The Broken Hill Project (Impact Earning 100%)
The Broken Hill Ni-Cu-PGE Project is located 20 km east of the World Class Broken Hill silver-lead-zinc mine in New South Wales, and consists of seven Exploration Licences covering 816 sq km in the south east part of the richly mineralised Curnamona Province (Figures 1 and 2).
Impact owns 100% of six of the licences. The mineral rights for the seventh licence, EL7390, are split as follows:
- 100% of the PGE-copper-nickel mineralisation; and
- 80% of the zinc-lead-silver Broken Hill-style mineralisation in EL7390 in joint venture with Silver City Minerals Limited (ASX:SCI). Impact will free-carry Silver City’s 20% interest to a Decision to Mine.
Golden Cross has a 1% gross production royalty on all metals to which Impact has rights for. Impact, at its election, also has the right to buy back the royalty for $1.5 million at any time up to a Decision to Mine, or leave the royalty uncapped during any production.
The project area contains several tens of strike kilometres of mafic-ultramafic sills, dykes and stocks that contain gossans and fresh outcrops with very high-grade PGE’s, nickel, copper, gold and silver mineralisation (Figure 2).
Impact has completed a significant amount of in-house research on these rocks which has lead to a new geodynamic framework for the Broken Hill area.
Implications for Exploration
The new geodynamic framework shows that the high grade nickel-copper-PGE mineralisation at Broken Hill was formed in a similar place to, at the same time as, and by the same processes that led to the formation of the Jinchuan deposit in China, one of the world’s largest magmatic sulphide deposits (Figure 3).
The confirmation of widespread alkaline intrusions across the Broken Hill region confirms there are at least several very deep seated structures in the area that have tapped the core-mantle boundary at about 800 million years ago and released mineralised magmas and fluids into the upper crust.
This new geodynamic framework has allowed the Broken Hill area to be viewed with “fresh eyes” in terms of its prospectivity for a wide range of mineral deposits formed later in the geological history than the major silver-lead-zinc deposit Broken Hill itself. A major target generation exercise based on this work is in progress.
These results add to previous work by Impact which has identified numerous areas for follow up work for high grade deposits of nickel-copper-platinum group metals (PGM)-cobalt both along the Rockwell to Little Broken Hill Trend and along the entire length of a mafic-ultramafic complex interpreted from regional magnetic and gravity data to extend over about 40 km of strike north east to the Moorkai Trend (Figure 2 and ASX Announcements 3rd May 2017 and 13th December 2018).
Very high grade primary nickel-copper-PGM-gold mineralisation has been discovered along this complex by Impact at both the Red Hill Prospect and also the Platinum Springs Prospect (Figure 2).
At Red Hill exceptional grades have been returned from drilling including a stand out intercept in vein hosted sulphide of:
1.2 metres at 10.4 g/t platinum, 10.9 g/t gold, 254 g/t (9.5 ounces) palladium, 7.4% nickel,
1.8% copper, 19 g/t silver and 0.5% cobalt (ASX Announcement 26th October 2015).
At Platinum Springs drilling returned a very high grade intercept in magmatic massive sulphide of
0.6 metres at 11.5 g/t platinum, 25.6 g/t palladium, 1.4 g/t gold, 7.6% copper, 7.4% nickel and
44.3 g/t silver (cobalt not analysed) (ASX Announcements 3rd February 2016 and 31st March 2016).
Both the Rockwell-Little Broken Hill Trend and the Moorkai Trend have been very poorly explored and many targets remain to be followed up.
For example, at Rockwell a coherent near-surface geochemical anomaly one kilometre long and
150 metres wide has been defined in shallow 2 metre deep auger drill holes along the north western margin of the complex with results of up to 0.1% nickel, 0.1% copper and 0.5 g/t PGM over a one metre thick intercept. There has been no drilling at depth.
Along the Moorkai Trend only Platinum Springs has been explored in detail. Exceptional high grade rock chip samples have been returned from numerous prospects between the Platinum Springs and Moorkai Prospects, a distance of about 9 km along the Moorkai Trend (ASX Announcement 13th December 2018).
It is evident that considerable scope exists to discover a significant nickel-copper-PGM-cobalt deposit within Impact’s Broken Hill project area.
In addition, it has been shown that alkaline magmas are the deep seated parental magmas to many world-class Iron Oxide Copper Gold Deposits (Figure 3). Impact interprets all of its data, in particular the association of high grade gold-copper with the high grade PGE mineralisation, to indicate the unusual mafic-ultramafic rocks at Broken Hill to be parental magmas for IOCG style mineralisation throughout the region.
This is an important exploration breakthrough for the company and comes at a time of record prices for palladium (currently ~US$1490/oz which is higher than gold). Exploration at Broken Hill will be reinvigorated as part of the 2019 field season.
A new Geodynamic Framework for Broken Hill
A new geodynamic framework for exploration has been identified following the widespread recognition of alkaline magmatic rocks throughout the Company’s ground holdings and the wider Broken Hill area.
Impact has shown that the very high grade palladium and platinum mineralisation at the Red Hill, Platinum Springs and Moorkaie Prospects and the Iron Oxide Copper Gold (IOCG) mineralisation at the Copper Blow Prospect (ASX:SCI) are hosted by and related to alkaline magmatic rocks (ASX Announcement 13th December 2018).
New work by Impact, done in conjunction with Independent Expert Emeritus Professor Ken Collerson of the University of Queensland, has now demonstrated that the alkaline rocks are related to a deep seated mantle plume that was related to the breakup of the Rodinia supercontinent about 800 million years ago.
