Complex sentence: The mine was composed of "Chiflones" 1,2,3,4, Pique Santa Maria, and Pique Arenas Blancas, this was the last mine closed, because of a grisu gas explosion where 21 miners died.
Split into simpler sentences: The mine was composed of "Chiflones" 1,2,3,4, Pique Santa Maria, and Pique Arenas Blancas. This was the last mine closed, because of a grisu gas explosion where 21 miners died.