Tullow Oil jumped after it discovered further oil in the first exploration well at one of its Kenyan projects, increasing its potential 'significantly'. Following an announcement in March that the well had encountered in excess of 20m of net oil pay, the well was then deepened from 1,041m to 1,515m and a total pay count greater than 100m has now been discovered. Insurance group Aviva was performing strongly after it announced that its CEO Andrew Moss has quit with immediate effect after the majority of its shareholders last week voted against the remuneration report. Mining stocks were among the worst performers by midday as they tracked metals prices lower. Vedanta Resources was a heavy faller, losing nearly five per cent, while Fresnillo, Randgold, Polymetal and Xstrata also suffered steep losses. FTSE 100 - RisersTullow Oil (TLW) 1,541.00p +4.90%Aviva (AV.) 312.20p +3.27%Hammerson (HMSO) 421.40p +2.53%Land Securities Group (LAND) 744.00p +2.06%Pearson (PSON) 1,173.00p +1.91%United Utilities Group (UU.) 639.00p +1.83%Tesco (TSCO) 325.00p +1.82%British Land Co (BLND) 501.50p +1.74%Severn Trent (SVT) 1,682.00p +1.69%Capital Shopping Centres Group (CSCG) 323.30p +1.67%FTSE 100 - FallersVedanta Resources (VED) 1,070.00p -4.63%Man Group (EMG) 85.05p -4.17%Fresnillo (FRES) 1,453.00p -3.52%Randgold Resources Ltd. (RRS) 4,953.00p -3.26%Wolseley (WOS) 2,232.00p -2.96%Schroders (SDR) 1,346.00p -2.96%Polymetal International (POLY) 857.00p -2.94%Schroders (Non-Voting) (SDRC) 1,060.00p -2.75%Ashmore Group (ASHM) 359.30p -2.60%Burberry Group (BRBY) 1,448.00p -2.36%NR