Nickel Projects
Yarrabubba and Quinns Lake Projects
The Nickel-Copper-PGM Potential and the Sudbury Analogue
The Yarrabubba-Quinns Lake area was recognised by Impact's technical team to have most of the geological characteristics of the World Class Sudbury nickel-copper-PGM mining camp. An extremely large sub-circular magnetic low in regional magnetic data on open file at the Western Australian Department of Resources and Industry was interpreted to be the signature of a buried structure caused by a major meteorite impact. Field work in the area identified specific geological features, including melt breccias, pseudotachylite dykes, shatter cones and a granophyre near the centre of the feature, all of which are features associated with large meteorite impact structures, including Sudbury. There is published geological evidence that the impact at Yarrabubba occurred about 1,100 million years ago, and that the crater and its contents have been subsequently extensively eroded and mostly covered by younger sediments.
Independent reports note that nickel was first discovered near Sudbury, in Ontario, Canada, in 1883 where up to 35 mines have produced nickel. By 2000 the Sudbury mining camp had produced more than 9.6 million tonnes of nickel, 9.6 million tonnes of copper and 10 million ounces of platinum, as well as byproducts comprising 69 thousand tonnes of cobalt, 85 million ounces of silver and 3.7 million ounces of gold. In 2002 the total pre-mining resource was estimated to be 1,648 million tonnes of mineralisation at an average grade of 1.2% nickel, 1.08% copper and 1.2 g/t PGM's. Further, this was estimated to comprise 21% of the World's total mined plus unmined nickel resources at that time, and the Sudbury camp production for 2002 was estimated at about 21% of the World's nickel production comprising about 114,000 tonnes of nickel together with 137,000 tonnes of copper, 58,000 ounces of gold and 366,000 ounces of PGM's.
At Sudbury the nickel-copper deposits are associated with an elliptical basin that is about 65 kilometres long and 27 kilometres wide, containing layers of norite and diorites up to 3 kilometres thick, called the "Sudbury Igneous Complex".
The Igneous Complex is interpreted to be the solidified remains of a molten mass of the Earth's crust that accumulated in a crater, both generated by a very large meteorite impact that occurred about 1,850 million years ago. It was subsequently deformed into an elliptical basin long after the impact event. Its interpreted pre-deformation near-circular shape (see below). There are many major concentric and radial fractures and faults around this basin that are part of the impact structure, which is called the "Sudbury Structure". Many of the concentric and radial structures also contain solidified melt rock and rock fragments, forming breccias that are locally mineralised to economic levels.
The Sudbury nickel-copper deposits occur mainly in structures near and beneath the contact between the Sudbury Igneous Complex and the underlying and surrounding ancient gneisses in "Footwall" Deposits, as well as in the radial and concentric offset dykes, called "Offset Dyke" Deposits. For example, the Frood-Stobie Mine is a Footwall deposit exploiting a steeply dipping sheet of massive and disseminated sulphide mineralisation, locally as a breccia cement and up to 100 m thick, along a strike length of 3 kilometres and to a depth of 1,500 metres inside a major concentric fault. The total contained pre-mining resource of this deposit has been estimated at 450 million tonnes. The Offset Dyke deposits contain most of the ore at Sudbury and are interpreted to be emplaced by downward and lateral injection of the sulphide melt, together with some of the silicate rock melt, that accumulate at the base of the crater.
For example, a new discovery reported in 2004 in the Copper Cliff offset dyke is estimated to contain a resource of over 20 Mt at a grade of 3.5% combined nickel and copper, and 5 g/t platinum group metals.
In addition to these Footwall and Offset Dyke deposits there are copper and PGM-rich nickel deposits that occur as veins in the footwall to the Sudbury Igneous Complex, and there are modest deposits of zinc-lead-copper within the sedimentary rocks that overlie the rocks of the Sudbury Igneous Complex. All of these are interpreted to have formed during a long lasting hydrothermal event that was triggered by the meteorite impact, involving heated groundwaters.