Nov 15 (Reuters) - Swedish mining and smelting group Boliden will close its exploration activities in the Outokumpu field and as a consequence of this take a 24.4 million euros ($25.26 million)impairment in the fourth quarter, it said on Tuesday ahead of an investor update. ($1 = 0.9660 euros) (Reporting by Anna Ringstrom and Marie Mannes, editing by Stine Jacobsen)