Hi, I came across this on eBay - 320806067478 I've seen the Perth Mints Chinese released dragons but never an Ox. 1/20 coloured Au Ox plus 1/2oz Ag Ox set in PM presentation box.
if I am not mistaken, this was an overseas issue particularly targeted to China. The PM has done the full lunar series once and has started again, so they have done all the lunar animals. Here is a great summary http://www.slideshare.net/goldpelican/perth-mint-lunar-coins