Newcrest said the latest life of mine plan at Telfer "indicates lower levels of ore mined and higher levels of waste from West Dome, lower gold recoveries, higher estimated closure costs and higher operating costs than previously forecast".
It also said there has been a reduction in the value attributed to a potential future block cave.
At Namosi, the gold miner pointed to an assessment of the potential project configurations that "has prompted a reassessment of the appropriateness to continue to carry forward previous study costs".
Meanwhile the cash flow result is inclusive of $48 million received in respect of the sale of the Bonikro project in Cote d'Ivoire, and $251 million spent buying a 27% stake in Lundin Gold.
With $460 million of the free cash flow being used to pay back debt, Newcrest's net debt as of June 30 is expected to be formalised at about $1 billion.
Newcrest will report its full audited accounts later this month.
Shares in Newcrest were up slightly to A$21.11 in morning trade, capitalising the company at $16 billion.