Exhibit 4.2

UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION (“DTC”), NEW YORK, NEW YORK, TO THE ISSUER OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR SUCH OTHER NAME AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC (AND ANY PAYMENT IS MADE TO CEDE & CO., OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC) ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

TRANSFERS OF THIS GLOBAL NOTE SHALL BE LIMITED TO TRANSFERS IN WHOLE, BUT NOT IN PART, TO NOMINEES OF DTC OR TO A SUCCESSOR THEREOF OR SUCH SUCCESSOR’S NOMINEE AND TRANSFERS OF PORTIONS OF THIS GLOBAL NOTE SHALL BE LIMITED TO TRANSFERS MADE IN ACCORDANCE WITH THE RESTRICTIONS SET FORTH IN THE INDENTURE REFERRED TO ON THE REVERSE HEREOF.

GOLDEN STAR RESOURCES LTD.

(A corporation continued pursuant to the federal laws of Canada)

5.00% Convertible Senior Unsecured Debenture Due June 1, 2017

Holder: CEDE & Co.

Golden Star Resources Ltd. (the “Company”), for value received, hereby acknowledges itself indebted and promises to pay to the order of the registered holder on June 1, 2017 (the “Maturity Date”), or on such earlier date as the principal amount hereof may become due in accordance with the provisions of the Indenture hereinafter mentioned and defined, the principal sum of

$77,490,000

(Seventy-seven million four hundred ninety thousand dollars)

in lawful money of the United States of America, on presentation and surrender of this Debenture at the principal office of the Indenture Trustee (defined below) in the manner specified in the Indenture, in The City of New York, State of New York, and to pay interest on the principal amount hereof to the Holder of record on the 15^th day of May and November in each year, as the case may be, at the rate of 5.00% per annum from and including the Issue Date or from and including the most recent Interest Payment Date to which interest has been paid or made available for payment on the Debentures then outstanding, whichever is later, to but excluding the next Interest Payment Date, in like money in semi-annual installments in arrears on the first day of June and December in each year (each such date an “Interest Payment Date”), commencing December 1, 2012 with overdue interest, if any, at the same rate after as well as before maturity and after as well as before default in payment of principal or interest. The December 1, 2012 interest payment will represent accrued interest from and including the Issue Date.

As interest on this Debenture becomes due, the Company (subject to early repurchase or conversion pursuant to the terms of the Indenture) shall forward or cause to be forwarded by courier or ordinary post to the registered address of the Holder of the Debenture for the time being, or in the case of joint Holders to the registered address of any one of such joint Holders, or in accordance with the procedures established by the Depository if this is a Book-Entry Only Debenture, electronic funds transfer for such interest, payable to the order of such Holder or Holders.

The forwarding of such electronic funds transfer shall satisfy and discharge the liability for interest on this Debenture to the extent of the sum represented thereby.

This Debenture is one of the 5.00% Convertible Senior Unsecured Debentures due June 1, 2017 (the “Debentures”) in the aggregate principal amount of up to $77,490,000 in lawful money of the United States created and issued under a Trust Indenture (the “Indenture”) dated as of May 31, 2012 made between the Company and The Bank of New York Mellon, as trustee (the “Indenture Trustee”). Reference is hereby made to the Indenture for a description of the rights of the Holders of the Debentures, the Company and the Indenture Trustee and of the terms and conditions upon which the Debentures are issued and held, all to the same effect as if the provisions of the Indenture were herein set forth, to all of which provisions the Holder of this Debenture, by acceptance hereof, agrees. To the extent that the terms and conditions stated in this Debenture conflict with the terms and conditions of the Indenture, the latter shall prevail. All capitalized terms used herein have the meaning ascribed thereto in the Indenture unless otherwise indicated.

The Debentures are issuable as fully registered Debentures in denominations of $1,000 and integral multiples of $1,000. The Debentures of any authorized denomination may be exchanged, as provided in the Indenture, for Debentures in equal aggregate principal amount. The Debentures may only be transferred in denominations of $1,000 and integral multiples of $1,000.

This Debenture and all other Debentures authenticated and issued under the Indenture rank pari passu with one another, in accordance to their tenor without discrimination, preference or priority. The Indenture does not contain any financial covenants or restrictions on the Company’s ability to pay dividends, incur indebtedness or issue or repurchase securities.

Subject to regulatory approval, the Company may, at its option, upon not less than 40 days and not more than 60 days prior notice, repay the principal amount of the outstanding Debentures at Maturity by issuing and delivering, for each $1,000 principal amount of Debentures, that number of fully paid and non-assessable Freely Tradable Common Shares equal to the number obtained by dividing such principal amount of Debentures by 95% of the Current Market Price of the Common Shares on the Maturity Date; provided, however, that no Event of Default shall have occurred and be continuing and the Company is a reporting issuer or equivalent in good standing or equivalent under Applicable Securities Laws in the United States and provinces of Canada in which the Company is a reporting issuer on Maturity. No fractional Common Shares will be delivered to the Holders upon such share redemption, but in lieu thereof, if such a fraction shall become owing, the Company will make an equivalent cash payment. Notwithstanding the foregoing, the aggregate number of Common Shares contemplated to be so issued, combined with any Common Shares issued upon conversion of the Debentures prior to the Maturity Date may not exceed 19.99% of the issued and outstanding Common Shares as of the date of the Indenture, unless the Company obtains (i) additional listing approval for the Common Shares to be so issued, if required, from the NYSE MKT, the TSX and/or any other relevant Recognized Stock Exchange, as applicable, and (ii) consent for the issuance of such Common Shares from the Holders of not less than a majority of the aggregate principal amount of the Debentures Outstanding at the time such consent is solicited. The balance of the amount payable at Maturity that is not repaid by the issuance of Common Shares (the value of such Common Shares being calculated by multiplying the number of Common Shares so issued by 95% of the Current Market Price of the Common Shares on the Maturity Date), shall be paid in cash.

Each $1,000 principal amount of Debentures is convertible at any time and from time to time prior to the close of business on the Business Day immediately preceding Maturity or the Payment Date, at the option of the Holder, into that number of Common Shares obtained by dividing $1,000 by the conversion price of $1.65 per Common Share, subject to adjustment upon the occurrence of certain events specified in the Indenture. No fractional Common Shares will be delivered to the Holders upon conversion, but in lieu thereof, if such a fraction shall become owing, the Company will make an equivalent cash payment. The accrued and unpaid interest on any Debentures so converted shall be paid in cash. Notwithstanding the foregoing, in lieu of delivering Common Shares to the Holder upon conversion of a Debenture, the Company may elect to pay cash to such Holder in an amount based on the daily volume weighted average price of the Common Shares on the NYSE MKT as measured over a period of 10 consecutive Trading Days commencing on the third day following the date of conversion or, if conversion occurs in the 12 Trading Days prior to Maturity, over the 10 Trading Days commencing with the 12^th Trading Day prior to Maturity (the “Cash Conversion Option”). Notwithstanding the foregoing but subject to certain exceptions as set forth in the Indenture, the Company shall not effect any conversion of the Debenture and the Holder shall not have the right to convert the Debenture in excess of that portion of the principal amount thereof that, upon giving effect to

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such conversion, would cause the aggregate number of Common Shares beneficially owned by the Holder and its affiliates to exceed 4.99% of the total outstanding Common Shares following such conversion (or 9.99% of the total outstanding Common Shares following such conversion if the Holder so elects and provides written notice to increase the threshold, which increase shall be effective 61 days after receipt of the notice by the Company). The foregoing limitations shall not apply to the Common Shares issuable on the Maturity of the Debentures, or to the Additional Shares (as defined below).

Upon the giving of notice by the Indenture Trustee of the occurrence of an Event of Default and declaration of acceleration made in accordance with the Indenture, the Debentures will become immediately due and payable.

The Company must commence, within 30 days of the occurrence of a Change of Control, an Offer to Purchase for all Debentures then Outstanding. The Offer to Purchase shall be made at a purchase price equal to 100% of the principal amount thereof, plus accrued and unpaid interest thereon, if any, to but excluding the Payment Date (the “Change of Control Purchase Price”). An Offer to Purchase shall be open for at least 20 Business Days and the Payment Date shall be the Business Day following the expiry of the Offer to Purchase. If 90% or more in aggregate principal amount of Debentures outstanding on the date the Company commences the Offer to Purchase have been tendered for purchase pursuant to the Offer to Purchase, the Company has the right following the expiration of the Offer to Purchase to redeem all, but not less than all, the Debentures remaining outstanding on the expiration of the Offer to Purchase at the Change of Control Purchase Price.

If 10% or more of the fair market value of the consideration for Common Shares in a Change of Control transaction consists of cash, equity securities that are not traded on a Recognized Stock Exchange, or other property that is not traded on a Recognized Stock Exchange (a “Cash Transaction”), Holders may, prior to the effective date of such transaction (the “Effective Date“), elect to convert their Debentures, in which case they shall be entitled to receive, in addition to the number of Common Shares to which they would otherwise have been entitled on conversion, an additional number of Common Shares (“Additional Shares”) determined by reference to the table set out in Schedule “C” to the Indenture based on the Effective Date of the Cash Transaction and the Common Share Price.

Any payments made by or on behalf of the Company under or with respect to the Debentures will be made free and clear of and without withholding or deduction for or on account of any Taxes, unless the Company or any other payor is required to withhold or deduct Taxes by Applicable Law or by the interpretation or administration thereof by the relevant Governmental Authority. If the Company is so required to withhold or deduct any amount for or on account of Taxes from any payment made under or with respect to the Debentures, the Company will make such withholding or deduction and will remit the full amount withheld or deducted to the relevant Governmental Authority as and when required by Applicable Law and the Company will pay such Additional Amounts as may be necessary so that the net amount received by each Holder of Debentures (including Additional Amounts) after such withholding or deduction will not be less than the amount such Holder would have received if such Taxes had not been withheld or deducted; provided, however, that no Additional Amounts will be payable with respect to any payment to an Excluded Holder.

