"Investors are citing concerns about a slowdown in (the economy of) China and concerns about the euro dropping and the dollar strengthening," said Jeremy Sussman, an analyst with Brean Murray Carret & Co.

Massey and Patriot are both major producers of metallurgical coal, whose demand is tied to steel production and construction demand.

Massey, which is also facing a challenge to its proposed re-election of three directors at a shareholder meeting scheduled for Tuesday, saw its shares sink more than 10 percent to 33.20 apiece.

Massey CEO Don Blankenship is also scheduled to testify later this week at U.S. Senate subcommittee hearing about the last month's explosion at its Upper Big Branch mine that killed 29 workers.

Patriot Coal's shares were down 8 percent at $16.57, extending the 5.4 percent sell-off from Friday when federal regulators shut one of its mines due to safety issues.