Mining stocks were bearing the brunt of the market-wide sell-off on Friday as traders adopted a cautious approach ahead of the weekend.Commodity prices were higher across the board today but that wasn't enough to increase investors' appetite for risk as the resource-heavy FTSE 100 dropped 1% in afternoon trade to its lowest level in three weeks."With the end of the quarter looming on Monday and political risks rising it would appear that investors could well be indulging in a little bit of portfolio adjustment and balancing into the end of the week today, and the end of the quarter, the other side of the weekend," said Senior Market Analyst Michael Hewson from CMC Markets.Antofagasta, Rio Tinto, BHP Billiton and Vedanta Resources were among the worst performers on the FTSE 100 today.Rio was shrugging off some upbeat comments from Nomura which labelled it as "one of the cheapest stocks" within its peer group.Gold prices rose to a one-week high of $1,345.2 an ounce earlier in the session after comments from Federal Reserve Bank of Chicago President Charles Evans who said that a stronger recovery is US economy is needed before the central bank begins to scale back quantitative easing.Nevertheless, precious metals producers were still trading in the red today, in line with the wider sector. Sentiment was dampened by Bank of America Merrill Lynch which lowered its gold-price forecast by 17% to $1,294 an ounce for 2014. The US bank said Randgold remains one of its preferred 'buys' in the sector due to low costs, a rising grade profile and strong balance sheet. However this wasn't enough to lift the stock today after TheStreet Ratings cut its own rating for the stock from 'buy' to 'hold'.Gold mining peers Fresnillo and Centamin were also trading with losses this afternoon.Top performing sectors so far todayElectricity 9,506.34 +0.78%Automobiles & Parts 8,199.60 +0.43%Fixed Line Telecommunications 3,917.18 +0.17%Aeronautics and Defence NULL 0.00%Alternative Energy 8,888.00 0.00%Bottom performing sectors so far todayIndustrial Metals & Mining 1,512.28 -3.71%Mining 16,660.44 -2.20%Forestry & Paper 11,245.30 -2.06%Household Goods & Home Construction 10,009.39 -1.99%Food Producers & Processors 6,766.78 -1.80%BC