"These practices can be a real threat to living beings. With this initiative we are lifting our voice to the world, asking that our natural resources be valued," he said at a ceremony to mark World Environment Day.

"This is a declaration of peace for nature and the environment. We will accept no more corruption affecting our environment," said Pacheco, who took office last month.

The decree was expected to affect two Vancouver mining firms, Vannessa Ventures Ltd and Wheaton River Minerals Ltd.

Vannessa recently submitted an environmental impact study for its Crucitas gold project in Costa Rica. Construction costs for the initial phase of mining were estimated at $27 million.

Wheaton River last week announced it had agreed to sell its Bellavista gold project in Costa Rica to Toronto-based Glencairn Explorations Ltd.

Environment and Energy Minister Carlos Manuel Rodriguez said the ban was imposed in part because authorities have struggled to establish environmental controls on open pit mining.

"Costa Rica does not have the capacity to implement and follow environmental control policies on these activities, so it is better to prevent them," Rodriguez said.

He said he would meet mining companies affected by the decree to work out the details on how they will close down the projects.