Steelmaker and iron ore exporter, OneSteel has downgraded full-year earnings guidance by 14%, a move that justifies the long slump in the share price this year.

In a filing with the ASX the company yesterday blamed the rapid appreciation of the Australian dollar and its adverse impact on domestic steel margins, as well as lower sales from bad weather and flooding.

The company's shares have fallen by almost 30% since February 18 (just before its interim report four days later) from $3.01 to $2.02 yesterday.

The shares in fact touched a 52 week low of $2.01 in trading yesterday.

The close of $2.02 yesterday was a fall of 11c on the day or just over 5%.

In fact the OneSteel fall yesterday saw rival BlueScope Steel's shares hit a new 52 week low of $1.58 during trading.

They closed at that level for a loss of 5c or 3% on the day.

OneSteel said it now expected net profit in the second half of the year "broadly in line" with the first half result of $116 million.

That would put net profit around $230 million, $40 million down on the earlier forecast full year profit of $270 million.

Annual iron ore sales would be 6 million tonnes, against the February target of 6 to 6.5 million tonnes.

OneSteel put the fall down to the higher Australian dollar, which had constrained sales and margins and Australian dollar revenue.

It also said that bad weather in the half year also would affect shipments and the proportion of medium grade ore sales.

As well as the foreign exchange rate, OneSteel said there was still a relatively high level of uncertainty around other key factors affecting its earnings, such as domestic and international prices and demand for steel and steelmaking inputs.

The steelmaker also blamed the high dollar for its flat net profit result of $116 million for the six months to December 30, compared to $117 million in the previous corresponding period.

When it reported those results in February, it said it expected margins to improve through the fourth quarter as price increases take effect.

That hasn't happened.

And that first half result, like those in the previous two halves of the 2010 financial year, came from earnings from the iron ore export business, which offset weak profits or losses in the steel business.

That won't change for the 2011 financial year.

And BHP Billiton said yesterday that it will spend around $260 million to extend its big diamond mine in northern Canada.

BHP said the project involved pushing back of the existing Misery open pit at the company's EKATI mine, which was mined from 2001 to 2005.

Stripping operations were expected to begin in October of this year with ore production beginning late 2015 and final production from Misery in mid-2017.

The estimated capital cost is $US323 million ($A301 million), of which BHP Billiton's share will be 80%.