The company said the longwalls were maintaining their high output with an increase in the use of longwall automation.

FY20 production guidance remains unchanged at 7Mt with longwall moves scheduled during the December 2019 and March 2020 quarters.

"Achieving improved development rates at Appin to support the operation's return to a three longwall configuration from the June 2020 quarter remains a focus," South32 said.

The company said it had also advanced study work at the Eagle Downs Metallurgical Coal project in Queensland ahead of a final investment decision scheduled for the December 2020 half year.