Macarthur Coal has rejected a $3.7bn takeover bid from New Hope.
The company, which previously rejected a takeover approach from Peabody Energy, said the New Hope offer did not represent an adequate premium for control of the site.
Meanwhile, Macarthur said it had not received a takeover offer from Xstrata - news which earlier shot Macarthur's shares to a 20-month high.
Macarthur is the world's largest producer of pulverised injection coal.
Coal prices have doubled since the start of 2009 while Chinese coal imports have tripled due to a revival in the steel industry.