Carl Icahn has snapped up a huge stake in Freeport-McMoRan, and the stock is ripping

Carl Icahn has picked his next target: Freeport-McMoRan.

Icahn and a group of other investors have snapped up an 8.46% stake in mining company Freeport-McMoRan, according to a joint filing.

The filing's with High River Limited Partnership, Hopper Investments LLC, Barberry Corp., Beckton Corp, and Icahn.

They think the stock is undervalued. They may also seek a board seat. From the filing:

The Reporting Persons acquired their positions in the Shares in the belief that the Shares were undervalued. The Reporting Persons intend to have discussions with representatives of the Issuer's management and board of directors relating to the Issuer's capital expenditures, executive compensation practices and capital structure as well as curtailment of the Issuer's high-cost production operations. The Reporting Persons may also seek shareholder board representation and to discuss the size and composition of the board. As of August 26, 2015, the Reporting Persons have not had any discussions with representatives of the Issuer's management or board of directors.

Shares of Freeport-McMoRan are ripping in the after-hours up more than 18.9%.

The stock closed up $2.27, or 28.66%, to end at $10.19.

The group of investors said in the report that they may seek a board seat, and had not had any discussions with the company's management prior to the filing.

Earlier this month, Icahn disclosed a stake in Cheniere. This week, he got two board seats.

Here's the five-day chart: