* Miners asked to answer 20 questions on tailings
* Information to be posted on company websites
* Ethical investors to meet again on tailings in May (Adds comment from ICMM, miners)
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 gain prominence after the collapse of a Vale tailings dam in Brazil in January killed an estimated 300 people.
The International Council on Mining and Minerals (ICMM) industry group 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, including the Church of England, overseeing around $80 trillion worth of investments.
Aidan Davy, chief operating officer of ICMM, which represents 27 miners including Vale, said it and its members recognised the value of enhanced disclosure.
He added that it was important "to get this information from all of the industry" not just the ICMM members.
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 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.
Anglo American in an email said it would make this information available. (Reporting by Barbara Lewis Editing by David Evans and Edmund Blair)