Yeah; I've heard this 40% number bandied about, but NEVER seen it in practice.
While ore types have changed, I kept some notes - including dumping my least productive runes well before then.
In my experience, every spot has a DIFFERENT colored ore percentage, that is intrinsic to that resource square. No matter the ore color, the tend to produce almost the same amount of ore each time, if allowed to fully refresh (+/- 2 large). And, the percentage of iron to colored ore holds true, for that spot, even if it goes to iron, and you have to use a prospector tool to get Dull copper from it. If it tends to give 50% colored, you'll get a bell curve based on 50% color from charting mining trips there - regardless of what color you get. Some places give 80-90% colored consistantly, like the TRAMMEL spot I went to that gave 30 swings of ore, 27 of which were colored (and counting doubles as one swing). And that is TYPICAL results for that spot, over the last 4 years.
There is no way in H-E-Double-toothpicks that a 40% chance that a human supposedly has, is going to go THAT far off the chart, repeatedly. BTW, for the statistically impaired, that's less than a 0.0000000004% chance of occurring, if the 40% chance value was valid in any way. And that is the chance of it occuring once. I don't want to have to dig up my old textbooks and try to figure out the chance of it happening TWICE in a row.