Geophysical survey to map limestone bedrock

[geo6]

The site is a karstic limestone landscape (mostly infilled sinkholes or depression valleys after salt removal process millions years ago).

The problem is that we do know what's under 5 to 10 m into the bedrock which consists of mostly interbedded clayey limestones. My questions are:

1. Is there value in doing surface survey such as TEM or ERT before specifying a drilling program since we already know what's going on at the top 10m ? Also the high clay content at the top could potentially disrupt the interpretation.
2. There are tons of resource drills with 100 to 200 m spacings. Will the betonite-filled boreholes interfere the surface survey results?
3. The next step could be doing downhole geophysics to confirm findings in TEM or ERT.

Any thoughts or input ? Thanks bunch !

 

[charnott]

Is there value depends largely upon the planned development. Ive used ERT extensively in the middle east looking for solution features but its not always appropriate, check with some local geophysical contractors. Be sure to look out for saline groundwater as this has had significant impacts on interpretation of survey data in this part of the world. Follow up with verification boreholes through any identified low resistivity zones and then assess whether further investigation is necessary i.e. cross hole geophysics, probing etc.

with regards the bentonite bets to check with your contractor but the variance in resistivity between the native rock and the bentonite may appear on the usrvey but being largely linear features they will be obvious and I dont think they'll have a detrimental affect on the survey.