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 6 November 2018, the Altair follow-up eight-hole drill program commenced and was completed on 8 December 2018, for a total of 2,648 drill metres. The aim of the program was to provide a clearer understanding of the geological setting and orientation of the Altair Zn-Cu mineralisation by drilling a pattern of close-spaced holes around ALDD002 (Figure 4). The holes were drilled with RC pre-collars and NQ2 diamond core tails.
Figure 4: Altair Prospect – drill hole location plan showing position of current & historic drill holes
Assay results for the primary mineralisation in the first four holes of this program have been received. Assays of the primary mineralisation in the remaining four holes and pre-collars for all holes passing through the supergene zone are still pending. A summary of the follow-up drill program and assay results received to date are presented below.
ALDD002*: This hole passed through a thick sequence of sulphidic black shale typically containing 10% to 20% pyrite within thin (generally <5mm thick) layers. Significant primary zinc-copper mineralisation was returned from the base of the black shale sequence, including 55.0m @ 3.32% Zn and 0.52% Cu from 184.0m, including 9.0m @ 6.69% Zn and 1.00% Cu from 213.0m. The zinc mineralisation was observed to occur as fine grained red/brown sphalerite associated with magnetic pyrrhotite in sub-millimetre stratiform layers interpreted to reflect original bedding plane deposition. Hole ALDD002 also intersected secondary supergene copper mineralisation, including 2m @ 2.4% Cu from 62m.
ALDD003: Drilled 60m to the west (up-dip) of ALDD002 on Section 6420N. The hole passed through the target sulphidic black shale sequence from surface to 149m. Anomalous (+0.2% Zn) primary zinc mineralisation was intersected over 21m between 127m and 148m, however no intervals exceeded 1% Zn (Figure 5). Minor supergene copper mineralisation was also intersected, including 1m @ 1.0% Cu from 59m.
ALDD004: Drilled 60m to the east (down-dip) of ALDD002 on Section 6420N (Figure 5). The hole passed through the target sulphidic black shale sequence from surface to 266m. Anomalous (+0.2% Zn) primary zinc mineralisation was intersected over 138m between 128m and 266m, including the following significant zinc-copper intercept:
- 39.0m @ 2.34% Zn and 0.48% Cu from 160.0m.
ALDD005: Drilled 60m to the south of ALDD002 on Section 6360N (Figure 6). The target sulphidic black shale sequence was intersected from surface to 242m. Anomalous (+0.2% Zn) primary zinc mineralisation was intersected over 38m between 108m and 146m and over 33m from 198m to 229m, however no intervals exceeded 1% Zn.
ALDD006: Drilled on Section 6360N. The hole intersected the target sulphidic black shale sequence from surface to 286m. Anomalous (+0.2% Zn) primary zinc mineralisation was intersected in several zones between 160m and 286m, and included the following significant zinc-copper intercept (Figure 6):
- 35.0m @ 2.64% Zn and 0.52% Cu from 251.0m.
Figure 6: Altair Prospect – cross section 7006360mN (+20m) showing significant zinc intercepts for ALDD006
ALDD007: Drilled 60m to the north of ALDD002 on Section 6480N (Figure 7). The hole intersected black shales from surface to 174m. Portable XRF analysis of the core and RC chips indicate the hole intersected a zone of elevated Zn levels between 100m and 130m down hole. Assay results are pending.
ALDD008: Drilled on Section 6480N (Figure 7). Black shale was intersected from surface to 175m. Portable XRF analysis of the core and RC chips indicate the hole intersected a zone of elevated Zn levels between 100m and 130m down hole. Assay results are pending.
Figure 7: Altair Prospect – cross section 7006480mN (+20m) showing interpreted zinc mineralised zones in ALDD007 & ALDD008
ALDD009: Drilled on Section 6420N, 120m further to the east (down dip) from ALDD002 (Figure 5). This hole passed black shale from surface to 255m. Portable XRF analysis of the core indicate ALDD009 intersected a zone of elevated Zn levels between 152m to 180m down hole. Assay results are pending for this zone.
ALDD010: The final hole of the follow-up drill program was drilled 120m to the south of ALDD002 on Section 6300mN. The hole was drilled to a depth of 271m, entirely within a highly deformed and altered sequence of intermediate volcanic agglomerate. Portable XRF analysis did not indicate any significant mineralisation. No samples were submitted for assay from ALDD010.
*Refer to the Company’s ASX announcements of 4 October 2018 and 23 October 2018
Discussion of Results
The Company is highly encouraged by the latest drill results from Altair. The follow-up drill program achieved its aim of providing additional understanding of the geological setting, orientation and plunge of the Altair primary zinc mineralisation. Based on this latest drill data, the Company interprets the sulphidic black shale that hosts the primary zinc mineralisation to have a shallow to moderate plunge to the southeast, the orientation either representing an embayment in the underlying volcanic sequence or post-depositional folding. Based on the geology observed in hole ALDD010, the Company interprets that there may be a faulted contact to the south, which possibly offsets the mineralised black shale.
The area of +1% zinc mineralisation is interpreted to be open to the east with a possible down-plunge direction towards the east-southeast. A plan and longitudinal section demonstrating the interpreted geological setting is shown in Figures 8 and 9.
Figure 8: Altair Prospect – Longitudinal Section 730 950mE (looking west)
Figure 9: Altair Prospect – Showing interpreted geology and priority follow up drill holes
Follow-up Work Program
The Company has designed a second follow-up drill program of seven holes (Figure 9) to test the continuation of the Altair mineralisation to the east. The program is scheduled to commence early in the new year, following completion of drilling currently underway testing for high-grade gold mineralisation at Butcherbird Shear / Premium Lode. The Company will also commence testing along strike to the north of the Altair discovery towards the Mensa Prospect, 5km to the north-northeast of Altair, where shallow historical drilling has identified anomalous copper and zinc mineralisation in a similar geological setting to Altair. To facilitate these plans, the Company is currently trialling a series of geophysical techniques (including gravity, magnetics and downhole EM) at Altair to determine which techniques are best suited for detection of this style of mineralisation.