Summary:
Production centres assessed within the DFS include Menzies (Lady Shenton Open Pit, Ancillary open pits proximal to Lady Shenton - Aspacia, Lady Harriet, Link Zone, Yunndaga - Underground) and Laverton (Lord Byron - Open Pit, Cork Tree Well - Open Pit, Alpha - Underground).
Menzies Geology
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. The Lady Irene prospect is west of the Menzies Shear Zone and thus within the Ora Banda domain, in a similar geological setting to the Sand Queen Gold Mine at Comet Vale, south of Menzies.
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 Mine Geology
Within the Lady Shenton pit, two subparallel lodes (Lady Shenton and Falconer) extend over a 300m strike length, and to a known depth of over 210m. During open pit mining in the mid 1990's, the Big Babe lode was exploited along with the Lady Shenton and Falconer lodes.
The Pericles deposit is made up of multiple parallel zones of moderately west dipping mineralisation which strikes approximately northeast over a distance of 700m and is likely the extension of the Lady Shenton mineralisation to the south. The majority of mineralisation is hosted in two broad amphibolite units with 2 to 10 metre thick lodes of moderately to Intense chlorite-biotite alteration with grades ranging from 0.2-100g/t Au. The main mineralised lode has two internal higher-grade east dipping shoots with average grades of 2-10g/t Au. These high grade zones are typically located on the hangingwall and footwall contacts of the lode boundaries with lower grade (1g/t Au) mineralisation between the zones.
The Stirling deposit is made up of multiple parallel zones of moderately west dipping mineralisation which strikes approximately northeast over of 500m. The majority of mineralisation is hosted within a broad amphibolite unit with 2 to 5 metre thick lodes of moderately to Intense chlorite-biotite alteration with grades ranging from 0.240 g/t Au. The main mineralised lode has an internal higher-grade shoot with grades of 2-10g/t Au commonly seen.
Laverton Geology
Cork Tree Well Mine Geology
The gold mineralisation in the exposed open pits is associated with steep east dipping sedimentary units, in particular the chert horizon located on the footwall of the sediment sequence.
Mineralisation at the Cork Tree Well mine was contained within interflow cherts and sediments which contained pervasive pyrite, pyrrhotite and magnetite mineralisation The sediments which host the gold mineralisation have been intruded by concordant porphyry sills which extend the length of the mineralised zone.
To the north of the pits the interflow sediments pinch out and are truncated by north-northeast to northeast (030° to 040°) trending shears. The mineralisation at Cork Tree North (Delta) is associated with a sheared quartz dolerite within a talc chlorite schist host. Gold is associated with quartz stringers within the quartz dolerite.
Lord Byron Mine Geology
The deposit is hosted within a thick sequence of amphibolite and interbedded chert/BIF (Banded Iron Formation) that strikes NNW-SSE in the south and NNE-SSW in the north and generally dips steeply to the east. The abrupt change in strike of the deposit is co-incident with a NW-SE trending structure named the Bicentennial Shear Zone (BSZ).
The BSZ is at least a 100m wide corridor characterised by intense alteration and ductile deformation. Within this corridor, gold mineralisation is mainly restricted to vein dominated domains which form multiple discontinuous sub-parallel lodes which dip steeply to the east. The veins are hosted in an intensely deformed and altered amphibolite, which displays a variety of fabrics ranging from massive 'porphyritic', to schistose. Lower-grade mineralisation is also hosted in primary and late volcanic breccias comprised of tabular clasts of vein quartz, coarse-grained pyrite and amphibolite.
The BIF is exposed at surface, within the project area with the maximum exposed thickness of these units being approximately 1km. Outcropping chert and 'cherty BIF is more common in the western half of the deposit, while alternating red and grey coloured magnetite and haematite BIF, or 'typical' BIF is more common in the east.
Alpha
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.
Dimensions
The Link Zone block model dimensions are 1,230m N-5, 1,250m E-W and 180m vertical. The actual mineralisation is from 1m to 8m thick and extends to a vertical depth below surface of 130m.
The Lady Shenton system block model dimensions are 1,600m N-S, 1,050m E-W and 450m vertical. The actual mineralisation is from 1m to 8m thick and extends to a vertical depth below surface of 235m at Pericles, 185m at Stirling, and 430m at Lady Shenton.
The Cork Tree Well 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 Lord Byron mineralized lodes extend over a continuous NW strike length of 760m from 6,777,240mN to 6,778,000mN. The lodes are confined within an EW extent of 690m from 503,780mE to 504,470mE.
Mineralisation has been modelled from surface at 440mRL to a vertical depth 300m to 140mRL.
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.