share buy back

Can anyone tell me what the maximum % of issued cap. can be bought back under a buy back? I checked the ASIC site and says anything over 10% requires a special resolution(makes sense).
Perhaps the best deployment of capital is buying more shares in itself. With 299.3 mill iss. shares.. 53.5C A cash to come (Fx @ .9750)less 5 c for Conv. Notes, tax uncertain at this point, lets assume 5 c, so net total 43.5c, plus Hawksville W.I worth circa 20c (A 60 mill), looking at 60-65c val, selling at 37.5 c by the look of the open. $130 mill net cash.
Buying back 50% of the iss. shares at 37.5 c costs A56 mill. leaving A74 mill cash and A 60 mill for W.I. giving A134 mill T.Assets with 150 mill shares outstanding, or 89 c per share. Whilst this is an academic argument as 50% of the cap. can't be bought at prevailing prices it should give those nervous holders some solace as the share px can only head south for so long before management could send a very strong signal to the market via an enlarged buy-back programme.