Nicholas Mangan is the son of a miner who explores mining, the environment and even the global political economy in his sculptures and videos. Nicholas's series about the Pacific island of Nauru's phosphate mining industry is owned by Te Papa, but it's currently on loan to the Dowse Art Gallery in Lower Hutt for as part of an exhibition called Limits to Growth. Lynn Freeman talks to Nicholas about the exhibition, which also compares a new form of mining - mining for bitcoins - with the ancient Rai stone money of the Micronesian island of Yap.