Mining stocks were the standout performers of the day on Thursday after upbeat comments from Citigroup about the sector.Analysts at Citigroup lifted its 12-month stance on the sector from 'neutral' to 'bullish', representing its first positive outlook for the industry in three years.The bank labelled BHP Billiton, Rio Tinto and Glencore Xstrata as its "key picks" in the sector, providing a big boost to each stock today. BHP, in particular, was upgraded from 'neutral' to 'buy'.Citi said: "While we remain concerned about the potential long-term structural demand story for commodities in China, and we are cognisant of a potential seasonal slowdown in the first quarter of this year, our move to 'bullish' reflects better bottom-up fundamentals, particularly from the major miners. "We would rather be too early than too late in making this call."Meanwhile, with a flat commodity price environment expected in the near term, Citi foresees a reduction in volatility across the sector.Others miners including Antofagasta, Anglo American, Fresnillo and Randgold Resources were making gains this afternoon.Russian precious metals firm Polymetal was also firmly higher after UBS raised its recommendation from 'neutral' to 'buy', saying that company is "well-positioned" for free cash flow growth as production gets back on track.Top performing sectors so far todayMining 16,553.95 +3.24%Gas, Water & Multiutilities 5,524.65 +0.93%Pharmaceuticals & Biotechnology 12,194.60 +0.86%Tobacco 34,720.67 +0.67%Industrial Metals & Mining 1,304.73 +0.60%Bottom performing sectors so far todayForestry & Paper 10,954.47 -2.49%Personal Goods 24,727.70 -2.18%Life Insurance 7,075.93 -1.63%Industrial Transportation 3,381.60 -1.53%Banks 4,989.72 -1.40%BC