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Peter Freedman

Magnometer To Survey 400 Acres Of Placer Ground?

7 posts in this topic

Hi All,

There has been a lot of talk on magnometers lately in the Journal. I have been looking to rent one for a week and survey some prospects, about 400 acres(not continuous). Seems that there are many companies that will rent magnometers. I am not sure which one would suit my needs. Basically, trying to follow black sands. I would also like to compare claims that are separated by 15 miles.

-Is there a way one can compare the readings from two separate plots and determine which ground is has more black sands.

-How long does it take to survey a 20 acre placer claim with a walking unit?

-Supposedly, there are pay streaks at 4 and 14 for level. Is there. Way to detect that ?

Can anyone recommend a model?

Many thanks,

Peter

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Peter,

 

You have an interesting project. :)

 

I would recommend two magnetometers. One magnetometer works as a reference station.

 

You need a reference station because the magnetic field changes up and down from "diurnal" effects.

 

The diurnal and regional field will be subtracted from the total magnetic field to get the amount of magnetic change related to black sand. I can provide numbers if you need them.

 

With reference to the time factor, it depends on the number of traverses and the speed of the traverse. A standard 20 acre (approx.) mining claim is 1500 feet long and 600 feet wide. If you survey along lines at 50 feet separation, it will require 12 traverses per claim x 1500 feet = 18,000 survey feet. Assuming it looks like a golf course, and you can walk along at 4 mph, you can expect the survey to take about 1 hour . In reality, you will need to take a stationary reading every 50 feet. The reading can take several minutes depending on the magnetometer. Three hundred and sixty readings adds 3 x 360 = 1080 minutes. If the project requires surveying 400 acres, equivalent to 20 claims x  20 hours = about 400 hours.  

 

Depth is a function of the amount of magnetic anomaly caused by the black sand.

 

Magnetometer surveys from one area can be compared to results from a different area if the readings are corrected for regional magnetic field and diurnal variation.

 

- Geowizard

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magnetometer surveys much also take into consideration the types of rock present - some types of rock have considerable magnetite or other magnetic minerals. In order to follow a channel, the channel must have enough magnetite to stand out from the surrounding country rock. This is sometimes the case, but not always.

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Also with the single proton magnetometer that Geowizard speaks of the magnetic material could be a couple hundred feet down so of no use to you.  I would rent a dual proton magnetometer since it uses the one side as a reference it's range is much shorter if I remember correctly.

 

Randy

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Peter, I would suggest you use the Resistivity method, specifically the Wenner Alpha, Wenner Beta, or Wenner-Schlumberger array configurations. These will measure the electrical resistivity of the ground depth at 1/2 there distance apart. So if you had a 3 meter spread then the Depth you would be measuring would be 1.5 m. This could be reduced to one meter spread with 0.5 m depth. By the same token you can increase the Spread to gain greater Depth. Any difference in the Electrical Conductivity of the Over Burden, down to Bedrock, 'and deeper 100s to 1000s of feet' would be measurable and be able to be displayed on the computer screen as a color cross-section with Dr. M.H.Lokes' RES2DINV or RES3DINV Software. The software can be found here

http://www.geotomosoft.com/downloads.php

the paper explaining the layouts an procedures can be found here

http://www.geo.mtu.edu/~ctyoung/LOKENOTE.PDF

 

for further information and discussions I would reference Carl Moorlands GeoTech website and forum. here is a post on the EPE Resistivity Logger that you would need to preform the surveys. 

http://www.geotech1.com/forums/showthread.php?15674-EPE-resistivity-logger  scroll down to POST #21 and read from there the rest above it just troubleshooting talk to get it to work.

 

Hope this Helps!!!

 

Sincerely

Bill "Lost Adams"

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Harry,  I usually post an answer to a question no matter how old the topic. The reason is that New info is always welcome to all that have an interest in a topic. What I hate to do is Search for a topic and find multiple topics and have to go through all just to find which ones have useful info in them. So why start a NEW Thread when there is one that can be Bumped Up.

 

 

 

Sincerely


Bill "Lost Adams"

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