Mineralisation and Prospectivity
The Red Mountain Project consists of two known prospects of VMS mineralisation;
Dry Creek and West Tundra Flats. These are the most prominent occurrences in the Bonnifield District and can be considered a single VMS camp.
At the Dry Creek Prospect, two horizons containing massive sulphide mineralisation have been found. The DC North Horizon occurs near the upper part of the Mystic Creek and hosts the majority of mineralisation defined to-date (Figure One). The DC South Horizon occurs lower in the section. Both zones dip steeply north.
The DC North Horizon can be traced for 4,500 metres. The central 1,400 metres (on the flanks of Red Mountain) host the Fosters and Discovery deposits.
At Discovery, mineralisation occurs as massive to semi-massive zinc-lead-silver rich sulphides within, and at the base of, an aphanitic, intensely quartz-sericite-pyrite altered, siliceous rock termed the “mottled meta-rhyolite”. This mineralization is commonly associated with overlying stringer and disseminated chalcopyrite-pyrite mineralisation assaying up to 4.3m @ 6.8% Cu (DC97-14).
At Fosters, mineralisation is hosted by a distinctive brown pyritic mudstone unit in the hangingwall of, and along strike from, the “mottled meta-rhyolite”. The mineralisation comprises disseminations and wispy laminations of sulphides and zones of semi-massive to massive sulphides. Sulphides include pyrite, sphalerite, galena and chalcopyrite. Precious metals are typically enriched, especially in the footwall portion of the mineralisation.
Mineralisation at both Fosters and Discovery pinches and swells along strike and down-dip, as is typical of VMS deposits. True width intersections are up to 40 metres at Fosters where there is evidence of growth faults, which typically act as feeders to the VMS system and can be important controls in localising thick ore accumulations. Identifying and targeting such growth faults along the VMS horizon will be an important part of exploration to expand and discover new deposits.
Drill intersection highlights for the both Fosters and Discovery deposits are presented in Table 3.
Additional observations for enhanced exploration prospectivity at Dry Creek include:
The distribution of massive sulphides as a series of stacked lenses (in part en-echelon) that favour further prospectivity in the hangingwall (eastwards) and footwall (westwards) along strike as well as down dip.
The presence of minor quartz porphyritic felsic intrusions within the growth fault could indicate the presence of a larger felsic intrusion in the footwall. VMS camp prospectivity is enhanced by the presence of large sub-volcanic intrusions thought to be an important heat source in contributing metals and fluid flow to create large VMS camps. In addition, such near paleo-surface intrusions commonly mark discharge structures that may lead to additional deposits.
The copper zone at Discovery indicates significant accumulation of sulphides in that area and therefore prospectivity for higher grades could be enhanced to the northeast rather than southwest.
In general, zinc grade increases with depth offering down-dip potential.
Multi-element geochemical analysis of mineralisation and intrusions enriched in fluorite supports the regional observations for a shallow water setting. This enhances prospectivity for high grade gold deposits, particularly in the hangingwall argillite, exhalite and oxidised felsic units. Earlier explorers may not have recognised the gold potential or sampled appropriately since gold mineralisation is often not associated with base metal sulphides.
Figure One: Dry Creek Prospect showing the surface projection of massive sulphide mineralisation and all drill hole traces on the DGGS geology map (sourced from the DGGS Preliminary Interpretative Report 2016-3 by Freeman et al., 2016).
Historical geological and geochemical data is less comprehensive than that available for Dry Creek; however, the following observations for enhanced exploration prospectivity at West Tundra Flats can be made:
Similar gold potential to Dry Creek in the hangingwall sediments and eastern margin of the area.
Zinc-rich intervals appear clustered towards the southwest presenting down-dip potential (with some indications of increased copper supporting that vector).
Broad-spaced drilling provides upside within the extent of mineralisation for the targeting of growth faults that may locally control thick accumulations of ore.