I thought that since people liked my initial posts here, I would give you a bit more, as it may help your prospecting.
People panning in modern streams often don't understand that probably most Victorian alluvial gold did not come from gravels in flowing water, but in the same streams in gravels metres to hundreds of metres below what was the level of flowing streams when the miners arrived. That is one reason why gold was often only first discovered after a few people had frequented a goldfield area for some time (e.g. shepherds).
Here is a typical Victorian stream in hillier country. You can see that there is a rather limited volume of gravel in it, the stream typically flowing over hard bedrock. It could all be turned over by a couple of miners at a rate of tens of metres of stream per week, over a width of 10 m if you are lucky in many cases, from gravels that vary from 1 or max 2 metres deep, to more typically tens of centimetres deep confined between areas of outcropping bedrock. It could be very rich, but there was often little gravel volume, so total gold production was not huge unless you got a good patch, and the miners soon worked it out. Most people panning in streams are panning the recycled leftovers of worked gravel, biut if they dig out crevices in the floor of the stream they get a bit of gold missed by the old-timers..
The reality is different in terms of where much alluvial gold came from (palaeoplacers). Alluvial production was from active stream systems (possibly a subordinate part of the total production), and on adjacent flats where buried river gravels were mined to depths of 30 m. It is difficult to determine how much of the shallow placer gold production of the Western Uplands was mined from Pliocene and younger sediments, relative to that produced from underlying, older but shallow, palaeoplacers. Much was probably recycled from gravel deposited at an earlier time, e.g. in the headwaters of Loddon River Group drainages. Older gravels of this type appear to have been mined from beneath younger colluvial deposits in the shallower alluvial gold workings of many goldfields (e.g. Ballarat).
Look at this gully. The water level was probably nearly 2 m higher than the base of the valley now, a bit swampy and ill-defined - allowing for 150 years of crap washing in, the gravels they were mining were probably below the present base of this gully, perhaps a metre or so (so 2-3 m below the water. Although in the same valley, and followed by a modern gully, the original gully and gold-rich gravels probably formed millions of years earlier.
Now look at this drawing done in goldfield times, and see the low mine dumps behind the opposite side of the gully.
These dumps were from shallow shafts, perhaps a few metres to ten metres deep, from which the miners were extracting gold-bearing gravel millions to probably often 15-30 million years old. Again, in the same valley, but offset from the modern flowing stream. Younger streams have successively moved back and forward sideways in the valley, covering these early gravels with clay and sand, and themselves have some gravel in them, but only a small volume. The ancient gravels were up to 50 metres wide in places (bigger rivers) and a good continuous layer of gravel in them 0.5 to 1 m thick was taken up the shafts. What they are doing in the picture is washing the gravel that they brought up the shafts in the modern flowing stream, often not working the modern stream itself, and all the waste crap they were bringing up was ending up in the modern stream. So when you pan the flowing stream now you are often panning a stream that never had much gold in it to start with, but which contains lots of gravel brought up the shafts (from which the gold had already been extracted). The miners would say they were working a "shallow lead" from their shafts.
You can see from this map of the Ballarat goldfield how the gold leads such as the Inkerman and Mopoke do not follow even the modern valleys (the Mopoke Lead cuts across modern Yarrowee Creek at right-angles in the bottom-right of the map.
After they finished (and 150 years) their shallow shafts now look like this.
You will commonly see these low mounds off to one side of the modern flowing stream, metres to tens of metres off to the side of it. The detectorologists often do better detecting these mounds (because the old miners mistakenly dumped some good gravel beside the shaft that they had brought up), than do the panners who now try working the stream.
Variations on the theme is that earthquakes have sometimes uplifted the old gravels, so that they are now on hillsides or hilltops above the modern streams (see White Hills Gravel in section). Another is that the old miners had limited resources and machinery, so usually only followed buried river gravels until they got more than 30 m below surface. Then goldfields went quiet and they moved on, later companies and syndicates moved in with good pumps and started to continue mining the gravels to greater depths (more than 150 m at Ballarat West). These were called "deep leads" (see bottom of palaeovalley in section).
Hope that helps.
me included.
