Altair Copper-Zinc Prospect
The Altair Copper Prospect is interpreted to be Volcanic-Hosted Massive Sulphide (VHMS) style copper mineralisation associated with black shales and intermediate volcanics (Figure 1). Drilling in the 1990’s by previous explorers intersected broad zones of copper mineralisation, including the following assay results:
- 44m @ 1.2% Cu from 56m (ALAC005);
- 24m @ 1.0% Cu from 64m (ALRC007);
- 20m @ 1.1% Cu from 52m (ALRC002); and
- 20m @ 0.9% Cu from 64m (ALRC006).
Figure 1: Geological plan of the central Gum Creek project area showing the location of Altair and Mensa Prospects
A single diamond drill hole ALDD002 was completed to a final depth of 370.1m in August 2018. A mud-rotary pre-collar was drilled to a depth of 41.6m. Below this depth, the core is strongly oxidised from the commencement of coring at 41.6m to 124.6m, and partly oxidised to 132.0m. From 132.0m to 239.0m the hole passed through a thick sequence of sulphidic black shale. The shales typically contain 10% to 20% pyrite within thin (generally <5mm thick) layers. These pyritic layers are oblique to a well-developed cleavage in the shale and are interpreted to reflect original bedding surfaces. Significant zinc-copper mineralisation was returned from the base of the black shale sequence with assay results reported as follows:
- 55.0m @ 3.32% Zn & 0.52% Cu from 184.0m
The zinc mineralisation occurs as fine to very fine grained red/brown sphalerite associated with magnetic pyrrhotite in folded sub-millimetre stratiform layers interpreted to reflect original bedding plane deposition. This zone is also anomalous in other elements, with average values for the 43m zone including gold (0.11g/t), silver (11g/t), cobalt (327ppm), lead (0.1%) and tin (110ppm).
Due to the early stage of the exploration activities, guidance on the true width of the intercept is not available.
Within the wider zinc intercept, a high-grade zone is present which returned the following result, based on a 5% Zn cut-off:
- 9.0m @ 6.69% Zn & 1.00% Cu from 213.0m
Underlying the black shale sequence from 239.0m to 335.8m is a complex pyrite-rich zone, composed of microcrystalline quartz-rich (cherty) layers intercalated with interpreted volcanic agglomerates. The agglomerate clasts are intensely chlorite and/or biotite altered and occur within an intensely silicified matrix containing coarse blebs, stringers (and massive zones) of pyrite and minor pyrrhotite. Although strongly pyritic throughout, this unit only carries weak zinc mineralisation, with zinc assays typically less than 0.1% Zn.
Below the chert-agglomerate zone from 335.8m to the end of hole at 370.1m is a dark green, strongly chlorite-altered andesitic volcanic. This unit is essentially sulphide free and is not anomalous in zinc or copper.
Figure 2: Altair Prospect – drill hole location plan showing anomalous zinc and copper intersections
Discussion of Results
The Company interprets the geological setting of the mineralisation at Altair to be that of a VHMS / SEDEX environment. Evidence for this interpretation includes:
- Restrictive black shale depositional environment, overlying an interpreted volcanic exhalative chert horizon;
- Extensive chlorite alteration and pyrite development in footwall intermediate volcanics;
- Evidence for mineralisation to have formed pre-deformation, and possibly syn-deposition; and
- Anomalous geochemical pathfinder elements characteristic of VHMS / SEDEX systems.
Volcanic-associated mineral deposits tend to occur in district-scale “camps”, with individual deposits occurring in favourable stratigraphic positions over many kilometres. In this respect, the Company considers the Teutonic Bore group of deposits, located approximately 200km southeast of Altair, to be a relevant analogy.
At Teutonic Bore, favourable stratigraphy is thought to extend over approximately 40km, and contains three former or operating mines (Teutonic Bore, Bentley, Jaguar), the Triumph development project, plus a number of other regional exploration prospects. The original Teutonic Bore deposit was discovered in 1976, followed by Jaguar in 2002, Bentley in 2008 and Triumph in 2014. Current Resources total 6.5Mt @ 5.6% Zn, 0.9% Cu, 85g/t Ag and 0.4g/t Au (refer Independence Group NL (ASX:IGO) announcement of 23 October 2017).
