<PAGE>

                                                                     EXHIBIT 4.3

                         SEVENTH SUPPLEMENTAL INDENTURE

     Seventh Supplemental Indenture (this "SUPPLEMENTAL INDENTURE"), dated as of
June 13, 2006, among the entities listed on Schedule 1 attached hereto
("GUARANTEEING SUBSIDIARIES"), each being a subsidiary of Peabody Energy
Corporation (or its permitted successor), a Delaware corporation (the
"COMPANY"), the Company, the other Subsidiary Guarantors (as defined in the
Indenture referred to below) and U.S. Bank National Association, as Trustee
under the Indenture referred to below (the "TRUSTEE").

                                   WITNESSETH

     WHEREAS, the Company has heretofore executed and delivered to the Trustee
the First Supplemental Indenture dated as of March 23, 2004 to the Indenture
dated as of March 19, 2004, (the "BASE INDENTURE," and, together with the First
Supplemental Indenture, the "INDENTURE") providing for the issuance of an
unlimited amount of 5-7/8% Senior Notes due 2016 (the "NOTES"); as supplemented
by the Second Supplemental Indenture, dated as of April 22, 2004; Third
Supplemental Indenture, dated October 18, 2004; Fourth Supplemental Indenture,
dated January 20, 2005; Fifth Supplemental Indenture, dated September 30, 2005;
and Sixth Supplemental Indenture, dated January 20, 2006.

     WHEREAS, the Indenture provides that under certain circumstances the
Guaranteeing Subsidiaries shall execute and deliver to the Trustee a
supplemental Indenture pursuant to which the Guaranteeing Subsidiaries shall
unconditionally guarantee all of the Company's Obligations under the Notes and
the Indenture on the terms and conditions set forth herein (the "SUBSIDIARY
GUARANTEE"); and

     WHEREAS, pursuant to Section 9.01 of the Base Indenture, the Trustee is
authorized to execute and deliver this Supplemental Indenture.

     NOW THEREFORE, in consideration of the foregoing and for other good and
valuable consideration, the receipt of which is hereby acknowledged, the
Guaranteeing Subsidiaries and the Trustee mutually covenant and agree for the
equal and ratable benefit of the Holders of the Notes as follows:

     1. CAPITALIZED TERMS. Capitalized terms used herein without definition
shall have the meanings assigned to them in the Indenture.

     2. AGREEMENT TO GUARANTEE. Each of the Guaranteeing Subsidiaries hereby
agrees as follows:

     (a)  Along with all Subsidiary Guarantors named in the Indenture, to
          jointly and severally Guarantee to each Holder of a Note authenticated
          and delivered by the Trustee and to the Trustee and its successors and
          assigns,

<PAGE>

          irrespective of the validity and enforceability of the Indenture, the
          Notes or the obligations of the Company hereunder or thereunder, that:

          (i)  the principal of and interest on the Notes will be promptly paid
               in full when due, whether at maturity, by acceleration,
               redemption or otherwise, and interest on the overdue principal of
               and interest on the Notes, if any, if lawful, and all other
               obligations of the Company to the Holders or the Trustee
               hereunder or thereunder will be promptly paid in full or
               performed, all in accordance with the terms hereof and thereof;
               and

          (ii) in case of any extension of time of payment or renewal of any
               Notes or any of such other obligations, that same will be
               promptly paid in full when due or performed in accordance with
               the terms of the extension or renewal, whether at stated
               maturity, by acceleration or otherwise. Failing payment when due
               of any amount so guaranteed or any performance so guaranteed for
               whatever reason, the Subsidiary Guarantors shall be jointly and
               severally obligated to pay the same immediately.

     (b)  The obligations hereunder shall be unconditional, irrespective of the
          validity, regularity or enforceability of the Notes or the Indenture,
          the absence of any action to enforce the same, any waiver or consent
          by any Holder of the Notes with respect to any provisions hereof or
          thereof, the recovery of any judgment against the Company, any action
          to enforce the same or any other circumstance which might otherwise
          constitute a legal or equitable discharge or defense of a Subsidiary
          Guarantor.

