THERE is a growing belief in the City that Griffin Mining's Caijiaying zinc mine just north of the Chinese capital Beijing could turn into a world class mine. Top broker Merrill Lynch obviously thinks so because rumours suggest it picked up a stake of around 5% - at 25p - in the recent £4.2m placing. Griffin, 1/4p up at 27 1/4p, wanted the cash to fund further exploration around the mine, which should be in full production next year.