Regional mapping and geophysical interpretation at Gum Creek suggests the target stratigraphy hosting the Altair prospect may extend at least 5km to the north to the Mensa Prospect (Figure 2). At Mensa, shallow drilling in the 1990’s by previous explorers intersected anomalous zinc mineralisation in a similar geological setting as Altair, including the following assay results calculated using a 0.1% Zn lower cut-off*:
- 6m @ 0.22% Zn from 50.0m in GMRC001; and
- 24m @ 0.19% Zn from 20.0m in GMRC002.
*Refer to the following open-file historical company technical reports submitted to the WA Department of Mines, Industry Regulation and Safety (DMIRS):
- WA Exploration Services Pty Ltd, Annual Report E53/665, Gum Creek Project, 1998. GSWA open-file report A54645
It is also possible that the favourable stratigraphy continues on the east side of the Gum Creek Greenstone Belt due to belt-scale synformal folding. At The Cup prospect, located approximately 40km southeast of Altair, Gateway Mining Limited has reported significant copper intersections including 80m @ 0.66% Cu from 65m in hole GRC200 (refer Gateway Mining Limited Annual Report 2012). Gateway interpret the mineralisation as being hosted within an intermediate to felsic volcano-sedimentary package, and that the host sequence, alteration and apparent metal zonation are highly suggestive of typical VHMS-style mineralisation.
It is important to note that base-metal geochemistry at Altair (and potentially more regionally) is strongly depleted to around 50m depth. As can be seen in Figure 3, the supergene copper mineralisation in ALRC006 and ALAC016 occurs below 50m depth, and was not intersected in the initial RAB and air-core holes drilled in the early 1990’s. This suggests that the historical wide-spaced and shallow drilling conducted in the Gum Creek Greenstone Belt may not have been an effective test for this style of mineralisation.
Figure 3: Altair Prospect – Cross section 7006420mN (± 20m)
On 26 March 2019, [ASX Announcement] the Company reported a Stage 2 drill program at the Altair Zn-Cu Prospect which confirmed extensions to the broad zinc-copper mineralisation first intersected in October 2018.
Assays results for the first six holes of the 2019 program included the following significant zinc-copper intercepts:
- 15.2m @ 2.33% Zn and 0.27% Cu from 136.0m in ALDD011, including
- 5.4m @ 3.84% Zn and 0.23% Cu from 137.0m
- 26.1m @ 1.93% Zn and 0.25% Cu from 244.0m and 43.5m @ 2.96% Zn and 0.50% Cu from 274.2m in ALDD012
- 78.0m @ 1.90% Zn and 0.32% Cu from 288.0m in ALDD014, including
- 14.0m @ 2.34% Zn and 0.51% Cu from 342.0m
- 35.6m @ 2.44% Zn and 0.43% Cu from 120.0m in ALDD016, including
- 19.0m @ 3.42% Zn and 0.54% Cu from 129.0m
Highlights of the drilling program also included:
- Broad continuous mineralisation delineated over a strike length of more than 450 metres and remains open to the east.
- The drill intercepts exhibited the geological and geochemical hallmarks of a major polymetallic, hydrothermal VHMS/SEDEX mineralising event.
- Final assay results for the six-hole program on the high-grade gold Butcherbird Shear / Premium Lode mineralised system at Swan have also been received
Stage 2 Drill Program
The program, consisted of 12 RC / Diamond drill holes for a total of 4,184.0m and was completed between 23 January 2019 and 5 March 2019. The aim of the program was to test the continuation of the Altair mineralisation along the interpreted down plunge direction towards the eastsouth east. Portable XRF data collected on the drill cores and RC samples indicate seven of the twelve holes have intersected broad zones of anomalous zinc mineralisation.