At this time, Broken Hill and the surrounding Curnamona Province were positioned close to the world class nickel-copper-PGE deposit of Jinchuan (>500 Mt at 1.2% nickel, 0.7% copper and 0.4 g/t total PGE) and the significant Lengquisheng deposit (>30 Mt at 0.8% nickel and 0.3% copper (unknown PGE), which after breakup drifted to become part of China (Figure 4).
In addition Impact has identified the first recorded example in the Broken Hill region of rocks of carbonatite composition formed by the fractionation of the alkaline magmas. This is significant given that such rocks are host to major copper-gold-cobalt PGE-Rare Earth Element (REE) deposits around the world.
These major deposits formed as an integral part of processes associated with the mantle plume and accordingly confirm that the Broken Hill area and Impact’s ground in particular have the correct geodynamic setting to host a range of deposit styles related to this geodynamic setting including major nickel-copper-PGE, IOCG and carbonatite-related deposits.
The on-going review and synthesis of previous exploration results at the Broken Hill Project has highlighted:
- that around 500 tonnes of ore was mined from the dormant Red Hill Mine between 1906 and 1937, with face samples returning a grade range of:
2 to 4% copper, 2 to 3% nickel, 5 to 41 g/t PGE and 22 to 70 g/t silver;
- rock chip assays over a 130 m by 30 m area trending northeast from the Red Hill Mine, close to the contact between the host ultramafic intrusion and the surrounding rocks returned a grade range of:
1 to 36 g/t PGE and 0.2 to 6.1% copper; and
- previous exploration drilling has not tested the mineralised areas.
- Significant potential for the discovery of bulk tonnage PGE mineralisation together with very high-grade nickel-copper-precious metal massive sulphides throughout the Project area.
- A joint venture with Golden Cross Resources, Impact can earn 80% by spending a further $550,000 by 2017.
- Widespread high grade copper, nickel and platinum group mineralisation confirmed at the Red Hill Prospect.Tens of kilometres of strike of the ultramafic intrusions yet to be tested.
- High-grade massive nickel-copper sulphides and precious metals have been found at the Mulga Springs Prospect and include 4 m at 17.9 g/t Pt+Pd+Au, 2.3% nickel and 3.2% copper from 43 m in hole GMS-006.
- Outcrops of some of the highest-grade PGE gossans in Australia occur in many places along the Mulga Springs Gabbro and include the very rare PGE metals osmium, iridium and ruthenium.
Previous exploration has focused along the basal contact of the Mulga Springs Gabbro, a series of shallow northeast dipping mafic-ultramafic sills extensively developed over 10 km of strike from the Mulga Springs Prospect in the south to Moorakie in the north (Figure 5). Previous exploration at Mulga Springs has:
- identified a representative 120 kg sample of gossan which returned 19.6 g/t platinum, 50 g/t palladium, 3 g/t rhodium, 3 g/t osmium, 4.4 g/t iridium, 2 g/t ruthenium, 0.57 g/t gold, 0.34% nickel and 0.71% copper;
- identified drill intercepts (Figure 6) in fresh sulphide at about 45 m depth of:
GMS-006: 4 m at 17.9 g/t Pt+Pd+Au, 2.3% nickel and 3.2% copper from 43 m; and
DD4: 2.1 m at 8.3 g/t Pt+Pd+Au, 3% nickel and 3.5% copper from 45 m;
- demonstrated potential for the discovery of large deposits of very high grade nickel-copper-PGE massive sulphides and bulk tonnage PGE mineralisation among many tens of strike kilometres of mafic-ultramafic sills, dykes and stocks similar to those at Norilsk in Russia and Jinchuan in China.
Work by Endeavour has shown that the main body of the gabbro also contains extensive PGE mineralisation (Figure 7) with better intercepts of:
GMS-017: 14 m at 0.82 g/t Pt+Pd+Au and GMS-013: 12 m at 0.46 g/t Pt+Pd+Au.
The Red Hill Mine
The Red Hill Mine occurs in ultramafic rocks that cross cut deformed and metamorphosed rocks of the Broken Hill Group. The ultramafic rocks outcrop over an area of 500 m by 250 m and mineralisation occurs close to the western contact.
Red Hill was mined for copper between 1906 and 1937 both at surface and underground, from a vertical shaft to a depth of 36 m. Old mine records sourced by Impact indicate that about 500 tonnes of ore was mined from four parallel ‘lodes’, each 1 m to 2.5 m wide. Face samples from the underground mine returned a grade range of 2 to 4% copper, 2 to 3% nickel, 5 to 41 g/t PGE and 22 to 70 g/t silver. The lodes are open along strike and at depth (Figure 8).
About 70 rock chip samples taken over a 130 m by 30 m area trending northeast from the Red Hill Mine returned assays with a grade range of 1 to 36 g/t PGE and 0.2 to 6.1% copper near the western contact of the ultramafic rocks. These results have not been followed up.
Investors should note that these assays may have been upgraded by near surface weathering. However, at the Mulga Springs Prospect (Figure 1), drilling beneath samples with similar surface grades has identified massive sulphide mineralisation in fresh rock at about 45 m below surface with intercepts of:
4 m at 17.9 g/t Pt+Pd+Au, 2.3% nickel and 3.2% copper from 43 m; and
2.1 m at 8.3 g/t Pt+Pd+Au, 3% nickel and 3.5% copper from 45 metres.
Work at the Broken Hill Project is ongoing, with re-analysis and synthesis of previous exploration results expected to confirm the potential for bulk tonnage PGE mineralisation.
A field programme has commenced at the Red Hill prospect and comprises field checking and soil and rock chip sampling. Re-processing of a previous ground EM survey over the area is also underway.