Complex sentence: He left the company (which became a crown corporation in 1944) to prospect for uranium minerals as an independent mine developer, and in the 1950s he brought the Gunnar Mine to production at Uranium City, Saskatchewan.
Split into simpler sentences: He left the company (which became a crown corporation in 1944) to prospect for uranium minerals as an independent mine developer. In the 1950s he brought the Gunnar Mine to production at Uranium City, Saskatchewan.