The Union Reefs mining area is located approximately 15 kilometres to the north of the town of Pine Creek and approximately 185 kilometres to the southeast of Darwin in the Northern Territory of Australia, immediately adjacent to the Union Reefs mill.
Historical production in the Union Reefs area dates back to 1880 with sporadic exploration continuing until 1991 when Acacia Resources/Anglo Gold Australia brought the property into production in 1995 with production continuing until 2003. During the 1995-2003 period, over 17 million tonnes of ore was mined at a grade of 1.63 grams/tonne gold (“g/t Au”) yielding over 800,000 ounces of gold. Production was from 12 open pits
The mineralization at Union Reefs is located in the Pine Creek Shear zone and consists of lode style veins up to four metres thick, stockwork veining and sheeted-vein systems, which are generally steeply dipping to either the east or the west depending on the location. The mineralization is located in two north/south trending zones within the shear, namely the Union Line and the Lady Alice Line (refer to Figure 2 below).
Mineralization is associated with arsenopyrite and other minerals containing sulphide including pyrite, pyrrhotite, sphalerite and galena in addition to sparse copper minerals. Coarse gold is also common in the mining area, with single grains up to five millimetres across documented by past miners.
Mineralization is hosted mainly by greywacke, carbonaceous shales and minor conglomerate of the Burrell Creek Formation.
In addition to the existing resources at Prospect Claim and Esmeralda, further potential at these and other areas have been identified. A brief summary of some of the more notable areas is outlined below.
Crosscourse
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Historically 13.9 million tonnes of ore was mined from the Crosscourse open pit at 1.63 g/t Au for production of 732,379 ounces of gold, which represents more than 83% of ounces produced from the Union Reefs project area. The historic strip ratio was 5.2 to 1;
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Currently Crosscourse is being used as a tailings storage facility meaning potential future open pit mining is limited and underground mining would have to incorporate the tailings into the design;
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Historic drilling indicates the orebody continues downplunge below the existing pit.
Some historic intersections on the E Lens, which plunges north into the wall of the pit, include:
Some historic intersections on the Western Lens, which cuts below the main ramp of the pit, include:
- 19m @ 10.62 g/t Au, 9m @ 24.40 g/t Au and 9m @ 4.00 g/t Au.
Additional drilling down dip of these areas is required to further evaluate mining potential.
Prospect Claim
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Historically, 412,000 tonnes of ore was mined at the Prospect Claim pit at 1.60 g/t Au for production of 21,242 ounces at a strip ratio of 7.6 to 1;
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The Prospect Claim pit was one of the last to be developed by AngloGold; and
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In addition to open pit potential, there is also potential for mining underground. However, further drilling is required as the underground potential was only tested to a depth of 30 metres below the historic open pit.
Big Tree/Millars
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Big Tree and Millars are small open pits with extensive historic workings identified during mining;
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Just over 10,000 ounces were produced by AngloGold from these two pits.
Some significant intercepts from drillholes in areas not yet mined include:
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2m @ 220.00 g/t Au, 5m @ 17.30 g/t Au, 3m @ 16.50 g/t Au and 2m @ 7.10 g/t Au at Millars; and
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4m @ 44.00 g/t Au, 4m @ 18.80 g/t Au, 4m @ 13.10 g/t Au, 5m @ 5.90 g/t Au, 3m @ 7.80 g/t Au and 2m @ 10.70 g/t Au at Big Tree
There is underground high grade narrow vein potential along with some open pit potential. Further drilling is required.
Lady Alice
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Lady Alice was the only pit to be mined close to 100 metres in depth outside of the Crosscourse pit and Union North pit;
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Historic mining at Lady Alice was over 573,000 tonnes of ore at a grade of 1.53 g/t Au for production of over 28,000 ounces of gold with a strip ratio of 7.3 to 1;
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There is potential for underground mining below the existing pit but further drilling is required; and
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There is open pit mining potential to the north and south along strike from the existing pit but historic drill intersections in this area require follow-up with more detailed drilling.
