Tasman has a very large and strategic tenement holding (EL6416, 1,079 km2) adjoining BHP Billiton’s world class Olympic Dam deposit in central South Australia (Figure 1). The prime target is iron-oxide associated copper-gold (IOCG) deposits of the Olympic Dam style, although potential for other base metal and diamond deposits has been recognised. The project was farmed out to Fortescue Metals Group (Fortescue) in mid 2019. Fortescue can initially earn a 51% interest by spending $4million+GST over 3 years.
Tasman explored this tenement for a number of years, with drilling having been conducted at a number of prospects. Tasman considers the most prospective of these to be Vulcan.
In late-2009 Tasman drilled the first hole at the Vulcan prospect, located about 30km north of Olympic Dam (Figure 1). The hole was drilled on the north-western margin of a large gravity anomaly, which compares very favourably in size with other IOCG deposits such as Olympic Dam or Carrapateena.
Tasman completed 8 diamond drill holes before negotiating a farm in with RIO Tinto Exploration (RTX) which commenced in late 2012 with a cash injection into Tasman of $10 million. RTX announced their withdrawal from the Farm-In in March, 2014 following the completion of a 9 hole, 12,000m drilling program managed by Tasman.
Significant assay results from the 17 holes drilled by Tasman at Vulcan are listed in Table 1 and their locations are shown in Figure 2. Photos of mineralised drill core are shown in Figures 3a to 3f.
Table 1 Assay Results from Previous Tasman Vulcan Drilling
Note: Assay results for holes VUD03 to VUD15 were prepared and first disclosed under the JORC Code 2004. These results have not been updated since to comply with the JORC Code 2012 on the basis that the information has not materially changed since it was previously reported. Note that these are down-hole intersections and true widths are not known at this stage.^no top cut applied, 2m minimum downhole width.
Vulcan is a very large IOCG system, where drilling to date has intersected a number of very thick intervals of alteration and low grade mineralisation over a large target area (about 12km2). Figure 2 shows the outline of the target area as defined by gravity data and the location of the 19 drill holes completed up to September 2021.
Holes VUD 7 and 17 confirmed that Vulcan hosts mineralisation of the same style, and of comparable thickness to that which makes up a very large portion of the nearby Olympic Dam IOCG deposit, particularly the large tonnage bodies that occupy the south-eastern part of Olympic Dam. PACE funded Re-Os age dating of the mineralisation at Vulcan gave an average age of 1590 Ma which is essentially the same geological age as other significant IOCG deposits such as Olympic Dam, Prominent Hill and Carrapateena.
Commencing in late 2020 Fortescue completed a two hole, deep diamond drilling program (holes VUD0018 and VUD0019) to test the Vulcan North gravity anomaly, the first holes drilled at Vulcan since 2013. Both holes intersected substantial downhole widths of hematite breccia associated with low grade copper mineralisation. These holes also intersected elevated gold, rare earths and palladium in places. Significant results are shown in Table 2.
Table 2 Assay Results from Recent Fortescue Vulcan Drilling
# downhole width, true thickness unknown, ^no top cut applied, 2m minimum downhole width.
Although drilling has so far not intersected thick and medium to high grade mineralisation, it has demonstrated the potential for economic grades and widths. Tasman believes there are a number of very positive outcomes from the drilling completed to date that confirm Vulcan is indeed the site of a very large hydrothermal system, comparable in gross size to Olympic Dam. It is quite possible that based on the size of Vulcan, the overall inadequacy of drill testing to date and the variable styles of the large IOCG systems in the region that a substantial deposit could be found with further exploration and investigation.
The very wide zones of copper mineralisation including those intersected in the most recent holes, VUD0018 and VUD0019, accompanied by elevated palladium, gold, molybdenum and rare earth element values, as well other elements, demonstrate the highly fertile nature of the Vulcan IOCG system.
A large area to the immediate west of Vulcan is believed by Tasman to be an attractive, if more “grass roots” style exploration target. This area, which includes the Zeus IOCG target (refer Figures 1&4) is about 90km2 in area and is highlighted by a number of moderate-strength gravity and magnetic anomalies which appear to occupy the area linking the Vulcan IOCG system to another large (but low grade and magnetite dominated) IOCG system at Titan and the adjacent undrilled Zeus prospect (Figure 4).
Available drilling data suggests that basement in most of this area is probably shallower than at Vulcan; for example the depth to basement is generally about 600m at Titan.