The Steam Engine Gold Deposit comprises at least two sub-parallel gold-bearing lodes, referred to as the Steam Engine Lode and the Eastern Ridge Lode, which are separated by about 600m. A third and potentially large zone of sub-parallel mineralisation (Dinner Creek Lode) exists a further 900m to the east of Eastern Ridge Lode and an area of gold mineralisation comprising multiple lodes (Southern Zone) is located between and to the south of the Steam Engine and Eastern Ridge lodes. The mineralisation is developed within north-north-east trending, west dipping lodes and are essentially mineralised shear zones comprising pyrite-quartz-muscovite-carbonate schist within amphibolite, metasediment and/or metatonalite. The gold-bearing lode zones are located within a shear zone and show strong continuity and a persistent dip to the west (the Steam Engine Lode typically dips around 50° to 60° to the west and the Eastern Ridge Lode typically dips at about 40° to 50° to the west).
Mineral Resource Estimate / Resource Drilling Program
During 2020, the Steam Engine Gold Deposit’s Mineral Resource Estimate was upgraded by 11% prior to the commencement of 2020 drilling programs. The revision of the Mineral Resource resulted in a JORC (2012) Indicated and Inferred Mineral Resource of 1.27 million tonnes at 2.3 g/t gold (0.5 g/t cut-off).
In March 2021, Superior announced a revised Mineral Resource estimate incorporating results from the 2020 drilling programs, which were completed by December 2020.
The revised JORC 2012 Mineral Resource estimate comprises the following:
1.73 million tonnes @ 2.2 g/t Au (122,000 ounces):
Steam Engine, Eastern Ridge and Southern Zone lodes over soil gold anomalies and conceptual corridors for high-grade ore shoots
2021 Scoping Study
A Scoping Study released during April 2021 indicated a robust financial and technical case for a near-term, low CAPEX, open pit mining and toll treatment operation.
The base case contemplated the mining of 65% of the March 2021 Mineral Resource to recover 70,000 ounces and assumed a gold price A$2,200 (US$1,900 @ 0.76 AUD/USD). Key outcomes are summarised in Table 1.
High-grade ore shoot system identified
Results from the 2020 Stage 1 and Stage 2 drilling programs identified at least two high grade ore shoot systems carrying up to bonanza grade gold mineralisation of 184 g/t gold. These high grade ore shoots are highly significant for their potential to substantially increase the total ounces and the overall project economics. Exploration in 2021 will target down-dip and where appropriate, lateral extensions to the high grade ore shoots.
At a larger scale, the Company also recognises the potential for the existence of an extensive high-grade ore shoot system developed at depth and related to the mineralised lode structures that are observed at surface. The currently identified near-surface mineralisation is significant and is an indication of a potentially substantial and extensively developed ore shoot system at depth. The Company is assessing the potential to apply a range of geophysical methods for the purpose of identifying larger zones of mineralisation for follow up with drill testing.
Soil geochemistry – evidence of a greater area of mineralisation
The Mineral Resource, as it currently stands, has been developed to shallow depths over only 30 percent of the 2.5 kilometre strike length of the historically mapped outcropping gold lodes (2.5km strike length does not include Dinner Creek Lode). Soil geochemical surveys over the project area and nearby surrounds indicate a significantly greater area of potential sub-surface gold mineralisation. Further programs of exploratory drilling to extend the mineralisation envelope will continue during 2021.
Potential third lode zone
Reconnaissance rock chip sampling of a 1.2 kilometre-length gossanous alteration zone located 900m east of the Eastern Ridge Lode returned up to 7.6 g/t gold. This zone of alteration parallels the Steam Engine and Eastern Ridge lodes and may represent a new, third gold lode zone. This lode zone is referred to as the Dinner Creek Lode. Recent geological mapping of the Dinner Creek Lode confirmed that the alteration zone shows alteration characteristics that resemble the Steam Engine Lode mineralisation and has a strike length of at least 2 kilometres.
Spectacular drilling results – January 2021
In January 2021, Superior announced the first batch of assays from Stage 2 drilling, including some spectacular results of up to 184 g/t Au (see ASX announcement 18 January 2021). The very high-grade results are interpreted to lie within one of at least two very high grade ore shoots. These high-grade ore shoots have the potential to significantly upgrade the Resource. Part of the 2021 drilling campaign will target the extensions to these ore shoots and also explore for additional high-grade shoots.
A Feasibility Study incorporating results from the 2020 drilling is underway for 2021. The Feasibility Study is currently based on the mining and processing assumptions made under the Scoping Study (i.e. the mining of 65% of the March 2021 Mineral Resource to recover 70,000 ounces with a toll treatment processing option). The basis of the Feasibility Study may be upgraded, depending on results from continued drilling programs during 2021.