Complex sentence: The Lisdrumgormley deposit was mined for lead as early as the 1840s and was the subject of further exploration during the mid- 1950s when the original shaft was reopened to a depth of 21 meters.
Split into simpler sentences: The Lisdrumgormley deposit was mined for lead as early as the 1840s. It was the subject of further exploration during the mid- 1950s when the original shaft was reopened to a depth of 21 meters.