Complex sentence: Large quantities of iron slag were found in the excavations at this site and, while small amounts of slag and tuyère fragments were encountered in excavations elsewhere on the site, iron smelting was most likely confined to this northwestern area of the site.
Split into simpler sentences: Large quantities of iron slag were found in the excavations at this site and. While small amounts of slag and tuyère fragments were encountered in excavations elsewhere on the site, iron smelting was most likely confined to the northwestern area of the site.