Mining stocks were making decent gains as a return of investor risk appetite and demerger talk surrounding sector giant BHP Billiton provided a boost.An upgrade to UK economic growth estimates for the second quarter and hopes of stimulus measures in Europe and China was driving gains across the London stock market on Friday.In China in particular, a host of recent disappointing economic indicators has prompted speculation that the government will deploy more measures to aid the recovery in the world's second-largest economy.China, the world's top metals consumer, reported industrial production, retail sales and bank lending figures this week that all missed analysts' forecasts.BHP Billiton shares were up 2.6% in afternoon trade after the world's biggest mining company by revenues said that it is considering a demerger of certain assets in an effort to make the business "simpler and more productive". The company, reiterated its focus on its "four pillars" - iron ore, copper, coal and petroleum - with potash being a potential fifth, suggesting that nickel, aluminium and bauxite assets could be spun off. It will update the market after the board reconvenes next week."Portfolio simplification has been muted for some time - the choice of a demerger route would suggest more market appetite for the rest of the assets within the group," according to analysts at broker SP Angel.Other stocks in the UK mining sector were also on the rise on Friday, including Rio Tinto, Anglo American and Glencore.However, precious metal producers such as Centamin, African Barrick Gold and Randgold were bucking the trend as gold and silver prices declined. Top performing sectors so far todayFood & Drug Retailers 3,337.54 +1.58%Tobacco 39,811.60 +1.41%Mining 18,152.81 +1.37%Fixed Line Telecommunications 4,302.62 +1.35%Real Estate Investment & Services 2,706.65 +1.21%Bottom performing sectors so far todayHealth Care Equipment & Services 5,811.91 -0.49%Industrial Transportation 2,825.55 -0.38%BC