100% of the Twin Hills project was acquired by GBM in early 2022 as part of its Drummond Basin strategy. At the time of acquisition, the project contained a known 633,000 ounces of gold and was acquired for a highly competitive $A 5.53/ounce. Resource work by GBM increased the JORC 2012 mineral resource to 999,200 ounces. The acquisition increased known resources in GBM’s Drummond Basin projects to 1.85 Moz Au, all within 70 km of a proposed central processing hub.
Historical drilling at Twin Hills has returned long and high grade intersections, including 140.6 m @ 5.2 g/t Au from 154 m (309 deposit) and 146 m @ 9.8 g/t Au from 104 m (Lone Sister). 300 individual metre samples exceed 30 g/t Au and peak gold grades are up to 2,940 g/t Au. It is GBM’s assessment that potential depth extensions and strike repetition of both the 309 and Lone Sister deposits have not been adequately tested. The project is considered highly prospective and is a major focus of GBM’s 2022 drilling campaign.
- 1,102 km² tenement package (644 km² granted and 458 km² underapplication) in the highly prospective Drummond Basin
- 100% owned by GBM Resources after strategic acquisitions in late 2021 and early 2022
- Mineralisation is high gold fineness, low sulphidation quartz sulphide class of, similar to high grade deposits like Round Mountain, Nevada
- High grade gold intercepts with 300 individual metre samples over 30 g/t Au
- Current resources of 23.1 Mt @ 1.3 g/t Au for 999,200 oz gold
- Major component of GBM’s Drummond Basin strategy, targeting 2 Moz+ gold
- Aggressive 2022 drilling campaign successfully targeted interception of high-grade mineralisation on previously untested areas, resource expansion and improved resource accuracy to support mining/development studies.
Geology and Resources
Known resources in the Twin Hill projects are centred at the 309 and Lone Sister gold deposits, approximately 7 km apart and linked by a major north-south structural lineament (see ASX announcements 20 July 2021 and 18 February 2022 for geological setting).
Mineralisation at both deposits belongs to the felsic dome related, high gold fineness, low sulphidation quartz sulphide class of mineralisation that has produced a number of notable high value gold deposits including the high-grade Sleeper deposit and large bulk minable style deposits like Round Mountain in Nevada (see ASX announcement 18 February 2022).
Significant progress has been made on the Twin Hills project during 2023 looking at key structural settings and refining existing and new targets for drilling and further exploration. (see ASX announcements 28 April 2023 and 9 June 2023 for more details.)
Resource work conducted by GBM demonstrated a significant increase in gold resources in the project. Resource upgrade work is continuing with new pit optimisation work commencing soon on the 309 deposit to evaluate opportunities to deepen a potential pit below the 0-RL used in the current resource statement.
2022 exploration and development
Analysis by GBM of historical drilling suggested that high grade shoots at 309 and Lone Sister may be open at depth. GBM has commenced a drilling campaign to test these targets. Phase 1 drilling, at the 309 deposit includes approximately 7,000 m of drilling targeting intersection of high-grade mineralisation on previously untested areas, resource expansion and improved resource accuracy. Phase 2, later 2022, will move to the Lone Sister deposit with a 6,000 m in drill plan. A camp and modern core cutting facilities are being utilised on site to support the larger drilling campaign envisaged.
Assay results from these and GBM’s other drilling campaigns are expected throughout 2022.
Since acquisition, GBM has also carried out analysis of deposit geometry and grade distribution. The results of this suggest that the 309 and Lone Sister resources may be successfully mined via a combination of bulk minable open pit and bulk underground mining methods.
Drilling results will also support conversion of a larger proportion of the current resource from Inferred to Indicated classification. This is prerequisite for planned mine design and feasibility studies.
Combined geochemical and structural targets
See ASX announcement 28 April 2023.
Comparison of soil geochemical and magnetic data has highlighted three soil anomalies greater than 8 km in length and a lower order anomaly all coincident with NW to NNW trending km-scale faults that parallel the overall basin forming architecture (Figure 2). The two large anomalies at Bullock Creek - Hill 253 and Lanark - Tourmaline Hill along with the Bendee prospect have had little systematic exploration and represent excellent exploration targets.
The highly prospective >10 km long Twin Hills Corridor (Figure 2 and 3) encompasses the 309 and Lone Sister deposits (of 23.1 Mt @ 1.3 g/t Au for ~ 1 Moz Au and 4.8 Moz Ag) and is defined by strongly anomalous soil geochemistry, favourably oriented structures, and IP anomalies. Multiple soil anomalies are present across areas of key target stratigraphy and are generally coincident with NW or NE striking structures observed in magnetics. The key anomalies are at the 309 Trent Targets, Lone Sister, and Southern Sister, with second order anomalies at LS7 and Lone Sister South and mapped sinter at Centipede. The >10 km² soil anomaly surrounding Lone Sister and Southern Sister is very poorly tested outside the immediate Lone Sister deposit area. Limited drilling at Southern Sister intersected prospective andesite host stratigraphy with moderate silicification and anomalous gold/arsenic. This highly prospective area will be a key focus of exploration.
