Lefroy Exploration Limited’s (ASX: LEX) latest results from 128 holes of a 199 hole-8000m aircore (AC) drill programme that tested the eastern limits of the Burns Cu Au corridor in Lake Randall in November/December 2021, have enhanced a growing Cu-Au intrusion related mineral system over a 2000m corridor.
Drilling on Lake Randall is currently underway. Burns is within the Eastern Lefroy tenement package, which is part of the wholly owned greater Lefroy Gold Project (LGP) located 50km southeast of Kalgoorlie.
The Burns prospect is situated on the eastern margin of a large interpreted felsic intrusion, termed the Burns Intrusion. The intrusion does not outcrop but features a distinctive annular aeromagnetic and gravity geophysical signature. The company has not yet established the association between the larger Burns intrusion and the diorite porphyry intrusions intersected at Burns, but research is ongoing to source evidence to support a view on the genetic relationship.
Broad high-grade gold mineralisation is hosted within a newly discovered hematite-pyrite- chalcopyrite-magnetite altered diorite porphyry that intrudes high Mg basalt at Burns. This porphyry, termed the Eastern Porphyry, is open to the north and south. The eastern extent of the Eastern Porphyry is now defined, on multiple drill sections, by foliated basalt (footwall basalt).
The copper and gold mineralisation hosted by both the diorite porphyry, basalt and massive magnetite veins is considered to be a new and unique style of Au-Cu mineralisation near Kalgoorlie, within a land position dominated by Lefroy.
These are two outstanding gold intersections from aircore drilling out beneath Lake Randall that further demonstrates the growing scale of the Burns copper gold system,” Managing Director, Wade Johnson, said.
“We are fortunate to have the specialised lake rig on site elsewhere on Lake Randall and immediately mobilising back to Burns to scope out the footprint of this new mineralisation.”
A detailed aeromagnetic survey completed over the broader Burns area in August 2021 defined multiple Burns look alike magnetic anomalies over a 3000m trend, known as the Burns Corridor. The company interpreted the anomalies to represent magnetite alteration zones within and surrounding porphyry dioritic intrusions that are additional, and similar in style, to Burns and which may host similar Au Cu mineralisation.
The company developed a sound geological model and commenced a staged drilling programme to assess the broader limits of the Burns mineral system and surrounding geology in October 2021. This staged drilling programme aimed to evaluate the multiple magnetic anomalies but also to place Burns in the geological context of the wider area and, expand the geological framework to increase the exploration search space. Stage 1 of the programme involved drilling land-based targets using an RC rig, with results reported earlier in 2022,
The Stage 2 program used a specialised lake aircore rig to evaluate aeromagnetic targets (e.g., Lovejoy, Kenny’s Dream) in Lake Randall (offshore) immediately adjacent to and along the Burns corridor. That work was completed in December 2021, with a total of 7989m of drilling in 128 holes completed on a nominal broad 160m by 80m hole centre pattern. The drill density was increased where favourable geology was encountered. Assay results have been received for the 128 holes from that campaign.
The lake AC programme was expanded and drilling recommenced in January 2022 with a further 301 AC drill holes completed to date. Additional drill targets were generated in Lake Randall based on geological information derived from the late 2021 campaign and interrogated with geophysical (gravity & aeromagnetic) datasets.
Twelve new drill targets were generated in Lake Randall and extend approximately 15km to the east over the company’s tenure. This programme is well underway and aims to discover new gold and/or gold copper mineral systems, peripheral and parallel to the Burns corridor beneath Lake Randall and to infill the geological knowledge gap in this largely unexplored area.
The key areas of focus are: –
- Extension of the Burns diorite complex northwest of Lovejoy and out to Neon
- Demagnetised zones within the strike extensions of the Lucky Strike, Havelock and Erinmore sedimentary iron formations
- Targets (e.g., Monte Cristo) associated with the convergence of the regional Mt Monger and Randall Faults
- Immediate southeast strike extension of the sequence that hosts the gold mineralisation at Lucky Bay
Encouraging gold mineralisation has been intersected in 3 holes on adjacent 80m spaced drill sections. Results are pending for a further four drill sections to the north that cover at least 400m of strike of the Eastern Porphyry, part of which is covered by transported sediments from the Lefroy Palaeodrainage.
Significant results from this programme include:
- 16m @ 3.79g/t Au from 20m in LEFA1088 Including 8m at 7.31g/t Au from 20m
- 24m @ 2.86g/t Au from 16m to EoH in LEFA1089 Including 16m @ 4.04g/t Au from 20m
- 20m @ 0.47g/t Au from 20m in LEFA1091 Including 4m @ 1.05g/t Au from 24m
