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kcm
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Re: Electrical Coring ( 13:23:11 SatJan 23 2016 )

Yes. It surveys the magnetic field similar, I suppose, to a magnetometer, but it's something I can use and interpret without extensive training.

kcm

  
geowizard
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Re: Electrical Coring ( 15:37:03 SatJan 23 2016 )

kcm,

If that's the case then it is important to know that the intensity of the magnetic field of the earth continually goes up and down. This variation is called "diurnal variation".

The diurnal variation is greater than the changes seen when looking for variations caused by magnetite and structural changes.

Measurements of changes in the magnetic field intensity require the use of TWO magnetometers.

A second magnetometer is placed in a fixed location near the area you are going to survey. During the survey, the fixed magnetometer is recorded so you know what the diurnal variation is. The diurnal variation is subtracted from the survey data.

Both magnetometers must have clocks that are synchronized. Because the magnetic intensity varies every instant in time, the time reference has to be the same. Usually, surveyors use the GPS time signal as a reference for both magnetometers.

Electrical surveying is subject to noise similar to magnetic surveys.

"It is a law of physics (Faraday's Law) that changes in a magnetic field will cause electrical current to flow in a conductor."

So, as the magnetic field changes due to diurnal variation, so does the voltage measured in an electric survey! :smile:

- Geowizard
[1 edits; Last edit by geowizard at 16:33:17 Sat Jan 23 2016]

  
geowizard
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Re: Electrical Coring ( 15:45:52 SatJan 23 2016 )

ELFs;

Elfs really do exist!

Electrical surveys are subject to noise from ELFs. We can't see them but the voltage can be measured.

When lightning strikes the earth (anywhere) there is an extremely large voltage that flows in the ground. That voltage can be measured at great distances. Actually over distances of thousands of miles!

Extremely Low Frequencies (ELFs) resulting from lightening storms become a source of electrical noise in the ground. The same laws of physics apply to ELF's.

When electrical current flows in a conductor (like the earth) an instantaneous MAGNETIC field is produced. So ELF's really do exist! :smile:

- Geowizard

  
geowizard
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Re: Electrical Coring ( 16:42:20 SatJan 23 2016 )

Telluric Currents;

You can read about telluric currents on Wikipedia.

https://en.wikipedia.org/wiki/Telluric_current

There is a branch of electrical prospecting that measures the currents. The currents are stronger in areas that are highly mineralized.

- Geowizard

  
Muley
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Re: Electrical Coring ( 07:47:20 SunJan 24 2016 )

Geo, If you ever decide to hold a hands on class, let me know, I'l buy a spot in it.:smile:

  
geowizard
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Re: Electrical Coring ( 14:18:54 SunJan 24 2016 )

Muley,

I have open seating everyday - all season long at Ophir!

You're welcome to attend anytime! :welcome:

- Geowizard

  
geowizard
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Re: Electrical Coring ( 17:28:33 SunJan 24 2016 )

Here's a link to the resistivity of rocks:

http://www.alaska-gold.com/resistivity_of_rocks.png

Although each type of rock has a relatively wide range of possible resistivities, the numbers for a given area will be within a narrow range and be identifiable as one rock type or another.

Earlier in this thread I showed how to calculate Resistivity and the schematic for a system that most members can probably fabricate from available parts.

- Geowizard
[1 edits; Last edit by geowizard at 17:29:26 Sun Jan 24 2016]

  
geowizard
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Re: Electrical Coring ( 18:10:07 SunJan 24 2016 )

References for self study;

There are books on this interesting subject like "Principles of Applied Geophysics" written by D. S. Parasnis. In this book the author points out that Electrical Sounding is referred to as "drilling". Early publications and marketing efforts by the Schlumberger brothers refer to it as Electrical Coring. :smile:

- Geowizard

  
geowizard
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Re: Electrical Coring ( 20:08:36 FriSep 1 2017 )

Readers may find relevant information;

This thread contains discussion on the subject of Resistivity and IP - both methods are commonly used in exploration for GOLD.

A company by the name of Arctic Geophysics offers these surveys in Canada and Alaska.

Visit www.arctic-geophysics.com

- Geowizard

  

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