* Gold hits session highs after weak Philly Fed activity numbers
* SPDR gold fund reports biggest 1-day outflow in 18 months
* Platinum group metals lower, South Africa supply concerns ease
By Jan Harvey
LONDON, Feb 21 (Reuters) - Gold partly recouped the previous session's losses on Thursday, gaining more than one percent as weaker-than-expected U.S. data raised concerns over the state of the economic recovery.
The Federal Reserve Bank of Philadelphia said business conditions unexpectedly weakened in February to the lowest since June 2012.
Spot gold rose 1.3 percent to a session high of $1,581.80 an ounce and was at $1,578.46 at 1536 GMT, still up 1.04 percent. U.S. gold futures for April delivery were little changed at $1,576.50.
Spot prices reached a low of $1,554.49 in earlier trade, their weakest since July. They slid 2.6 percent on Wednesday after Federal Reserve minutes suggested the bank may wind down its ultra-loose monetary policy sooner than expected.
Quantitative easing tends to support gold, as it keeps interest rates low while stoking fears of inflation.
"Following weak Philly Fed data, there is some mild re-evaluation going on," HSBC analyst James Steel said.
"And also throughout this decline, we have had decent demand from the Far East, but the rebound is still tepid."
The metal remained vulnerable to further losses, however, after sliding through key chart support levels the previous day, as speculative interest remains lacklustre.
The largest gold-backed exchange-traded fund, New York's SPDR Gold Trust reported its biggest outflow in 18 months on Wednesday, coinciding with the price drop.
Tumbling prices attracted buying interest in the physical markets overnight in Asia, with analysts and traders reporting high volumes traded on the Shanghai Gold Exchange.
Financial markets were weak across the board on Thursday. Oil prices fell heavily for a second day, while European shares and the euro were hurt by weak euro zone PMI activity data and uncertainty surrounding Italy's election at the weekend.
CHARTS POINT TO LOSSES
While it has steadied after breaking a succession of support levels in the last week, gold is poised to post further losses before finding a base, according to analysts who study past price moves to determine the future direction of trade.
"Gold plummeted down through the bottom of its bearish trend channel (yesterday)," ScotiaMocatta said in a note.
"There is a long-term support trendline drawn off July 2011 lows which is currently providing support around $1,568. We expect this to break, and selling pressure to intensify," it said. "Support is at $1,526, the May 2012 low."
The platinum group metals cut some earlier losses but remained lower as concerns over supply from major producer South Africa eased.
Unlike gold, which is chiefly an investment and jewellery metal, platinum and palladium are used primarily in catalytic converters, and are therefore more heavily exposed to downturns in the economic cycle.
They have benefited from rising appetite for industrial commodities this year, but the strength of their climb has left them vulnerable to a correction, analysts said.
"They just went too far, too quickly," Standard Chartered's Daniel Smith said. "If you look at the net speculative positions, they were dangerously long. The longer-term story is still a good one, but you're going to see corrections within the uptrend."
Spot platinum was down 1.4 percent at $1,621.99 an ounce, while spot palladium fell 0.7 percent at $731.97 an ounce.
Silver rose 0.9 percent to $28.80, having hit a six-month low of $28.26 an ounce in he previous session.
