WRAPUP 2-U.S. judge rules for Asarco in $6-bln stock case

* Judge rules in favor of Asarco over Grupo Mexico unit

* Asarco had charged fraudulent transfer of stake

* Grupo Mexico shares slide 15 pct (Adds Grupo Mexico comment, analyst comment; Changes dateline, pvs only NEW YORK)

NEW YORK/MEXICO CITY, April 2 (Reuters) - A federal judge in Texas has ordered a Grupo Mexico unit to return as much as $6 billion in stock and dividends to bankrupt U.S. copper miner Asarco LLC, sending shares in the Mexican parent company tumbling.

U.S. District Court Judge Andrew Hanen, in the southern district of Texas in Brownsville, made his ruling on Wednesday in the fraudulent transfer case, according to court records.

"Justice has ultimately prevailed," Asarco's President and Chief Executive Officer Joseph Lapinsky said in a statement.

"This award is for the benefit of Asarco's creditors in the bankruptcy and should assist the company in its efforts to successfully emerge from Chapter 11 in the coming months."

Asarco brought the case against Americas Mining Corp, a subsidiary of Grupo Mexico (GMEXICOB.MX), accusing it of fraudulently transferring to itself Asarco's then 54.18 percent controlling interest in Southern Copper PCU.N.

Shares in Grupo Mexico tumbled 15 percent to 9.30 pesos in Mexico City before trading was halted by the stock exchange.

The ruling to hand over the shares and cash to its bankrupt unit is bad news for Grupo Mexico and Thursday's stock tumble leaves it at around fair value, said Inigo Cossio, an analyst at Actinver brokerage in Mexico City.

"If the judge had told Grupo Mexico they don't have to return it to Asarco, really, Asarco would have had to sort things out themselves with their creditors," Cossio said.

Grupo Mexico said in a filing it was studying the ruling.

Asarco, formerly a Grupo Mexico subsidiary, said that Americas Mining paid it around $747 million for the Southern Copper stake. After Asarco went into bankruptcy in 2005, it sued Americas Mining, saying it was not paid fair market value and seeking to get back the stock as well as dividends.

Judge Hanen ruled in favor of Asarco and ordered Americas Mining to give back over 260 million shares of Southern Copper stock, which based on Wednesday's closing price is worth approximately $4.68 billion.

Americas Mining must also pay damages of about $1.35 billion, comprising of dividends AMC received of $1.94 billion and prejudgment interest of $329 million, less the $747 million that AMC had paid for SPCC and interest of $164 million, Asarco said.

Asarco said it will own an approximate 30-percent equity interest in Southern Copper as a result of the ruling.

Asarco, which operates three copper mines in Arizona, filed for bankruptcy protection in 2005 after it was sued for $1 billion over environmental cleanup and asbestos claims.

Last month, it filed a bankruptcy reorganization plan to reorganize itself under a $1.7 billion deal with India's Sterlite Industries (STRL.BO).

Grupo Mexico acquired Asarco in a leveraged buyout in 1999, but lacks board control of the company due to the bankruptcy. It has said it was still interested in taking back control of Asarco.

On Wednesday, Grupo Mexico said it had raised its stake in Southern Copper to 80 percent from 75.1 percent.

The case is: Asarco LLC, Southern Peru Holdings, LLC v Americas Mining Corp, Civil No. 1:07-CV-00018.

(Additional reporting by Noel Randewich and Robert Campbell in Mexico City)

(Reporting by Steve James and Matt Daily; Editing by Derek Caney, Phil Berlowitz and Bernard Orr)