Exploration group Ovoca Resources has said it does not know why its shares rose by over 50 per cent on Tuesday, from 20 cents to 31 cents, a day before it detailed a $500,000 joint venture with an offshoot of mining giant Anglo-American.

A spokesman for Ovoca said, however, that the move simply brought the share price back to the level where it was a week ago before it was hit by a sharp fall.

After the announcement yesterday, the shares rose to a high of 35 cents before closing two cents lower on the day on 29 cents.