Native title custodians say they have “serious concerns” with a plan by billionaire Gina Rinehart’s flagship company to build a new mine at Mulga Downs in Western Australia and are yet to give their consent to the project.

Rinehart’s Hancock Prospecting originally planned to produce 20 million tonnes of iron ore each year at Mulga Downs in the Pilbara, but slashed the project size to 12 million tonnes last October as part of efforts to soothe objections raised by the Banjima native titleholders.