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<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="5" face="Times New Roman" style="font-size:18.0pt;font-weight:bold;">UNITED STATES<br> SECURITIES AND EXCHANGE COMMISSION</font></b></p>
<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="2" face="Times New Roman" style="font-size:10.0pt;font-weight:bold;">WASHINGTON, DC 20549</font></b></p>
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<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="5" face="Times New Roman" style="font-size:18.0pt;font-weight:bold;">FORM&nbsp;8-K</font></b></p>
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<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="3" face="Times New Roman" style="font-size:12.0pt;font-weight:bold;">CURRENT REPORT<br> Pursuant to Section&nbsp;13 or 15(d)<br> of the Securities Exchange Act of 1934</font></b></p>
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<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">Date of report (Date of earliest event reported):&#160; <b>August&nbsp;27, 2013 (August&nbsp;21, 2013)</b></font></p>
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<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="5" face="Times New Roman" style="font-size:18.0pt;font-weight:bold;">Arch Coal,&nbsp;Inc.<br>  </font></b><font size="2" style="font-size:10.0pt;">(Exact name of registrant as specified in its charter)</font></p>
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<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="2" face="Times New Roman" style="font-size:10.0pt;font-weight:bold;">Delaware</font></b></p>    </td>
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<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="2" face="Times New Roman" style="font-size:10.0pt;font-weight:bold;">1-13105</font></b></p>    </td>
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<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="2" face="Times New Roman" style="font-size:10.0pt;font-weight:bold;">43-0921172</font></b></p>    </td>   </tr>
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<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">(State or other jurisdiction of<br>   incorporation)</font></p>    </td>
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<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">(I.R.S. Employer Identification No.)</font></p>    </td>   </tr>  </table>
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<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><b><font size="2" face="Times New Roman" style="font-size:10.0pt;font-weight:bold;">CityPlace One<br> One CityPlace Drive, Suite&nbsp;300<br> St. Louis, Missouri 63141<br>  </font></b><font size="2" style="font-size:10.0pt;">(Address, including zip code, of principal executive offices)</font></p>
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<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">Registrant&#146;s telephone number, including area code:&#160; <b>(314) 994-2700</b></font></p>
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<p style="margin:0in 0in .0001pt;text-indent:.25in;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">Check the appropriate box below if the Form&nbsp;8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:</font></p>
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<p style="margin:0in 0in .0001pt .25in;"><font size="2" face="Wingdings" style="font-size:10.0pt;">o</font><font size="1" style="font-size:3.0pt;">&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; </font><font size="2" style="font-size:10.0pt;">Written communications pursuant to Rule&nbsp;425 under the Securities Act (17 CFR 230.425)</font></p>
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<p style="margin:0in 0in .0001pt .5in;text-indent:-.25in;"><font size="2" face="Wingdings" style="font-size:10.0pt;">o</font><font size="1" style="font-size:3.0pt;">&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; </font><font size="2" style="font-size:10.0pt;">Soliciting material pursuant to Rule&nbsp;14a-12 under the Exchange Act (17 CFR 240.14a-12)</font></p>
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<p style="margin:0in 0in .0001pt .5in;text-indent:-.25in;"><font size="2" face="Wingdings" style="font-size:10.0pt;">o</font><font size="1" style="font-size:3.0pt;">&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; </font><font size="2" style="font-size:10.0pt;">Pre-commencement communications pursuant to Rule&nbsp;14d-2(b)&nbsp;under the Exchange Act (17 CFR 240.14d-2(b))</font></p>
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<p style="margin:0in 0in .0001pt .5in;text-indent:-.25in;"><font size="2" face="Wingdings" style="font-size:10.0pt;">o</font><font size="1" style="font-size:3.0pt;">&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; </font><font size="2" style="font-size:10.0pt;">Pre-commencement communications pursuant to Rule&nbsp;13e-4(c)&nbsp;under the Exchange Act (17 CFR 240.13e-4(c))</font></p>
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<p style="margin:0in 0in .0001pt;"><b><font size="2" face="Times New Roman" style="font-size:10.0pt;font-weight:bold;">Item 1.04 Mine Safety &#150; Reporting of Shutdowns and Patterns of Violations.</font></b></p>
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<p style="margin:0in 0in .0001pt;text-indent:.5in;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">On August&nbsp;21, 2013, Thunder Basin Coal Company, L.L.C., a subsidiary of Arch Coal,&nbsp;Inc., received an imminent danger order under section 107(a)&nbsp;of the Federal Mine Safety and Health Act of 1977 at the Black Thunder mine in Campbell County, Wyoming related to the reported manner in which a shovel was moved.</font></p>
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<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">2<a name="PB_2_190913_5335"></a></font></p>
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<p style="margin:0in 0in .0001pt;text-indent:.25in;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.</font></p>
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<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">Dated:   August&nbsp;27, 2013</font></p>    </td>
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<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">/s/   Robert G. Jones</font></p>    </td>   </tr>
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<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">Robert   G. Jones</font></p>    </td>   </tr>
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<p style="margin:0in 0in .0001pt;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">Senior   Vice President &#150; Law, General Counsel and Secretary</font></p>    </td>   </tr>  </table>
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<p align="center" style="margin:0in 0in .0001pt;text-align:center;"><font size="2" face="Times New Roman" style="font-size:10.0pt;">3<a name="PB_3_190919_5796"></a></font></p>
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{"company-data": {"conformed-name": "ARCH COAL INC", "cik": "0001037676", "assigned-sic": "1221", "irs-number": "430921172", "state-of-incorporation": "DE", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "8-K", "act": "34", "file-number": "001-13105", "film-number": "131062485"}, "business-address": {"street1": "CITY PLACE ONE STE 300", "street2": "ARCH MINERAL CORP", "city": "ST LOUIS", "state": "MO", "zip": "63141", "phone": "3149942700"}, "mail-address": {"street1": "CITYPLACE ONE SUITE 300", "street2": "ARCH MINERAL CORP", "city": "CREVE COEUR", "state": "MO", "zip": "63141"}, "former-company": {"former-conformed-name": "ARCH MINERAL CORP", "date-changed": "19970411"}}
UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
WASHINGTON, DC 20549
FORM 8-K
CURRENT REPORT
Pursuant to Section 13 or 15(d)
of the Securities Exchange Act of 1934
Date of report (Date of earliest event reported):
August 27, 2013 (August 21, 2013)
Arch Coal, Inc.
(Exact name of registrant as specified in its charter)
Delaware
1-13105
43-0921172
(State or other jurisdiction of
incorporation)
(Commission File Number)
(I.R.S. Employer Identification No.)
CityPlace One
One CityPlace Drive, Suite 300
St. Louis, Missouri 63141
(Address, including zip code, of principal executive offices)
Registrant's telephone number, including area code:
(314) 994-2700
Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:
o
Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)
o
Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)
o
Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))
o
Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))
Item 1.04 Mine Safety – Reporting of Shutdowns and Patterns of Violations.
On August 21, 2013, Thunder Basin Coal Company, L.L.C., a subsidiary of Arch Coal, Inc., received an imminent danger order under section 107(a) of the Federal Mine Safety and Health Act of 1977 at the Black Thunder mine in Campbell County, Wyoming related to the reported manner in which a shovel was moved.
2
Signatures
Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.
Dated:   August 27, 2013
Arch   Coal, Inc.
By:
/s/   Robert G. Jones
Robert   G. Jones
Senior   Vice President – Law, General Counsel and Secretary
3