated sulphides associated with felsic porphyries (Fimiston style mineralisation). The deposits at Mt Percy were mantled by lateritic duricrusts that formed local topographic highs. Mining at the Mt Percy Open Pits mainly focused on mineralisation in the saprolite and lateritic residuum and did not penetrate deeply into fresh rock.

Mt Charlotte
The Mt Charlotte Operational Area is located between the Goldfields Highway and Williamstown residential area.

At the Mt Charlotte deposit stratigraphy consists of the basal Hannans Lake Serpentinite, overlain successively by the Devon Consols Basalt, Kapai Slate, Paringa Basalt, Golden Mile Dolerite and Black Flag Beds. The Golden Mile Dolerite is the dominant lithology at the Mt Charlotte operations. The Black Flag Beds have historically been intersected by drives at Mt Charlotte, but this is a minor lithology within the mine.

Gold mineralisation at Mt Charlotte is stockwork style: an intersecting mesh of conjugate quartz veins that preferentially form within Unit 8 of the Golden Mile Dolerite, due to this stratigraphic control the veins form a steeply plunging pipe-like ore body. The veins are composed of coarse quartz-carbonate with minor scheelite, tourmaline and albite. Extensive wall rock alteration occurs around the veins, the alteration assemblage is quartz-albite-sericite-sideriteankerite-pyrite.

Mt Ferrum is a shear-hosted Fimiston-style lode located 600m east of the Sam Pearce decline of the Mt Charlotte mine. Mineralisation is hosted within Paringa Basalt and strikes NNE. Infill resource definition drilling has identified a series of hangingwall and footwall structures, and stockwork mineralisation in Williamstown Dolerite to the west of the main lode. Mineralisation is thought to be controlled by the structural architecture and is the subject of a geological review currently underway. [2020, AR, p.20]

Kal East is a narrow, high-grade Fimiston-style lode lying 250m to the east of existing infrastructure at the Mt Charlotte mine. Infill resource definition drilling has identified more complexity than expected, defining a series of hangingwall and footwall structures. Mineralisation is hosted primarily within Williamstown Dolerite and the highest grade is constrained within a steeply dipping southerly plunging shoot. Internal zones within the Williamstown Dolerite are important in controlling the distribution of gold. [2020, AR, p.20]

Belgravia is a series of mineralised lodes lying 100m north of existing infrastructure at the Mt Charlotte mine. Mineralisation is hosted within pillowed and variolitic Devon Consols Basalt in proximity to the Hannans Lake Serpentinite, the contact of which is intruded by felsic porphyritic rocks. Infill resource definition drilling has identified eight separate NNW- striking lodes with en échelon geometry. The lodes are overprinted by stockwork mineralisation, with veins dipping to the north similar to the Mt Charlotte-style stockwork orientations. [2020, AR, p.20]

The KCGM Goldfield is part of the Norseman-Wiluna Belt, a greenstone belt consisting of volcanic and sedimentary rocks and surrounded by extensive granite.

The main host rock for mineralisation in the Kalgoorlie district is the Golden Mile Dolerite, the largest of the dolerites in the area. There are two main styles of mineralisation. The Fimiston Style consists of classic Golden Mile lodes with abundant sulphides and tellurides.

The highest gold grades are typically associated with gold tellurides and alteration minerals with high vanadium contents.

The Fimiston Open Pit (the “Super Pit”)
Mining the Pit is a carefully planned sequence involving cooperation across a wide range of departments, specialist teams and partner contractors.

No other open pit operation in the world has as many voids as the Fimiston Open Pit. A century of mining on the Golden Mile left over 3,500 kilometres of historical underground workings stretching the length of the Mile and extending more than 1,200 metres below the surface.

Once the old workings have been marked, they are drilled to confirm their boundaries. The risk of working near voids has prompted KCGM, with partner contractor Ausdrill, to develop the long-reach drill and a remote drill to better and more safely navigate voids.

