" I am having a mold problem on my roof, almost black in some areas, did
have
many trees overhanging, cutting down or limbing up most to allow more sun
and air movement. However I did notice, everywhere I had any metal
(galavanized) there is not any mold for a path all the way down the roof
underneath. I guess it is the Zinc in the metal that kiils the mold.

It is the zinc, indeed.
Drive around the neighborhood and you will see streaks of fresh looking
shingles downslope from most galvanized pipe vent shields. Those that are
painted when installed won't confer this benefit, tho. Older homes may have
lead shields around the pipes; that appears even more toxic to mold, as the
streaks are really light colored downstream from these older vents.