Metal Detecting in an A-Star?

[Micropedes1]

I have TWO of them already completely downloaded, with a hard copy of flight line profiles and the EM analysis. Geosoft Oasis Montaj downloaded and installed with at least some of the survey raw data input and saved. Add to that the EM interpretive maps within the survey showing areas of high resistance and high conductivity. Another map showing major and minor faulting within the area. And lastly correlation with several hundred stream and soil samples all showing chemical analysis via atomic absorption. I've been busy.

I am open to suggestion. And highly motivated. Lead onward!

[Geowizard]

Magnetometer;

Okay... I would also add for your reading pleasure the magnetometer!

The surveys include a magnetometer and as mentioned previously the magnetometer readings are corrected for diurnal variation.

So?

The surveys provide Residual Magnetic Intensity (RMI). "Perturbations" in the magnetic field of the earth are caused by changes in the magnetic susceptibility of the rocks. Rocks have varied amounts of magnetic particles of iron. The Iron particles behave like small magnets. When you consider a large mass of rock with millions upon millions of small magnets, the rock looks like a magnet. When a magnet is placed in the magnetic field of the earth, it causes a distortion (perturbation) of the normal magnetic field. The magnetometer measures the total field and the measurements are recorded at the rate of ten times per second along the flight line.

Interpretation of signals is INCOMPLETE without magnetic data!

For example, the question; Is it Salt water mineralization? Saltwater is non-magnetic... no Magnetic signature!

- Geowizard

[Geowizard]

Iron association with precious metals;

Iron is one of the most abundant minerals on earth. Iron IS associated with many precious metal deposits (think black sand). Igneous host rock has abundant iron representing increased magnetic susceptibility AND a lively RMI signature!

Mineralization in the form of precious metals is known to have an origin from deep in the MANTLE of the earth's crust. Structural deformation of the crust creates a conduit for intrusion of precious metals via hydrothermal processes.

Still with me?

When the crust of the earth is DEFORMED, the rock structure becomes deformed and the magnets become distorted in their magnetic orientation. Knowing this to be true, the RMI is an indication of changes in the structure of the rocks! Structure is important in identification of areas that might have been intruded by hydrothermal fluids containing precious metals.

- Geowizard

[Geowizard]

Magnetite;

Magnetite deposits produce a SIGNIFICANT magnetic signature. IF... an anomaly ALSO has a LARGE magnetic anomaly, it may be a magnetite deposit.

I have been able to interpret areas in Alaska that have outstanding Banded Iron Formations referred to as BIF's. BIF's have tremendous economic importance!

A final note on IRON... GOLD is often associated with IRON.

- Geowizard

[Geowizard]

There's more...

A large anomaly with NO magnetic signature is NON MAGNETIC!

- Geowizard

[Geowizard]

Fissures;

A FISSURE is a horizontal separation of rock in the surface of the earth. Often times, a fissure has NO structural deformation. Some fault zones are referred to as FISSURE-FAULT zones. With no angular distortion, there may be little or no magnetic perturbation in the magnetic field. It is possible that an intrusive occurs on a fissure! Hence, little or NO response and a response!

- Geowizard

[Jim_Alaska]

Jim, do you mind divulging the location of those UA maps that you were referring to earlier?

Glen, I was just getting into gold prospecting at the time I mentioned. I had zero knowledge of what I was doing, just flying by the seat of my pants, so-to-speak. Most of my interest at that time was information for trapping purposes.

Now that you have asked about where I got those maps, my old brain struggles to remember exactly. At first I had thought that they were from the same place at UAF that I got the false color images for looking at remote land for trapping. But now thinking back on it, it may have been from the geology department at UAF, or even the Ak. Department of Natural Resources, just off campus. I'm sorry I can't remember exactly Glen, but it was a long time ago, early eighties to be exact.

I think I may still have those maps buried somewhere. I do remember struggling to interpret just what the maps were telling me, because I had no idea about the technology involved other than that they were generated by airborne magnetometer, while flying a precise grid. Eventually I was able to make some sense out of the maps by looking at one place I had maps for while scouting some trapping ground from a hilltop on my trap line.

Originally I had bought the map for this location because I wanted to see if there might be anything of interest that I could access right from my trap line which I had cut out of the wilderness by hand. The map also showed the next ridge from the one I was on and I could also see the actual ground on that ridge from my ridge top location.
What I saw on that ridge was a well laid out series of "brush lines" that had been done by a large mining company as part of their claim process. I only found this out because I looked at the claim status of that ground once I actually saw the brush lines from afar.

I said all that to say that once I put together what I was seeing on the maps with what I was seeing on the ground, I could easily see that the process of generating these maps by Magnetometer readings had probably lead to the discovery of these claims.

In my early prospecting days I was friends with Jim Madonna, who was the mining professor at UAF and also owned a prospecting store in Fairbanks. He was a fountain of mining information for me in those early days. He helped me in identifying samples I brought to him, since I had no idea what I was looking at once I had a sample in hand.

Edited to add: Most of what I wrote probably has nothing to do with what you asked Glen. Like most old guys, once I get to reminscing I get real wordy.

[Micropedes1]

I am the same way; when I get to talking "gold" I seem to just get carried away.

If you come across one of those old maps, look down in the lower corner and see if they indicate a source.

[Geowizard]

Jim,

I suspect that you are referring to the same "Rainbow Maps" that are the product has available online. I referred to the page in a post above. That web page shows a listing of all of the presently published surveys. Geophysical surveys have been conducted over the past several decades.

- Geowizard

[Jim_Alaska]

Jim,

I suspect that you are referring to the same "Rainbow Maps" that are the product UAF and Alaska DGGS has available online. I referred to the DGGS page in a post above. That web page shows a listing of all of the presently published surveys. Geophysical surveys have been conducted by the State of Alaska over the past several decades.

- Geowizard

Wiz, I seem to remember that these were Geophysical as well as Geochemical Surveys. If I ever come across these maps I will post a source.