TIMELINE-Twists and turns in the tortured China-Rio saga

(For full coverage of the Rio Tinto case, click [ID:nSP473911])

August 13 (Reuters) - China formally arrested four staff of miner Rio Tinto (RIO.AX)(RIO.L) on suspicion of obtaining commercial secrets this week, but has opened the way to easing political rancour over the case by leaving aside separate state secrets accusations.

Australian Stern Hu and three Chinese employees from the Anglo-Australian mining giant, who have been detained since July, are suspected of "using improper means to obtain commercial secrets about our country's steel businesses", the official Xinhua news agency said on Wednesday.

Here is an overview of key twists and turns in the case that has shaken global commodities markets and threatened to strain relations between Australia and its top trade partner, China.

* Feb. 12, 2009 - Under a landmark deal, China state-owned aluminium group Chinalco says it will invest $19.5 billion in Anglo-Australian miner Rio Tinto. The deal would be China's biggest overseas investment, and a rescue plan to halve Rio's $38 billion debt. [ID:nSYD405125]

* Feb. 18 - Australian politicians question the deal, warning it could make Australia a branch of Beijing's economy. [ID:nSYD238248]

* March 25 - Australia's competition watchdog clears deal. [ID:nSYD216738]

* May 26 - Rio Tinto agrees a 33 percent price cut on iron ore, a key ingredient in steel-making, with Japanese and Korean steel mills. Under iron ore's opaque, traditional 'benchmark' price-setting system, the agreement should dictate the global basis price for all mills, including those in China, the world's biggest steelmaker. [ID:nSYD24132]

* May 27 - China rejects the iron ore price cut, unsurprisingly given its calls for a cut of 40-45 percent. Its move threatens to scupper the benchmark. [ID:nSYD388525]

* June 5 - After months of scrutiny and shareholder pressure, Rio-Chinalco deal collapses. Rio says it will instead raise $21 billion through a rights issue and a joint venture with one-time suitor BHP Billiton (BHP.AX) (BLT.L). Chinalco expresses disappointment.

The collapse leaves China vulnerable to just two suppliers -- the Rio/BHP combination and Brazil's Vale (VALE5.SA) -- which control 70 percent of global iron ore trade. [ID:nSYD73514]

For a FACTBOX on the BHP/Rio joint venture see [ID:nSYD413783]

For a TIMELINE on how the deal unravelled see [ID:nSP402097]

For a FACTBOX listing the iron ore industry's top buyers and suppliers see [ID:nSP408660])

* June 30 - A deadline for the agreement of annual iron ore term prices passes with China and big miners deadlocked. [ID:nSP492237]

* July 2 - First sign of a compromise on iron-ore prices. Negotiating body China Iron and Steel Association (CISA) says it may accept a reduction only slightly deeper than the 33 percent cut agreed by other Asian mills. [ID:nSYD508129]

* July 8 - Four Shanghai-based Rio staff, including its top China-based iron ore salesman, the China-born Australian citizen Stern Hu, and three Chinese colleagues, are detained by Chinese authorities. [ID:nSYD436642]

* Aug 12 - China formally arrests the four Rio Tinto employees on suspicion of violating commercial secrets and taking bribes. Rio denies unethical behaviour by employees. [ID:nSP508871] [ID:nSYU007013]

For a Q+A on the Rio arrests see [ID:nSP458731]

Source: Reuters (Compiled by Gillian Murdoch and Muralikumar Anantharaman, Editing by Bill Tarrant)