ARMS split from Bakries culminates in Twitter spat with Rothschild

* Shareholders hope ARMS will return more

* UK market watchdog investigation into ARMS ongoing

* Founders exchange insults on Twitter (NYSE: TWTR - news)

* ARMS gives no timeframe for $400 mln return (Recasts with details on Twitter exchange)

By Silvia Antonioli and Stephen Eisenhammer

LONDON, March 25 (Reuters) - Coal miner Asia Resource (LSE: ARMS.L - news) Minerals (ARMS) on Tuesday announced its long-awaited split with the Indonesian family that helped found it, sparking bitter posts on Twitter between a family member and fellow ARMS founder Nat Rothschild.

Indonesia-focused ARMS, previously known as Bumi, was founded in 2010 by the influential Bakries and financier Nat Rothschild, with the aim of giving London investors access to promising Indonesian coal assets.

The business suffered from boardroom rows, allegations of wrongdoing and falling coal prices. Its shares have lost almost 80 percent of their value since the business was set up.

Tuesday's fiery Twitter exchange between Rothschild and Aga Bakrie, a member of the politically-connected Bakrie family, demonstrated the extent to which the company founders' relationship had soured.

"Whilst your dad is an evil genius (yes I'm paying Nirwan a compliment), the word on the street is that you are extremely DUMB," tweeted Rothschild, who has a stake of about 16 percent in ARMS, to Bakrie.

To this Bakrie replied: "Dumb, I believe that's the word that has been associated with you by most of the people that I have met."

In an attempt to revive the business's fortunes, ARMS shareholders voted in December to split from the Bakrie family, but this took longer than expected due to difficulties of raising the necessary cash.

As part of the separation process, outgoing ARMS Chairman Samin Tan bought the Bakries' 23.8 percent stake in ARMS through investment vehicle Borneo Lumbung Energy & Metal Tbk. ARMS sold its 29.2 percent stake in Jakarta-listed miner PT Bumi Resources to the Bakries for $501 million. The deal pushed Borneo's ARMS stake to 47.6 percent.

In another tweet Rothschild thanked the Bakrie for buying Bumi Resources (Jakarta: BUMI.JK - news) to which he referred as "a worthless piles of turd".

The Bakrie member replied that Indonesia is an amazing investment haven.

LOOKING AHEAD

With the split now completed, ARMS will focus on turning around its other main Indonesian subsidiary, Berau Coal , while giving up a stake in Asia's top thermal coal exporter PT Bumi Resources (Other OTC: PBMRF - news) .

"I feel vindicated. There were a number of stakeholders saying this would never happen. I can't say it has been easy, it was a complicated transaction, but to have achieved this is excellent for our shareholders," ARMS Chief Executive Nick von Schirnding said in a phone interview.

"Our focus is on our subsidiary now. We need to regain credibility and today's announcement is the first step in that direction."

ARMS said it would return $400 million to shareholders but did not give any timeframe.

Shareholders welcomed the completion of the separation but said they hoped ARMS would return closer to the $501 million it got from the deal.

"I think it's important to return the maximum amount of money because there is no appetite from the major shareholders, certainly not from me, to entrust money with the management team in London to redeploy that capital," Rothschild said.

"We want the business ... to be run as efficiently as possible and for all dividends to be passed through to shareholders."

ARMS said it was cooperating with regulatory investigations. Britain's Financial Conduct Authority (FCA) and the Takeover Panel, an independent body that supervises takeovers to ensure fair treatment for all shareholders, are investigating the company's formation in 2010 and subsequent events.

Last year Rothschild asked the FCA to look into whether ARMS made misleading statements to the market.

ARMS said it would now try to trace and return to shareholders money the company says is owed by the former head of its Berau subsidiary Rosan Roeslani.

The company in November started arbitration proceedings seeking to recover $173 million from Roeslani in Singapore, but said on Tuesday it will take all appropriate actions with authorities in the UK, Indonesia and other relevant jurisdictions. (Editing by Jane Merriman, David Holmes and Andrew Hay)