Dart Mining (ASX: DTM) says it has confirmed the mineral system model at its Rushworth gold holdings in Victoria, with sulphides showing up in phase-two diamond drilling results as key indicators for high-grade structures.
One diamond hole at the company’s Star of the West target intercepted 0.24m at 8.8 grams per tonne gold from 56.2m downhole in quartz within a broad zone of sulphide mineralisation that cored through 7.1m of disseminated sulphides going 0.75g/t from 50.8m. That intercept also bored through 0.42m at 3g/t gold in a sandstone unit carrying abundant pyrite from 50.58m.
Additionally, the same hole also jagged two deeper, higher-grade intercepts of 0.3m going 2.87g/t gold and 0.3m at 1.45g/t in a 3.6m gold-in-sulphide zone running 0.44g/t from 161.8m that includes pyrite, cubic pyrrhotite and acicular arsenopyrite.
Dart notes that the dominance of acicular arsenopyrite and fine-grained pyrite are recognised characteristics of sulphide mineralisation at Agnico Eagle’s nearby Fosterville Gold Mine, about 25km east of Bendigo.
Management says the association of high-grade gold occurrences as part of the internal structures of broad envelopes of lower-grade gold and sulphide mineralisation at Star of the West has been an important revelation and takeaway from the drilling program.
Receiving high-grade results from reef structures within zones of gold-bearing sulphide mineralisation is a key step to refining our mineral systems model of the project. Today’s results confirm our optimism surrounding the results from a potential stacked reef system at Growlers Hill and add a second prospective target zone within 500m at the Star of the West prospect.
Dart Mining chairman James Chirnside
The Star of the West holes tested the Shellback Reef structure, an east-west trending, steeply south-dipping fault between the target and the Growlers Hill fault – an eastward distance of about 500m.
At Growlers Hill, follow-up sampling of a previous diamond hole has given up a 0.55m intercept going 7.48g/t gold from just 23.1m downhole, while further geological interpretation has highlighted the possible existence of stacked sub-parallel saddle reefs. The interpretation is supported by old geological sketch maps of the mine area that depict mining of mineralised quartz bodies arrayed as a series of north-south-oriented, lens-like structures.
Additionally, the new interpretation suggests that the stacked reefs may plunge southwards, meaning that two of the drillholes could have drilled above the most westward of the mineralised structures. The new understandings arising from the drilling program will assist Dart in getting to grips with the more complex structural architecture at Rushworth than exists in some other parts of the Victorian goldfields.
The company’s principal targets have been the mineralisation plumbing systems offered by key structural intersections, most notably where the planes of bedding-parallel thrust faults intersect big north-south structures.
Dart’s key target structures have been compression-initiated, thrust-hosted quartz veins, north-south faults cutting east-west bedding and saddle reefs – probably the most familiar of the structures reported in accounts of historical mining, especially in connection with Bendigo.
With a new level of comprehension under its belt, Dart is looking at a phase-three diamond drilling campaign after it sees what further information the results from two holes at Star of the West have to offer.
Meanwhile, the company is pressing on with drilling at the Phoenix Reef, which has been the focus not only of historic mining, but also more recent exploration. It is targeting repeat thrust faults at depth below the historic mining and existing exploration.
The company has also had its Star of the West tenement exploration licence application accepted, with the application now progressing through advertising and native title negotiations. The ground was formerly held under a mining licence by a third party.
Management says it is “just getting started”, with the Growlers Hill and Star of the West prospects just the first two targets to be drilled from a long list and it is happy with rig penetration rates and the overall rate of progress.
Trialling its new structural and sulphide indicators that point to high-grade gold zones should be an interesting procedure for Dart. It’s a bit like finding a mysterious old key that might just belong to a long-locked and rather mysterious safe hidden away in the basement.
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