Mining bosses shift focus from debt and start to see new investment potential

* Copper, oil offer potential

* Structural deficits returning

* Capital (Other OTC: CGHC - news) expenditure on horizon after next year - BHP (Adds quotes, context)

BRUSSELS, May 10 (Reuters) - The bosses of big mining firms are starting to see potential for new investment as record low margins set the scene for higher commodity prices, they said on Tuesday, marking a change in tone from the focus on cost-cutting and asset sales.

A prolonged commodities rout has forced even the biggest players to sell assets to deal with piles of debt.

But BHP Billiton said it expected capital expenditure to rise after next year, while Glencore (Xetra: A1JAGV - news) said structural deficits were returning, led by zinc, and copper also faced "supply challenges".

Andrew Mackenzie, BHP's chief executive, said the firm was particularly positive on copper and oil but was not just waiting for prices to recover.

In a copy of a speech he gave to a conference in Miami, he anticipated a $3.6 billion increase in BHP's productivity gains up to the end of 2017 with costs set to fall to half the level seen five years ago.

He also said capital expenditure would rise after next year as the company made decisions on projects such as the Gulf of Mexico Mad Dog oilfield and Chilean copper mine Spence.

Speaking at the same conference, Ivan Glasenberg, chief executive of Glencore, said "record low sector margins are setting the scene for the next price upswing" after a plunge in investment.

Going forward he said growth needed to be redefined as cash flow per share, rather than production volume, and said Glencore (Amsterdam: GX8.AS - news) was well placed as divestment progressed well and April disposals should be completed this quarter. (Reporting by Barbara Lewis; Editing by Susan Fenton)