The Indenture contains provisions for the holding of meetings of Holders and rendering certain resolutions passed at such meetings by, or by instruments in writing signed by, the Holders of the majority (or, in certain cases, 75% or the consent of each Holder who is affected thereby) in aggregate principal amount of the Debentures Outstanding binding upon all Holders, subject to the provisions of the Indenture.

This Debenture may only be transferred upon compliance with Applicable Securities Law and the conditions precedent in the Indenture on the register kept at the principal office of the Indenture Trustee and at such other place or places, if any, and/or by such other registrar or registrars, if any, as the Company with the approval of the Indenture Trustee may designate, and may be exchanged at any such place, by the Holder hereof or his executors or administrators or other legal representatives or his or their attorney duly appointed by an instrument in writing in form and execution satisfactory to the Indenture Trustee, and upon compliance with such reasonable requirements as the Indenture Trustee and/or registrar may prescribe, and such transfer shall be duly noted thereon by the Indenture Trustee or other registrar.

This Debenture shall not become obligatory for any purpose until it shall have been authenticated by the Indenture Trustee for the time being under the Indenture.

This Debenture shall be governed by and construed in accordance with the laws of the State of New York.

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The Holder of this Debenture, by receiving and holding same, hereby accepts and agrees to be bound by the terms, and to be entitled to the benefits of this Debenture and of the Indenture and confirms the appointment of the Indenture Trustee, in accordance with and subject to the respective provisions thereof.

[Execution and certification on next page]

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IN WITNESS WHEREOF Golden Star Resources Ltd. has caused this Debenture to be signed by its officers duly authorized to sign.

DATED as of the 31^st day of May, 2012.

TRUSTEE’S CERTIFICATE OF AUTHENTICATION

This Debenture is one of the 5.00% Convertible Senior Unsecured Debentures due June 1, 2017 referred to in the within-mentioned Indenture.

DATE OF AUTHENTICATION: May 31, 2012

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Appendix I

For the purposes of a Global Debenture only:

PRINCIPAL AMOUNT GRID

TO THE GLOBAL DEBENTURE No. 1

5.00% Convertible Senior Unsecured Debentures due June 1, 2017

CUSIP 38119T AE4

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APPENDIX II

FORM OF ASSIGNMENT

FOR VALUE RECEIVED, the undersigned hereby sells, assigns and transfers unto             , whose address and social insurance number or social security number, if applicable, are set forth below, this Debenture (or $             principal amount hereof*) of Golden Star Resources Ltd. (the “Company”) standing in the name(s) of the undersigned in the register maintained by the registrar appointed by the Company with respect to such Debenture and does hereby irrevocably authorize and direct the Indenture Trustee to transfer such Debenture in such register, with full power of substitution in the premises.

Dated:                         

Signature of Holder

Address of Transferee:

(Street Address, City, Province/State and Postal Zip Code)

Social Insurance Number or Social Security Number of Transferee, if applicable

Securities Act Compliance

In connection with any transfer of this Debenture, the undersigned confirms that this Debenture is being transferred

[please check one]:

Unless one of the boxes is checked, the Indenture Trustee will refuse to register any of the securities evidenced by this certificate in the name of any person other than the registered holder thereof, provided that if box (4) or (5) is checked, the Company may require, prior to registering any such transfer of securities, in its sole discretion, such legal opinions, certifications (including an investment letter in the case of box (4)) and other information as the Company may reasonably request to confirm that such transfer is being made pursuant to an exemption from, or in a transaction not subject to, the registration requirements of the Securities Act.

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Signature Guarantee

The signature(s) to this assignment must correspond with the name(s) as written upon the face of this Debenture in every particular without alteration or any change whatsoever. The signature(s) on this form must be guaranteed by one of the following methods:

Canada and the USA: A Medallion Signature Guarantee obtained from a member of an acceptable Medallion Signature Guarantee Program (STAMP, SEMP, MSP). Many commercial banks, savings banks, credit unions, and all broker dealers participate in a Medallion Signature Guarantee Program. The Guarantor must affix a stamp bearing the actual words “Medallion Guaranteed”.

Canada: A Signature Guarantee obtained from a major Canadian Schedule I chartered bank. The Guarantor must affix a stamp bearing the actual words “Signature Guaranteed”. Signature Guarantees are not accepted from Treasury Branches, Credit Unions or Caisses Populaires unless they are members of a Medallion Signature Guarantee Program.

Outside North America: For holders located outside North America, present the certificate(s) and/or document(s) that require a guarantee to a local financial institution that has a corresponding Canadian or American affiliate which is a member of an acceptable Medallion Signature Guarantee Program. The corresponding affiliate will arrange for the signature to be over-guaranteed.

The registered Holder of this Debenture is responsible for the payment of any documentary, stamp or other transfer taxes that may be payable in respect of the transfer of this Debenture.

Signature of Guarantor:

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