Scottish888,
I would have to believe there is a significant variation between sites and countries.
In Northern California where I play there is one particular stream that goes all the way out to the main river. I'm certain the "Old Timers" { 1849, 1920/1930} found color in the lower portion of the stream and followed it up till the color quit. They then backed up testing both sides of the stream for color, found it, followed it uphill and Bingo the Vein. How do I know this? There is an 8' diameter hole bored into the hard rock with narrow gauge tracks and an ore cart in the mine.
I would also Guess that the 'Color' they found was fairly rough/good size as the gold did not travel more than about a mile in the stream till it reached the main river.
We are looking at the distance traveled, the gradient of the stream moving the Au, the amount of water during winter through Summer available to move the Au, the type of soil along the stream, "catch basins" along the stream, how much Ice in the actual Vein to help break the ore loose from the mother rock and probably a few hundred or more active events that cause the ore to come loose from the vein and things that break it apart on its travel down stream and deposit it where it is findable. One of those Active Events is Time, how long did "the elements" work on the vein before the Au was discoverable?
But at least you have an actual stream with placer in it that came directly from the Vein of gold in a rock wall. One fork of the stream ran right over the the rock that held the Au and eventually the abrasion, weather, pH of the soil, etc. broke through the rock to the vein and started pulling the Au into the stream.
Rugged country to get into but the Old Timers with crude equipment/clothing/boots etc. did it, got it first and kept working the mine till the vein ended some 100' into the mountain. That had to be a disappointment!! There was no "easy come, easy go" in this area as it was all hard work just hiking the mountains and even harder sampling and boring that 8' diameter hole! Quite a puzzle to work out especially where Glaciation is thrown in as well as active Volcanoes, Major Earthquakes/Mountain Formations,. TIME and the like..........63bkpkr
(note: In this area I find Ocean Animal Fossils at 6000', so big time earth fractures/movement. Also in the area there has been Major Hydraulic Mining up to 8000'[buried ancient rivers with gold in them]). Heavy Duty Stuff so think Big changes all around gold bearing veins!
Ok, one more. If there are Ocean Animal Fossils at 6000' elevation {and there are} then was the Gold injected into fissures in bedrock that was underneath the ocean? Or, for Caliofornia, it has been speculated that as the mantle along the Coast folded up along the coast line forming vertical fissures that were later filled with gold bearing molten rock and then the land mass continued to change as the young earth did all sorts of cataclysmic jittering and jiving? Yeah, too many things to think about. Hope this helps!
