Summary:
Production centres assessed within the DFS include:
• Laverton: Fish Underground (existing operation), Lord Byron Open Pit, Cork Tree Well Open Pit, Alpha Underground.
• Menzies: Yunndaga Underground, Lady Shenton Open Pit, Aspacia Open Pit.
The Menzies Gold Project (MGP) is located along the western margin of the Menzies greenstone belt and, apart from the Lady Irene prospect, within a broad (2km-5km wide) zone of intense ductile deformation often referred to as the Menzies Shear Zone. This broad highly deformed shear zone is probably the northern continuation of the Bardoc Tectonic Zone and is a major crustal feature of the Eastern Goldfields. The gold deposits within the MGP and those further south (e.g. at Goongarrie and Bardoc) have many similar characteristics.
Gold mineralisation is widespread and occurring within a broad range of host rocks in 3 general styles:
1. Single, larger quartz veins (i.e. "quartz reefs"). These tend to contain only small amounts of sulphides, but the vein selvages are commonly more sulphidic. These veins vary from about 10cm up to about 2m thickness, 20m to about 200m in length and typically pinch and swell repeatedly along strike and down-dip.
2. Close-spaced sheeted quartz vein zones. These are comprised of multiple, typically close-spaced quartz veins or veinlets in a schistose matrix, constituting a distinct shear zone that may be concordant with lithological boundaries or cross-cutting 2 or more rock types. These mineralised shear zones appear as distinctly banded siliceous, sulphidic rocks and are typically mylonitic. These sheeted vein zones are commonly from 1m to 3m thick and up to a few hundred metres in length.
3. Sulphidic biotitic shear zones. These are comprised of schist containing variable amounts of brown-to-bronze biotite and small thin irregular quartz veinlets ("stringers"), along with diffuse silica-flooding and disseminated sulphides. These shear zones are usually about 1m to 3m thick and can be a few hundred metres in length.
Lady Shenton System (LSS) and Yunndaga
Mineralisation is Archean mesothermal lode gold style. Gold mineralisation is hosted in multiple sub parallel gold mineralised shear/fracture zones either within a sequence of metamorphosed mafic amphibolites or at the contact between mafic amphibolite and ultramafic or metamorphosed sediments. Stratigraphy strikes NW and dip SW. Most of the mineralisation is close to sub parallel to the stratigraphy and dip ~40° to 50° SW, plunging south. The weathering intensity varies across the area, and each deposit, from 10m vertical depth around Selkirk to around 60m at Lady Harriet.
Jasper Hills (Lord Byron & Fish) deposits are located within the Irwin Hills area that consists of a small, layered greenstone belt surrounded by predominantly granitic rocks of the Yilgarn Block. The layered succession consists of metamorphosed mafic, ultramafic and sedimentary rocks with minor pyroclastic rocks. The sequence is thought to face east forming the eastern limb of the Elora Anticline. A regional NNW-SSE trending steeply east dipping schistosity has developed, and major faults also follow this trend. Metamorphic grades range from greenschist to amphibolite facies with higher grades at the edges of the greenstone with granitoid plutons. Much of the project area has extensive aeolian and alluvial cover and outcrop is poor. The Lord Byron deposit is hosted within a thick sequence of amphibolite and interbedded chert/BIF. Specific zones of mineralisation have been defined; supergene in the south, the main NW trending shear hosted lodes, and multiple BIF hosted lodes through the north and south. The Fish deposit is an orogenic style Archaean lode gold deposit hosted by a series of narrow quartz-magnetite-amphibole BIFs with coarse granoblastic texture, interbedded with amphibolite derived from basalt and dolerite.
The Alpha gold deposit is hosted within a NW striking shear that subcrops in the SE. The geology at Alpha is comprised of foliated basalt and mafic schist. The upper tertiary surface can be up to 10m thick. It includes recently deposited soil, and hardpan up to 4m thick. Beneath the surface layer is a zone of saprolite which has been described as soft, machine-rippable and indurated in places. Between 40m and 80m depth the saprolite is more cohesive and firmer. The footwall (west wall) may be less oxidized than the hanging wall. The basement within the project area is comprised of mafic volcanic rocks with interleaved narrow units of ultramafic rocks, some dolerite, and interflow volcanogenic sediments, consistent with Association 1 (tholeiitic basalt, high magnesian basalt and ultramafic units, relatively minor interflow sediment and laterally extensive banded iron formation (BIF)).
Cork Tree Well (CTW) deposit within the Duketon Greenstone Belt lies along the western limb of the Erlistoun synclinal structure. The sequence includes mafic volcanic lavas, tuffs, and tuffaceous sediments with minor interflow graphitic shales and banded iron formation. The gold mineralisation in the Cork Tree pits is associated with steep east dipping sedimentary units, particularly the chert horizon located on the footwall of the sediment sequence. The mine area consists of footwall, high magnesium basalts altered to chlorite schist overlain by graphitic shales containing chert and banded iron beds and younger hanging wall tholeiitic pillow basalts.
Dimensions
• The Aspacia block model dimensions are 704m N-S, 752m E-W and 216m vertical. The actual mineralisation can vary from 0.1m up to a maximum of 12m thick in specific domains and extends to a vertical depth below surface of 190m.
• The CTW South block model dimensions are 3,200m N-S, 1,200m E-W and 350m vertical. The actual mineralisation is from 1m to 20m thick and extends to a vertical depth of 300m below surface.
• The LSS deposits consist of three main lodes with strike extents varying between 280m to 500m along a NW-SE strike. The average thickness of the lodes range between 3m to 10m thick. The lodes have been modelled to 320m vertical depth and generally dip to the SW.
• The Lord Byron mineralized lodes extend over a continuous NW strike length of 820m from 6,777,180mN to 6,778,000mN. The lodes are confined within an EW extent of 720m from 503,780mE to 504,500mE. Mineralisation has been modelled from surface at 440mRL to a vertical depth 305m to 135mRL.
• The Fish resource area extends over a continuous strike length of 405m from 6,780,860mN to 6,781,265mN. The multiple mineralised lodes are confined within an EW extent of 215m from 511,250mE to 511,465mE. Mineralisation has been modelled from surface at 465mRL to a vertical depth 315m to 150mRL.
• The Alpha mineralisation extends along a NW strike length of 1.4km from 6,823,080mN to 6,822,340mN. The lodes are confined within an EW extent of 1.24km extending from 472,150mE to 473,390mE. Mineralisation has been modelled from surface at 490mRL to a vertical depth of 285m to 205mRL.
• The Yunndaga mineralisation strikes at 320° over a continuous length of 1.2km and is contained within an area defined from 6,706,960mN to 6,707,930mN and within an EW extent from 311,200mE to 312,025mE. Mineralisation has been modelled from surface at 420mRL to a vertical depth 334m to 86mRL.