Rio Tinto is among the stocks dragging on the mining sector after increasing its offer for Riversdale Mining to A$16 a share in cash, securing the backing of management for a deal worth A$3.9bn (£2.5bn).The mining giant admitted earlier this month it had talked to the Sydney-based firm, which has interests in African coal, about a A$15 a share takeover valuing the business at £2.2bn (A$3.5bn).Elsewhere in mining, Anglo American, another faller today, has completed the sale of interests in five undeveloped coal assets in Australia for A$577m (£376m) to a consortium that includes Korea Electric Power Corporation, POSCO and Cockatoo Coal.Retailers are going well amid hopes of a last minute sales rush ahead of Christmas day.HMV is the strongest performer in terms of percentage gains although the film and music retailer is sharply off levels before it reported sharply wider half year losses last week.Top performing sectors so far todayHealth Care Equipment & Services 3,840.84 +2.18%Mobile Telecommunications 3,927.36 +1.06%Automobiles & Parts 5,258.31 +0.94%General Retailers 1,721.17 +0.86%Real Estate Investment & Services 1,565.72 +0.86%Bottom performing sectors so far todayTechnology Hardware & Equipment 609.60 -2.78%Mining 27,913.39 -0.71%Industrial Engineering 6,851.75 -0.54%Industrial Metals & Mining 8,157.86 -0.49%Alternative Energy 4,047.78 -0.33%