ENR poormans WA1, page-60

https://hotcopper.com.au/posts/64834063/single

@Dequavious

Welcome to posting on HC.

First post - challenging one. The first of many to come I hope.

The underlying issues (false positives, structural disruptions) are correct. Perhaps so obvious to me that they may be more implicit rather than actually stated in my attempts at interpretation of mag and gravity.

As is usual for me lots of words and a few images which I hope add something.

Sorting out false positives from the real in geophysics requires a lot of science with the drill bit often being the only way to come up with something definitive. Statistically some 1 out of 3000 targets becomes a mine. Trying to increase the odds is why a lot of effort goes into the type of questions you raise.

I hadn't registered that the ENR hole may have bottomed out in BIF.



Standard BIF. Oriented core (red Lines with half arrows) indicate the bif is sub vertical with some folding (common). The Mag Gravity anomaly at EA1 was interpreted as a sub vertical pipe like structure which IMO raises questions about the BIF unit.

Switching to the Laverton area Magnetics - accidental but fortuitous - to show what BIF's look like in a greenstone (lower) metamorphic environment.



The BIFs here are narrow linear features with strong, if local, magnetic highs. They exhibit local structural deformation. Mixed with them will be other lithologies some of which are variably magnetic. Occasionally alteration destroys the magnetite in Bif and can be associated with gold or other minerals..

Wallaby and Mt Weld are two blips on this magnetic image that are of high economic significance.
Wallaby surprised many and has produced well in excess of the 5Moz Au on the image. It is a special type of intrusive that surprisingly contains a lot of gold zones. [Within this image Some 30-40Moz of Au have been produced. Mostly areas much smaller than the rectangle around Wallaby.]
Mt Weld is a large carbonatite easily visible at this scale. Contrast with Luni and P2. The latter is closer but since the background is different it isn't as blatant.

Back to West Arunta


Rocks in this area are at a higher metamorphic grade than Laverton. Not certain about the age but suspect younger by a considerable amount of time.

The magnetics near the Toro REE target are reminiscent of BIFs and some BIF is recorded as part of lag sampling done some 10 years ago. Up to 4% TREO was reported and the Chinese Deposit Bayan Obo mentioned. A comment made but quietly dropped? Forgotten because they are/were uranium focused. Open file assays are not too impressive with perhaps some elevated REE elements (La/Y) but only phosphorous in the 1% range that I noted.

Assuming the Toro REE target is part of a BIF the structural dismemberment to the east is possibly indicative of complex structure on a more regional scale. Is this why EA1 is an isolated pod Bif rather than a more linear zone.? Possible BIF zones dot the map as isolated highs. Locally some larger and more linear perhaps like the one south of Luni.

In the image above there are many magnetic features. High 'amplitude' bifs are probable but locally grade into zones of high magnetite bearing units in the P1 and EA1 areas where there is also hematite alteration. The area from P1-EA1 and perhaps further east has a moderate magnetic signature with trends perhaps because it only has shallow cover. It is complex and probably gneissic after metasediments with minor mafics.

The carbonatites at P2 and Luni put the cat amongst the pigeons as these intrusives may be real wild cards that resemble other geophysical anomalies and the only way to distinguish may be geochemistry (possible but also unreliable if cheaper than the main alternative of drilling.

The stars in the SW and west of the image above are isolated mag +- gravity targets some of which have been tested for IOCG potential (e.g. Top up Rise) Any of the blips could be significant [ Havieron and Wallaby are two that have the goods but so many others are false positives that eat away at limited budgets]

Feel I am going in circles. : Companies ..

• Go through the latest targeting data available
• prioritise them and drill test with feed back into stage one.
• WA1 had the luck to hit mineralised carbonatite in 2 of 3 targets which will keep them busy.
• ENR are gathering up to date gravity which will feed back into the targeting. Many are likely to be false positives/offset/folded as geophysics is not at Star Trek tricorder level yet.