What is the most aplicable geophysical method to know the paleotopographic properties of a quartz Precambrian basement hidden under the limestone and dolomite formations?
i think refraction method might be ideal and the cheapest. however you need long spread length (probably 48 channels or more with 5 meters spacing) and a good source provided all rocks above basement have much lower velocity. reflection is good but expensive and much more cumbersome in term of processing.
Depending on the conductivities you have, I would suggest a Stratagem MT survey or similar. An AMT survey will also work. There are many systems available but I use Stratagem or Phoenix systems with AMT coils.
These systems are expensive to buy if you do not have them. However the stratagem is much cheaper to buy than Phoenix.
If it's 150m depth then you're likely to need a spread of 750m to get a result from refraction, and will need a bigger source than a sledge hammer. It would work, but it is probably not going to be cheap.
why don't You try with environmental seismic noise?. I don't know the geological framework You are working in and the extension of the study area but, if the boundary beetwen the Precambrian basement and the carbontae sequence features a significant impedance contrast, elaboration of seimic noise can give intereting results. And it is very cheap compared to other geophysical methods. Please read:
Bonnefoy-Claudet, S., Cornou, C., Bard, P.Y., Cotton, F., Moczo, P., Kristek, J. and Fäh, D. (2006a). H/V ratio: a tool for site effects evaluation. Results from 1-D noise simulations. Geophysical Journal International, 167, 827-837
A simple method is the use Vertical Electrical Sounding (VES). Total current electrodes spread of 600m (that is AB/2 of 300m) would give you a depth of 150m. One of the advantage of this method is that you can decide to increase or decrease your spread on the field. This will be possible if you plot the resistivity value against current electrode spread divided by 2 (AB/2 ) on the field as you are taking the readings. The moment the resistivity values start to increase with out decreasing possible is an indication of soundings on the precambrian basement.
I am agree with Ganyiu, the Vertical Electrical Sounding should be a chepeast solution of this task. Do you now something about tectonic situation, or karstification of carbonates overlaying quartz complex? Do you have imagination about a shape of quartz. ? Apparent resistivity should be sufficient tool for detection of such task.