     (c)  The following is hereby waived: diligence presentment, demand of
          payment, filing of claims with a court in the event of insolvency or
          bankruptcy of the Company, any right to require a proceeding first
          against the Company, protest, notice and all demands whatsoever.

     (d)  This Subsidiary Guarantee shall not be discharged except by complete
          performance of the obligations contained in the Notes and the
          Indenture.

     (e)  If any Holder or the Trustee is required by any court or otherwise to
          return to the Company, the Subsidiary Guarantors, or any custodian,
          Trustee, liquidator or other similar official acting in relation to
          either the Company or the Subsidiary Guarantors, any amount paid by
          either to the Trustee or such Holder, this Subsidiary Guarantee, to
          the extent theretofore discharged, shall be reinstated in full force
          and effect.

     (f)  The Guaranteeing Subsidiaries shall not be entitled to any right of
          subrogation in relation to the Holders in respect of any obligations
          guaranteed hereby until payment in full of all obligations guaranteed
          hereby.


                                       2

<PAGE>

     (g)  As between the Subsidiary Guarantors, on the one hand, and the Holders
          and the Trustee, on the other hand, (x) the maturity of the
          obligations guaranteed hereby may be accelerated as provided in
          Article 6 of the First Supplemental Indenture for the purposes of this
          Subsidiary Guarantee, notwithstanding any stay, injunction or other
          prohibition preventing such acceleration in respect of the obligations
          guaranteed hereby, and (y) in the event of any declaration of
          acceleration of such obligations as provided in Article 6 of the First
          Supplemental Indenture, such obligations (whether or not due and
          payable) shall forthwith become due and payable by the Subsidiary
          Guarantors for the purpose of this Subsidiary Guarantee.

     (h)  The Subsidiary Guarantors shall have the right to seek contribution
          from any non-paying Subsidiary Guarantor so long as the exercise of
          such right does not impair the rights of the Holders under the
          Subsidiary Guarantee.

     (i)  Pursuant to Section 9.04 of the First Supplemental Indenture, after
          giving effect to any maximum amount and any other contingent and fixed
          liabilities that are relevant under any applicable Bankruptcy or
          fraudulent conveyance laws, and after giving effect to any collections
          from, rights to receive contribution from or payments made by or on
          behalf of any other Subsidiary Guarantor in respect of the obligations
          of such other Subsidiary Guarantor under Article 9 of the First
          Supplemental Indenture shall result in the obligations of such
          Subsidiary Guarantor under its Subsidiary Guarantee not constituting a
          fraudulent transfer or conveyance.

     3. EXECUTION AND DELIVERY. Each of the Guaranteeing Subsidiaries agrees
that the Subsidiary Guarantees shall remain in full force and effect
notwithstanding any failure to endorse on each Note a notation of such
Subsidiary Guarantee.

     4. GUARANTEEING SUBSIDIARY MAY CONSOLIDATE, ETC. ON CERTAIN TERMS.

     (a)  The Guaranteeing Subsidiaries may not consolidate with or merge with
          or into (whether or not such Subsidiary Guarantor is the surviving
          Person) another corporation, Person or entity whether or not
          affiliated with such Subsidiary Guarantor unless:

          (i)  subject to Section 9.04 of the First Supplemental Indenture, the
               Person formed by or surviving any such consolidation or merger
               (if other than a Subsidiary Guarantor or the Company)
               unconditionally assumes all the obligations of such Subsidiary
               Guarantor, pursuant to a supplemental Indenture in form and
               substance reasonably satisfactory to the Trustee, under the
               Notes, the Indenture and the Subsidiary Guarantee on the terms
               set forth herein or therein; and

          (ii) immediately after giving effect to such transaction, no Default
               or Event of Default exists.


