More pieces have been put together in the jigsaw puzzle that is the largest undeveloped gold prospect in the country – at Sams Creek near Takaka in Nelson.
Discoveries made in the likely multimillion-ounce resource over the past two years by Perth-based company MOD Resources may have unlocked the key to finding where the highest gold grades are located in the massive deposit.
The porphyry dyke is at least seven kilometres long, up to 60 metres wide but plunges steeply down to a depth of about one kilometre. The dyke is believed to have been formed by molten rock about 100 million years ago, which would have carried gold mineralisation up from deep in the earth.
If Sams Creek is to be developed as an underground mine, the highest grades will need to be mined to make it economic. So far the best grade is 20 metres at six grams a tonne, with the longest gold intersection 60 metres at 2.4 grams a tonne.
The Sams Creek formation is known as an intrusion-related gold deposit (IRGD), many of which are known globally to contain multimillion-ounce resources and contain higher grades at depth.
Paul Angus, MOD’s project manager at Sams Creek, in a presentation to the AusIMM minerals conference in Hamilton, said exploration has now defined at least three major folds in the dyke.
The highest gold grades have been found in the fold hinges, he says. More gold-bearing arsenopyrite-pyrite quartz veins form along these hinges.
“Most of the mineralisation is occurring on the axis of these folds, which is quite different to what our previous thinking was.
“There is probably a million ounces of gold on one fold, another half a million ounces of gold on another fold hinge. There is obviously other mineralisation occurring between the folds,” he says.
“It’s a quite compelling model for exploration.”
The folds are quite long, possibly over some kilometres. In the three kilometres from the Main Zone (where a resource of over one million ounces has been defined) to the Western Outcrops there is potential for another million ounces of gold, he says.
A drilling programme of widely spaced drill holes is planned with the objective of testing the potential of fold extensions for one and a half kilometres west of the Main Zone.
MOD halted drilling at Sams Creek in the middle of the year while it concentrated on drilling its Kalahari copper belt prospect in Botswana and because of current investment sentiment toward gold as gold prices dipped.