* Euro, gold surrender gains after Spanish debt auction * Markets cautious as yields rise on longer-dated paper * Anglo American Platinum maintains 2012 output target (Releads, updates prices, adds comment) By Jan Harvey LONDON, April 19 (Reuters) - Gold prices turned lower on Thursday, extending a four-day drop, with initial resilience after a widely-anticipated auction of Spanish debt giving way to selling as appetite for the euro and so-called higher-risk assets like commodities evaporated. Spain sold all the bonds they wanted at auction on Thursday, but rising yields suggested concerns the government will not be able to tame its deficit were growing. Spot gold was down 0.2 percent at $1,634.89 an ounce at 1214 GMT, while U.S. gold futures for June delivery were down $3.50 an ounce at $1,636.10. The precious metal was tracking losses in the euro, which fell 0.3 percent against the dollar, and stock markets, which traders said had also been hit by unconfirmed rumours that France's sovereign rating may be downgraded. "Gold is moving in line with 'riskier' asset classes, and given higher risk aversion and growing uncertainty, prices are moving lower," Commerzbank analyst Daniel Briesemann said. "And since the dollar is stronger again today, that's also weighing on the price of gold." Reasonable demand at a Spanish bond sale failed to soothe concerns about the sustainability of the country's debt. Worries about the euro zone helped lift gold last year, but they have since become negative for the precious metal as the dollar took precedence as the safe haven of choice. Attention is now turning across the Atlantic, to a Federal Reserve meeting next week, at which policymakers will discuss U.S. monetary policy. "(The euro zone debt crisis) is just one variable in the gold equation going forward," LGT Capital Management analyst Bayram Dincer said. "The other... is the Fed's upcoming meeting. That will be the next factor to determine the future direction for gold." Gold traders are awaiting fresh clues on whether a third round of quantitative easing, which would keep interest rates, and consequently the opportunity cost of holding bullion, at rock-bottom levels, is on the cards. Minutes from the Fed's March meeting released this month showed support thinning for further bond purchases. GOLD STICKS TO RANGE From a chart perspective, gold remains firmly in the $1,630-1,657 range it has held this week, lacking strong external drivers to break out. Physical buying interest from the world's top two gold consumers, India and China, has been sluggish, even after a three-week strike by India's jewellers came to an end. A break above the top of its current range could precipitate a rise towards $1,680/$1,690, analysts said, while decent support is seen near its April lows at $1,611 an ounce. "We remain bearish gold so long as it trades below 1680, the last high," ScotiaMocatta said in a note late on Wednesday. Silver was down 0.6 percent at $31.42 an ounce, while spot platinum was flat at $1,573.19 an ounce and spot palladium was 0.5 percent lower at $651.94 an ounce. The gold:platinum ratio, which measures the number of gold ounces needed to buy an ounce of platinum, edged down to 1.04 on Thursday from the one-month high it hit earlier this week, as platinum clawed back some lost ground against the yellow metal. Platinum, which is heavily exposed to the European car market, has struggled to overcome soft demand in recent years. "We still favour gold," Standard Bank said in a monthly report. "We see $1,630 and $1,600 as good levels to establish a long position for a move higher. Physical demand for gold in Asia is strong below $1,650." "From a cost-of-production perspective, platinum provides value between $1,600 and $1,550," it added. "The platinum market has tightened up after the recent strike at an Impala Platinum mine in South Africa. However, we believe that industrial demand will remain absent above $1,750 - and this should cap upside." (Editing by William Hardy)

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