Finding Depth to bedrock

[Seden]

I like to prospect and placer mine gold on the weekends and the bane of placer mining is determining the depth to bedrock. If anyone knows how to design Geophysical equipment I'd like to talk with you.

Randy Seden
[email protected]

[99thpercentile]

The standard method for finding depth to bedrock is a seismic refraction survey. I usually use 24 channel Geometrics StrataView with vertical geophones and a sledgehammer source. It is a pretty simple survey to do and the interpretation can be done by hand if so desired.

Ryan

[Seden]

EM method?

Ryan,

Thank you for answering my question so quickly. Would you mind if I email you directly as I have further questions.

Thank you,

Randy Seden
[email protected]

[Unregistered]

That's fine, my email address is in my profile.

[email protected]

[Seden]

Refraction Depth profiling

If TDEM is too complicated would it be possible to make a simple refraction seismometer to do a depth only reading? It seems if they can do it with depth finding equipment it seems that if you changed the time constant to take into consideration the different travel times for dirt compared to water it could make for a low cost system.

Randy

[99thpercentile]

The Geometrics Geode is a simple seimograph. The problem is that you need to record multiple channels of data simultaneously, with 24 channels being the standard for the low end systems. It is possible to buy cheaper A/D systems now that work in this situation. Check out this website for building an inexpensive seismograph.

http://www.infiltec.com/seismo/

[Seden]

Pc soundcard software

Thank you for the site for building a seismograph. I know that they make seismic software that uses a Mac's soundcard,do you know of software for the IBM PC? That makes the most sense of all,just plug in a homemade geophone to the soundcard's input.

Randy

[asguard]

The standard method for finding depth to bedrock is a seismic refraction survey. I usually use 24 channel Geometrics StrataView with vertical geophones and a sledgehammer source. It is a pretty simple survey to do and the interpretation can be done by hand if so desired.

Ryan

Hello Ryan,
Would you recommend this technique in a environment where there is much undergrowth, trees etc. wheeled gpr doesn`t seem to suitable for the terrain.
Or perhaps ER ?

Cheers
Asguard

[99thpercentile]

I'm confused by the question. "Would you recommend this technique in a environment where there is much undergrowth, trees etc. wheeled gpr doesn`t seem to suitable for the terrain. Or perhaps ER ?" It seems as if you are still asking about looking for depth to bedrock, if this is correct then seismic refraction is still probably the easiest method. I would never use GPR for this, although a resistivity survey may work depending on depths and soil moisture levels.

The issue of vegetation is common to all geophysical surveys which require cables or sensors that must contact the ground. For a depth to bedrock survey you would at most do two orthogonal survey lines so you only have to clear a limited amount of vegetation. Seismic surveys for oil companies sometimes go through the middle of a rainforest. In that case they clear lines that are about two meters wide that can go on for many kilometers.

Hope this helps.

[asguard]

I'm confused by the question. "Would you recommend this technique in a environment where there is much undergrowth, trees etc. wheeled gpr doesn`t seem to suitable for the terrain. Or perhaps ER ?" It seems as if you are still asking about looking for depth to bedrock, if this is correct then seismic refraction is still probably the easiest method. I would never use GPR for this, although a resistivity survey may work depending on depths and soil moisture levels.

The issue of vegetation is common to all geophysical surveys which require cables or sensors that must contact the ground. For a depth to bedrock survey you would at most do two orthogonal survey lines so you only have to clear a limited amount of vegetation. Seismic surveys for oil companies sometimes go through the middle of a rainforest. In that case they clear lines that are about two meters wide that can go on for many kilometers.

Hope this helps.

Thanks Ryan,

Was actually looking for a better way to find a few bodies, not bedrock. Just a point of interest. Don`t think the Viet govt would allow a bulldozer tearing tracks through rice paddies and forest, to find 4 more, considering the way thinks work in the world, and no commercial interest.

All the best

[Akfisherman]

Depth to bedrock

Subbottom profilers....I currently own and am interested in selling both systems. They were used and still are used to identify bedrock depth for placer gold mining. I have used both extensively in Nome Alaska and Montana. Single channel reflection of acoustic waves. Interfaced with software you can display realtime data very accurately.

Jerry

[Seden]

Sub-bottom profilers

Jerry,

So how much are these units selling for?

Randy

[Akfisherman]

Subbottom Profilers for Sale

I'm selling both units for $5K. The units are used in a marine environment routinely for engineering applications and shallow hazards surveys.
Thanks
Jerry

[BillA]

Jerry
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