Interesting rticle written by KZR's Geoligists as he believes 99% of the tenements in the Pilbara are moose pasture. The very next day KZR announce their projects & it's nowhere near the hot spots. Hahaha
Keep Your Wits About You In The Pilbara
- Published on Published onOctober 5, 2017
Roland Gotthard
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Geologist contracting to Kalamazoo Resources Limited
54 articles
So, in case you were asleep the last few months you'd have noticed a little exuberance around the Pilbara recently regarding gold. Something about Novo Resources live streaming some prospecting where they dig up some, admittedly sexy looking gold nuggers.
Obligatory meme.
There's been a land rush up there when the word Witswatersrand got splashed about. Aussie geologists pooh-poohed it, naturally, and got caught napping by the market response and the videos and photos and the ludicrous cash being funnelled in to chasing cooked up alluvials. If modern alluvials aren't for responsible listed entities then surely 2.7 billion year old alluvials can be!
If you cook a turd sandwich it is still a turd sandwich, let's be frank.
You do have your work cut out for you in understanding the prospectivity of all of the dozens of land-banking tenement squatters turned millionaires and the juniors fighting like hobos out the back of a KFC scrapping over a McNugget, what with every man and his dog dealing in on this (and why not, your share price quintuples). So in order to muddy the waters, some expostulation.
The Fortescue Group
This is the stratigraphic column of the Fortescue Group, with the prospective units helpfully highlighted.
Not sure that the Hardey Formation is a goer, but hey, 2/3 of the ASX reckons it is so why the hell not, let's peg over the top of it.
The needle in a haystack issue with all of this Hardey / Mt Roe nearology gold rush is of course finding a klick or ten worth of mineralised conglomerate in amongst all of the unmineralised pebbles. You want to be in the pink bits and preferably on those red lines, though it's a bit of a crap shoot at the Nullagine end what with the deformation.
The Mt Roe basalt was erupted subaerially upon underlying pyritic fluvial strand bar and braided stream conglomerate and/or glacial shelf sands and sediments.
Novo Resources Ltd schematic section of their Purdy's reward deposit. Lol @ pillows.
The gold obviously doesn't get in there from the Mt Roe basalt if Novo's section interp at Purdy's reward is correct, and given it's subaerial (columnar jointing, vesicular and amygdaloidal) it's got buckleys of being epithermal within the Mt Roe like some claim. So the gold has to be sourced from the subjacent Warrawoona and maybe Apex Basalt / Euro Basalt which were laid down 300-400Ma previously and subjected to 3 or 5 deformations previously. Mmmm....squishy.
Thorne and Trendall (2001) provide a handy depositional palaeoenvironment cartoon you can literally imagine as the 2.9Ga equivalent of the Klondike today, sans grizzlies.
You want to be in the yellow bit, preferably the red bits. So you want to be under the Mt Roe Basalt over or downstream of subjacent greenstone belts which feed the gold into the alluvials. Granites are probably death for placers but hey, ypou have to be unreasonably optimistic to be speculating on this to begin with so don't write yourself off.
So that's the red bits, maybe the blue bits if you just want to play nearology or gambler's ignorance.
The Mt Roe erupted, as these things do, in fault-bounded grabens and basins. Ergo, faults which bound these basins likely shed gold nuggets from eroded uplands into shallow marine / fluvial basins and the basalt then sloughed on top. The controlling faults which control fault basins therefore have a higher likelihood of hosting gold nuggets within conglomerates above or below the Mt Roe basalt, because there's a pedigree with faults and gold.
There appears to be fault control on the preservation of the Mt Roe; without a proper isopach map and detailed investigation and mapping to identify the bouding faults, the interpretation of the bounding faults relies on lineament interp. Given faults tend to be reactivated multiple times, the following is a reasonable rough interpretation on a craton scale.
(yoinked off RTR:ASX announcement today)
So there's probably a limited number of places in the whole lower Fortescue Group where the unconformity is in proximity to underlying gold-mineralised alteration systems shedding off faults into braided alluvial fans and lenticular strand-bar gravel beds and there are preserved gravels under the Mt Roe basalt. Suspiciously the Novo/Artemis Mt OscarWits and DeGrey's nuggs match these criteria so I'm confirming my own model bias here. So away we go:
So, in terms of nearology, there's nearology and farology. Most of the land rush is, under this model, farology AKA crap.
You can pick your faults that control the depocentres of the Mt Roe and the subjacent sediments differently, you can plug in different groups in the older Pilbara Supergroup because not all of them are equally mineralised. But at the end of the day, this isn't all Wits, and it isn't at all like the Wits.
I cbf plastering the tenement holder status on this. But suffice to say, it's mostly pegged up and it's 99% moose pasture IMHO, and some listed company is going to have to get to grips with actual prospectivity. But that's for 5 years from now.
Happy gambling HotCopper!
References
Thorne & Trendall, 2004. GSWA Bulletin 144: Geology of the Fortescue Group, Pilbara Craton, Western Australia.
Rumble Rersources Ltd ASX Release, 5th October 2017.
