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Author Topic: Finding the depth to bedrock  (Read 22552 times)

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Offline auhunter

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Finding the depth to bedrock
« on: October 21, 2008, 02:20:58 PM »
Does anyone know of an inexpensive device to find out the depth to bedrock, underlaying the gravel overburden?

Do fishfinder work?  I've heard this somewhere, but have never used one.

Offline bcdigger

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Re: Finding the depth to bedrock
« Reply #1 on: October 21, 2008, 07:26:48 PM »
I think you would need GPR or Seismograph  (Both are not inexpensive)

I believe fish finders only work under water?
You'll always wonder unless you dig it

Offline iso9001

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Re: Finding the depth to bedrock
« Reply #2 on: October 21, 2008, 07:33:23 PM »
Shovel and a tape measure   lol!!!@*



Seriously tho, I would like to know too!

Offline 1oz

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Re: Finding the depth to bedrock
« Reply #3 on: January 07, 2009, 11:24:25 PM »
hi,
i was thinking of this problem just the other day, it may sound simple and would only work for "shallow" situations (say 1to 2m) but the way we used to find water mains was using a half inch steel rod sharpened and with a tee handel.

all you do is "push" the rod into the ground till you hit something solid....bingo!, with practice you can tell if the object is a "floater" or the real target.

it's cheap too ;D

Offline sniper

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Re: Finding the depth to bedrock
« Reply #4 on: October 20, 2009, 10:11:57 AM »
i Know this is a little late but maybe some newbies can learn from it, what i do is look at aris reports, so much of this land has been worked that their are a lot of work reports on most areas and they do include drill reports, such as depth to bedrock, what kind of bedrock, how much gold if any was found ect. as well as the site has "bedrock mapping" which gives your average depth to bedrock for given areas. Hope this helps out a few people

Offline garyww

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Re: Finding the depth to bedrock
« Reply #5 on: October 22, 2009, 11:29:06 AM »
The geophysical equipment is getting smaller and smaller everyday and less expensive as well but it's still pretty costly so for most of us it's the shovel or a 'probe' as mention in earlier responces. Here's my probe, if I can get the picture to post. It's about 60-inches long and works well once you get the hang of how to use it effectively. These do work remarkably well as you gain experience.

Offline garyww

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Re: Finding the depth to bedrock
« Reply #6 on: October 22, 2009, 11:36:38 AM »
Once you start using a probe it doesn't take to long to tell the difference between 'rocks' and larger solid objects as the 'signal' up the rod is very differnet in both sound and 'feel'. Unfortunately about the longest rod a person can handle is only 6 feet long and then they become somewhat impractical. With a slightly sharpened end they will go thru fairly well compacted gravels with just minimal pressure. You don't want the end sharpened like a pencil point but more like an elongated round-nosed 38 caliber bullet to get the best feedback up the shaft.

Offline garyww

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Re: Finding the depth to bedrock
« Reply #7 on: October 22, 2009, 11:55:01 AM »
There is also a good rule of thumb that geologist use that is applicable to historically recent geology as far as accumulated overburden is concerned is that is that you can figure about 1/8-inch per year or about a foot per century on typical soils in typical areas, not streambeds, but just over regular ground. Distance to 'ancient' bedrock can be from 20 to 600 feet depending on where you're prospecting and that's why we look for cuts in the hillsides or creek banks where we can see some kind of profile to estimate from. Most of us when prospecting tend to get to focused into a small area and really need to step back and look at the larger picture of the sites we're working. Mother nature tells the story but we need to learn how to read her language. I've been doing this for about 40 years and figure that I'm still in Kindergarten with respect to learning how to read geologic history.

Offline Wild Bill

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Re: Finding the depth to bedrock
« Reply #8 on: February 16, 2011, 08:20:51 AM »
My best advice for deep bedrock conditions is to auger down to bedrock. I am not sure of your budget or location, but boring is a whole lot cheaper then coring.
Good Luck

Offline AUssie

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Re: Finding the depth to bedrock
« Reply #9 on: August 25, 2011, 09:32:19 PM »
The geophysical equipment is getting smaller and smaller everyday and less expensive as well but it's still pretty costly so for most of us it's the shovel or a 'probe' as mention in earlier responces. Here's my probe, if I can get the picture to post. It's about 60-inches long and works well once you get the hang of how to use it effectively. These do work remarkably well as you gain experience.

Gary,

Can you re post the pic of your probe? (the one you use for mining of course, this is a kid friendly site)

Guy

 


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