After threatening the $US50 a tonne mark for the first time in almost a decade, the price of iron ore has failed to hold above the key level for long, sinking in offshore trade on continued worries about the balance between supply and demand.

At the end of the latest session, benchmark iron ore for immediate delivery to the port of Tianjin in China was trading at $US49 a tonne, down 3.9 per cent from its prior close of $US51 a tonne.

The figure is a record low since The Steel Index began releasing the data in 2008.

It brings the commodity’s current losing streak to six days.

During this period the price has dropped more than 11 per cent, with the falls intensifying over the past two sessions.

Meanwhile, the price for iron ore delivered to the port of Qingdao, China — another closely-watched pricing guide — slumped 3.5 per cent to $US49.53, the weakest level since Metal Bulletin began formulating the data in May 2008.

Shares of the big miners, Rio Tinto, BHP Billiton and Fortescue Metals, have been smashed in the past month as a fall in the price of the nation’s biggest export accelerated amid continued new supply and a surprise slowdown in Chinese steel production this year.

Fortescue and smaller miners have been hit hardest, with the iron ore price now at levels where only BHP and Rio are comfortably making a profit after costs are accounted for.

And to make matters worse for Fortescue, the Perth iron ore miner built up by Andrew “Twiggy” Forrest, prices for its lower-grade ore are plummeting even faster than the benchmark ore the bigger miners are expanding production with.

“Low-cost supplies from Australia and Brazil continue to keep the market oversupplied,” Commonwealth Bank commodities analyst Vivek Dhar said.

“China’s steel futures for October delivery have now dropped for six consecutive days as concerns mount over China’s weakening economic growth and steel production.”

Iron ore’s record peak of $US185.60 a tonne in 2011 now seems an eternity ago, with current prices likely the lowest miners have seen since 2006, tracing back to a period when they agreed yearly benchmark contracts with Chinese steelmakers.

The Steel Index price is down 28 per cent this year and 62 per cent from the start of 2014, when prices were $US135 a tonne and it was common for miners to declare there would be a “price floor” at $US100.

Now, Singapore iron ore futures traders are betting that ¬prices will fall below $US50 a tonne by June and will not climb back by the start of 2019, the furthest futures contracts go.

Investors continued to sell mining stocks yesterday in the face of falling iron ore prices, with Fortescue falling 6.5c, or 3.3 per cent, to $1.90, Rio falling 82c, or 1.4 per cent, to $56.41 and BHP falling 69c, or 2.2 per cent, to $30.33.

In March, the plummeting iron ore price sent Rio shares down 11 per cent, in its worst monthly performance since March last year. Fortescue, which most analysts believe will struggle to meet mining and debt costs at current prices, slumped 22 per cent in March, its worst monthly performance in more than four years.

Recent falls in 58 per cent grade iron ore have been more severe than the benchmark, which contains 62 per cent iron.

The lower grade ore fell to $US43.20 a tonne on Tuesday night, bringing its 2015 losses to 31 per cent.

“The 58 per cent iron price provides an idea of the iron ore price that Australian iron ore miners like Fortescue Metals and Atlas Iron realise,” Mr Dhar said.

“As Rio and BHP continue to increase production and as (Gina Rinehart’s) Roy Hill (and other higher-grade mines) come online in the next 18 months, we could see this discount widen further.”

Another stakeholder feeling the pain is iron ore junior BC Iron, which yesterday received a reprieve from the West Australian government on the payment of royalties. The deal will allow $12 million in potential payments to be deferred by up to two years.

The stock price of BC Iron dipped 2.7 per cent yesterday despite the reprieve, with the closing price in line with a post-crisis low. Meanwhile, fellow iron ore miner Atlas Iron is trading around an all-time low, while Mt Gibson Iron is threatening post-crisis troughs.

More pain could be ahead as Deutsche Bank predicts a retreat below $US40 a tonne at some stage this year. Few analysts are quite so bearish, though Deutsche’s average price expectations of $US51 a tonne fall broadly in line with the sharply revised forecasts we are seeing on a seemingly daily basis from analysts.

Among others to declare new projections this week, London-based Capital Economics has tipped iron ore to end the year around $US45 a tonne, while Westpac is tipping a $US47-$US57 a tonne range.

ANZ and Citi have also tipped falls below $US50 a tonne over the past week, while US-based iron ore miner Cliffs warned last month that the tactics of BHP Billiton, Rio Tinto and Vale had the potential to push prices as low as $US30.

Fortescue is almost certainly operating in the red at current prices, likely losing $US2-$US3 a tonne if selling product at $US49 a tonne. This week is the first time during the bear market that prices have fallen below the miner’s operating costs.

Meanwhile, rivals BHP and Rio still maintain healthy margins despite the collapse in prices thanks to operating costs that are now below $US20 a tonne. Continued price weakness could, however, be expected to hamper future dividend payments.

In offshore trade, London-listed stock of both mining giants traded flat against a rising broader market.