Magnetotelluric Surveys is an electromagnetic geophysical method and a method of geophysical study on land. It is useful when analysing underground masses for mineral resources and one of the most popular techniques for Nevada and Lithium Triangle brine developers.
The basic idea of MT surveys is to measures the electrical conductivity of the ground mass underneath the survey area. The method of doing this uses the time differences and delays in the earth's electrical and magnetic electrical fields to determine resistivity. In relation to Lithium brine aquifers, the saltier the brine (if any), the less resistance there will likely be. The output in then compiled into a colourful graph as shown below and is readable as ohm-meters with the help of an accompanying scale. I have used Reedy Lagoon Corporation (RLC) MT surveys as the example. They have 3 different projects in Nevada but this the the one for Columbus Salt Marsh. Just for disclosure, I am a holder of this company's shares.
The graph shows us essentially a cross section and allows us to identify areas of lower resistivity, which is then used to assess drill hole locations, as well as how far down to drill. For instance, we observe that there are a number of dark purple areas indicating <1 ohm-meter for RLC. From this, management has inferred that the large purple masses may have the highest chance of lithium being present and hence we see the planned 1400m, 800m and 600m drill holes.
What we want to see is areas of low resistivity, ideally <1 ohm-meters. Given that Columbus Salt Marsh is known to have anomalous lithium present according to the USGS, the lower this number is the greater the concentration likely to be present.
From my knowledge, the Argentinean Projects have resistivity of ~0 ohm-meters (even negative in some cases). Below is a few MT survey results relating to Lithium America's Cauchari-Olaroz project. Orocobre currently mines in this area and has achieved ~700mg/L Li. These images are annoyingly blurry though but the message is clear; their brines are have very low resistivity.
It was because of this comparison that I stated that Lida Valley has suboptimal MT surveys figures (~45 ohm-meters). Although this doesn't mean there will not be any lithium, it could potentially mean that the concentrations the company might find may not be very high according to the MT surveys; reducing the economics.
Scotty South looks better as I'm sure you'll agree.
It is also because of this comparison that RLC looked particularly attractive with all 3 project's MT Surveys returning at least one <1 ohm-meters areas each and hence my view on its potential. Individual research is recommended of course.
"The lower resistivity values may be related to brines, with typical resistivity values of < 1.0 ohm/m, associated with interpreted structural features within the basin." - Ernest Burga and others (see report linked below).
I am not a geologist but after doing my own research, comparisons and numerous phone calls with RLC managing director Geof Fethers (who is a professional Geologist), these are my conclusions in regard to Magnetotelluric Surveys.
Please feel free to correct me.
http://lithiumamericas.com/wp-content/uploads/2017/05/LAC_43-101_FINAL_May112017_web.pdf
