Yarrol Gold Project
The Yarrol Gold Project was the site of historical mining activities along a significant extent of the Yarrol fault zone where mining exploited steeply-dipping mineralised structures intermittently in the 1800’s through to the 1930’s, with historical gold production averaging an estimated grade of 10g/t gold. Further exploration and assessments conducted in the 1980’s and 1990’s included mapping, surface geochemistry, geophysical surveys and drilling which led to 3D modelling over two prospect areas of gold mineralisation to approximately 80m depth.
Historical drilling reported to the Queensland Department of Resources totals over 17,800m of reverse circulation and diamond drilling from 201 drill holes averaging 89m in length (with only 4 holes to date exceeding 160m length) and the deepest hole on the project a 300.2m deep vertical hole returning 4m @ 3.63g/t gold from 192m depth with no follow-up to date. Amongst the predominantly shallow drilling situated proximal to outcropping mineralisation, historical drill assay results include1:
- 12.0m @ 20.2g/t gold from 100m including 2m @ 58.6g/t gold – YLRC020
- 12.0m @ 1.91g/t gold from 18m and;
25.0m @ 2.92g/t gold from 42m including 15m @ 4.37g/t gold and;
2.4m @ 3.19g/t gold at end of hole – YARD043
- 20.0m @ 3.19g/t gold from 26m – YARC077
- 8.0m @ 3.7g/t gold from 13m and
9.0m @ 3.33g/t gold from 48m including 1m @ 9.58g/t gold – YARC022
- 23m @ 1.83g/t gold from 63m YARC0303
- 32m @ 1.38g/t gold from 38m including 6m @ 4.69g/t gold – YARC024
1refer to Many Peaks Release dated 2 May 2023
Little drilling activity for gold has taken place since that time and insufficient drilling material is retained for validation work to update previous estimates in accordance with the principles of the 2012 edition of the JORC Code. EMX Royalty Corp. (TSX.V:EMX) initiated validation work, completing two confirmatory diamond drillholes within the footprint of previous drilling. Drill holes DD22-YA187 and DD22-YA188 totalling 218m of diamond drilling were drilled as part of a 50 hole program at Yarrol in recent months, returning:
- 17.8m @ 4.01 g/t gold from 61 meters in drill hole DD22-YA187
- 12.0m @ 0.91 g/t gold from 92 meters in drill hole DD22-YA188
Each hole intersected mineralisation associated with the main diorite intrusion. However, recent observations indicate that various other phases of intrusions and surrounding sediments are also mineralised with further work required to define key structural controls on mineralisation. It is also notable that the selected sample intervals taken from drill holes DD22-YA187 and DD22-YA188 began and ended in gold mineralisation and additional intervals will be sampled and analysed from both holes.
Mineralisation Style & Geology Setting
The Yarrol Gold & Plateau Cobalt Projects host an extensive corridor of gold mineralisation featuring several shallowly drilled zones of gold mineralisation and multiple undrilled surface geochemistry anomalies requiring follow-up work (Figure 7). Locally, the basement rocks are comprised of Devonian to Lower Permian sediments and volcanic units intruded by gabbro to granite composition stocks. Gold mineralisation at Yarrol is present as quartz sulphide veins and zones of silicification developed in and around compositionaly variable suite of dioritic to granite phase intrusions. The metalliferous corridor is associated with the north-south trending regional scale Yarrol fault zone.
The mineralised corridor extending from the Mt Weary Gold Project through the Yarrol Gold Projects is masked by extensive zones of Tertiary basalt plateaus. The basalt volcanics post-date gold mineralisation events forming a geochemically barren cover to the basement rocks hosting gold in the Yarrol Province, and present potential for masked gold mineralisation along the trend.
