Rio Tinto Plc, the world's second-largest iron ore miner, has joined China's first iron ore trading platform as an official member, China Beijing Metals Exchange (CBMX) announced on Friday.

A signing ceremony was held in Singapore between senior officials of both sides, according to a statement on the CBMX website.

The agreement will require producers to sell a pledged volume of their ore output through the platform. The exchange will bring steelmakers from China, the world's largest consumer of iron ore, and leading iron ore producers into a common platform, after top miners abandoned a 40-year annual benchmark pricing system in 2010.

The announcement came just one day after Brazilian mining giant Vale signed a memorandum of understanding with CBMX.

Fortescue Metals Group Ltd. (FMG), the third-largest iron ore miner in Australia, also joined the platform as a member on March 20.

Created on Jan. 16, the state-backed spot online trading platform will reflect supply and demand conditions of the iron ore market "objectively" and help foster a fair, reasonable, and transparent global iron ore pricing mechanism, the statement said.

China's major steel companies - including Baosteel Group Corp, Hebei Iron & Steel Group Co Ltd, Wuhan Iron and Steel Group Corp, Shougang Group, Angang Steel Co, and China National Minerals Co Ltd, a subsidiary of China Minerals Corp - have agreed to join the new platform.

BHP Billiton Ltd. is the only top iron ore miner that has yet to join the CBMX, as it had previously given strong support to a similar trading platform in Singapore, the GlobalORE.

China accounts for 60 percent of the global seaborne iron ore trade and has the world's largest iron ore spot market.