UPDATE 3-Espirito Santo to file for creditor protection for Rioforte -sources
* Espirito Santo group must pay back 847 mln euros on Tuesday
* Debt owed to Portugal Telecom, which is merging with Brazil's Grupo Oi
* PT-Oi merger terms to be revisited if debt not made
* Banco Espirito Santo shares tumble, bond yields keep climbing (Adds Fitch, new BES chief's statement, closing prices)
By Sergio Goncalves and Axel Bugge
LISBON, July 15 (Reuters) - Portugal's Espirito Santo clan is preparing to file for creditor protection for one of its key holding companies, sources said on Tuesday, moving to ringfence prized assets as a deadline for a $1 billion plus debt repayment to Portugal Telecom looms.
The filing will be made by the company, Rioforte, in Luxembourg, where it is registered, one source close to the process said, adding that the move was aimed at preventing insolvency that would trigger a fire sale of assets.
Rioforte indirectly holds a stake in Portugal's largest listed bank Banco Espirito Santo, shares of which plummeted 14.6 percent to an all-time closing low on Tuesday. This extended their losses in the past month to 62 percent due to investors' worries about the bank's exposure to family debt.
The jitters jolted financial markets last week in Europe and beyond, raising new concerns about Portugal generally only two months after it exited an international bailout deal. Continuación...