30 September 2011
The difference is because MCX trades on gold futures. These futures are for a particular expiry. Right now contracts are for October 2011, December 2011 and so on. Gold in the market are spot rates and hence the obvious difference. You can see mcxindia.com market data for real time prices.
Also MCX futures closely mirror the sentiments in the international markets and reflect quite strongly to any news. Spot market rates are less sensitive to these factors which also creates differences.
In simple words, reason is similar to the reason why there is a difference between Reliance cash price and Reliance October future.