** Shares in German copper producer Aurubis NAFG.DE are down around 8% in early Frankfurt trade
** A local trader points to majority shareholder Salzgitter SZGG.DE launching on Tuesday a 500 million euro bond offer exchangeable for Aurubis shares
** Salzgitter said that initially about 3.4 million shares, or about 7.5% stake, in Aurubis will be underlying the bonds
** The trader sees "still a slightly negative effect on Salzgitter via significant dilution of their Aurubis stake"
(Reporting by Emanuele Berro)
((emanuele.berro@thomsonreuters.com))