Complex sentence: Nauru is a phosphate rock island, with rich deposits close to the surface, which allow for simple strip mining operations; moreover, it has some phosphate reserves which are presently (as of 2011) not economically viable for extraction.
Split into simpler sentences: Nauru is a phosphate rock island, with rich deposits near the surface, which allow easy strip mining operations. It has some phosphate reserves which are presently (as of 2011) not economically viable for extraction.