* Miners asked to answer 20 questions on tailings
* Information to be posted on company websites
LONDON, April 5 (Reuters) - Ethical investors working on a global standard for tailings dams have written to 683 listed resource companies, including major miners, asking for information to be made public within 45 days about every facility they control.
The safety of dams used to store mining waste known as tailings has risen in profile after the collapse of a Vale tailings dam in Brazil in January killed an estimated 300 people.
Industry group the International Council on Mining and Minerals (ICMM) said in March it was working with the United Nations Environment Programme (UNEP) and the Principles for Responsible Investment (PRI) to develop new standards.
"It is essential that investors can establish a clear line of sight on which company has which tailings facility and how that facility is being managed. The current disclosures from companies are largely inadequate," Adam Matthews, director of ethics and engagement for the Church of England Pensions Board, said in a statement.
The PRI brings together ethical investors overseeing around $80 trillion worth of investments.
The demand for disclosure has been sent by the Church of England Pensions Board and the Swedish Council on Ethics following meetings in March and on April 1. The investors will meet again in May.
They are asking companies to disclose on their websites within 45 days answers to 20 questions, covering issues such as the height of dams, their volume, engineering records and safety checks.
If they cannot provide the requested information, they have to state what action they are taking to address the situation.
The two biggest listed miners BHP and Rio Tinto said they would not comment on the letter, sent on Friday, until they had assessed its contents. (Reporting by Barbara Lewis; editing by David Evans)