From mineweb. Very interesting. Well worth a read imo. NB the part that I have highlighted. The whole article has relevance to THX and other explorers in the area (ie how difficult it is and what special skills are needed), but imo the highlighted part is pertinent to Red Bore because of the depth 0f C5 and its proximity to RB. SFR probably has a pretty good idea what's in RB, especially since it now has the seismic survey work interpreted. Remember that it was done along the border of RB.
Finding DeGrussa(s)
How Sandfire tapped an underappreciated region for VMS prospectivity.
Kip Keen |
30 June 2015 17:10
Officially opening the DeGrussa mine, Sandfire MD Karl Simich (left), WA premier Colin Barnett (middle) and Derek La Feria (right).
It was late 2008, in the midst of the global financial crisis, and Sandfire Resources had just laid off its entire staff. Karl Simich, Sandfire’s Managing Director and Chief Executive Officer, says the staff cuts could have gone slower. But Simich wasn’t keen to drag on a demoralizing process. “It felt like death by a thousand cuts,” Simich recalls. “We turned out all of our full-time and part-time staff which is a very difficult thing to do.”
Simich, speaking to me over the phone, is relating the story of how Sandfire would come to find the DeGrussa copper-gold deposit not long thereafter. It’s now in operation in Western Australia and, as an emerging region for VMS prospectivity, Sandfire recently showed the first real proof of significant VMS mineralization beyond the mine.
The company, very lean going into 2009 – just Simich and some board members – regrouped with a new strategy. Get a small gold mine going on ground they had been toying with for a decade or so. “And what I said to my technical co-director was: if he could just pull together a small gold resource we would be able to secure a plant and equipment facilities probably very cheaply, or potentially for free, and then have a third party toll treat…and we could use that, hopefully, to generate funds to keep the lights on, the company going.”
The project, what would become the DeGrussa copper-gold mine, was then known as Old Highway. It was near the old highway in the area. As Simich makes clear, they did not have VMS targets on their minds, at least not primarily. The region was little known for VMS deposits, and better known for gold. Simich points to the Plutonic gold mine, once a Barrick operation, but now under Northern Star’s roof. It is in the region – about 1,000 kilometres northeast of Perth – and has over the decades produced six million ounces gold. Simich and his colleagues had oxide gold in their sights, a near-surface, quick to production, kind of target. In early 2009 they hired back some geologists to oversee an exploration program under technical director John Evans.
The first priority target, as it turned out, didn’t gain any traction. It wasn’t a matter of lacking field results, but not being able to gain permission to get on the ground. Simich says the local indigenous people weren’t playing ball. So it was on to the second target, what would become DeGrussa.
They drilled an oxide gold anomaly. It didn’t look good. “We were getting mixed results to great frustration,” Simich says. “But some of those results were showing some signs of copper mineralization, some oxidized copper, and we were starting to get a little sulphide mineralization.”
That forced the still lean crew at Sandfire to reconsider the target for potential copper, which would mean drilling deeper. It was a close thing. The story goes that a gung-ho company geologist Margy Hawke got “permission belatedly” – which is to say, she went rogue in the field – to keep drilling with the reverse circulation rig past the oxide gold target at depth. Ground conditions were awful, with heavy faulting. Simich was in Perth and, as he put it, “complaining about technical successes and commercial failures.” He continued, “But ultimately we decided to spend an extra A$50,000 on vertical RC holes to see if anything was going on under the initial target, which was shallow oxide gold.”
It was. DeGrussa’s VMS mineralization popped up in the RC chips. The company geologists recognized it quickly. It was April/May 2009. The RC intercepts returned dozens of metres of several percent copper and at that point it was clear Sandfire was on to something. The discovery was obvious a couple months later.
The first diamond drillhole into the target showed heavy sulphides and strong copper mineralization. It would enable Sandfire to get funds to drill out what would become a decent sized VMS reserve in several lenses at DeGrussa (now standing at 10.6 million tonnes @ 3.5% copper and 1.3 g/t gold, roughly the same as three years ago.) Remarkably, the deposit got to production just a few years after discovery.
DeGrussa(s) next?
Since 2009 the obvious question from an exploration standpoint has been: is there more beyond DeGrussa? DeGrussa itself remains a fairly open target, with one of the lenses (Conductor 5) showing increasing widths as Sandfire drills it. There is also the question of depth potential, which is relatively untapped. Sandfire has been spending about A$20 million a year on exploration. That’s helped hold reserves fairly steady. But, until this year at least, the work didn’t bear obvious fruit outside the very near mine area.
This changed a couple weeks ago through exploration on ground Sandfire holds in a joint-venture with Talisman Mining (Sandfire earning in to 70%).
Like DeGrussa, the latest discovery at the Springfield target wasn’t obvious at first. In going after it, Sandfire was following up on a drillhole by Talisman. It had sulphides sniffs. But Simich says they didn’t think at the time that the sulphides spoke to another VMS deposit.
Still, it was interesting enough – just as in 2009 – for the team to check out. They cleaned out an old Talisman drillhole and did some electro-magnetic (EM) work to see if they could see anything anomalous. A conductive feature was interpreted. So they redrilled. They did more EM. “We saw an EM target light up,” Simich says.
Now they drilled another hole. But they had to abandon it a few hundred metres down, unable to control the drillhole’s direction. They redrilled again. And finally they hit an intercept that most economic geologists would appreciate: massive sulphides, including chalcopyrite, over 17 metres that graded 18.5% copper and 2.1 g/t gold. In one photo of the intercept, a grinning company geologist holds a section grading 25% plus. It is a lot like DeGrussa, Simich says.
“Now to get to that point we had been doing extensive work over the last four, five years, in the entire region spending significant amounts of money chasing the elusive, repetive nature of these VMS orebodies,” Simich says.
Driving the current exploration program is a focus on volcanics associated with the DeGrussa orebody, and a careful consideration of geophysics. Simich describes the area as very complicated geologically. Folding and faulting affect the region heavily. “Therein causes some of the difficulty,” Simich says. “But therein also creates some of the opportunity.” The faulting in the region cuts up the DeGrussa deposit, as it does conductivity, Simich says. It could very well be the same story at the newly identified Springfield target.
But Sandfire geologists now know the ground quite well. It gives them a leg up on finding additional mineralization. Simich puts it this way, “We have an orebody we’re actually mining. We’re down there and we can see the faults. We can see the counterplay between the stratigraphy and what’s going on. We can see mineralization in the orebody, adjacent to the orebody, above the orebody, underneath the orebody. We can use that to provide us a degree of intellectual property and understanding in geological knowledege that is specific to us and no one else has. We’re fortunate in that regard.”
The next drillhole (#5) into Springfield is start this week. It’s to target 80 metres along strike from drillhole 4a, which is now complete.
Certainly no one can say this one hit so far, about 400 metres downhole, will lead to a new mineable deposit. But it has proven an important point about DeGrussa – whatever comes next – that it is not alone.
Location of DeGrussa
Source: Sandfire
(20min delay)