You're right @nk. BLK expect AISC to be $1500 - $1700 / oz for FY19 (downgraded in the Dec'18 quarterly from previous re-confirmed expectations of $1250 - $1450 / oz).
Looking at gold production from (Jan'17 to Dec'18): $233.076m (costs) to produce 139,252 oz = AISC $1674 /oz.
Are you expecting the AISC to improve considerably when they mine Williamson?