                                       3

<PAGE>

     (b)  In case of any such consolidation, merger, sale or conveyance and upon
          the assumption by the successor corporation, by supplemental
          Indenture, executed and delivered to the Trustee and satisfactory in
          form to the Trustee, of the Subsidiary Guarantee endorsed upon the
          Notes and the due and punctual performance of all of the covenants and
          conditions of the Indenture to be performed by the Subsidiary
          Guarantor, such successor corporation shall succeed to and be
          substituted for the Subsidiary Guarantor with the same effect as if it
          had been named herein as a Subsidiary Guarantor. Such successor
          corporation thereupon may cause to be signed any or all of the
          Subsidiary Guarantees to be endorsed upon all of the Notes issuable
          hereunder which theretofore shall not have been signed by the Company
          and delivered to the Trustee. All the Subsidiary Guarantees so issued
          shall in all respects have the same legal rank and benefit under the
          Indenture as the Subsidiary Guarantees theretofore and thereafter
          issued in accordance with the terms of the Indenture as though all of
          such Subsidiary Guarantees had been issued at the date of the
          execution hereof.

     (c)  Except as set forth in Articles 4 and 5 of the First Supplemental
          Indenture, and notwithstanding clauses (a) and (b) above, nothing
          contained in the Indenture or in any of the Notes shall prevent any
          consolidation or merger of a Subsidiary Guarantor with or into the
          Company or another Subsidiary Guarantor, or shall prevent any sale or
          conveyance of the property of a Subsidiary Guarantor as an entirety or
          substantially as an entirety to the Company or another Subsidiary
          Guarantor.

     5. RELEASES.

     (a)  In the event of a sale or other disposition of all of the assets of
          any Subsidiary Guarantor, by way of merger, consolidation or
          otherwise, or a sale or other disposition of all to the capital stock
          of any Subsidiary Guarantor, then such Subsidiary Guarantor (in the
          event of a sale or other disposition, by way of merger, consolidation
          or otherwise, of all of the capital stock of such Subsidiary
          Guarantor) or the corporation acquiring the property (in the event of
          a sale or other disposition of all or substantially all of the assets
          of such Subsidiary Guarantor) will be released and relieved of any
          obligations under its Subsidiary Guarantee; provided that the Net
          Proceeds of such sale or other disposition are applied in accordance
          with the applicable provisions of the Indenture, including without
          limitation Section 4.10 of the Indenture. Upon delivery by the Company
          to the Trustee of an Officer's Certificate and an Opinion of Counsel
          to the effect that such sale or other disposition was made by the
          Company in accordance with the provisions of the Indenture, including
          without limitation Section 4.10 of the First Supplemental Indenture,
          the Trustee shall execute any documents reasonably required in order
          to evidence the release of any Subsidiary Guarantor from its
          obligations under its Subsidiary Guarantee.


                                       4

<PAGE>

     (b)  Any Subsidiary Guarantor not released from its obligations under its
          Subsidiary Guarantee shall remain liable for the full amount of
          principal of and interest on the Notes and for the other obligations
          of any Subsidiary Guarantor under the Indenture as provided in Article
          9 of the First Supplemental Indenture.

     6. NO RECOURSE AGAINST OTHERS. No past, present or future director,
officer, employee, incorporator, stockholder or agent of the Guaranteeing
Subsidiaries, as such, shall have any liability for any obligations of the
Company or any Guaranteeing Subsidiaries under the Notes, any Subsidiary
Guarantees, the Indenture or this Supplemental Indenture or for any claim based
on, in respect of, or by reason of, such obligations or their creation. Each
Holder of the Notes by accepting a Note waives and releases all such liability.
The waiver and release are part of the consideration for issuance of the Notes.
Such waiver may not be effective to waive liabilities under the federal
securities laws and it is the view of the Commission that such a waiver is
against public policy.

     7. NEW YORK LAW TO GOVERN. THE LAW OF THE STATE OF NEW YORK SHALL GOVERN
AND BE USED TO CONSTRUE THIS SUPPLEMENTAL INDENTURE.

