Interesting goldpick and nice rock.
This vein was above an old hard rock mine in what i think was a rhyolite outcrop. The vein showed no sign of magnatism and did not signal my falcon probe at all, which made me think sulphide. Was also the first thing that popped into mind.
excalibur63, the colour seems to be on most of the surface that has been exposed, though some is more just a brown colour. On one rock it is just like a skin but on other bits there is a quartz crust with the ore being the rest.