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                                                                     EXHIBIT 4.3

                          SUPPLEMENTAL INDENTURE NO. 2

                          dated as of October 26, 2004

                                      among

                            CENTURY ALUMINUM COMPANY,
                                    as Issuer

                          The Guarantor(s) Party Hereto

                                       and

                            WILMINGTON TRUST COMPANY,
                                   as Trustee

                            -------------------------

                1.75% CONVERTIBLE SENIOR NOTES DUE AUGUST 1, 2024

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      THIS SUPPLEMENTAL INDENTURE No. 2 (this "SUPPLEMENTAL INDENTURE"), entered
into as of October 26, 2004, is among Century Aluminum Company, a corporation
duly organized under the laws of the State of Delaware (the "COMPANY"), Berkeley
Aluminum, Inc., a corporation duly organized under the laws of the State of
Delaware, Century Aluminum Holdings, Inc., a corporation duly organized under
the laws of the State of Delaware, Century Aluminum of West Virginia, Inc., a
corporation duly organized under the laws of the State of Delaware, Century
Kentucky, Inc., a corporation duly organized under the laws of the State of
Delaware, Century Louisiana, Inc., a corporation duly organized under the laws
of the State of Delaware, Hancock Aluminum LLC, a limited liability company duly
organized under the laws of the State of Kentucky, Metalsco, Ltd., a corporation
duly organized under the laws of the State of Georgia, NSA, Ltd., a limited
partnership duly organized under the laws of the State of Kentucky, Skyliner,
Inc., a corporation duly organized under the laws of the State of Delaware,
Virgin Islands Alumina Corporation LLC, a limited liability company duly
organized under the laws of the State of Delaware, (each an "UNDERSIGNED") and
Wilmington Trust Company, as trustee (the "TRUSTEE").

                                    RECITALS

      WHEREAS, the Company and the Trustee entered into the Indenture, dated as
of August 9, 2004 (the "ORIGINAL INDENTURE," as amended heretofore and as
amended and supplemented by the Supplemental Indenture No. 1 of even date
herewith between the Company and the Trustee and this Supplemental Indenture, is
hereinafter called the "INDENTURE"), relating to the Company's 1.75% Convertible
Senior Notes due August 1, 2024 (the "SECURITIES");

      WHEREAS, the Company has agreed in Section 6.09 of the Indenture to cause
certain of its Subsidiaries to provide Securities Guaranties in certain
circumstances; and

      WHEREAS, each Undersigned is required pursuant to such Section 6.09 to
execute and deliver this Supplemental Indenture to evidence its Securities
Guaranty.

                                    AGREEMENT

      NOW, THEREFORE, in consideration of the premises and mutual covenants
herein contained and intending to be legally bound, the parties to this
Supplemental Indenture hereby agree as follows:

      Section 1. Capitalized terms used herein and not otherwise defined herein
are used as defined in the Indenture.

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      Section 2. Each Undersigned, by its execution of this Supplemental
Indenture, agrees to be a Guarantor under the Indenture on the terms set forth
below.

      Section 3. Subject to the provisions in this Supplemental Indenture, each
Guarantor hereby irrevocably and unconditionally guarantees, jointly and
severally, on a senior unsecured basis, the full and punctual payment (or
delivery, as the case may be), if and when due, of (i) the principal amount or
interest due on any Security, whether on the Final Maturity Date, upon
redemption or repurchase, or otherwise, (ii) the Make Whole Premium payable, if
any, on any Security, and (iii) all other amounts payable by the Company under
the Indenture (including, without limitation, the Company's obligation to
deliver Cash, Common Stock, or other securities, assets or property (including
Cash) upon conversion of the Securities). Upon failure by the Company to pay (or
deliver, as the case may be) punctually any such amount if and when due, each
Guarantor shall forthwith on demand pay (or deliver, as the case may be) the
amount (or consideration) not so paid (or delivered) at the place and in the
manner specified in the Indenture. To the extent that the Company has an
election to deliver the form of payment, each Guarantor shall have the same
right of election.

      Section 4. The obligations of each Guarantor are unconditional and
absolute and, without limiting the generality of the foregoing, will not be
released, discharged or otherwise affected by

            (i) any extension, renewal, settlement, compromise, waiver or
      release in respect of any obligation of the Company under the Indenture or
      any Security, by operation of law or otherwise;

            (ii) any modification or amendment of or supplement to the Indenture
      or any Security;

            (iii) any change in the corporate existence, structure or ownership
      of the Company, or any insolvency, bankruptcy, reorganization or other
      similar proceeding affecting the Company or its assets or any resulting
      release or discharge of any obligation of the Company contained in the
      Indenture or any Security;

            (iv) the existence of any claim, set-off or other rights which the
      Guarantor may have at any time against the Company, the Trustee or any
      other Person, whether in connection with the Indenture or any unrelated
      transactions; provided that nothing herein prevents the assertion of any
      such claim by separate suit or compulsory counterclaim;

            (v) any invalidity or unenforceability relating to or against the
      Company for any reason of the Indenture or any Security, or any provision
      of applicable law or regulation purporting to prohibit the payment by the

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      Company of the principal amount, Make Whole Premium, if any, or interest
      due on any Security or any other amount payable by the Company under the
      Indenture; or

            (vi) any other act or omission to act or delay of any kind by the
      Company, the Trustee or any other Person or any other circumstance
      whatsoever which might, but for the provisions of this paragraph,
      constitute a legal or equitable discharge of or defense to such
      Guarantor's obligations hereunder.

      Section 5. Each Guarantor's obligations under its Securities Guaranty will
remain in full force and effect until the principal of, Make Whole Premium, if
any, and interest on the Securities and all other amounts payable by the Company
(including, without limitation, the Company's obligation to deliver Cash, Common
Stock, or other securities, assets or property (including Cash) upon conversion
of the Securities) under the Indenture have been paid in full. If at any time
any payment of the principal of, Make Whole Premium, if any, or interest on any
Security or any other amount payable by the Company (including, without
limitation, the Company's obligation to deliver Cash, Common Stock, or other
securities, assets or property (including Cash) upon conversion of the
Securities) under the Indenture is rescinded or must be otherwise restored or
returned upon the insolvency, bankruptcy or reorganization of the Company or
otherwise, each Guarantor's obligations hereunder with respect to such payment
will be reinstated as though such payment had been due but not made at such
time.

      Section 6. Each Guarantor irrevocably waives acceptance hereof,
presentment, demand, protest and any notice not provided for herein, as well as
any requirement that at any time any action be taken by any Person against the
Company or any other Person.

      Section 7. Upon making any payment with respect to any obligation of the
Company pursuant to this Supplemental Indenture, the Guarantor making such
payment will be subrogated to the rights of the payee against the Company with
respect to such obligation; provided that the Guarantor may not enforce either
any right of subrogation, or any right to receive payment in the nature of
contribution, or otherwise, from any other Guarantor, with respect to such
payment so long as any amount payable by the Company hereunder or under the
Securities remains unpaid.

      Section 8. If acceleration of the time for payment of any amount payable
by the Company under the Indenture or the Securities is stayed upon the
insolvency, bankruptcy or reorganization of the Company, all such amounts
otherwise subject to acceleration under the terms of the Indenture are
nonetheless payable by the Guarantors hereunder forthwith on demand by the
Trustee or the Holders.

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      Section 9. Notwithstanding anything to the contrary in this Supplemental
Indenture, each Guarantor, and by its acceptance of Securities, each Holder,
hereby confirms that it is the intention of all such parties that the Securities
Guaranty of such Guarantor not constitute a fraudulent conveyance under
applicable fraudulent conveyance provisions of the United States Bankruptcy Code
or any comparable provision of state law. To effectuate that intention, the
Trustee, the Holders and the Guarantors hereby irrevocably agree that the
obligations of each Guarantor under its Securities Guaranty are limited to the
maximum amount that would not render the Guarantor's obligations subject to
avoidance under applicable fraudulent conveyance provisions of the United States
Bankruptcy Code or any comparable provision of state law.

      Section 10. The execution by each Undersigned of this Supplemental
Indenture evidences the Securities Guaranty of such Guarantor, whether or not
the person signing as an officer of the Guarantor still holds that office at the
time of authentication of any Security. The delivery of any Security by the
Trustee after authentication constitutes due delivery of the Securities Guaranty
set forth in the Indenture on behalf of each Guarantor.

      Section 11. The Securities Guaranty of a Guarantor will terminate and be
automatically released upon the release or discharge of the guarantee of the
Senior Notes of such Guarantor as set forth in Section 6.09(b) of the Indenture.

      Section 12. This Supplemental Indenture shall be governed by and construed
in accordance with the laws of the State of New York.

      Section 13. This Supplemental Indenture may be signed in various
counterparts which together will constitute one and the same instrument.

      Section 14. This Supplemental Indenture is an amendment supplemental to
the Indenture and the Indenture and this Supplemental Indenture will henceforth
be read together.

      Section 15. The recitals contained in this Supplemental Indenture shall be
taken as the statements of the Company and the Guarantors, and the Trustee
assumes no responsibility for their correctness. The Trustee makes no
representations as to the validity or sufficiency of this Supplemental
Indenture.

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

                                       CENTURY ALUMINUM COMPANY,
                                         as Issuer

                                       By:  /s/ Daniel J. Krofcheck
                                           -------------------------------------
                                           Name:  Daniel J. Krofcheck
                                           Title: Vice President and Treasurer

                                       WILMINGTON TRUST COMPANY, as
                                         Trustee

                                       By:  /s/ Kristin F. Long
                                           -------------------------------------
                                           Name:  Kristin F. Long
                                           Title: Financial Services Officer

                                       CENTURY ALUMINUM OF WEST
                                         VIRGINIA, INC., as a Guarantor

                                       By:  /s/ Daniel J. Krofcheck
                                           -------------------------------------
                                           Name:  Daniel J. Krofcheck
                                           Title: Vice President and Treasurer

                                       BERKELEY ALUMINUM, INC., as a
                                         Guarantor

                                       By:  /s/ Daniel J. Krofcheck
                                           -------------------------------------
                                           Name:  Daniel J. Krofcheck
                                           Title: Vice President and Treasurer

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                                       VIRGIN ISLANDS ALUMINA
                                         CORPORATION LLC, as a Guarantor

                                       By:  /s/ Daniel J. Krofcheck
                                           -------------------------------------
                                           Name:  Daniel J. Krofcheck
                                           Title: Vice President and Treasurer

                                       CENTURY KENTUCKY, INC., as a
                                         Guarantor

                                       By:  /s/ Daniel J. Krofcheck
                                           -------------------------------------
                                           Name:  Daniel J. Krofcheck
                                           Title: Vice President and Treasurer

                                       METALSCO, LTD., as a Guarantor

                                       By:  /s/ Daniel J. Krofcheck
                                           -------------------------------------
                                           Name:  Daniel J. Krofcheck
                                           Title: Vice President and Treasurer

                                       SKYLINER, INC., as a Guarantor

                                       By:  /s/ Daniel J. Krofcheck
                                           -------------------------------------
                                           Name:  Daniel J. Krofcheck
                                           Title: Vice President and Treasurer

                                       NSA, LTD., as a Guarantor

                                       By: Metalsco, Ltd., its general partner

                                       By:  /s/ Daniel J. Krofcheck
                                           -------------------------------------
                                           Name:  Daniel J. Krofcheck
                                           Title: Vice President and Treasurer

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                                       HANCOCK ALUMINUM LLC, as a
                                         Guarantor

                                       By:  /s/ Daniel J. Krofcheck
                                           -------------------------------------
                                           Name:  Daniel J. Krofcheck
                                           Title: Vice President and Treasurer

                                       CENTURY LOUISIANA, INC., as a
                                         Guarantor

                                       By:  /s/ Daniel J. Krofcheck
                                           -------------------------------------
                                           Name:  Daniel J. Krofcheck
                                           Title: Vice President and Treasurer

                                       CENTURY ALUMINUM HOLDINGS,
                                         INC., as a Guarantor

                                       By:  /s/ Daniel J. Krofcheck
                                           -------------------------------------
                                           Name:  Daniel J. Krofcheck
                                           Title: Vice President and Treasurer