Greenfields and Brownfields Exploration at the Tritton Copper Operations (NSW)
The Tritton tenement package in NSW comprises six exploration and mining licences, covering 2,160km2 of highly prospective ground for base metal deposits within the Girilambone Basin. Since modern exploration commenced in the 1980s, more than 750,000 tonnes of copper has been discovered within the 100% Aeris-owned Tritton tenement package.
The nearby Canbelego Project (Aeris 30%) is held through a Joint Venture with Helix Resources.
The greenfields exploration strategy within the Tritton tenement package is based on growing the operation through the discovery of large Tritton or Murrawombie-sized deposits of more than 10 million tonnes.
Prior to 2016, greenfields exploration at Tritton was sporadic and punctuated with prolonged periods focused on resource definition drilling at the Tritton, Murrawombie, North-East, Larsens and Avoca Tank deposits. However, in mid-2016, Aeris commenced a strategic two-year $7.5 million greenfields exploration program. The program, which commenced in November 2016 and ran until early in 2019, included:
- High powered moving loop electromagnetic (HP MLTEM) surveys conducted over the prospective corridors from Budgery to Avoca Tank and Kurrajong, with the aim of detecting mineralisation up to 500 metres below surface. The results of this survey saw multiple EM conductors detected and led to drill targeting at the Kurrajong prospect;
- The drill program at the Kurrajong prospect, which was highly successful and intersected sulphide mineralisation over 1,100 metres down plunge. An exploration target of 3 to 4 million tonnes at copper grades ranging from 1.5% to 2.0% has now been defined;
- Completion of a regional mapping program to identify and extend the prospective Budgery Sandstone corridor across the northern half of the tenement and extended the prospective corridor by some 60 kilometres, with potential to extend a further 40 kilometres; and
- The completion of two airborne EM surveys over the northern half of the tenement resulting in the identification new potential bedrock EM anomalies.
Tritton – Budgerygar Corridor
The Tritton – Budgerygar corridor is a highly prospective copper rich mineralised system extending some two kilometre strike length.
The level of geological understanding of the Tritton deposit has increased significantly during the year as the underground development exposes more of the mineralised system. Although the Tritton deposit was discovered in the mid 1990s and mining commenced in 2004 the geological understanding is continually evolving. In recent years the geology has changed at depth and as the mining front has exposure to more of the geology, it has also allowed a greater understanding of the mineralised system.
The deposit has transitioned from a tabular north/south trending system to an elongated east-west trending ellipsoid, with the deposit thickness increasing from a minimum of 20 metres to more than 80 metres in places. Copper grades have steadily decreased with the increasing depth. As the mineralised system has changed with increasing depth, internal high grade copper shoots have been identified within the Measured Mineral Resource classified sections of the Tritton deposit. It appears that the high-grade shoots may extend deeper within sparsely drilled sections of the deposit, with further work planned in the coming year to better define their potential to be mined.
Several drill programs have been completed targeting down plunge extensions (below 4,000m.RL level) to the Tritton mineralised system. Notable assay results include:
- TRGC1001 returned 21.5m @ 2.26% copper;
- TRGC1009 returned 17.0m @ 1.57% copper;
- TRGC1010 returned 7.0m @ 5.26% copper and 6.8m @ 1.82% copper; and
- TRGC1011 returned 2.6m @ 2.28% copper.
TRGC1023 returned 23.4m @ 1.86% copper. Within the larger 2,000 metre (horizontal) Tritton – Budgerygar mineralised corridor there are numerous drill hole intersections peripheral to both deposits which contain elevated (+0.5% Cu) intersections over multiple metres. The sparsely drilled North Wing prospect immediately north of Tritton, is considered highly prospective and drilling is planned to target extensions to the sulphide mineralisation previously intersected.
Further drilling is planned within the Tritton – Budgerygar corridor in the coming year, focused on increasing the Mineral Resource base at the Tritton deposit and surrounding mineralisation extensions including North Wing and Budgerygar.
Murrawombie – Avoca Tank Corridor
Opportunities for drilling to test mineralisation extensions outside of the Indicated Mineral Resource at the Murrawombie deposit were limited during the year. Towards the end of the year, underground drilling was completed targeting extensions to the Indicated Mineral Resource along strike (north) and down plunge. Drilling in both directions intersected copper sulphide mineralisation, highlighting the potential to increase the Mineral Resource base. Copper mineralisation was traced a further 100 metres along strike (north) beyond the reported June 2019 Mineral Resource envelope.
Within the upcoming year, drilling will focus on extending mineralisation along down plunge beyond the current Indicated Mineral Resource footprint. Additionally, copper sulphide mineralisation has been intersected in the hangingwall (HW) to the main mineralised system. This is an exciting discovery highlighting the prospectivity of the field and potential to increase the Mineral Resource base from near mine exploration.
