Where does a majority of the particals come from?  Maybe the clutch basket?  What's a high wear and tear part causing it?

Every time you shift gears it knocks off a small fragment off the corners of the dog and socket on the transmission gears.  The ratchet on the kick starter looses some metal off of the edges of the oneway teeth every time the kick starter is used. 

Every time you use the clutch there is clutch dust added to the oil.  The clutch dust from kevlar  or carbon fiber clutch plates is more abrasive than dust from OEM fiber clutch plates.  There is some metal that wares off  the tabs on the clutch plates and basket when the tabs slide up and down in the clutch basket slots.  There is also some ware on the tabs and basket every time the load changes directions hammering the tabs and slots in the basket.

There has to be some metal that constantly being lost off the teeth of all of the gears but I think this loss is very very small.