|The watermelon-seed shaped nuggets were originally eroded out of an ancient gold system and re-deposited via rivers in a large outwash zone.|
Novo has traced the nugget-rich, 2.7 billion year old conglomeratic package almost continuously along an 8-km strike length. The rocks dip 10 degrees to the southeast under a cover of basalts.
“We’ve never drilled the target, and have no information about the conglomerates down-dip,” Hennigh says. “There’s a historic drill hole that an Australian mining company did 55 km south of Purdy’s which returned 1 metre of 12 gram gold. And from what we see in the photos, it looks similar so we’re hopeful this could be a big system.”
Hennigh has been hunting for a Witwatersrand-type deposit in Western Australia’s Pilbara craton for years, and for a good reason: the Archean-age chunk of crust was once adjoined to South Africa’s Kaapaval craton and its prolific gold deposits.
Both the Kaapaval and Pilbara are two of the oldest cratons left on earth. They formed 3.9 billion years ago, when chains of volcanic islands accreted continents of greenstone belts surrounded by an ocean and in an atmosphere devoid of oxygen.
The Wits basin got its start around 3 billion years ago when the greenstone belts of the Kaapaval craton began to erode, blanketing a 300-metre long basin with sediments up to 7 km thick.
The majority of the gold is found in two stratigraphic levels of the Wits basin — the Main Reef and Bird Reef — and is often associated with carbon.
However, the source and deposition of gold in the Wits has been debated for a hundred years. The most accepted theory is the modified paleoplacer model — gold was washed down from the surrounding gold-rich greenstone belts, and later remobilized as the basin was deformed over the course of history.
A competing theory is that the gold was carried in acidic solutions that migrated through the unconsolidated sediments and deposited in chemical traps, such as the carbon-bearing reefs.
“The tenor of gold we’re seeing at Purdy’s Reward is quite different than the Witwatersrand Basin. The Central Rand Formation in the Basin is a series of conglomerates that are 1-metre thick and contains really fine gold, whereas at Purdy’s Reward it’s 10-metres thick with really coarse gold,” Hennigh says. “What we’re potentially dealing with is a proximal version of the Witwatersrand, closer to the gold source.”
Unlike Witwatersrand, the conglomeratic horizon at Purdy’s Reward is hosted within a 50- to 100-metre thick package of sedimentary rocks underlying basalt flows, rather than a thick sedimentary basin.
Novo has consolidated a 7,600-sq km land position south of the city of Karratha, targeting possible extensions of the gold-bearing conglomerate horizon seen at Purdy’s Reward and a similar horizon at its Comet Wells project, 3 km southwest.
Purdy’s Reward is subject to an earn-in agreement with Australian explorer Artemis Resources, whereby Novo is entitled to earn 50% interest in the paleoplacer gold targets at the project, whereas Artemis retains 100% interest in all of the other minerals.