(Wall Street Journal Asia) - Zijiin Mining Group Co., China's biggest gold producer by capacity, said China's securities regulator is investigating a possible breach of disclosure rules after the company took more than a week to report a major toxic chemical leak at its Fujian copper plant.

On July 12, the company issued a statement saying a rapid rise in underground water level damaged the waterproofing layer at the base of Zijinshan Copper Mine's wastewater containment pool. The statement came nine days after the leakage started to contaminate a reservoir and the nearby Ting River on July 3.

The company's Hong Kong shares plunged 19.9% between July 13 and Monday following news of the spill. However, they ended 7.4% higher Tuesday in a technical rebound, analysts said.

Hong Kong- and Shanghai-listed Zijin said in a statement it will fully cooperate with the China Securities Regulatory Commission, and will disclose information required by the regulator.

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