     8. COUNTERPARTS. The parties may sign any number of copies of this
Supplemental Indenture. Each signed copy shall be an original, but all of them
together represent the same agreement.

     9. EFFECT OF HEADINGS. The Section headings herein are for convenience only
and shall not affect the construction hereof.

     10. THE TRUSTEE. The Trustee shall not be responsible in any manner
whatsoever for or in respect of the validity or sufficiency of this Supplemental
Indenture or for or in respect of the recitals contained herein, all of which
recitals are made solely by the Guaranteeing Subsidiaries and the Company.

     IN WITNESS WHEREOF, the parties hereto have caused this Supplemental
Indenture to be duly executed and attested, all as of the date first above
written.

PEABODY ENERGY CORPORATION              US BANK NATIONAL ASSOCIATION
("COMPANY")                             ("TRUSTEE")


By: /s/ WALTER L. HAWKINS, JR.          By: /s/ PHILIP G. KANE, JR.
    ---------------------------------       ------------------------------------
Name: Walter L. Hawkins, Jr.            Name: Philip G. Kane, Jr.
Title: Vice President and Treasurer     Title: Vice President


                                       5

<PAGE>

                                 EXISTING SUBSIDIARY GUARANTORS:

                                 AFFINITY MINING COMPANY
                                 AMERICAN LAND DEVELOPMENT, LLC
                                 AMERICAN LAND HOLDINGS OF ILLINOIS, LLC
                                 AMERICAN LAND HOLDINGS OF INDIANA, LLC
                                 AMERICAN LAND HOLDINGS OF KENTUCKY, LLC
                                    f/k/a BTU VENEZUELA, LLC
                                 APPALACHIA MINE SERVICES, LLC
                                 ARCLAR COMPANY, LLC
                                 ARID OPERATIONS INC.
                                 BEAVER DAM COAL COMPANY
                                 BIG RIDGE, INC.
                                 BIG SKY COAL COMPANY
                                 BLACK BEAUTY COAL COMPANY
                                 BLACK BEAUTY EQUIPMENT COMPANY
                                 BLACK BEAUTY HOLDING COMPANY, LLC
                                 BLACK BEAUTY MINING, INC.
                                 BLACK BEAUTY RESOURCES, LLC
                                    f/k/a BLACK BEAUTY RESOURCES, INC.
                                 BLACK BEAUTY UNDERGROUND, INC.
                                 BLACK HILLS MINING COMPANY, LLC
                                 BLACK STALLION COAL COMPANY, LLC
                                 BLACK WALNUT COAL COMPANY
                                 BLUEGRASS MINE SERVICES, LLC
                                    f/k/a BLUEGRASS COAL COMPANY
                                 BTU EMPIRE CORPORATION
                                 CABALLO COAL COMPANY
                                 CENTRAL STATES COAL RESERVES OF ILLINOIS, LLC
                                    f/k/a PEABODY DEVELOPMENT LAND HOLDINGS, LLC
                                 CENTRAL STATES COAL RESERVES OF INDIANA, LLC
                                 CENTRAL STATES COAL RESERVES OF KENTUCKY, LLC
                                 CHARLES COAL COMPANY, LLC
                                    f/k/a CHARLES COAL COMPANY
                                 CLEATON COAL COMPANY
                                 COAL PROPERTIES, LLC
                                    f/k/a COAL PROPERTIES CORP.
                                 COALSALES, LLC
                                 COALSALES II, LLC
                                 COALTRADE INTERNATIONAL, LLC
                                 COALTRADE, LLC
                                 COAL RESERVES HOLDING LIMITED LIABILITY
                                 COMPANY NO. 1
                                 COAL RESERVES HOLDING LIMITED LIABILITY
                                 COMPANY NO. 2
                                 COLONY BAY COAL COMPANY


