Why is Rio Tinto stock sliding today?

Rio Tinto's stock experienced a decline of 3.2% to A$173.52 today, as a contract dispute with China’s centralised iron ore buyer threatens the miner's short-term earnings outlook. China Mineral Resources Group (CMRG), which negotiates on behalf of over half of China's annual iron ore imports, has instructed domestic steel mills to halt talks for Rio Tinto's flagship Pilbara Blend ore while price negotiations ongoing.

This comes as a surprise, considering Rio Tinto's previously strong protection against CMRG pressure, given the company's partnership with Chinalco, a major shareholder and Simandou iron ore project partner in Guinea. The freeze appears to include Rio Tinto specifically, prompting investors to question the extent of protection that partnership provides, intensifying the sell-off.

Currently, iron ore prices hover near the US$100 per tonne mark, driven by declining Chinese steel output, further complicating the outlook. The Australian mining sector, including peers BHP, Fortescue, and South32, is also declining on the ASX, collectively dragging the index down 1.4%.