Complex sentence: The Galena mine has a long history dating back to 1887 but the modern history and mining commenced by ASARCO in 1953 in an effort to explore and exploit outcrops of silver-lead ore.
Split into simpler sentences: The Galena mine has a long history dating back to 1887. However, recent mining began in 1953 by ASARCO, in an effort to explore and exploit outcrops of silver-lead ore.