Markets are forward looking byron, all that information is known...

Markets are forward looking byron, all that information is known and thus you would expect to be priced in. Unless the production cost increases/reduction in grades is greater than expected or something of that nature (which is entirely possible given recent price action). However other miners have dropped by larger % amounts in recent times, OZL is not isolated, but I would have thought for a low cost producer it would have held up a little better.