In a recent presentation, Kavango Resources’ consulting geologist Jeremy Brett spelt out just exactly why he thinks the opportunity on offer at the firm’s Kalahari Suture Zone project is so significant.
Author: Alexander Crossing
Brett, more than anyone, should know.
He spent a significant amount of time working on the Kalahari Suture Zone, or “KSZ”, some 20 years ago, and was only too pleased to be able to bring his deep knowledge to bear when he hooked up with Kavango last year.
Brett spoke at some length about the potential of the KSZ, focussing on particular on a more recent area of interest; the potential existence of an iron-oxide-copper-gold, or “IOCG”, system starting at depths of around 900 metres and beyond.
First off, though, he laid out the geological context in which the Kalahari Suture Zone operates.
It is, he said, a north-south striking feature in the southwest of Botswana that shows up as magnetic in aeromagnetic surveys.
Interest in recent years has focussed on the potential for mineralisation at shallower depths than the potential IOCG target, as from about 500 metres there are strong indications that the rocks offer what Brett called “a good host environment” for nickel, copper and platinum group elements.
In many ways, that shallower mineralisation resembles the great Norilsk nickel deposit in Russia, so it’s by no means to be sniffed at.
But the IOCG target also bears comparison to a world-class mining project–BHP’s Olympic Dam project in Australia.
Given the immense yield in metals that Olympic Dam has already delivered, never mind what’s still to come, it’s hardly surprising that Kavango is drawn into a closer investigation of its own Olympic Dam lookalike.
The key to understanding the opportunity that’s on offer, said Brett, is an appreciation of the target known as the Great Red Spot.
“This,” said Brett, “is a large magnetic body, five kilometres by eight kilometres, at the northern end of the KSZ. It lies at the nexus of multiple interpreted regional faults and structures.”
That may sound a bit too much like geospeak, but essentially, what it means is that the potential that mineralising events have occurred in these rocks is very high.
And the thing about IOCGs is that they are big.
Typically, said Brett, they are ten kilometres long, or more.
But how do you go about finding one and proving it up?
One important early step is to focus on the iron oxide portion of the iron oxide-copper-gold structure.
Essentially, Brett explained, IOCGs are big heat systems – and the incredible temperatures involved cause alteration to the rocks.
“In the case of IOCGs,” he said, “the alteration can lead to various types of iron oxide alteration.”
Specifically, magnetite and haematite.
Both occur in IOCG systems, but they have different qualities, which is helpful from an exploration perspective.
Magnetite is magnetic, so it shows up on a magnetic survey.
Haematite is quite dense, so it shows up on gravity survey.
If you find the two in close proximity or overlapping, it can be a sign that you’re on the right track.
And in the case of Kalahari Suture Zone, the initial indications are good.
Brett showed a slide which showed the geophysics of Botswana, as rendered from space. This satellite gravity map highlights the present of a gravity anomaly in proximity to the Great Red Spot.
So, a big tick in the box right there.
What’s more, the aeromag and gravity survey data can now be complemented by data gleaned from Kavango’s recent drilling programme. This intersected 4% magnetite–another encouraging sign.
Accordingly, Kavango has undertaken some detailed modelling of the geological structures it now thinks are operating at depth at the Kalahari Suture Zone.
Brett spoke of a ring structure that the company has modelled above the Great Red Spot, as well as a series of vertical dykes running up from it–all of which could be of potential interest. According to the model, multiple structures have intersected the Great Red Spot, giving more potential for intrusions.
And in addition, there are also multiple intrusions going due south of Great Red Spot.
So, plenty to ponder there.
Brett also highlighted the broader geological setting, noting that most IOCGs are located at the edges of cratons, thickened portions of the earth’s crust.
“Cratons,” he said, “are where you have faulting and fractures, which are great conduits for intrusions.”
The Great Red Spot itself is on the edge of what’s known as the Kaapvaal Craton, and so once again fits the model.
Certainly, there’s enough here to merit plenty of further work.
After all, as Brett pointed out, Kavango now has at least as much information as Western Mining had back in the 1970s when they took the decision to go for discovery at Olympic Dam.
Back then, they had magnetics and gravity data.
“They drilled on those two criteria,” said Brett, “and we’ve got those.”
But time has moved on, and these days Kavango has an extra tool it can bring to bear – audio-magnetotellurics.
Kavango’s already deployed this newfangled resistivity technology, and the results returned have given grounds for further optimism.
“We have a lot of complexity, and this is what I was hoping to see,” says Brett. “And complication is generally quite good in looking for ore deposits. You want complications, you want structural complexity, you want changes.”
The information gleaned represents the company’s first steps to identifying new targets in the Great Red Spot.
It looks like the Kalahari Suture Zone has plenty more secrets that it might, at last, be ready to yield.
Author: Alexander Crossing
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