Exploration and Development
The Company’s proposed strategy for the Gum Creek Gold Project comprises three key objectives:
- undertake extensional and infill drilling to grow the known resources and lift defined resources into higher-confidence JORC categories;
- undertake regional exploration targeting new gold discoveries outside of the known resources; and
- carry out development studies (including but not limited to metallurgical and processing investigations) on the free milling and refractory mineralisation.
High-Grade Mineralisation Intersected at Premium-Butcherbird Prospect
- A first pass, twelve-hole diamond drill program to test the Butcherbird Shear and Swan Premium Lode intersected high-grade gold mineralisation, 5.0m @ 10.6g/t Au from 257.0m in SBDD073;
- Results received from first four holes, with assays from remaining eight holes expected in September; and
- A single diamond drill hole to test previously reported broad Volcanic-Hosted Massive Sulphide (VHMS) style copper mineralisation intersected semi massive sulphide mineralisation at the Altair Prospect. Assay results pending.
On 17 September 2018 the Company provided an update on its recent exploration activities [here]. Activities reported included:
- Diamond drilling at the Butcherbird Shear and Swan Premium Lode Exploration Targets, including initial gold assay results from the first four diamond holes of an initial twelve-hole program;
- Air-core (AC) assay results for Wahoo East and Toedter West; and
- Diamond drilling at the Altair Copper Prospect.
Premium Lode and Butcherbird Shear
As reported in the Company’s Announcement dated 7 July 2018, Horizon undertook a reinterpretation of the geological controls on high-grade gold mineralisation in the Premium Lode and Butcherbird Shear at the northern end of the Swan system. This reinterpretation highlighted the potential to significantly increase the underground Mineral Resources in this area with additional exploration drilling.
Following the geological reinterpretation, the Company estimated Exploration Targets of between 30,000oz to 100,000oz contained gold for the Premium Lode and 270,000oz to 800,000oz contained gold for the Butcherbird Shear.
An initial diamond drill program of 12 holes totalling 4,897 drill metres on the Premium Lode and Butcherbird Shear Exploration Targets commenced in late June 2018 and was completed on 22 August 2018. The aim of the program was to assess the validity of the Exploration Targets by drilling a broad spread of holes to test and support the predicted thickness and grade of the models in those areas.
Figure 1: Long section looking west showing historical and new drill hole pierce points testing the Butcherbird Shear and Premium Lode.
Figure 2: Cross section 6983780N looking north showing historical and new drilling intercepts on the Butcherbird Shear and Premium Lode
Zones of quartz flooding with minor sulphide mineralisation were intersected at the anticipated target depth in most holes. True widths of the quartz flood zones intersected in the current program are estimated to be up to 5 metres.
In addition to the intercepts interpreted to be on the Butcherbird Shear, several other unexpected quartz-sulphide structures were intersected. At this stage the Company is unable to correlate these structures with the known lodes and is therefore uncertain of their economic significance.
Gold assay results were received for holes SBDD075, 076, 077, 078 and 080. Significant assay results interpreted to reflect the Butcherbird Shear include:
- 8.0m @ 19.7g/t Au from 297.0m in SBDD080;
- 6.6m @ 10.9g/t Au from 265.9m in SBDD076; and
- 5.0m @ 10.6g/t Au from 257.0m in SBDD073.
In addition to these interpreted Butcherbird Shear intercepts, several other unexpected quartz-sulphide structures were intersected, including:
- 0.8m @ 17.4g/t Au from 132.0m in SBDD075;
- 6.0m @ 7.9g/t Au from 134.0m in SBDD076;
- 2.2m @ 9.6g/t Au from 128.55m in SBDD077; and
- 3.0m @ 9.8g/t Au from 148.9m in SBDD080.
Photograph of mineralisation in hole SBDD073 with individual 1 metre gold assays shown in red.
