(ShareCast News) - Shares in Great Western Mining fell on Thursday morning despite the AIM-listed miner reporting an "excellent result" from its M2 copper-gold prospect in the Black Mountains of Nevada.After a pair of surveys at the M2 site, GWM said the geologic style known as iron-oxide-copper-gold (IOCG) prevalent at the site seemed to continue over a larger area than initially found.Favourable geologic conditions to unearth IOCG mineralisation beneath Bass Mountain was found to be "almost 4.0 km long, over 1.0 km wide, and open to further southwest extension", according to the company's independent geological consultant."We have been able to increase the size of projected IOCG volumes significantly, and confirm favourable geology for a high-grade underground IOCG deposit, where the consistent copper-gold ratio could also indicate significant quantities of gold," said chief executive David Fraser."The identification of two high grade silver-copper prospects adjacent to our primary copper-gold target is an exciting development. We look forward to updating shareholders as work continues."Shares in Great Western were down 2.9% to 0.43p at 09:45 on Thursday.