'Fake market signal': China slams big miners China's top economic planning agency has lashed out at the world's top three iron ore miners, accusing them and some traders of manipulating the market to drive an 80 per cent rally in ore prices in just six months. Some miners were buying back iron ore cargoes from the spot market as a way to lift prices of the key steelmaking raw material, the agency added. BHP bought 100,000 tonnes of the raw material in January in a rare move that market participants saw as a strategy by producers to stem a decline in prices. "You can always accuse someone of manipulation, but it's very hard to justify it," said an analyst with an Asian brokerage who declined to be named because of the sensitivity of the issue. It's a free market, there's no regulation. Benchmark iron ore prices slumped to a three-year low of around $US87 a tonne in early September as Chinese demand shrivelled. But prices have since rallied at a break-neck pace, gaining over 25 per cent in December alone and hitting a 15-month high of $US152.50 a tonne in January. While part of the spike was due to restocking by Chinese steel mills ahead of Australia's cyclone season, the rally was exacerbated by miners' price manipulation and an unreasonable pricing mechanism, the NDRC said in a strongly-worded statement. The planner also said miners had taken advantage of a "non-transparent tender process to push up prices." Major iron ore miners sell a small portion of iron ore cargoes via tenders, whose results influence world iron ore indices. "High tender prices are taken into the Platts' iron ore index assessment, which means an index with a small volume of spot deals ends up being used as a price reference for long-term contract settlement," the NDRC said. Chinese steel mills have been forced to ditch a decades-old practice of annual iron ore pricing since 2009 in favour of spot pricing based on indices. The China Iron & Steel Association, an industry body representing large Chinese steelmakers, has lobbied the government to investigate possible price manipulation by miners and traders, a senior official said at the industry conference last month. Profits at China's large steel mills slumped 98 per cent in 2012, as slower economic growth hit steel demand in the world's largest consumer, the China Iron & Steel Association has said.