I'd say the main reason why production for this quarter is going...

I'd say the main reason why production for this quarter is going to drop is because there is no more ore left to blend with daily mining activities from the stockpile.
From the quarterly
'During the March Quarter 95,633 tonnes of ore was trucked from Surveyor Mine to the Mt Garnet processing plant. A total of 28,081 tonnes held in stock from the previous quarter from the Mt Garnet Mine, was included in the processing at a blend ratio of approximately 3:1 (Surveyor : Mt Garnet). 17,309 tonnes of Zinc concentrate 4,210 tonnes of lead concentrate and 4,596 tonnes of copper were hauled to Townsville Port for export. '