Thank you for your answers, grubstake I looked at the Regolith Mapping of Bendigo article. It is very detailed and I will not try to say I understand it, even though I have read similar articles they are all incredibly detailed and complicated, no doubt these zones are what gold miners look at.
What interests me is the late Tertiary age up to now, which is probably not really mentioned very much. In other words the zone our detectors work in. Along side my house (in gold country) we dug trenches for various service, (power, water etc). The top 200-250mm was clay, then a 100mm of layer of quartz, another 150mm layer of clay, another 80mm of quartz. Near by is a small quartz reef plus a sedimentary rock reef.
I imagine the clays are from a time of rain and vegetable grow, and the quartz layers from a time where the quartz reef broke down due to heat or cold. The concentrated quartz was washed down possibly due to very heavey rain or melting ice to form a layer of predominately small 10-15mm quartz pieces. In the shallow gold workings here the old timers dug down into these quartz layers looking for gold.
Our detectors work in 300-450mm typically, so therefore are we looking at 20-30,000 years of erosion or 1 million years of erosion?
As I walk around with my detector I ponder what the answer is, and if we under stood this more we all might find more gold.
Cheers