Complex sentence: Ocean Company invested a further £500,000 in 1900 to make the collieries production more economic, so that by 1902, annual output was 327,000 tons by 2,000 men.
Split into simpler sentences: Ocean Company invested a further £500,000 in 1900, making the colliery more economic. By 1902, annual output was 327,000 tons by 2,000 men.