Colorado-based gold miner Atna Resources on Thursday filed for Chapter 11 bankruptcy protection, saying operational problems at its Pinson mine, in Nevada, the low gold price and a lack of investor interest had rendered it without sufficient liquidity to meet obligations. Atna had filed voluntary petitions under Chapter 11 of the Bankruptcy Code in the US Bankruptcy Court for the District of Colorado, and added that it would seek simultaneous relief in Canada under the Companies' Creditors Arrangement Act, in the Supreme Court of British Columbia, in Vancouver.