Discussion of Results
Zones of quartz flooding with minor sulphide mineralisation were intersected at the anticipated target depths in most holes. True widths of the quartz flood zones intersected in the current program are estimated to be up to 5 metres. Together with the assays received so far, the results are interpreted to be supportive of the modelled Exploration Targets.
For holes SBDD073, SBDD076 and SBDD080, intersected thicknesses and gold grades exceed the parameters used to estimate the Butcherbird Shear Exploration Target.
The Company notes that the gold mineralisation in the Swan system is highly variable and that correlation of high gold grades, even between closely-spaced drill holes, can be difficult. For this reason, the Company urges caution when considering the economic significance of the results obtained to date.
Follow Up Work Program
The Company is highly encouraged by the results of the initial program. As is apparent from the long section in Figure 3, there are very few drill holes in the vicinity of holes SBDD076 and SBDD080. Diamond drilling to infill this area is planned as a priority once all results of the current program have been received and a new and more comprehensive evaluation of the economic significance of the results is completed.
It is important to note that in addition to the interpreted Butcherbird Shear intercepts, several other unexpected quartz-sulphide structures were intersected. At this early stage and until all assay results have been received, the Company is unable to correlate these structures with the known lodes and is therefore uncertain of their economic significance.
The Company plans to provide a further update including a discussion of any material changes to the potential scale or quality of the Exploration Targets resulting from the initial exploration drilling program.
Figure 3: Long section looking west showing historical and new drill hole pierce points testing
the Butcherbird Shear and Premium Lode
Altair Copper 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 4). 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 4: Geological plan of the central Gum Creek project area showing the location of Altair and Mensa Prospects
Recent Drilling by Horizon Gold
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 5: 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 4). 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 10, 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 6: Altair Prospect – Cross section 7006420mN (± 20m)
Follow-up Work Program
The zinc grade of the ALDD002 intercept is an order of magnitude greater than any historical Altair drill result and clearly justifies further drilling. A program of follow-up drill holes will commence November 2018 to determine the orientation and extent of the zinc and copper mineralisation. In addition, the Company will re-examine the prospectivity of the interpreted target stratigraphy extending north from Altair and including the Mensa Prospect.
Toedter West Air-core Drilling
Air-core drilling of the Toedter West and Wahoo East prospect areas was completed in late July 2018 and assay results have now been received.
Toedter West is a series of small coincident magnetic and electromagnetic geophysical targets over a strike length of 6km. These targets were interpreted by the Company to be possible sulphide-bearing banded iron formations (BIFs) prospective for gold mineralisation. A single reverse circulation (RC) hole (GWRC482) drilled at Toedter West by the Company in 2017 intersected 1m @ 20.6g/t Au from 133m. At the eastern end of the target is the Toedter prospect, which has an existing Mineral Resource of 34,200oz.
A total of 87 holes for 2,775 drill metres was completed at Toedter West in the current program. Four-metre composite samples were submitted for analysis by fire assay using 30g charge. Best assay results from the Toedter West program include:
- 3.0m @ 0.71g/t Au from 76m in GPAC1353.
Drill hole traverse locations are shown in Figure 7.
Whilst the initial results have not met the Company’s expectations, it should be noted that only a limited extent of the 6km strike length of the target have been tested. A further refinement of the targeting criteria is now recommended.
Figure 7: Plan of Toedter West Prospect showing air-core drilling traverses on coloured EM conductivity and greyscale magnetics
Wahoo East Air-core Drilling
The Wahoo East prospect is interpreted from magnetics as an untested shear zone that has been intruded by a late granitic body. A total of 74 drill holes for 3,711 drill metres tested this target. Four-metre composite samples were submitted for analysis by fire assay using 30g charge. No significant results were returned from Wahoo East, and no further work is planned at this time.
Drill hole traverse locations are shown in Figure 8.
Figure 8: Plan of Wahoo East Prospect showing AC drilling traverses on coloured TMI magnetics