What the hell is Magnetotelluric (MT) and Audiomagnetotelluric (AMT) surveying ?

Originally posted by HomeBrand ↑

Thank you for the time you have taken to respond to my question. I appreciate it absolutely.

May I dumb down your identity of a "plume".

The way I am thinking a plume is.....based on your suggestion, I'm conceptualising that a plume is like a lava lamp (don't laugh!). I'm thinking a plume, over time, rises from the bottom and head to the top as potentially a bubble of potential mineralisation. In the diagram you displayed could this "bubble" be seen as the fluid reservoir? (ie) the "bubble" within 1-3 kms of the surface, rather than the very deep primary source 10's/100's klm below surface. The "deposit scale", as depicted, is emitted form the plume causing the near surface mineralisation (ie) up to 1,000m below surface (if proven economic)?

I appreciate that measurements/depths/geological settings are not uniform across the globe, but general rules of thumb would help me to conceptualise this in my own mind.

Now for the real interpretation, I'm in SGQ who have run MT/AMT over potential Ni-Co deposits in WA. They are highlighting structures below surface up to 1000m. April 22 2020 ann is a succinct summary of the surveys done to date, with the balance expected early next week (overdue actually).

If you can sum up SGQ in 25 words or less, I would be absolutely chuffed with your view.

TBH, I am thinking of doing a geological course to bridge the gap so I am not bamboozled by the jargon so I can make more informed investment decisions.

Again, thank you.

HB

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@HomeBrand

Magnetotelluric (MT)
The images and following text should help fill in any gaps.

The following image and text represents the results from BBMT (broadband MT) undertaken during August 2017 on the Jupiter MT anomaly in the Curnamona Basin in South Australia. AMT has not yet been run over the Jupiter MT anomaly.

C = Conductive zone or potential feeder zone (possible conduit for magmatic/ hydrothermal fluid flow)
R = Resistive zone (e.g. granite)

A conductive sedimentary layer (C1) from the surface to ~200 m, thins to <100 m about 40 km along the profile. Below the sediments to 15 km there is a resistive upper crust (R1, R2 and R3) almost across the whole profile, except for a conductor (C3) located 80 – 100 km along the profile at a depth of 4 km. The lower crustal anomaly (C4) is widespread starting from a depth of 15 km which is probably the brittle-ductile boundary and extending to at least the Moho. Finally, there is a near vertical conductor (C2) 45 km along the profile that connects the most conductive part of the lower crust C4 to the near surface, where the sedimentary cover is thinnest.

A significant feature from the 2D resistivity inversion is C2 that has a footprint from the brittle-ductile boundary near 15 km above the C4 conductor, to the topographic basement high. A possible cause of this footprint is from fluids accumulating at and below the brittle-ductile boundary, until overpressure results in hydro-fracturing of the brittle crust above resulting in a conductive footprint from the alteration of fossil fluid pathways, usually through zones of weakness, which have previously been observed at mineral deposit locations such as Olympic Dam.

The mid-crust conductor, C3, is situated at the boundary near a major unnamed fault that is situated on the eastern edge of the 1590 Ma magmatic Benagerie Ridge that may have acted as a pathway for the fluids. It is possible to speculate that the large C3 conductor, of width ~15 km and possible extent > 100 km, might have resulted from a large scale thermal event that weakened the crustal rheology, and when compounded with paleo-stresses led to the eventual formation of the deep sub-basin C1 during the Cambrian period.

Source: Finding Haystacks: A New Approach to Mineral Exploration (G. Heinson, Ben Kay, Kate Robertson, Stephan Thiel)
https://emiw2018.emiw.org/fileadmin/emiw2018/Documents/EMIW2018_Session_3_abstracts.pdf

St George Mining Limited
MT coverage provided St George the opportunity to reduce its exploration risk for mineral occurrences before committing to expensive diamond drilling.

The MT survey looks like it has identified the deep, mantle tapping faults that were the conduits for the nickel-copper sulphides they are seeing near surface. The MT survey is potentially identifying a large mineral system, with potential for significant mineralisation at depth.

Only RC and/or diamond drilling will help prove up Management's theory on the results of its recent MT surveys, particularly at depth.

Cheers

These are only my thoughts and it does not constitute investment advice. Before acting on any information you read and before making any financial or investment decisions, you should always consult your advisor(s) or other relevant professional experts.