12vic,
possibly the mark up could have been due to the gold price movement in Uk trading time and the MM might have thought the OZ price would kick on , ie. he was trying to anticiplate future events? not much movement in currency at end of last week .
Re RIO, I often wonder there could be an arbitrage opportunity ! probably not as the logistics and time taken to transfer stock to Australia means you might be out on a limb so to speak . But worth thinking about for anyone who has account with both Uk and OZ broker . BLT also had quite a big price differential lately but is has narrowed in last week and even slow moving Bramnles had a similar experience!!