Mining stocks were out of favour on Tuesday on the back of rising concerns about a slowdown in China, falling metal prices and a poor reaction to production figures at sector heavyweight Rio Tinto.A measure of new credit in China declined by almost a fifth in March, figures from the People's Bank of China showed today. Meanwhile, the growth in money supply slowed to its lowest rate since 2001, sparking fears that the world's second-largest economy may struggle to meet growth targets this year.Mining stocks are heavily exposed to changes in the outlook for the world's top metals consumer and were bearing the brunt of the disappointing data during today's session."A slump in Chinese demand would hurt economies with close trade links to China, with commodity exporters likely to be especially hard-hit," according to analysts at Capital Economics.An across-the-board decline in metal prices was also weighing on mining stocks today with gold down 1.8%, silver 2.7% lower and copper down 2.2%. Gold, in particular, was retreating from a three-week high.British-Australian miner Rio Tinto, which has a market capitalisation of around £61bn, said it started the new financial year strongly with record first-quarter iron ore production, but output eased when compared with the end of last year. The stock was down 2.6% at 3,319.5p by 14:25 on Tuesday.Iron ore production rose at an annual rate of 8% to 66.4m tonnes in the first three months of the year, a record for Rio's first quarter. However, output was down 6% when compared with the fourth quarter of 2013 due to "disruption caused by seasonal weather patterns" in the Pilbara region of Australia."Rio Tinto delivered mixed first-quarter results with iron ore and coal exceeding our expectations but most other commodities lacking," said Analyst Hunter Hillcoat from Investec. Nevertheless, he said the key highlight from the statement was that guidance across all of the key commodity classes has been maintained, particularly iron ore.Others in the sector including Fresnillo, Randgold Resources, BHP Billiton and Anglo American were also suffering heavy losses in London.Top performing sectors so far todayIndustrial Transportation 3,023.97 +2.03%Industrial Metals & Mining 1,124.35 +1.61%Gas, Water & Multiutilities 5,894.91 +1.44%Electricity 9,731.22 +1.36%Automobiles & Parts 8,856.59 +1.28%Bottom performing sectors so far todayMining 16,813.57 -1.95%Forestry & Paper 10,464.37 -1.87%Technology Hardware & Equipment 1,131.24 -1.21% Telecommunications 4,755.29 -0.84%General Retailers 2,818.43 -0.68%BC