MELBOURNE/SYDNEY (Reuters) - Top investors in Rio Tinto (>> Rio Tinto plc) (>> Rio Tinto Limited) say they want the global miner's new boss to proceed cautiously on acquisitions, focusing on the core, cash-generating iron ore business and on developing his own copper mines before looking for new assets.

Jean-Sebastien Jacques, who will take over from Rio's veteran boss Sam Walsh in July, was previously the head of its copper and coal business. His appointment on Thursday has been read by some as an effort to rebalance the iron ore-focused miner and a pointer - given his negotiating credentials - towards deals.

The front-runner for the job had been iron ore boss Andrew Harding, whose division generated nearly 90 percent of the group's earnings in 2015. Jacques' copper and coal unit made up just 6 percent of the total.

But shareholders said Jacques should tread with care.

While the Frenchman may be taking over as more than $30 billion worth of mine comes onto the block amid the toughest mining downturn in decades, it is unlikely that many assets will be of the high quality, large, long-life caliber - so-called "tier one assets" - they said.

"We don't want them to be going out and aggressively acquiring stuff," said Andy Forster, a portfolio manager at Argo Investments, the second-largest Australian stakeholder in Rio.

Outgoing CEO Walsh said in February the most desirable copper assets were locked in the hands of other big miners and it would take a longer period of weak copper prices before those players crack.

Bankers have named mines including Cobre Panama, owned by First Quantum Minerals (>> First Quantum Minerals Limited), Freeport McMoRan's (>> Freeport-McMoRan Inc) Cerro Verde in Peru and Grasberg in Indonesia, which is co-owned by Rio Tinto, or Anglo American's (>> Anglo American plc) Los Bronces and Collahuasi in Latin America as potential targets.

Among the easier options would be taking control of Grasberg and mopping up Rio Tinto subsidiary Turquoise Hill Resources (>> Turquoise Hill Resources Ltd), which holds the majority stake in the massive Oyu Tolgoi copper mine in Mongolia.

The more ambitious, according to some bankers, could include a tilt at indebted Anglo American (>> Anglo American plc), or at least some of its assets.

But Rio investors that Reuters spoke to wanted more of the old, conservative approach and less of the boom year mega-deals like Rio's acquisition of Alcan aluminum group and Mozambican coal, two debacles which led to the exit of Walsh's predecessor and brought in a period of conservatism.

TIGHTEN THE SCREWS

While Jacques has built a reputation as a sharp negotiator, working on the Oyu Tolgoi project in Mongolia, he is also seen as an astute salesman, having overseen the sale of the Northparkes copper mine and the Bengalla coal mine in Australia - both at higher than expected prices.

"We would be more impressed by what he divests, more coal, uranium, etc. than acquisitions - and how he tightens the screws on underperforming assets," said Peter O'Connor, a mining analyst with Shaw & Partners in Sydney.

"Whilst some desire a 'growth junkie', we would like a CEO who inspires the optimization of return on invested capital from every existing asset."

In the meantime, shareholders say they are braced for some reshuffling at the top. Several said they would not be surprised to see iron ore chief Harding and Chief Financial Officer Chris Lynch eventually leave after missing out on the top job.

Chairman Jan du Plessis too, after seven years in the job and having resolved the chief executive role, may also move on, company executives said.

"Short-term sentiment might be affected, but there are plenty of good people out there looking for jobs," said Tim Schroeders, a portfolio manager at Pengana Global Resources Fund.

(Additional reporting by Freya Berry and Anjuli Davies in LONDON; Editing by Clara Ferreira Marques and Alex Richardson)

By Sonali Paul and James Regan