Not to be a smartA or anything, but they will make them more visible on the surface after some good rains wash away the soot/etc.
As to what I think your question is going for, it could make a small difference in that heat can speed chemical reactions like oxidation, but I don't think it would be much, and it sure wouldn't extend very deep into the rock.
No, it wont affect the quartz. There might be a spot that gets hot enough quick enough to thermally crack a crystal, but it will be rare if at all. Qtz is about as chemically inactive as it gets.
Wait until after a good rain and it should be good hunting.