                                       6

<PAGE>

                                 COLORADO YAMPA COAL COMPANY
                                 COOK MOUNTAIN COAL COMPANY, LLC
                                    f/k/a COOK MOUNTAIN COAL COMPANY
                                 COTTONWOOD LAND COMPANY
                                 COULTERVILLE COAL COMPANY, LLC
                                    f/k/a WILLIAMSVILLE COAL COMPANY, LLC
                                 CYPRUS CREEK LAND COMPANY
                                 CYPRUS CREEK LAND RESOURCES, LLC
                                 DIXON MINING COMPANY, LLC
                                 DODGE HILL HOLDING JV, LLC
                                 DODGE HILL OF KENTUCKY, LLC
                                 DODGE HILL MINING COMPANY, LLC
                                 DYSON CREEK COAL COMPANY, LLC
                                 EACC CAMPS, INC.
                                 EAGLE COAL COMPANY
                                 EASTERN ASSOCIATED COAL, LLC
                                    f/k/a EASTERN ASSOCIATED COAL CORP.
                                 EASTERN COAL COMPANY, LLC
                                 EASTERN ROYALTY CORP.
                                 EMPIRE MARINE, LLC
                                 FALCON COAL COMPANY
                                 GALLO FINANCE COMPANY
                                 GOLD FIELDS CHILE, LLC
                                    f/k/a GOLD FIELDS CHILE, S.A.
                                 GOLD FIELDS MINING, LLC
                                 GOLD FIELDS ORTIZ, LLC
                                    f/k/a GOLD FIELDS OPERATING CO. - ORTIZ
                                 GRAND EAGLE MINING, INC.
                                 HAYDEN GULCH TERMINAL, INC.
                                 HIGHLAND MINING COMPANY, LLC
                                    f/k/a HIGHLAND MINING COMPANY
                                 HIGHWALL MINING SERVICES COMPANY
                                 HILLSIDE MINING COMPANY
                                 HMC MINING, LLC
                                 INDEPENDENCE MATERIAL HANDLING, LLC
                                    f/k/a INDEPENDENCE MATERIAL HANDLING COMPANY
                                 INDIAN HILL COMPANY
                                 INTERIOR HOLDINGS, LLC
                                    f/k/a INTERIOR HOLDINGS CORP.
                                 JAMES RIVER COAL TERMINAL, LLC
                                    f/k/a JAMES RIVER COAL TERMINAL COMPANY
                                 JARRELL'S BRANCH COAL COMPANY
                                 JUNIPER COAL COMPANY
                                 KANAWHA RIVER VENTURES I, LLC
                                 KAYENTA MOBILE HOME PARK, INC.


                                       7
<PAGE>

                                 LOGAN FORK COAL COMPANY
                                 MARTINKA COAL COMPANY, LLC
                                    f/k/a MARTINKA COAL COMPANY
                                 MIDCO SUPPLY AND EQUIPMENT CORPORATION
                                 MIDWEST COAL ACQUISITION CORP.
                                 MIDWEST COAL RESERVES OF ILLINOIS, LLC
                                 MIDWEST COAL RESERVES OF INDIANA, LLC
                                 MIDWEST COAL RESOURCES, LLC
                                 MOUNTAIN VIEW COAL COMPANY, LLC
                                    f/k/a MOUNTAIN VIEW COAL COMPANY
                                 MUSTANG ENERGY COMPANY, L.L.C.
                                 NEW MEXICO COAL RESOURCES, LLC
                                 NORTH PAGE COAL CORP.
                                 OHIO COUNTY COAL COMPANY
                                 PATRIOT COAL COMPANY, L.P.
                                 PATRIOT MIDWEST HOLDINGS, LLC
                                 PDC PARTNERSHIP HOLDINGS, LLC f/k/a PDC
                                    PARTNERSHIP HOLDINGS, INC.
                                 PEABODY AMERICA, INC.
                                 PEABODY ARCHVEYOR, L.L.C.
                                 PEABODY COAL COMPANY, LLC
                                    f/k/a PEABODY COAL COMPANY
                                 PEABODY DEVELOPMENT COMPANY, LLC
                                 PEABODY ELECTRICITY, LLC
                                 PEABODY ENERGY GENERATION HOLDING COMPANY
                                 PEABODY ENERGY INVESTMENTS, INC.
                                 PEABODY ENERGY SOLUTIONS, INC.
                                 PEABODY HOLDING COMPANY, LLC,
                                    f/k/a PHC ACQUISITION CORP.
                                 PEABODY INVESTMENTS CORP.
                                 PEABODY NATURAL GAS, LLC
                                 PEABODY NATURAL RESOURCES COMPANY
                                 PEABODY POWERTREE INVESTMENTS, LLC
                                 PEABODY RECREATIONAL LANDS, L.L.C.
                                 PEABODY SOUTHWESTERN COAL COMPANY
                                 PEABODY TERMINALS, LLC
                                    f/k/a PEABODY TERMINALS, INC.
                                 PEABODY VENEZUELA COAL CORP.
                                 PEABODY VENTURE FUND, LLC
                                 PEABODY-WATERSIDE DEVELOPMENT, L.L.C.
                                 PEABODY WESTERN COAL COMPANY
                                 PEC EQUIPMENT COMPANY, LLC
                                 PINE RIDGE COAL COMPANY, LLC
                                    f/k/a PINE RIDGE COAL COMPANY
                                 POINT PLEASANT DOCK COMPANY, LLC
                                 POND CREEK LAND RESOURCES, LLC


