Summary:
The Golden Mile deposit occurs in the Kalgoorlie Terrane within the southern portion of the NNW trending Archaean Norseman-Wiluna Greenstone Belt. The greenstone belt has been multiply deformed and regionally metamorphosed to grades varying from lower greenschist to amphibolite grade.
The stratigraphy covered by the Fimiston Project tenements consists of a basal ultramafic unit called the Hannan Lake Serpentinite. This ultramafic unit is overlain successively by the high magnesian Devon Consols Basalt, Kapai Slate, tholeiitic Paringa Basalt and the Black Flag sediments. Differentiated zones of dolerite and gabbro texture occur within the mafic sequence. The Golden Mile Dolerite, hosting the bulk of the Golden Mile and Mount Charlotte gold mineralisation, is a strongly differentiated layered gabbro, approximately 700m in thickness. The Golden Mile Dolerite is situated conformably between the Paringa Basalt and the Black Flag sediments. This entire stratigraphic sequence is intruded by numerous porphyry dykes of intermediate to felsic composition.
The Fimiston style gold mineralisation, which accounts for the bulk of the economic gold ore of the Golden Mile deposit, is hosted dominantly in the Golden Mile Dolerite with lesser mineralisation hosted in the Paringa Basalt. The Golden Mile deposit is an intensely mineralised Archaean shear zone system developed between the Adelaide and Golden Pike faults. Gold mineralisation occurs over a north-south strike length of 4,250m, a width of 1,850m and has been historically mined to a depth of about 1,200m underground.
The mineralisation consists of numerous narrow, generally 1-2m wide, but locally up to 20m wide, vertically and laterally extensive lodes, up to 1,200m vertical and over 1,000m along strike length. The Fimiston lodes occur in three principle orientations: Main 140o/80oW, Caunter 115o/55oW to 80oW and Cross Lodes 050o/90o to 80oN-S. The deposit lies within a regional syncline and is divided into the Eastern Lode System and the Western Lode System, divided by the steeply dipping reverse Golden Mile Fault. The Main and Caunter lodes are the dominant sets in both the Western and Eastern Lode Systems. The lodes in the Western Lode System display good lateral and vertical continuity whereas lodes in the Eastern Lode System are segmented by numerous steep reverse faults. The lodes in the Western and Eastern Lode System form a funnel shaped array which is sub-vertical in the Western Lode System and steeply west dipping in the Eastern Lode System.
The Fimiston resource extends 4.3km’s north-south, 1.5km’s east-west, and 1.8km’s vertical.
Mineralised domains are categorised by overall geometry and divided into Main, Caunter, Oblique, and Cross lodes. Main lodes are predominantly sub-vertical with a northsouth strike, Caunter lodes strike north-north-west dipping approximately 65° west, and Cross lodes strike east-west with a sub-vertical dip. Oblique lodes are less common but are effectively conjugate to the Caunter lodes.
The Mt Charlotte style gold mineralisation is hosted within the Golden Mile Dolerite and is predominantly associated with pyrite in carbonate alteration haloes around quartz veins, with a minor proportion as relatively coarse free gold within the veins, commonly close to their margins. The veins vary in width from a few millimetres to a maximum of about two metres but are commonly between two centimetres and 50 cm wide. The vein spacing varies from 20 cm to tens of metres but is typically from 50 cm to two metres in areas mined as ore. Quartz is the dominant vein-fill mineral; accessory vein minerals include calcite, ankerite, scheelite, pyrite, pyrrhotite, and gold.
The Hidden Secret style gold mineralisation is hosted within the Williamstown Dolerite at the contact with the Kapai Slate and Devon Consols Basalt and spatially associated with a porphyritic intrusion and the Towns Fault. Gold is hosted in deformed a quartz vein 2-20cm wide. Vein minerals include pyrite, telluride, silica, carbonate and fuchsite.
Mineralisation and grade continuity is predominantly affected by rock type, structural setting within the stratigraphy and mineralisation style.
Mineralisation styles are a combination of:
• Mt Charlotte style stockwork veining (variable density, N plunging qtz veining with gold associated with quartz-Ankerite-Pyrite-Siderite vein halos).
• Fimiston lode style veining (steep dipping N-S qtz veining with Ankerite-Sericite-Siderite-Au/Ag Telluride halos).
• Hidden Secret lode style veining (moderately SE dipping quartz vein with pyrite, telluride, silica, carbonate, and fuchsite).
• Dispersed mineralisation within the oxide and transitional regolith profiles.
Rock type, structural deformation and vein density plays a role in the style, continuity, and stratigraphic positioning of mineralisation within the Golden Mile Dolerite, Paringa Basalt, Williamstown dolerite and Devon Consuls basalt as well as local variations within these units.
Fairplay is hosted dominantly within the Williamstown Dolerite and Paringa Basalt and is spatially associated with the Acre Fault. Thin shear and stockwork veins contain quartz, pyrite, telluride, carbonate, fuchsite, roscoelite, and gold. Lode style orebodies at Mt Ferrum are considered Fimiston-style gold, and consist of shear zones with fine disseminated pyrite, quartz carbonate veins and broad breccia zones.
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.
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.
The Mt Charlotte Project covers an area of 2.6km N-S x 2km E-W x 1.7km Vertical. Within the project area on a deposit scale the project can be broken into.
Mt Ferrum (600mN x 600mE x 600mZ) which is a combination of Fimiston style subvertical lodes within the Paringa Basalt and Charlotte style stockworks within and on the contacts of the Williamstown Dolerite.
Hidden Secret/Belgravia (700mN x 300mE x 600mZ) is a moderately west dipping, south plunging lode style orebody with overprinting stockwork style mineralisation associated with the Little Wonder deposit within the Dev Consuls Basalt.
Kal East (600mN x 300mE x 400mZ) is a Fimiston style lode deposit hosted within the Williamstown dolerite overprinted by stockwork style mineralisation.
Mt Charlotte Mine (1.2kmN x 300mE x 1.7kmZ) is a subvertical north plunging stockwork style deposit hosted within the Golden Mile Dolerite U8 layer. Mineralisation is bound to the north by the Charlotte fault and south by the Lord Nelson fault.