Assay results for the first six holes of the program are as follows:
ALDD011: drilled on Section 6360N (Figure 3) to intersect the primary zinc-copper mineralisation approximately 100m east of hole ALDD006. This hole has returned three primary zinc-copper intercepts. Based on a 1% Zn lower cut-off grade, the upper zones returned an intercept of 15.2m @ 2.33% Zn and 0.27% Cu from 136.0m. The central zone, which equates to the primary zinc-copper intercepts in holes ALDD006 and ALDD012 on Section 6360N returned 13.0m @ 1.57% Zn and 0.42% Cu from 232.0m. The lower zone, returned 11.0m @ 2.28% Zn and 0.49% Cu from 294.0m.
ALDD012: drilled 100m to the east (down plunge) of ALDD011 on Section 6360N (Figure 3). The hole passed through the target sulphidic black shale sequence from surface to 317.6m. Portable XRF analysis of the core indicated the hole intersected a broad zone of anomalous (+0.2%) zinc-copper mineralisation between 244 – 317.6m, which returned the following intercepts:
- 26.1m @ 1.93% Zn and 0.25% Cu from 244.0m; and
- 43.5m @ 2.96% Zn and 0.50% Cu from 274.2m.
ALDD013: drilled 60m due south of ALDD012 on Section 6300N. The hole skimmed in and out of the target sulphidic black shale sequence from surface to 295m, intersecting only weak, patchy zinc-copper mineralisation with the best result being 7.0m @ 1.06% Zn and 0.12% Cu from 174m. Drill hole ALDD013, together with holes ALDD015 and ALDD018 that were subsequently drilled on Section 6300mN, are believed to have effectively closed-off the Altair zinc-copper mineralisation towards the south and southeast (see “Discussion of Results” section below).
ALDD014: drilled 100m to the east of ALDD012 on Section 6360N. The target sulphidic black shale sequence was intersected from surface to 366m. Portable XRF analysis of the core indicated the hole intersected a broad zone of anomalous (+0.2%) zinc-copper mineralisation between 260 – 366m, which returned the following intercepts:
- 16.0m @ 1.70% Zn and 0.19% Cu from 264m; and
- 78.0m @ 1.90% Zn and 0.32% Cu from 288m.
ALDD015: drilled on Section 6300N, 100m to the east (down plunge) of ALDD013 . The hole intersected the target sulphidic black shale sequence from surface to 365m but did not intersect any primary zinc-copper mineralisation.
ALDD016: drilled 100m to the east (down plunge) of ALDD009 on Section 6420N). The hole intersected the target black shale sequence from surface to 312m. Portable XRF analysis of the core and RC chips indicated the hole intersected two broad zones of anomalous (+0.2%) zinc-copper mineralisation which returned the following intercepts:
- 35.6m @ 2.44% Zn and 0.43% Cu from 120.0m, including 19.0m @ 3.42% Zn and 0.54% Cu from 129.0m; and
- 17.0m @ 1.19% Zn and 0.34% Cu from 160m.
Assays results for the remaining holes of the program will be reported as soon as they become available.
Discussion of results
The Company is extremely encouraged by the latest Altair drill results. The latest drill program achieved its aim of providing a much greater understanding of the geological setting, orientation and plunge of the Altair primary zinc-copper mineralisation. Based on the results, the Company interprets the sulphidic black shale that host the Altair zinc-copper mineralisation, to occupy a narrow, steep-sided, trough-like depression in the underlying mafic volcanic sequence that formed by a combination of structure and possibly folding. In plan view, the trough has a gentle
arcuate shape, which is open down plunge towards the east.
Within the trough filled host shale sequence, the Altair primary zinc-copper mineralisation forms a thick, steeply south dipping, contiguous lens of mineralisation that mirrors the trend of the trough described above (Figure 8). The mineralisation appears to be thicker and slighter higher grade when
in proximity with the underlying mafic volcanic sequence at the base of the trough feature. From the base of the trough, the mineralisation rises steeply towards the north, into the saprolitic clay zone developed above the fresh rock interface. The Altair zinc-copper mineralisation and trough feature described above remains open to the east.
Holes ALD017, 019 and 022 (assay results pending) all contain significant zinc-copper intercepts based on portable XRF analysis of their respective cores.