Mining stocks were out of favour on Monday afternoon on the back of concerns about a slowing Chinese economy, with the sector falling to its worst levels in three years.Plummeting commodity prices, a slowdown in Chinese growth and worries that stimulus measures in the US could soon be scaled back have hit miners hard since the start of the year, with the value of the FTSE 350 mining index falling by 18% year-to-date.The gauge is now trading at levels not seen since mid-2009 following a series of economic indicators from China clouded the outlook for the world's second-largest economy. Unexpected declines in Chinese inflation and bank lending in May, as well as worse-than-expected falls in money supply growth, industrial production and export growth last month dampened market sentiment today. Furthermore, following the announcement this weekend that export growth fell to a 10-month low in May, Barclays Capital has slashed its Chinese growth targets from 7.9% to 7.4% for 2013 and from 8.1% to 7.4% for 2014.Vedanta Resources, Anglo American and Rio Tinto were among the worst performers on the FTSE 100 this afternoon.Even precious metals producer Polymetal was lower despite signing two export sales contracts with Chinese off-takers for a volume of up to 50,000 tonnes of refractory gold concentrate produced at the Mayskoye gold project. The move will allow it to start generating free cash flows at its newest mine by the third quarter, the company said.Polymetal and EVRAZ were also making headlines on the news that the Russian mining peers will both be exiting the FTSE 100 index this week after some sharp falls so far this year.African Barrick Gold, Ferrexpo and Lonmin were among the heaviest fallers on the FTSE 250.Top performing sectors so far todayIndustrial Transportation 2,767.43 +1.53%Industrial Engineering 9,436.49 +1.22%Media 5,438.79 +1.03%General Retailers 2,416.08 +0.90%Food & Drug Retailers 4,403.93 +0.80%Bottom performing sectors so far todayIndustrial Metals & Mining 1,416.98 -3.12%Forestry & Paper 8,697.87 -1.94%Mining 15,814.68 -1.71%Health Care Equipment & Services 4,202.97 -1.48%Life Insurance 5,838.20 -1.21%