** Shares of IGO IGO.AX fall 15.1% so far this week
** Stock set for steepest weekly drop since March 31, if trends hold
** Lithium producer slipped 7.2% on Wednesday after posting a drop in annual sales revenue to A$512.5 million ($329.69 million) vs A$822.6 million last year
** Co also flagged an impairment charge to its troubled Kwinana lithium refinery in Western Australia
** Added, impairment charge could be between A$70 million-A$90 million
** Stock up 2.7% at A$4.55 on the day, bringing YTD losses to 4.6%
($1 = 1.5545 Australian dollars)
(Reporting by Nikita Maria Jino in Bengaluru)
((Nikita.Jino@thomsonreuters.com;))