The Torrens Project (EL5614) is a joint venture between Aeris Resources (70% interest) and Kelaray Pty Ltd (a wholly owned subsidiary of Argonaut Resources NL) and is exploring for iron-oxide copper-gold (IOCG) systems.
EL5614 is located within the highly prospective Stuart Shelf Region of South Australia and lies within 50 kilometres of Oz Minerals’ Carrapateena deposit and 75 kilometres from BHP’s Olympic Dam mine. The Torrens Anomaly, a large regionally significant coincident magnetic and gravity anomaly with a footprint in excess 120km2 (larger footprint than Olympic Dam) is located within EL5614.
Within the Torrens Project area, geophysical modelling/interpretation has identified 28 geophysical anomalies based on gravity and magnetic geophysical datasets. Of the 28 anomalies identified, 12 are based on gravity only anomalies.
 A gravity only anomaly in the Eastern Gawler Craton can be associated with a range of different geological rock/alteration features including but not limited to an IOCG system.
Limited drilling, totalling six drill holes between 1977 and 2008 defined a large magnetite dominant with lesser hematite alteration system interpreted to form the distal component of a large IOCG system. Zones of anomalous copper mineralisation (≥0.1% Cu) were intersected from several drill holes with the most significant mineralised zone associated with TD2 (246m @ 0.1% Cu).
Exploration activity on the project had been suspended since 2008 due to uncertainty regarding the Native Title status of the project area, and Aboriginal Heritage restrictions.
On 9th August 2016, Justice Mansfield of the Federal Court handed down his decision on the Lake Torrens Overlap Proceedings (No3). These proceedings were in respect of overlapping applications for a determination of native title rights over the lands and water of Lake Torrens, claimed by three separate native title claimant groups. The Torrens Project EL5614 is located within the disputed claim area. Justice Mansfield ruled that none of the overlapping claims had been proved. All claimants have made appeals to the full court. The court has not yet made a decision on the appeals and it may dismiss all the appeals. In the interim, the effect of the Mansfield decision is that the area of the project has no Native Title granted, nor any recognised Native Title claimants.
On 31 March 2017 the joint venture partners were granted a summary determination by the South Australia Environmental Resources and Development Court, in the absence of any Native Title claimants, of the Native Title authority for the conduct of exploration activities on EL5614 This allows the joint venture to submit the plan of activity with supporting environmental impact assessments. The State regulators will review and can approve the exploration activities.
On the 15 February 2018, the South Australian Minister for Aboriginal Affairs and Reconciliation approved an application by the Torrens Joint Venture under Section 23 of Aboriginal Heritage Act 1988. The authorisation allows for up to 70 deep diamond drill holes over an area of 120km² over the Torrens geophysical anomalies. This was the final approval required to enable the Torrens Joint Venture to proceed with on-ground exploration activities, including a major drill program.
An airborne gravity survey was flown over the entire exploration tenement (EL5614) during the March 2018 quarter. The high resolution gravity survey supersedes previous gravity data compilations dating back to the 1970s. The increased accuracy from the new gravity survey will better define rock density contrasts which will be used to more accurately define prospective targets for drilling.
On 5 December 2018, Aeris announced that the drilling and helicopter support contracts had been awarded in preparation for the drill program at Torrens. Mobilisation of equipment commenced in mid December with drilling commenced in mid January 2019.
The drilling program was heli-supported utilising a specialised heli-portable drill rig. Ten 6 metre x 2.8 metres raised work platforms will be transported by helicopter onto the lake and bolted together to act as a stable platform on the lake surface. The drill rig will be flown onto the platform in 16 sections and then re-assembled on the platform. Personnel, equipment, drill consumables and other materials will be transported via helicopter from the exploration camp to the work platform on the lake surface.
Drill Platform on Lake Torrens
The Stage 1 drilling campaign will consist of 8-10 drill holes focusing on the highest priority targets. The Torrens anomaly sits under approximately 400 metres of cover and drill holes are expected to be between 700 metres and 1,500 metres depth.
By early January 2019, key infrastructure (including an exploration camp to accommodate the workforce for the Phase 1 drilling program) and equipment had been mobilised to site. The heliportable drill rig and supplementary equipment, including work platforms, had also arrived onsite. Site based activities are now focused on completing the remaining infrastructure requirements to support drilling on Lake Torrens, including installation of the work platforms on the salt lake surface and water supply infrastructure for drilling. The various sections of the drill rig will then be transported by helicopter onto the work platforms and assembled.
The Stage 1 drilling campaign will consist of 8-10 drill holes focusing on the highest priority targets. The Torrens anomaly sits under approximately 400 metres of cover and drill holes are expected to be between 700 metres and 1,500 metres depth. On 21 January 2019, Aeris announced that drilling had commenced on the first hole.
The first drillhole, TD7 from the Phase 1 drill program at Lake Torrens was successfully completed as announced on 7 March 2019. Click here Torrens Project drilling Update.
