Complex sentence: This expedition also proved successful in its primary goal by discovering copper in the Coppermine River basin; however, an intensive search of the area yielded only one four-pound lump of copper and commercial mining was not considered viable.
Split into simpler sentences: This expedition also proved successful in its primary goal by discovering copper in the Coppermine River basin. However an intensive search of the area yielded only one four-pound lump of copper and commercial mining was not considered viable.