Spot gold gained 0.2 percent to $1,643.29 an ounce by 0024 GMT, holding above the key 200-day moving average at about $1,636. U.S. gold inched up 0.3 percent to $1,644.30. Worries about the euro zone debt crisis mounted on Wednesday, after Fitch warned the European Central Bank to ramp up its debt purchases to avoid a "cataclysmic" collapse of the single currency, sinking the euro to its 16-month low against the dollar. * Spain will hold the first bond auction of the year later in the day, just hours before the ECB's first monetary policy announcement and interest rate decision for 2012. Investors will also watch December economic data from China due on Thursday. Annual inflation is expected to have eased for the fifth consecutive month. Along with weakening economic activity, it could lead to further policy easing. Holdings of SPDR Gold Trust, the world's largest gold-backed exchange-traded fund, edged down 0.4 tonnes to 1,254.159 tonnes by Jan 11, after staying unchanged for more than two weeks. U.S. stocks held firm near recent five-month highs on Wednesday as investors awaited key bond market tests for Europe in the next two days that could determine the direction of the euro zone crisis. The euro remained in the doldrums in Asia on Thursday, having lurched to a fresh 16-month low on the dollar as markets turned nervous ahead of a bond sale by Spain.