Polo Resources co-chairman Stephen Dattels has been upping his holding in the mining investment company.Regent Mercantile Holdings, a company wholly owned by the trustee of a trust under which Dattels is a beneficiary bought 6,364,828 shares at 5.82p a share, spending about £370,000.Dattels now has about 220m shares in the company, or about 9.4%. His purchase was announced the day after Polo said non-executive director Ian Stalker took 1.77m shares at 5.56p a time, lifting his stake to 5.07m shares. The shares have appreciated since Dattels's last purchase. He took 12m at 5.25p a time in March, having paid 5p a time for 15m in November.The share price was lifted by an announcement last week of a buyback of 25m shares at 5.64p a time.Polo has investments in coal, iron ore and gold assets around the world. Dattels, a former executive at Canada-based mining giant Barrick Gold, was founder and chairman of Australian coal miner Caledon resources, one of Polo's investments. Stalker is a chemical engineer and a director at Spain-focused miner Berkeley Resources. Top Director BuysPolo Resources Ltd. (DI) (POL) Director name: Mr Stephen R DattelsAmount purchased: 6,364,828 @ 5.82p Value: £370,433UK Coal (UKC) Director name: Mr Keith HellerAmount purchased: 110,383 @ 39.98p Value: £44,131UK Coal (UKC) Director name: Mr Keith HellerAmount purchased: 92,289 @ 40.00p Value: £36,916Communisis (CMS) Director name: Mr Alistair BlaxillAmount purchased: 50,000 @ 31.35p Value: £15,675Aberdeen New Dawn Inv Trust (ABD) Director name: Mr David James Buchanan ShearerAmount purchased: 1,500 @ 885.34p Value: £13,280Top Director SellsITV (ITV) Director name: Mr Adam CrozierAmount sold: 101,510 @ 74.66p Value: £75,787Kingfisher (KGF) Director name: Mr Ian CheshireAmount sold: 11,754 @ 274.58p Value: £32,274