I think, GOLD isn't 'strong' enough to replace all nearby BMTL and BRMT. So, better make change to IRON:

(WARNING: I use my own 'scripting language' because I don't understand C++ and LUA.)

IF NOT element_check(nearby,GOLD)

   {

   IF element_check(nearby,WATR)

   OR IF element_check(nearby,SLTW)

   OR IF element_check(nearby,OXYG)

   OR IF element_check(nearby,LOXY)

   THEN change_particle(self,BMTL,)

   change_property(self,tmp,10)

   END

   }

I wish this will be helpful.