The deposits discovered on the Tritton tenement package typically have a long down plunge extent and the same is expected to be true at the Avoca Tank deposit. Future exploration drilling of the deposit will be most efficient from an underground platform. However, to assist with feasibility studies, a small drilling program of up to 3 drill holes to test the vertical extension of the deposit is planned. This program has the aim of helping to improve the understanding of the deposit’s structural controls to optimise future underground drilling locations.v
The HP MLTEM survey completed over the Kurrajong prospect detected two strong bedrock conductors commencing at 400 metres below surface. The detection of the plates provided the impetus to commence a limited drill program testing the potential extents to mineralisation intersected from previous drilling at the prospect. The initial two holes (TKJD014 and TKJD015) targeted the interpreted mineralised extensions at 150 metres up and down plunge. Both drill holes intersected massive sulphides:
- TKJD014 returned 19.4 metres @ 2.2% Cu; and
- TKJD015 returned two intersections of 4.60 metres @ 5.1% Cu and 5.65 metres @ 2.5% Cu.
These results were encouraging enough for Aeris to extend the drill program with a further 12 drill holes completed in November 2018. The drilling program extended the limits of sulphide mineralisation to 300 metres along strike and 1,100 metres down plunge.
Within the large sulphide envelope, an exploration target was defined ranging from 3 to 4 million tonnes at 1.5% to 2.0% copper.
The Company has now commenced the process to obtain the necessary regulatory approvals to allow further drilling to occur at Kurrajong with the aim to progress the exploration target to an Inferred Mineral Resource.
To date, the majority of the on-ground exploration within the Tritton tenement package has been focussed within the southern half, along the prospective “Budgery Sandstone” corridor between the Budgery and Avoca Tank deposits.
Exploration of the northern part of the tenement package has been limited until the recently completed airborne EM surveys, with previous exploration limited to one airborne EM survey flown in the late 1990s. A recent review of the historical EM survey data from the late 1990s indicated it was largely ineffective in detecting concealed mineralisation below surface.
Recent regional mapping and follow-up geophysical interpretation over the northern half of the tenement package was successful in identifying the continuation of the Budgery Sandstone unit for a further 65 kilometres than originally thought. Additionally, the prospective corridor was interpreted to extend a further 40 kilometres further northwest, into an area now covered by EL 8810.
EL8810 was granted in late 2018 and is located adjacent to the north-west corner of the current Tritton tenement package. The new tenement, covering an area of 296km2, brings the total Tritton tenement package to 2,160km2, covering the known 155 kilometre strike extent of the Budgery Sandstone unit.
An initial trial airborne EM (AEM) survey was flown over selected areas of the Tritton tenement package in January 2018 to determine the effectiveness of this method in the detection of potential bedrock conductors. The survey was successful in identifying 4 new potential bedrock conductors along the northern margin of the tenement package.
A second AEM survey covering the remainder of the under-explored northern half of the tenement package (617km2 – excluding EL8810) was flown in January 2019 and identified a further 25 EM anomalies, including 9 high-priority targets. The airborne EM survey was flown using the SKYTEMTM 312 EM system, which is designed and optimised for deep conductor bodies. This system enabled exploration to quickly and cost-effectively identify potential copper sulphide mineralisation.
A ground based moving loop electromagnetic (MLTEM) surveying was completed over the AEM conductive bodies. The MLTEM survey was designed to filter out the AEM anomalies which are legitimate bedrock conductors from those which are related to noise or near surface cover responses.
Aeris’ exploration focus on the Tritton tenement package within FY2020 is principally within the northern half of the tenement package, focusing conductive bodies detected from AEM and MLTEM geophysical surveys.
A modest drill campaign, totaling three drillholes was completed within the Murrawombie to Avoca Tank prospective corridor following the completion of a geological review and additional MLTEM survey data. Two drillholes targeted geophysical anomalies, one 1.5 kilometres north west from Murrawombie and the other 500 metres south of Avoca Tank. The third drillhole targeted down plunge extensions to mineralisation at the Caribou prospect (located within the Larsens – Northeast mining province). Previous exploration drilling activities at the Caribou prospect intersected variable amounts of copper sulphide mineralisation with several encouraging results including;
- TCBD007 6.0m @ 3.45% Cu (true thickness approx. 4m);
- TLRNM006 4.7m @ 3.05% Cu (true thickness approx. 2m);
- TLRNM002 28.8m @ 1.56% Cu (true thickness approx. 16m) including 15.5m @ 2.03% Cu (true thickness approx. 10m).
Drillhole TCBD010 was drilled targeting 100 metres down plunge to the known mineralised system. The drillhole intersected a broad zone of pyrite +/- chalcopyrite disseminations and minor stringer veins (total sulphide content <5%) over an approximate 40 metre interval (assays pending). Strong chlorite alteration was observed throughout the sulphide interval which is commonly in close association to mineralised systems elsewhere in the region.
A downhole EM (DHEM) survey was completed down TCBD010. The DHEM survey detected an off-hole conductor above the drillhole which corresponds with the mineralised zone intersected from previous drilling. The modelled plate extends further down plunge than previously modelled DHEM plates (combined total plunge extent 200 metres).
The drill results and modelled DHEM plates at the Caribou prospect are encouraging and may reflect a similar mineralised system to the Larsens deposit (~1Mt @ +2% Cu), located 300 metres to the west.
The remaining two drillholes did not intersect sulphide mineralisation. MNWD002 targeting an IP anomaly north west from Murrawombie intersected a graphitic shear at the target depth. Drillhole TAVD002 targeted a potential MLTEM conductor south of Avoca Tank.