At the close
Every stock in coal sector, except Peabody (BTU) & Canadian Natural (CNQ), saw large profit taking orders at the close.
Granted the wooosh at the close for CMK was much more dramatic than the others encountered, but, technically it broke it's support level of $1.77 (formerly resistance) and after a day like today you cannot fault anyone for taking some profit.
If the stock is being manipulated, the acquirer could be accumulating a sizable position, keeping the price down artificially with plans of a low ball offer before the REAL production comes to fruition and prices them out. JMTCW.