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

Originally posted by Clark888: ↑

@HomeBrand

If you were still wondering about Magnetotellurics (MT) vs Audio-Magnetotellurics (AMT) the following may be of interest.

Ausmex Mining Group (ASX: AMG or 'Ausmex') used MT and AMT with spectacular results during 2018-2019, it is currently looking for copper-gold deposits at Burra in South Australia.

A challenge for the global mineral exploration industry is to identify world-class deposits under thick layers of sedimentary cover. Traditional approaches target the small-scale economic ore deposit, with declining rates of success over past decades. However, an alternative approach is to image deeper parts of the Earth's crust to find a much larger footprint where the metals originated. By finding the deep source mining companies can also map potential pathways through the upper crust to define new prospective areas beneath sedimentary cover. So, rather than looking for the needle, it is better to first identify the haystack.

MT is a passive geophysical tool that is highly sensitive to minor interconnected conducting mineralogy and fluids, and thus is ideal for distinguishing between lithosphere of different degrees of enrichment. Additionally, the sensitivity to these minor phases means that fossil fluid pathways associated with the ascent of mineralising fluids and metals are detectable with MT. Mining companies are specifically looking for a 'plume'.

MT is capable of penetrating the entire lithosphere of the Earth, potentially tens to hundreds of km deep.

AMT is a higher-frequency magnetotelluric technique for shallower investigations (around 1-3 km depth). While AMT has less depth penetration than MT, AMT measurements often take only about one hour to perform and use smaller and lighter magnetic sensors.

As you can see from the diagram below, MT is shown on the LHS and is looking at the 'architecture' of the lithosphere.

AMT is shown on the RHS of the diagram, and is looking at the 'deposit' scale for mineral accumulations.

View attachment 2228631

Ausmex Mining Group (ASX: AMG or 'Ausmex') completed AMT during April 2019 on a previous MT grid (that had been completed during October 2018), with spectacular results around Burra in South Australia. Ausmex said AMT was designed to increase the data resolution from the initial regional 10 km spaced MT survey completed during October 2018 and focus on the surface to 2,000 metre depth, progressing the conductive zone to exploration and drill targets:

https://www.asx.com.au/asxpdf/20190409/pdf/4445b8lyhhvbxl.pdf

Subsequently, Ausmex released a number of ASX releases during August 2019 including the following announcement that confirmed the validity of AMG’s approach of using MT and AMT to identify plumes and structures which originate from the deep conductive structures that lie approximately 20 kms below Burra:

https://www.asx.com.au/asxpdf/20190814/pdf/447ggcxt2f4zjq.pdf

Figures 1-6 in the above ASX release are interesting, it shows you the modelling mining companies can do with the results of AMT.

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.

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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