Located adjacent to Meekatharra in Western Australia, drilling is continuing to achieve outstanding results with an aggressive exploration program continuing through FY2022.
The Mulga Bill prospect at Side Well is a large intrusive-related gold system (IRGS). The large footprint and high grade of pathfinder elements including bismuth, molybdenum, arsenic and silver indicate significant size potential at Mulga Bill, and recent drilling programs have backed this up with outstanding high-grade gold intersections.
- 6m @ 31.25g/t Au from 130m in 21MBRC002
- 3m @ 34.5g/t Au from 32m in 21MBAC022
- 8m @ 13.36g/t Au from 151m and 4m @ 7.33g/t Au from 111m in 21MBRC017
- 8m @ 7.51g/t Au from 68m in 21MBRC016.
AC drilling has defined a broad zone of supergene gold dispersion at Mulga Bill over a strike length in excess of 3.7km. Within this, Great Boulder’s RC drilling programs have defined two parallel high-grade lodes a strike of 900m and 500m respectively, both of which remain open along strike and with potential for additional lodes to the north and south.
About the Side Well gold project
Side Well tenement E51/1905 is a 48-block Exploration Licence covering an area of 131.8km2 immediately east and northeast of Meekatharra in the Murchison province. The project overlies the Meekatharra – Wydgee greenstone belt and includes upper greenschist-facies rocks of the Luke Creek and Mt Farmer groups. Within the project area these lithologies are folded into a large regional syncline known as the Pollele syncline. Alluvium and lacustrine clays overlie the area.
Regional exploration has been conducted around Side Well by a number of companies over the past 30 years, including Dominion Mining (1992 to 1995), WMC Resources (1996-97), Accent Resources (2009) and Doray Minerals (2010 to 2016). Dominion were the first company to identify significant gold mineralisation in drilling with intersections such as 2m @ 1.67g/t Au and 4m @ 1.4g/t Au in regional RAB traverses .
Dominion Mining and WMC Resources explored the greenstone belt from Andy Well to Side Well during the 1990’s. Dominion discovered significant gold mineralisation at Side Well in 1993, including 26m @ 2.19g/t in hole HAR3015. Shortly afterwards WMC drilled the discovery holes at Andy Well. WMC eventually concluded that the project area did not meet their exploration criteria of a 6Moz discovery, commenting in their 1998 report that “potential for a near-surface WMC-sized position (e.g. 6Moz) was significantly downgraded. The potential for smaller, perhaps million ounce, positions remains significant.” The decision by WMC to leave the area eventually led to the Andy Well project being picked up by Doray Minerals in joint venture with Scott Wilson.
Doray were successful in identifying high-grade gold in drilling at Matilda (3m @ 35.48g/t Au from 76m in hole MNAC0463) and then Mulga Bill where several significant hits in Air-Core (AC) and Reverse Circulation (RC) drilling included 10m @ 3.41g/t Au from 185m in SWRC006, 14m @ 5.30g/t Au from 86m in SWRC012 and 5m @ 6.69g/t Au from 110m in MNAC0454. In January 2013 Doray flew a heli-TEM survey over the project area which provided additional detail for their structural interpretation on the controls to mineralisation. After 2015 Doray’s exploration focus shifted closer to Andy Well as they experienced success at Gnaweeda, while the corporate focus shifted to the ramp-up of operations at Deflector, south of Yalgoo.
Much of the Side Well area is covered by transported alluvium, rendering conventional soil sampling techniques unreliable. This also presents opportunities, and GBR intends to trial a range of analytical techniques to identify underlying mineralisation.
It is a widely accepted principle of Yilgarn exploration that all the significant future discoveries will be made under cover, and this is particularly true in historic mining areas such as Meekatharra.
The only surface sampling recorded over the project area was a 182-point lag sampling program conducted by WMC over the Jones Well area on a 100 x 200m grid in 1997-98. Samples were assayed for Au and As, with the results highlighting a coherent Au-As anomaly at 3ppb Au, with a peak of 14ppb Au. Ten air-core holes were subsequently drilled to test this target with no significant results, indicating that the surface sampling may have been ineffective.
Side Well priority targets
Mulga Bill prospect: Gold was first identified at the northern end of Mulga Bill by Dominion, who initially referred to the prospect as Side Well. RAB hole HAR3015 intersected 26m @ 2.19g/t Au from 66m in 1993. Although detailed logging is unavailable, subsequent drilling in the area would suggest that this horizon was at least partially weathered.
Dominion drilled follow-up air-core holes either side of HAR3015, as well as a scissor hole above it, all of which failed to replicate the 26m interval. In their 1993 report Dominion concluded that the result “appears to be a classic case of RAB smearing quartz in samples of damp puggy mafic clays .”
