- 952 km² tenement package in the highly prospective Drummond Basin
- 100% owned by GBM Resources after completion of strategic acquisition in 2021
- Current resources of 15.9 Mt at 1.0 g/t Au for 514,500 ounces of gold at East Hill and South Hill areas, along with Illamahta
- Gold mineralisation between Yandan Main to East Hill defines a kilometre long trend that contains 900,000 oz Au from both historic and the current Mineral Resource Estimate (MRE)
- The new geological model is specific to the East Hill deposit which has a MRE of 443,000 oz Au with the key geological focus being the high grade core of 1.1 Mt @ 5.7 g/t Au for 201,000 oz Au
- The model for East Hill demonstrates that the known mineralisation is the top of a hot spring epithermal and vein texture system
- Vein textures and mineralogy suggest drilling to date has only tested the upper parts of the system with potential for stronger grades and more ounces at depth
- The Generator Fault potentially off-sets the mineralisation to the north and implies that the high grade veins exist below this fault line (reverse fault)
- Significant opportunity for the high-grade vein gold discovery under the existing resource
- Clear analogies to known deposits with bonanza grade veins at depth
The Yandan Gold Project was acquired by GBM in early 2021, as part of its Drummond Basin strategy to develop a 2-3 Moz gold project in the region. At the time of acquisition, the project contained 521,000 of gold in a JORC 2021 inferred resource. Post-acquisition, GBM developed a revised geology model for the project, and a corresponding drill program. Drill results from 2021 confirmed a high grade core to the East Hill mineralisation, as well as finding significant gold intercepts in drill holes that currently sit outside of the resource model (see Exploration and Development below). Future drilling will be used to complete validation/testing of the geology model.
The project also contains a number of underexplored regional targets, including at Northeast Ridge and Illamahta, each with significant historical drill intersections.
In addition to gold resources, the Yandan Gold Project contains significant historical mining infrastructure, including water dams, tailings dam, a power line and an air strip. This infrastructure is being considered by GBM as a possible site for a central processing hub for its Drummond Basin projects (Yandan, Twin Hills, Mt Coolon).
The Yandan Project is located approximately 40 km to the west of the township of Mount Coolon and 155 km southeast of Charters Towers, north Queensland. Tenure covers an area of approximately 952 km² and comprises exploration permits (EPM8257, EPM27644, EPM27591, EPM27592) and two granted mining leases (ML1095, ML1096).
Within the Yandan project is a revised JORC 2012 Mineral Resource of 15.9 Mt at 1.0 g/t Au for 514,500 ounces of gold at East Hill, South Hill and Illamahta as reported by Mining Associates.
The Mineral Resource is based on a large open pit (~0 to 330 m from surface) at East Hill and a shallower open cut at South Hill.
Exploration and Development
2021 drilling at the project (see ASX announcement 16 August 2021) confirmed the high grade core at the centre of the East Hills mineralisation, including intercepts:
- 21YEDD006A – 214 m @ 1.6 g/t Au, including 26 m @ 5.4 g/t Au from 321 m
- 21YEDD007 – 189 m @ 2.0 g/t Au, including 16 m @ 4.6 g/t Au from 328 m
Drilling also extended the boundaries of the resource, with 21YEDD002 returning 30 m @ 1.06 g/t Au from 274 m. This intersection sits outside the current resource model.
Following the successful phase 1 drilling program in 2021, GBM is currently advancing geological models for the project. This will support further drilling and updating of the Mineral Resource Estimate.
New East Hill Geology Model and Exploration Target
The East Hill deposit is a clear example of a hot spring low sulphidation epithermal system. Volcanic facies contacts at a high angel to the overall stratigraphy suggests that the deposit likely formed in a graben or half graben within the broader Yandan Trough. The style of mineralisation is partly controlled by host rock with breccias generally formed in coarse tuffs and fine-grained tuff and lava hosting veins. The Epiphany Conglomerate with clasts of silica-illite altered andesite, sinter and epithermal veins suggests hydrothermal eruption breccia was present and forms a distinct marker horizon (Figure 1A).
Sedimentary units with hydrothermal components (sinter and Epiphany Conglomerate) interbedded with St Anns Formation limestone and siltstone imply that the East Hill mineral system has been rotated, likely by regional folding, from an original position of horizontal bedding and steeply plunging mineralisation to north dipping bedding and south plunging mineralisation. The Generator Fault that truncates high grade mineralisation at East Hill is now interpreted to be post-mineral and reverse movement is implied by andesite (older) juxtaposed over St Anns Formation siltstone, limestone and Epiphany Conglomerate (younger) (Figure 1B and 1C).
Vein composition and textures at East Hill clearly demonstrate that the known mineralisation represents the top half of the hot spring and vein texture model (Berger and Eimon, 1982., Morrison et al., 1990). The presence of hydrothermal alteration and epithermal veins below the Generator Fault together with gold grades that increase down plunge suggest that the Yandan system remains open at depth with potential for better grades and significantly more ounces. With strong similarities to well known epithermal deposits Favona in New Zealand and Golden Promise in USA, it appears likely that high-grade veins exist below the Generator Fault (Figure 1C). These high grade veins are our key exploration target at Yandan.
Yandan mineralisation (Yandan Main to East Hill) defines a 1 km trend that contains 900,000 oz Au (historic and current resources). Hot spring epithermal systems often have better grades and more ounces at depth with high-grade veins present underneath similar epithermal systems at Favona (Figure 6) and Golden Promise (Figure 7) (See ASX announcement 22 March 2023 - for Figure 6 and 7). The geological model developed for East Hill implies that the Generator Fault off-sets mineralisation to the south. Initial drilling will likely target locations immediately to the north of known mineralisation (Figure 2).