Blasting is usually conducted three or four times a week between 7am and 6pm. Blast times are planned around production requirements, which usually require blasting at 1pm or 5pm, but this can vary.

The shovels and trucks in Load and Haul operate 24 hours a day, 365 days of the year, moving the ore and waste rock from the Pit floor to the next step in the gold recovery process – the Primary Crusher. The WENCO Production Monitoring Control System coordinates the dig plan of the blast with the schedule supplied by the mining planners in the Mine Technical Services Department to create an operating manual for the Pit for that day.

Mt Charlotte Underground Mine
Mining at Mt Charlotte commenced in 1893, however, large-scale mining did not commence until 1962. Operations at Mt Charlotte initially centred on the Reward Shaft and the Man & Supply Shaft (decommissioned). The Cassidy Shaft and associated headframe were developed in the early 1980s to access deep ore, with the Cassidy headframe still currently in place. Mt Charlotte is currently the only active underground operation managed by KCGM and is scheduled to continue production until 2024. [2019, Mine Closure Plan, p.124]

The main historical method of mining at Mt Charlotte was open stoping. Typically, large stable open stopes were mined and then the rib/crown pillars were mass blasted, with waste rock fill above cascading onto the broken ore. Currently stoping under rock fill (SURF) is used to recover remnant resources. Extraction is from drawpoints until waste rock dilution becomes excessive. Ore from Mt Charlotte is transported to the Fimiston Plant via the Sam Pearce Decline. The underground stopes are backfilled with either mine waste or crushed rock for stability purposes. Fill is delivered through the Glory Hole. Development of the Hidden Secret deposit located 400m east of Mt Charlotte commenced during 2016. Planned stope extraction will utilise the modified Avoca method. [2019, Mine Closure Plan, p.124]

The Cassidy Headframe and shaft at Mt Charlotte are maintained as a primary form of egress, while the Sam Pearce Decline acts as the primary access; several other smaller vent rises assist with underground ventilation. The Cassidy Headframe is the last headframe remaining on the Golden Mile and has been identified by the community for potential retention for heritage and tourism purposes. The associated winders and winder house may also be retained. [2019, Mine Closure Plan, p.126]

Overland Conveyor
A conveyor previously used to transport ore has been reversed and is now used to convey waste rock from the Fimiston Operational Area to the Glory Hole for underground fill. The conveyor passes under Boorara Road and over Williamstown Road. An unsealed access road is in place along the length of the conveyor. [2019, Mine Closure Plan, p.126]

The Mt Charlotte Underground Mine currently produces ore at the rate of 1.15M tonnes per annum (tpa) which is transported directly to the ROM at the Fimiston Plant via the Sam Pearce decline located within the Fimiston Open Pit north eastern wall. Waste rock produced during mining at Mt Charlotte is not brought to the surface, instead it is used to backfill underground voids. Small volumes of waste rock from the Fimiston Open Pit are crushed at Fimiston before being conveyed to the ‘Glory Hole’ Pit to be used for backfilling of underground stopes at Mt Charlotte. [2019, Mine Closure Plan, p.34]

The ore from the Fimiston Open Pit and Mt Charlotte Underground Mine is processed at KCGM’s Fimiston and Gidji Processing Plants.

The process of extracting gold from sulphide ore begins when the trucks deliver the ore from the blast site to the ROM (run of mine) pad at the Fimiston Plant. Here the crusher reduces it to chunks of rock about the size of a fist. The ore is then ground into very fine particles less than one-fifth of one millimetre in diameter in large rotating SAG (Semi Autogenous Grinding) and Ball Mills which look like huge steel drums.

Water is added to the process, creating mud-like slurry which is pumped to large tanks called flotation cells. Air is added to the bottom of the agitating flotation cells and the resulting froth which gathers at the top contains nearly all the gold. This combination of free gold, gold-bearing pyrite and telluride particles is known as sulphide concentrate.

The concentrate is dried by filtering before it ........