North Stawell Minerals (ASX:NSM) reports it has encountered ‘high-grade’ gold anomalism from a reverse circulation (RC) drilling program at the Lubeck Tip Prospect, located at the Stawell Gold Mine in Victoria.
Follow-up splitting of composite samples were completed on 7 of the 13 anomalous holes drilled during the first phase of drilling at Lubeck Tip.
Of the 7 holes re-split, 5 returned anomalous grades.
Anomalous gold at Lubeck Tip appeared as ‘broad’, ‘low-grade’ gold smears prior to composite re-splitting. Three of the holes re-split resulted in similar intercepts, with ‘wide’, ‘low-grade’ anomalies.
Two holes were converted from ‘broad’, ‘low-grade’ gold intersects into ‘narrow’, ‘discrete’, ‘high-grade’ gold intercepts.
‘High-grade’ gold mineralisation is spatially associated with the coincident magnetic and gravity anomaly that defines the Lubeck Tip target.
Current drill spacing (over 200m) has insufficiently tested the width and strike of the Lubeck geophysical anomaly with the 1m @ 5.05g/t Au intercept in NSAC0172 remaining open for 750m to the north, and completely open to the south and to the east.
Further infill drilling is planned to test the significant intersections in NSAC0172 and NSAC0173.
Geophysical inversion modelling interprets the source of the Lubeck Tip coincident magnetic and gravity anomaly (a basalt dome) to be near surface.
The company reports that drilling has only intersected Cambrian metasediments downhole. This suggests that the ‘roof’ of the ore system is intact, explaining the ‘broad’, ‘low-grade’ gold smears seen at Lubeck Tip.
The 1m @ 5.05g/t Au and 1m @ 3g/t Au intersections in NSAC0172 and NSAC0173 respectively are potentially indicative of the Central Lode structure seen at the 5Moz Stawell goldfields.
Anomalous results include grades over 0.05g/t Au, and grades are combined into composites where the adjacent assay results have an average grade greater than 0.05g/t Au. No external dilution is applied. Up to 2m of internal dilution is included in intercepts.
Stated thicknesses are downhole and unlikely to be representative of true mineralisation widths.
North Stawell Minerals CEO Russell Krause said follow up testing of composite results at Lubeck Tip represents primary greenfield success for the company’s regional AC program.
“The drilling has confirmed a geophysics target is now demonstrated to include prospective geology, alteration, structural setting, and high-grade gold linking Lubeck Tip closely to the ‘Stawell-Type’ mineralisation model”
“The drilling has confirmed a geophysics target is now demonstrated to include prospective geology, alteration, structural setting, and high-grade gold linking Lubeck Tip closely to the ‘Stawell-Type’ mineralisation model.
Composite sample splitting has transformed a broad, low grade gold smear into a narrow, high-grade primary gold zone. These results warrant thorough phase 2 drilling programs to determine the source of this anomaly.
Lubeck Tip has had very little drilling with over 200m drill spacing and remains open in all directions and at depth.
We are proud to announce that the 1m @ 5.05g/t Au result in NSAC0172 is the third highest grade AC result drilling through the Murray Basin Cover in our tenement package (1925 holes for 108,000m).
This result came from the twelfth hole drilling into the formerly untested target.
The success of the phase 1 AC program at Lubeck Tip has proven that North Stawell’s exploration strategy can be employed efficiently and applied to other purely geophysical targets within our tenement suite.
Major phase 2 work programs have been designed to follow up these encouraging results. North Stawell is in a fortunate position of having a healthy cash balance to fund significant follow up work, starting shortly.”
Early results from an RC drilling program over the southern portion of North Stawell’s tenements completed in June 2022 have added to the successes of the FY22 regional Phase 1 aircore (AC) drill program.
The company is exploring for repeats of the multi-million ounce Stawell Gold Mine under a ‘thin blanket’ of unmineralised sedimentary cover.
A distinct advantage of exploring this type of mineralisation is that a basalt core controls mineralisation sites and the basalt can be remotely mapped with geophysics.
The company notes that high-resolution airborne gravity survey conducted in the June Quarter of 2021 completed the data suite required to efficiently explore. An AC drilling rig tested regional targets for 8 months from October 2021. Within the basalt structures additional targeting is possible.
Observations of controls on mineralisation in the Stawell Gold Mine and modelling of ore-controls indicate that mineralisation is most likely to occur on the contacts (or proximal to the contacts) of the basalt thereby creating spaces where gold mineralisation can be deposited.
Drilling is prioritised where these locations are interpreted in geophysics analysis.
Multiple suites of early to middle Devonian granites intrude into the regional Cambro-Ordovician sediments. This creates the opportunity to explore for Intrusion Related gold (IRG) and thermal aureole gold (TAG) deposits (e.g the Wonga Deposit and mine in Stawell).
Identifying major structures that intersect or lie adjacent to granites is important as they have proven highly prospective for IRG and TAG mineralisation.
North Stawell Minerals is an Australian-based gold exploration company, solely focused on discovering ‘large-scale’ gold deposits in the highly prospective Stawell Mineralised Corridor in Victoria.
The company is exploring prospective tenements located along strike and to the immediate north of the Stawell Gold Mine, which has produced in excess of 5Moz of gold.
North Stawell’s granted tenure has a total land area of 450km-square. It believes there is potential for the discovery of large gold mineralised systems under cover, using Stawell Gold Mine’s Magdala ore body as an exploration model to test the 51km of northerly strike extension of the underexplored Stawell Mineralised Corridor.
The multi-million ounce Magdala Mine (or Stawell Mine) is owned and operated by Stawell Gold Mines (SGM) and makes an excellent model for exploration.
The style of mineralisation is termed Orogenic Gold, and has many similarities to other Victorian gold deposits (e.g Bendigo, Ballarat, Fosterville) where the mineralisation exploits structures that are developing as the host rocks are compressed, folded and faulted.
The mine is 3.5km long, approximately 400m wide and mined to a depth of around 1,600m.
The mineralisation is centred on a large buttress of doubly-plunging basaltic rock (the Magdala Dome). Ore shoots are on, or proximal to the margins of the basalt, occurring where the structures that control the mineralisation bend and warp around the basalt.
Stawell Mine was founded in the 1850s, as gold occurred close to the surface and was not obscured by a blanket of sedimentary cover.
Over 80% of North Stawell’s tenements are masked by sediments, but the underlying rocks and structures are similar to Stawell.
Multiple repeats of basaltic domes are interpreted throughout the North Stawell tenements and elsewhere along the Stawell Corridor. Some of these have ‘Stawell-Type’ mineralisation, with basalt domes intrinsically associated with mineralisation, can be detected with geophysics, and identified through the cover.
Now geophysical processing and acquisition by the company is levering off the geophysics response to find domes as a pathway to mineralisation.
Multiple shears, thrusts, faults and folds occur through the North Stawell tenements. These also have potential to host orogenic gold systems without basalt domes.
However, they are more challenging to target through the covering sediments as they lack the geophysical signature of the domes found in ‘Stawell-Type’ mineralisation.
IRG and TAG type deposits are possible as late granites intrude the folded rocks with potential to remobilise and upgrade existing mineralisation or be mineralised themselves.
Images: North Stawell Minerals Ltd