JUNEAU — Alaska’s highest court ruled Friday that an initiative seeking to restrict large-scale mining in the Bristol Bay region seriously impedes a regulatory process set out in state law and is unenforceable.

The Alaska Supreme Court affirmed a lower-court ruling in litigation over the initiative passed by Lake and Peninsula Borough voters in 2011.

The initiative was aimed at the Pebble mine project and the potential development of the massive gold and copper prospect near the headwaters of a world-class salmon fishery.

It would have barred local officials from issuing a development permit when a mining activity could result in the digging and disturbance of topsoil of more than 640 acres and would damage or degrade salmon habitat.

In its decision, the Supreme Court found the initiative impedes implementation of state law putting Alaska’s Department of Natural Resources in charge of matters affecting the exploration, development and mining of state mineral resources because the initiative “purports to give the borough veto power over mining projects on state lands within its borders.”

The appeal was heard by three of the court’s five members.

Then-Chief Justice Dana Fabe and Justice Peter J. Maassen did not participate.

The Pebble deposit is on state land.

The state and Pebble Limited Partnership, the group behind the Pebble project, sued over the initiative.

The lower-court ruling was appealed by initiative sponsors.

Pebble is pleased with the high court’s ruling, company spokesman Mike Heatwole said by email Friday.

So, too, is the state Department of Law, which continued to review the case, department spokeswoman Cori Mills said by email.