This doesn't sound like placer mining to me. Are you searching for buried "extinct" stream bed contacts? BTW - For the non-Californians... They pulled more gold out of California in 20th century than the 19th. Different equipment, & methods of course. But it's still a very popular hobby to head up into the mountains in late spring, after the snow melt surge, and pan for gold. You can actually go camping for a week and work a borrowed claim, and come back with several thousand dollars in gold flake. There have been a few big hits over the last 30 or so years, where someone came home with over $300,000. But these are very very unusual. The hobby miners work the claims that are too small to be of commercial interest, and/or re-work antique 19th century mining tailings piles.


Anyhow... I suspect you're thinking single receiver. You use multiple receivers. You can pluck that info off the primary signal in a geophone array. Your shot propigates across the array, followed by the echos. The wavelet analysis is quite a task. I have a B.Sci in Geology (CSU no less!), and I have only the vaguest understanding of it.


You can buy used geophones from Larry Cochrane over at the Redwood City Public Seismic Network. http://www.seismicnet.com/


All this is probably overkill. You're not trying to find oil. It might help to describe the size of the area you wish to analyze.


Also, have you considered a gravitometer. You would be surprised what they can tell you.


Rob