IIRC the base Mining skill (which increases cycle speed)
mining(base skill) (5% to yield for mining turrets )
mining upgr( mining 3 ) (lowers cpu for mining lasers )
astrogeology (mining 4)(5% to yield for mining turrets )
there is no skill that affects gas harvest except the skill itself
maybe game doesnt recognise gas harvesters as mining turret but as standalone turret with aility to harvest gas