Mosaic Co. and the Sierra Club said Tuesday that they have settled environmental litigation that was blocking the expansion of a huge phosphate mine in Florida.

The South Fort Meade mine in south central Florida is important to Plymouth-based Mosaic, one of the world's largest fertilizer producers, because it is particularly cost-efficient and historically accounts for about 20 percent of all U.S. phosphate production. Phosphate is a key fertilizer ingredient.

The main Meade mine is largely played out, and Mosaic has been counting on a 7,000-acre expansion. But the Sierra Club and other environmental groups have claimed the expansion would damage wetlands, successfully getting a federal court to halt it last summer.

The litigation has cast a pall of uncertainty over Mosaic's phosphate operations. "It's been a bit of an overhang on the company's stock price over the last several quarters," said Jeff Stafford, an analyst at Morningstar Inc.

"The fact that this low-cost phosphate mine will now be able to operate again is a big positive for the company .... I think you should see a positive move in the stock when trading begins [Wednesday]."

The settlement was announced after the market closed Tuesday. Mosaic closed at $56.91, up $1.28 or 2.3 percent. In after-hours trading, which is often an indicator of a stock's next-day performance, Mosaic was up another 3.65 percent.

The settlement calls for Mosaic to donate to Florida or a nonprofit organization a 4,171-acre tract of land known as Peaceful Horse Ranch. Mosaic bought the land for about $10 million in December.

The company will also preserve 130 acres of land that it would have otherwise mined, do certain environmental mitigation and monitoring on its site and take other conservation actions close to a nearby river.

"Mosaic is pleased to have reached a reasonable agreement to end litigation that has loomed over the employees at our South Fort Meade mine ... and we look forward to bringing it back to full production," Mosaic Chief Executive Jim Prokopanko said in a news release.

The mine employs about 220 people.

The South Fort Meade extension will allow Mosaic to mine there for 10 more years. With mining mostly shut down since summer, Mosaic has been making up for lost production partly by running all-out at its other three Florida mines

Beverly Griffiths of the Sierra Club of Florida said phosphate mining is one of the most "intensive" land uses. It involves stripping away native soils to get at the minerals below, and digging pits that can hurt rivers like the Peace River near Mosaic's South Fort Meade mine.

"The settlement provides much better protection to the Peace River than if we had not sued," Griffiths said.

The Peaceful Horse Ranch, a key to the settlement, will likely be made into a state park. The ranch has about 3,500 acres of wetlands and 14 miles of frontage on the Peace River and Horse Creek, the latter of which converges with the former.

Mike Hughlett • 612-673-7003