Later air-core drilling by Doray Minerals 500m south of this hole hit began to identify zones of supergene mineralisation within a broad, north-south corridor. As their exploration continued they tested some sections with a series of RC holes and two diamond tails, with highlights including 14m @ 5.30g/t Au in SWRC012 and 10m @ 3.41g/t Au in SWRC006. By this stage mineralisation had been defined over a strike distance of 3km within a corridor 750m wide. The corridor is defined by supergene gold dispersion within the weathered horizon, with an anomalous copper footprint providing a broader dispersion halo in the same horizon to highlight the overall trend.
Mulga Bill is located in the centre of the Pollele syncline, within felsic to intermediate volcanics and volcaniclastics of the Yaloginda Formation. Previous explorers have hypothesised the position of gold mineralisation at Mulga Bill is influenced by the nearby Gabanintha shear, and Doray interpreted a mineralised felsic to intermediate intrusion which may also be a key influence to mineralisation. Although the drilling is currently sparse, the distribution of significant gold values suggests a possible north-northeast trend to the higher-grade zones, however this hypothesis requires testing with infill drilling.
The better intersections drilled by Doray are within the southern half of the Mulga Bill area. This section was drilled on sections 400m apart, meaning the entire southern 1,600m of Mulga Bill has only been tested by five fences of drilling. Infilling this area and extending the high-grade mineralisation zones will be a priority for GBR.
Matilda prospect: Doray’s air-core intersection of 3m @ 35.48g/t Au in hole MNAC0463 at Matilda sits on the west side of the project, on the eastern side of the Paddy’s Flat belt above a discontinuous linear magnetic feature caused by banded iron formation (BIF) and cherts of the Yaloginda Formation. Petrographic analysis of RC chips from hole SWRC003 at Matilda identified a carbonate-chlorite-sericite-altered porphyry, possibly andesite, however SWRC003 failed to intersect significant grade at depth beneath MNAC0463.
The high-grade intersection in MNAC0463 was logged as moderately weathered, fine-grained quartz-feldspar-mica schist. Holes either side were simply logged as upper to lower saprolite, suggesting positive identification of the host lithology would be unreliable, and there may be a supergene component to the gold interval. Aside from the two holes drilled underneath the discovery hole looking for continuity at depth, the adjacent drill fences are lines of relatively shallow holes 400m to the north and south.
Further drilling is required at Matilda to confirm its stratigraphic position relative to the Paddy’s Flat belt. There is more than 5km of strike along this trend to the hinge of the syncline, most of it untested by drilling. To the east of the fold hinge the stratigraphy swings back to the south, down the east side of the Side Well project towards Gabanintha.
Gabanintha trend: On the eastern side of the project, the lithologies corresponding to the Paddy’s Flat belt strike southwards towards Gabanintha, abutting granites and monzogranites of the Walganna and Big Bell suites. South of Side Well there is a series of workings and old mines in this stratigraphic horizon, including Bourke’s Find, Fishers, Tal Val, New Australia and the Gabanintha group of mines.
Within the project this prospective horizon has only been tested by a single line of air-core holes ranging in depth from 16m to 95m. The target horizon is approximately 18km in strike length.
There is no record of any surface sampling on this trend.
Jones Well: Jones Well occurs at the northern end of the Side Well project. The area is structurally complex, with folded BIF abutting a small (6km) ovoid granite. Thin magnetic units wrapping around the granite could be BIF or a contact halo, but in either case the position of a brittle intrusive plug within a large regional structural corridor may create classic dilational positions for gold mineralisation. Smaller areas of low magnetic response adjacent to the BIF suggest there may be other smaller intrusives adding further complexity to the structural setting.
Jones Well is immediately adjacent to Westgold’s Maid Marion deposit, which contains a JORC resource of 700,000t @ 1.52g/t for 34,000 ounces Au . Maid Marion is located approximately 1.2km from the tenement boundary in a similar BIF setting. Since that resource statement was announced, Westgold have released highlights from more recent drilling, including these intersections in the December 2019 quarterly report:
- 4m @ 5.29g/t Au from 8m in 19MMRC018
- 4m @ 6.52g/t Au from 8m in 19MMRC023
- 4m @ 5.23g/t Au from 44m in 19MMWB001
Jones Well was explored by Dominion and then WMC during the 1990’s, with lag sampling by WMC defining an Au-As anomaly which was subsequently tested with a fence of ten air-core holes. WMC’s exploration report states that the area is covered by a layer of thin pisolitic gravel, with mineralization related to a clay zone and talc-chlorite ultramafic beneath the cover. No significant mineralisation was seen, which may indicate that the lag sampling was ineffective.
High-resolution magnetics will be a useful tool to resolve the structural interpretation in this area, followed by drilling to confirm the lithologies.
HISTORIC PRODUCTION AND CURRENT JORC RESOURCES IN THE MEEKATHARRA AREA.
|Project||Historic Production (‘000 oz)||Resources (‘000 oz)|
|Paddy’s Flat ||2,300||1,335|
|Meeka North ||100||41|
|Andy Well ||300||505|