UK's Petra Diamond slides after UK tax authority's wind-up petition against unit
** Shares of diamond miner Petra Diamonds PDL.L down 15.6% at 4.5p
** UK tax authority HM Revenue & Customs (HMRC) has filed a winding-up petition against co's non-operating UK unit, PDUK Treasury, over £5.65 mln ($7.46 mln) corporation tax bill
** Co says petition relates solely to unit and does not directly affect group's mining operations
** Says it is evaluating the potential consequences for its financing arrangements and ongoing refinancing talks
** YTD, stock down 72.4% including session losses
($1 = 0.7573 pounds)