* Silver hits 31-year peaks as oil, grains hit new highs
* Bernanke suggests Fed's resolve to complete stimulus
* Coming up: US FOMC March meeting minutes 1800 GMT, Tues (Recasts, updates prices, market activity; new byline, changes dateline, previously LONDON)
By Frank Tang
NEW YORK, April 5 (Reuters) - Gold prices rose to an all-time highs above $1,450 an ounce on Tuesday, as new peaks in crude oil and grains fueled inflation fears and a downgrade of Portugal's credit rating fed safe-haven demand.
Bullion prices broke out after a struggle to sustain new highs in the last month, and silver soared to a 31-year peak after Federal Reserve Chairman Ben Bernanke suggested he was committed to complete a $600 billion stimulus program as scheduled in June.
"What it shows is that big money continues to believe gold will go higher...because Bernanke wants to grow at any cost," said Axel Merk, portfolio manager of the $600 million Merk Mutual Funds. "The other reason for gold to go up is that there was a downgrade in Portugal, so people realize there are still some issues."
Spot gold <XAU=> was up 1.1 percent to $1,446.40 an ounce at 11:46 a.m. EDT (1546 GMT), off the session high, a record $1,450.14 an ounce.
U.S. gold futures for June delivery <GCM1> rose 1.1 percent to $1,448.80 in modest trading volume.
Silver <XAG=> gained 1.2 percent to $38.88 an ounce, after hitting a session high of $38.99, the highest since the Hunt Brothers cornered the market in the early 1980s, when prices briefly hit a record of just below $50 an ounce.
Silver has outperformed gold in recent months, rising 22 percent in the first quarter compared with gold's 0.7 percent. The gold:silver ratio, which shows how many silver ounces are needed to buy an ounce of gold, fell to a 28-year low at 37.3.
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Graphic showing gold:silver ratio:
http://r.reuters.com/seh88r
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On Monday, Bernanke said an increase in U.S. inflation has been driven primarily by rising commodity prices globally, and was unlikely to persist. His comments contrasted with those of other U.S. central bank officials, some of whom called for tighter monetary policy. [
]Rising oil and grain prices boosted gold's inflation hedge appeal. Brent crude rose to a 2-1/2-year highs on geopolitical risks to supply from the Middle East, while corn futures hit a record high as worries over tight supplies persisted. [
] [ ]Platinum <XPT=> rose 0.5 percent to $1,788.20 an ounce, while palladium <XPD=> also gained 0.5 percent to $783.40. Prices at 11:46 a.m. EDT (1546 GMT)
LAST NET PCT YTD
CHG CHG CHG US gold <GCM1> 1448.20 15.20 1.1% 1.9% US silver <SIK1> 38.935 0.441 1.2% 25.9% US platinum <PLN1> 1796.40 9.40 0.5% 1.0% US palladium <PAM1> 787.85 3.45 0.4% -1.9% Gold <XAU=> 1446.40 9.85 0.7% 1.9% Silver <XAG=> 38.88 0.46 1.2% 26.0% Platinum <XPT=> 1788.20 8.75 0.5% 1.2% Palladium <XPD=> 783.40 3.90 0.5% -2.0% Gold Fix <XAUFIX=> 1433.50 -1.00 -0.1% 1.6% Silver Fix <XAGFIX=> 38.08 -38.00 -1.0% 24.3% Platinum Fix <XPTFIX=> 1787.00 1.00 0.1% 3.2% Palladium Fix <XPDFIX=> 780.00 5.00 0.6% -1.4% (Additional reporting by Jan Harvey and Silvia Antonioli in London; Editing by David Gregorio)