An adviser to the potash exploration company Sirius has exercised an option on 900,000 of the company's shares.Sirius has sold the shares for £54,000, or 6p per share, giving the adviser a profit on yesterday's close of £180,000.Since yesterday Sirius has fallen back slightly, to 21.91p (a 15.5% drop). In the last 12 months however the stock has gained 155%.BS