Appreciate the input brethren.So many positives for Cohiba in...

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Wilb008

171 Posts.

238

08/07/21

14:17

Post #: 54372707
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Originally posted by Ignatz01: ↑

Hi RazzleDazzle

Geophysics is a bit of a dark art at the best of times.

IOCG’s geophysical signatures vary widely, particularly their magnetic and gravity signatures. For example, the Olympic Dam deposit produces a huge 17 mGal gravity anomaly, but only a 1000 nT magnetic anomaly, while at the other end of the spectrum, Ernest Henry (a n IOCG deposit in the Cloncurry region) produces a ~2 mGal gravity anomaly and 7,000 nT magnetic anomaly. I think the use of gravity and magnetics concurrently is a very wise idea - which they did undertake.

It should also be noted that the Olympic Dam deposit exists beneath 350m of cover sequence and CHK's ground and BHP's Oak Dam West are closer to 900m which has a marked dilution on any geophysical signature. One of the reasons why magnetotellurics is a great aid at depth.

The CSIRO did an excellent study on the IOCG deposits and their variability as a function of five main physical characteristics:
1. size;
2. percentage of Iron;
3. depth below surface;
4. magnetite vs. hematite content; and,
5. Koenigsberger ratio (i.e., induced: remanent magnetisation).

It really indicates that no one geophysical method should be used in isolation and for that matter no technical methodology should be used in isolation. That is why mineralogy, petrology, etc. are also vital elements.

Oak Dam West, if I remember rightly had up to a 30mGal gravity anomaly and when the anomaly was drilled it was entirely uneventful. The big finds have been away from the gravity anomaly to a large extent.

From what I have seen the magnetotellurics (AMT) gave a very solid indication of the presence of a reasonably continuous feeder system which recent work has postulated is critical for formation of large scale IOCG deposits - my understanding is that BHP and OZ Minerals have used AMT extensively.

Gravity, magnetics and AMT in isolation can be quite misleading so I advocate using as many in concert as possible. And at the depth we are talking about at Horse Well any small shift in any of the 1 - 5 above could have a marked impact on the "signature". I think it is very wise to spend considerable time analysing the crap out of data to get a holistic view - it is not lazy management it is good technical rigour and it takes time. Always bugs me when management gets hammered as being slow/lazy when it appears that they are actually being thorough.

The Gawler Craton is about 440,000 sq km so even when looking for a 50 sq km footprint like Olympic Dam that represents (on a surface area basis not volumetrically) around 0.01% - pretty much a needle in a haystack exercise. To get the results they have to date looks pretty good.

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Appreciate the input brethren.
So many positives for Cohiba in the mid - distant future.
I trust Mordi and the crew & would bet my yarmulke that they come through with the goods.

CHK Price at posting: 1.9¢ Sentiment: Hold Disclosure: Held
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