** Shares of Australia's St Barbara SBM.AX fall as much as 14.5% to A$0.325, their biggest intraday pct drop since April 23
** Stock at lowest since May 30
** SBM last down 11.2% at A$0.3375 as of 0230 GMT
** Gold miner lowers full-year gold production guidance for its Simberi gold mine in Papua New Guinea to 50,000-52,000 ounces from 55,000-65,000 ounces stated earlier
** SBM also raises the all-in sustaining cost guidance for Simberi to A$4,400-A$4,700 from A$3,900-A$4,200
** About 12.2 million shares change hands vs 30-day avg of 6.4 million shares
** Stock up 68.9% YTD, including session's move
(Reporting by Anjali Singh in Bengaluru)
((anjali.singh2@thomsonreuters.com))