                                       8

<PAGE>

                                 POND RIVER LAND COMPANY
                                 PORCUPINE PRODUCTION, LLC
                                 PORCUPINE TRANSPORTATION, LLC
                                 POWDER RIVER COAL, LLC
                                    f/k/a POWDER RIVER COAL COMPANY
                                 POWDER RIVER RESOURCES, LLC
                                 PRAIRIE STATE GENERATING COMPANY, LLC
                                 RANDOLPH LAND HOLDING COMPANY, LLC
                                 RIVERS EDGE MINING, INC.
                                 RIVERVIEW TERMINAL COMPANY
                                 SCHOOL CREEK COAL COMPANY, LLC
                                 SENECA COAL COMPANY
                                 SENTRY MINING, LLC
                                    f/k/a SENTRY MINING COMPANY
                                 SHOSHONE COAL CORPORATION
                                 SNOWBERRY LAND COMPANY
                                 STAR LAKE ENERGY COMPANY, L.L.C.
                                 STERLING SMOKELESS COAL COMPANY, LLC
                                    f/k/a STERLING SMOKELESS COAL COMPANY
                                 SUGAR CAMP PROPERTIES
                                 THOROUGHBRED, L.L.C.
                                 THOROUGHBRED GENERATING COMPANY, LLC
                                 THOROUGHBRED MINING COMPANY, L.L.C.
                                 TWENTYMILE COAL COMPANY
                                 UNION COUNTY COAL CO., LLC
                                 YANKEETOWN DOCK, LLC
                                    f/k/a YANKEETOWN DOCK CORPORATION


                                        By: /s/ WALTER L. HAWKINS, JR.
                                            ------------------------------------
                                        Name: Walter L. Hawkins, Jr.
                                        Title: Vice President


                                       9

<PAGE>

ADDITIONAL GUARANTORS:

                                        BTU WESTERN RESOURCES, INC.


                                        By: /s/ WALTER L. HAWKINS, JR.
                                            ------------------------------------
                                        Name: Walter L. Hawkins, Jr.
                                        Title: Vice President & Treasurer


                                        FORT ENERGY, LLC


                                        By: /s/ WALTER L. HAWKINS, JR.
                                            ------------------------------------
                                        Name: Walter L. Hawkins, Jr.
                                        Title: Vice President & Treasurer


                                       10

<PAGE>

                                   SCHEDULE 1

                          NEW GUARANTEEING SUBSIDIARIES

BTU Western Resources, Inc., a Delaware corporation
Fort Energy, LLC, a Delaware limited liability company


                                       11