Drillhole TD7 targeted a coincident magnetic and gravity anomaly defined from the FALCON geophysical survey flown early in 2018. TD7 was located approximately 1.5 kilometres from the shoreline of Lake Torrens and was drilled to a total depth of 858.6 metres. This drillhole (TD7) targeted a coincident magnetic and gravity anomaly defined from the FALCON geophysical survey flown early in 2018.
Preliminary geology observations of TD7 include a 60 metres wide intersection with hematite + K feldspar+ sericite altered non-magnetic interval. Hematite is recognised as an accessory mineral associated with IOCG mineralisation within the Gawler Craton.
Preliminary geology observations have identified a broad zone of skarn-like alteration containing magnetite ± K feldspar ± quartz ± chlorite. The alteration assemblage was expected and is consistent with similar magnetite dominant alteration intersected within previous drillholes on Lake Torrens.
Within the broader magnetite skarn, a 60 metres wide hematite + K feldspar + sericite altered nonmagnetic interval was intersected. The presence of hematite is important for several reasons:
1. Hematite is recognised as an accessory mineral associated with IOCG mineralisation within the Gawler Craton. Although not all hematite occurrences directly correlate with mineralisation, it does indicate the rocks have been exposed to an oxidizing fluid event which are a prerequisite for the formation of IOCG mineralization; and
2. The hematite alteration zone may help to explain the modelled gravity high anomaly within the broader magnetic high. Petrophysics data is being collected from TD7 and once complete will be used to update and refine the geophysical models to assist with refining drill targets.
The drill target, whilst prospective for IOCG mineralisation, is not the highest priority target and was chosen for the first drillhole, in part, given its proximity to the shoreline (1.5 kilometres).
Drill core from TD7 will be transported to Adelaide for sample preparation (core cutting) and assaying next week, with assay results expected in towards the end of April.
Assay results from TD7 reported no significant copper mineralisation with the highest grade interval being 20m @ 0.15% Cu from 542 metres downhole, though the presence of elevated Cerium concentrations that were intersected toward the bottom of the drillhole were encouraging. Cerium and other rare earth elements (REE) are considered important geochemical vectors toward potential iron-oxide-copper-gold (IOCG) systems.
TD8 drillhole targeted a deep gravity anomaly further out under Lake Torrens.
Drilling of TD8 commenced on the 23rd February and is the first drillhole to be drilled beyond 4 kilometres from the Lake Torrens shoreline.
On 27th February the drillhole intersected an unexpected aquifer at approximately 100 metres downhole, which resulted in artesian water flow. Drilling activities was suspended once the aquifer was intersected and remediation actions enacted to stop the flow of water reporting to surface. The decision was made to discontinue drilling activities at TD8.
On 13 March, drilling of TD9 commenced. The updated drilling methodology was successful in managing an artesian aquifer intersected from 67 metres downhole. However, unconsolidated sand layers through the aquifer have proven more difficult to control than anticipated. Whilst addressing operational issues resulting from the unconsolidated sand horizons, an unintended consequence was water flowing from the drill collar which ultimately could not be appropriately managed. Consequently, the drillhole was discontinued at 145 metres and rehabilitated.
Drilling of TD10 commenced on 24th April 2019 and reached the target depth of ~1,280 metres on 28th May 2019. Drillhole TD10 had targeted a significant coincident gravity and magnetic anomaly, and intersected basement at 767 metres downhole. This drillhole passed through intensely altered host rocks containing variable amounts of K-feldspar, magnetite and hedenbergite. Trace amounts (visual observations)of pyrite and chalcopyrite were identified (assay results pending).
By the end of June 2019, two drill holes (TD7 and TD10) had been completed to target depths. Encouragingly, drill hole TD7 encountered low levels of copper mineralisation and elevated Cerium concentrations. Cerium and other rare earth elements (REE) are considered important geochemical vectors toward iron oxide- copper-gold (IOCG) systems. Assay results for drill hole TD10 are pending.
UPDATED GEOPHYSICAL INTERPRETATION
A detailed interpretation of the airborne Falcon gravity gradiometric survey flown over the project area in March 2018 was recently finalised. The Falcon survey was designed to enhance the gravity and magnetic geophysical signatures over the tenement, both of which are the primary datasets used to interpret the basement rocks which host IOCG mineralisation within the eastern Gawler Craton.
The geophysical interpretation from the Falcon Survey supports earlier observations that the Torrens project remains highly prospective for IOCG mineralisation. Areas of interest considered most likely to host an IOCG system are located within a broad spread of magnetic rich and moderately dense rocks. This background environment combined with the depth of the target zone (+450 metres from surface) makes the target anomalies more difficult to interpret than previously anticipated
Oblique view looking north east at the Torrens project area showing
A) shallow gravity response from the Falcon survey and B) modelled basement gravity (dark grey) and magnetic (light grey) bodies.
The unique drilling platform designed to enable drilling to occur from the surface of Lake Torrens performed exceptionally well and following modifications to drilling processes and procedures, the second completed drill hole (TD10) was successful in drilling through the aquifer.
By the end of June 2019, the camp and contractors had been demobilised and drilling activities paused while the drill data and updated geophysical survey information is reviewed.