IP targets adjacent to the 309 deposit
Priority combined geophysical, geochemical and geological targets have been identified immediately to the south of the 309 deposit. A clear IP resistivity anomaly is defined at the 309 deposit and likely reflects intense silicification associated with the mineralisation system. Two additional IP resistivity anomalies, Coreshed and 309 South (Figure 4 A and B), define a SSE plunging trend sub-parallel to the km-scale structural fabric that links 309 and Lone Sister deposits. The Coreshed and 309 South resistivity anomalies are coincident with + 10 ppb Au soil anomalies and outcropping silicified milled matrix breccia that also hosts the 309 deposit. Shallow drilling with anomalous results of 0.5 - 1.9 g/t Au has tested part of the Coreshed anomaly but did not test the 309 South anomaly.
Resource extension targets
Recently released Mineral Resource Estimates (MRE) of 10.6 Mt @ 1.5 g/t Au and 2.3 g/t Ag for 309 and 12.5 Mt @ 1.2 g/t Au and 10.0 g/t Ag for Lone Sister provide a combined Twin Hills resource of ~1 Moz Au and 4.8 Moz Ag. Both deposits have potential for open pit and bulk mine underground extraction. The 309 deposit remains open along the NNE and WNW structural orientations that define the orebody (Figure 5). Broad intervals of + 4 g/t Au define priority high grade resource step out drill targets and include intersections of 49 m @ 5.18 g/t Au from 310 m in 309DD22005 and 54 m @ 4.63 g/t Au from 362 m in THRCD827. High grade drill intercepts, including the intercept of 49 m @ 5.18 g/t Au in 309DD22005, can be associated with late-stage visible gold as electrum.
Mineralisation at Lone Sister is defined from surface for over 420 m of elevation and contains a high-grade core with a width of 20 to 37 m g/t Au. Broad high-grade intersections within the resource include 29 m @ 7.98 g/t Au from 139 m in LRCD143 and 37 m @ 36.53 g/t Au from 211 m in LRCD015. Mineralisation plunges moderately to the north and high grade remain open at depth e.g., 20 m @ 4.32 g/t Au from 401 m in LRCD066 (Figure 6). Down plunge extension of Lone Sister mineralisation is a priority resource step out drill target.
See ASX announcement 9 June 2023.
Integrated analysis of magnetic, radiometric, and geochemical data was used to define the structural architecture of the Twin Hills area. Two main fault sets are evident and strike NW and NNW and NE to ENE (Figure 7). The faults are clearly defined in Drummond Basin cycle 1 and older rocks but are not evident in the embayment of younger Drummond Basin cycle 2/3 in the centre of the project area. We suggest the NW - NNW and NE - ENE architecture may have developed during cycle 1 deposition. Thus, some of these faults could be basin bounding / basin forming structures and potentially excellent hosts for substantial undiscovered mineralisation. Broad, km-scale, north trending and plunging folding is inferred from map patterns though the effect of the folding on the earlier faults is unclear.
Structural controls on gold mineralisation
A clear spatial relationship between faults and gold mineralisation is evident at Twin Hills with most known prospects sited on, or immediately adjacent to, interpreted structures (Figures 7, 8, 9). The Lone Sister and 309 Deposits both sit at the intersection of interpreted faults as do several other prospects. The structural interpretation will be used in conjunction with other datasets to target future exploration programs.
Gold in soil geochemistry also highlights the main structures with strong NW striking soil anomalies at Bullock Creek and Lanark - Tourmaline Hill (Figure 8). Between 309 and Lone Sister soil geochemistry is clearly focused along key structures, even at levels as low as 3-5 ppb Au (Figure 9). The > 7.5 km² soil anomaly between Lone Sister and Southern Sister is focused around favourably oriented structures and will be a key target for future exploration.
Historical 309 development and studies
The 309 Deposit was mined by BMA Gold Limited (BMA) from 2005-2007 with gold production of 72,979 t @ 10.0 g/t Au for 23,490 ounces of gold. In this time approximately 1,200 metres of decline (5.0vm x 5.2 m, 1 in 7 gradient) and significant level development to access the Area 2 mineralisation was completed (see figure 10 below). With the development completed to Area 2 it may represent an opportunity to access remaining underground ore.
The Twin Hills project contains a series of existing established infrastructure and essential facilities as summarised below (Figures 11 and 12):
• An exploration shed
• Core farm
• The mine portal/boxcut
• Maintenance shed
• Waste dump
• The utility shed
• Accommodation donger footings
• Evaporation pond
• Access road
In 2010 the then owners of the Twin Hills Project completed a Mine Development Study.
The Pajingo and Twin Hills operations in 2010 were held under a Joint Venture of NQM Gold 2 Pty Limited (a subsidiary of North Queensland Metals) and HSK Gold Australia Pty Limited (a subsidiary of Heemskirk Consolidated Limited). The Joint Venture was comprised of NQM Gold 2 Pty Limited (60%) and HSK Gold Australia Pty Limited (40%). NQM Gold Pty Limited (NQM) were the operators and managers of the Pajingo Mine.
Key results of this study at the time (A$1,100/oz Au Price) were:
Snowden provided an optimisation inventory of 1.1 Mt @ 3.9 g/t Au for 127 koz Au.
Revised engineering has reconfigured the decline (shown below), level accesses and vent raises to lower development metres from 5,008 m to 4,930 m.
Optimised ore blocks falling below a 2.5 g/t Au cut off were removed in the engineering design phase and as a result it is estimated that initial mine designs will deliver a probable mine reserves as follows: