For some weekend reading I have been doing a bit of research into the nature of the Walford Creek AML mineralisation. There is a vast amount of literature out there with some of the better stuff subscription only. Vaguely recall others discussing variations of this on HC so excuse any repetitions.
This PDF, combined with personal knowledge, with references to some of the larger Proterozoic deposits in the Mt Isa to McArthur River geological domain is the research that went into the comments below.
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Four major types of Zn/Pb +- other credits are:
- Sedex
- VMS
- Mississippi Valley
- Replacement
- other types... present but from memory less significant globally.
These share some features but have significant differences that make it more appropriate to separate them into mostly distinct types.
The greater Mt Isa area is IMO dominantly
Sedex rather than VMS.
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McArthur River and Teena are more like a "proper" Sedex type where as Mt Isa and Walford Creek appear to have had a later influx of copper rich fluid.
At Mt Isa the copper forms a separate very pure Cu deposit the origins of which are probably still the subject of debate.
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At Walford Creek the copper appears to be a late stage overprint of earlier Pb/Zn mineralisation that may be an overprint on susceptible pyrite rich units.
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Metal zonation in VMS deposits also tends to be quite distinct - Cu rich base to Zn/Pb to barite top is a fairly common one. Walford shows some aspects of this but has probably formed below the sea floor probably by multiple pulses of fluids moving up the Fish River Fault (FRF).
Black smokers occur at the interface of basin floor and ocean, from my readings, and as such tend to be more related to VMS though they may be a minor local? aspect of Sedex. More research needed to support this statement.
AGE OF MINERALISATION
Mineral event 4 of the GSA is between 1700-1640 Mya and represents a peak for Pb/Zn in geological time. Includes Mt Isa/Broken Hill/McArthur River and others.
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Why this peak? One suggestion has to do with the evolution of oxygen in the earth's atmosphere from very low 3500 Mya to high in the Great Oxidation Event (2200-2400Mya?) and then oscillating around. Combine this with plate tectonics and global environmental issues and these are some things that may contribute.
The later Central African copper belt deposits possibly relate to similar events.
AML and Walford Creek.
An early presentation gives these resource figures and location data
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These are the first figures I saw for Walford and didn't seem too impressive on the grade side when cobalt wasn't a buzzword.
The company was contemplating an open pit mine which seems to have been put on the back burner for the time being while they fine tune the resource and exploration potential based on the revised geological model above.
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Metal prices 2015/6 still fairly reasonable except Co at present.
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The January 2018 resource is significantly more Cu and Co rich but may require a larger UG mining component.
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Exploration Potential?
Recent drilling, combined with historical work, is showing the geological model to be standing up quite well for some 7 Kms west of the well drilled resource. The depth for
some of this strike means UG exploitation would be necessary if the economics hold up.
To have the entire 18 Kms evenly mineralised is probably a dream that won't come true but it will be tested in due course as well as possible eastern targets.
The continuity of such mineralisation can be astounding as shown by the major known deposits in the area.
Walford seems to be "stretched" along strike rather than down dip which somewhat limits the potential size (strike length X dip 'length' X thickness). However, with a potential 20+ Kms of strike (?how much economic) and one or two (Py1 and 3) zones as "ribbons to 30+m thick at potentially good grades the upside is such that someone's comment about a buyout by a major could well be on the cards.
A weak analogy could be made to size and continuity of the Kamoa/Kakula complex in the DRC. Discovered in the last 15 years these two deposits have some dimensions well in excess of 10 Kms.
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If you've made it this far well done. The above is rambling but to make a much more compact post takes a lot of time. Churchill "1 hour speech I can do off the top of my head but a 5 minute one takes a lot of preparation" . Not Churchill but that's my excuse for indulging myself this weekend and many others.
Hope this gives you some ideas Prawn_man.
GLTAH DYOR
(20min delay)
