Major diversified miners are due to post surging first half results after a strong rebound in prices with demand driven by China and India.

Vale and Anglo American kick off the results season on Thursday and Friday respectively.

Investors expect a more cautious tone for the second half as prices look to have peaked and they will be watching whether costs are being kept under control.

In general we're looking at some headwinds going into the second half, said analyst Alison Turner at Panmure Gordon in London.

Some of the prices that we've seen in commodities in the first half probably look to have been something of a windfall, that we may not see repeated in the second half, she added.

The average price of copper during the second quarter was 50 percent higher than the same period a year ago, but after touching highs in April, it has shed about 12 percent.

Spot iron ore prices <.IO62-CNI=SI> have given up nearly 30 percent since hitting peaks in the second quarter.

The firms' outlook statements will probably reiterate that they are cautious about the coming months but confident about medium-term demand, driven by China and Inda, analysts said.

The heads of Rio Tinto and BHP Billiton have recently warned about the impact of Europe's debt crisis slowing global growth and China's efforts to cool growth weighing on commodities demand.

China's always the biggest risk for these companies, now, said Tim Schroeders, a portfolio manager at Pengana Capital in Australia, adding that he was confident that even if China's annual growth slowed to 8 percent, that would still be good for commodity prices.

VALE

The world's biggest iron ore producer, Brazil's Vale , will release its results after the close of markets on Thursday.

A key issue for Vale, as well as for the No. 2 and 3 iron ore producers -- Rio Tinto and BHP Billiton -- is the change in pricing for the raw materials used to produce steel, from an annual benchmark to quarterly figures.

Vale's net profit is expected to soar nearly five-fold to $3.83 billion in the second quarter on higher prices and sales volumes, according to the average estimate of six analysts.

ANGLO AMERICAN

Anglo American , listed in London and Johannesburg, which posts results on Friday, will be under scrutiny by investors worried about its huge Minas Rio iron ore project in Brazil.

Worries have simmered since news reports said earlier this month that land tenure issues would probably delay the start-up of the new mine by one year until 2013.

Shareholders will also be hoping that the group, which owns the world's biggest platinum producer, Anglo Platinum , will reinstate dividends after suspending them last year during the downturn to conserve cash.

Anglo has previously said it plans to restart payouts either at the interim stage or at the end of the year.

It is expected to post a 90 percent jump in first half underlying earnings per share to $1.73, according to a consensus of 12 analyst estimates gathered by the company.

XSTRATA

Anglo-Swiss Xstrata issued production results on Tuesday that largely disappointed analysts, showing a 3 percent decline in copper and flat coal output, its main products.

Production gains are key for Xstrata since it has shifted focus from being an acquisition machine to growth by building new mines and expanding existing ones.

Investors will also be scrutinizing costs, said Turner at Panmure Gordon. Certainly in the case of both Anglo and Xstrata, they've made quite a lot of promises on in terms of the performances they're going to deliver on the cost front.

Xstrata, which reports on August 5, is expected to post a 200 percent rise in first half EPS to 76 cents, according to a consensus of 11 analysts' forecasts compiled by the company.

RIO TINTO

Analysts said the main factor confounding forecasts for Rio and BHP was pricing for iron ore, which is Rio's most important product, making up two thirds of underlying profit last year.

People are unsure about iron ore prices, in particular, and the mix of contract and spot pricing, said Schroeders at Pengana Capital.

Rio Tinto, which reports on August 5, is expected to more than double first-half underlying profit to $5.5 billion compared to $2.57 billion a year ago, according to the average of forecasts by 22 analysts polled by the company. The forecasts ranged from $4.74 billion to $7.0 billion.

Investors will be keen to hear about details of Rio's expansion projects and progress with the regulatory approvals for a planned iron ore joint venture with BHP that is expected to result in total synergies of $10 billion.

BHP BILLITON

Analysts said results for BHP -- the world's biggest mining group -- could benefit from having a bigger portion of sales on shorter term iron ore pricing rather than quarterly pricing.

BHP, which reports on August 25, is expected to post net profit before one-offs of $7.06 billion for the second half of its fiscal year that ends in June, up 54 percent from $4.59 billion in the same period last year, according to Thomson Reuters data.

While BHP has the strongest balance sheet of the major miners, fund managers discounted the likelihood of BHP launching a share buyback.

This is because Chief Executive Marius Kloppers is cautious about the outlook, it will need to pay Rio Tinto around $5.8 billion if their iron ore joint venture goes ahead and it has a long pipeline of projects to fund.

In this uncertain environment where commodities have come off a bit, I think they're more likely to keep their powder dry, said Peter Chilton, an analyst at Constellation Capital Management, which owns BHP and Rio shares. One fund manager said he expected BHP would look at capital management next year.

Chilton said BHP would want to hold on to capital for any acquisition opportunities, including those that might come up from BP , which trebled its divestment target to $30 billion on Tuesday.

(Additional reporting by Brian Ellsworth in Rio de Janeiro; editing by Elaine Hardcastle)

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