At or near the unconformity to the basement rocks the Co-Mn horizon forms a laterally extensive, sub-horizontal replacement zone with within topographic lows and channels of the basement unconformity hosted in unconsolidated sand and gravel sediments up to 40m thickness. The unconsolidated sediments have been preserved from weathering by the basalt plateaus. The Co-Mn horizon is interpreted to be either hydrothermal replacement style mineralisation or potentially supergene enrichment of manganese, with anomalous cobalt, nickel and copper from a lateral source. The Co-Mn horizon is observed in subcrops and drainages across a 4km extent of the breakaway slope beneath the basalt plateau located 6km north of historical gold drilling within Yarrol.
Plateau Cobalt Project
Surface mapping and geochemistry programs at the Yarrol Project designed to expand the footprint of gold anomalism completed through 2022 encountered several zones of outcropping cobalt-enriched manganese oxide mineralisation. Surface sampling programs demonstrated that the zones of manganese oxide mineralisation encountered in the field consistently returned over 1% cobalt, accompanied by enrichments in both nickel and copper in manganese cemented sediments. Of the 65 rock chips collected from the target horizon through 2022, results averaged 1.07% cobalt and 12.8% manganese and peak rock chips ranging up to 2.24% cobalt and 1.68% cobalt (both in >15% manganese) (refer to Many Peaks Release dated 2 May 2023).
The Cobalt enriched material is interpreted to be replacement style mineralisation (from either supergene or hydrothermal processes) forming in the basal units of Tertiary (Eocene) aged fluvial sediments which have been preserved by a thin overlay of later Tertiary (Oligocene) volcanic basalt flows (Figure 2). The manganese horizon is believed to form a laterally extensive, sub-horizontal replacement zone(s) ranging from manganese dominant replacement to a hematite replacement within channels of the sedimentary basin. The cobalt enriched material observed at surface (Figure 5) has been identified at multiple locations across a 4km extent of the breakaway slope beneath a basalt plateau within the Yarrol land holding (“Plateau Cobalt Project”).
Initial Drilling successfully confirms the cobalt previously reported from surface returning multiple >1% cobalt results across a 4km extent (Figure 5) has continuity laterally into the extensive plateau for up to 1km into the hillside on sub-horizontal horizons and returning up to 1.05m @ 0.252% cobalt from 18.5m depth (CODD01) in initial drill results (refer to ASX release dated 25 May 2023). Several stacked mineralised zones of manganese replacement have been observed in drilling across the 4km extent tested overprinting a heavy mineral sands depositional profile.
Cobalt and manganese oxides overprint a broader heavy mineral sands (HMS) profile with initial assays for titanium oxide (TiO₂) correlating with a suite of valuable heavy minerals. (Figure 6).Preliminary mineral studies have identified several valuable heavy minerals including zircon and several titanium bearing minerals such as rutile, ilmenite, leucoxene, and titanite.
Further analyses comprised of geochemical assays and heavy mineral separation tests are ongoing for previous air core drilling at the Plateau Cobalt Project. The recognition of the cobalt and manganese oxides overprinting sediments containing heavy minerals sands is also being utilised to vector further exploration activity. Correlations between heavy minerals sands and cobalt anomalism have been observed in geochemistry and mapping shedding out of the larger plateau at Yarrol which extends up to an 18km x 8km area within the Yarrol Project. This provides a basis for further exploration potential, subject to a successful air core drilling campaign scheduled for June 2023.
Figure 2: Plateau Project area inset with drill collar locations, proposed drill locations, and cobalt rock chip sampling locations on modified Queensland Dept. of Resources 100k geology.
Figure 3: Cross Section of reported Diamond drill results (with 2x vertical exaggeration) illustrating cobalt enriched manganese oxide replacement forming in the base of HMS horizons intersected.
Figure 4: Cobalt in manganese oxide horizon in hole CODD001 returning 1.05m @ 0.26% cobalt, including 0.25m @ 0.83% cobalt at the base of a 12.45m interval of sediments with heavy minerals sands returning 3.28% TiO2 from 7.1m depth.