<PAGE>

                          [LETTER HEAD OF RIO TINTO]



PRIVATE AND CONFIDENTIAL
------------------------

Guyanor Ressources S.A.
Lotissement Calimbe II
Route du Tigre
97337 Cayenne
French Guiana

Attention: President

And

Societe de Travaux Publics et
de Mines Auriferes en Guyane SARL
Lotissement Calimbe II
Route du Tigre
97337 Cayenne
French Guiana

Attention: President


29 December 2000
Ref: 201036b.KHH


Dear Sirs:

           Paul-Isnard Option and Joint Venture - Heads of Agreement

We refer to our recent discussions concerning Guyanor Resources S.A. ("Guyanor
Ressources") and its wholly owned subsidiary, Societe de Travaux Publics et de
Mines Auriferes en Guyane SARL ("SOTRAPMAG"), pursuant to which you have agreed
to grant Rio Tinto Mining and Exploration Limited ("Rio Tinto") an option to
acquire an interest in and enter into a joint venture for the purpose of
exploration and later possible evaluation, development and mining of that
certain area in French Guiana known as the Paul-Isnard Property (the
"Property").  For ease of reference, Guyanor Ressources and SOTRAPMAG are
collectively referred to herein as "Guyanor".

Certain of the mineral rights comprising the Property are directly held by
Guyanor Ressources and others are held by SOTRAPMAG. Guyanor Ressources hereby
undertakes to retain and exercise control of SOTRAPMAG to the extent necessary
to fulfil the obligations of Guyanor Ressources and SOTRAPMAG hereunder to Rio
Tinto.

                                                                    Page 1 of 17
<PAGE>

Rio Tinto understands that, on June 4, 1996, SOTRAPMAG entered into an Option
and Joint Venture Agreement (the "La Source JVA") with ASARCO Incorporated
("ASARCO") and La Source Developpement SAS ("La Source") with respect to the
Property.  ASARCO's rights and obligations under the La Source JVA were
terminated on May 28 1998 pursuant to a letter of termination.  La Source's only
remaining right under the La Source JVA is the 2.5% Net Profit Interest referred
to in Clause 9.1(c) hereunder.

It is the intent of the parties that these Heads of Agreement will be replaced
by a more detailed Option and Joint Venture Agreement (the "Joint Venture
Agreement") to be executed by the parties within twelve (12) months of the date
of this letter. The Joint Venture Agreement will contain super majority
provisions to protect Guyanor's minority rights in the Joint Venture as set out
in Clause 4.3 below. Until superseded by the more detailed Joint Venture
Agreement, these Heads of Agreement shall govern the rights and obligations of
the parties with respect to the subject matter hereof.

1.     Scope of the Option and Possible Joint Venture

1.1    From the date hereof until the third anniversary of these Heads of
       Agreement, Guyanor grants to Rio Tinto an exclusive option to establish a
       joint venture (the "Joint Venture"), with respect to Guyanor's right,
       title and interest in the Property for the purpose of exploration and
       later possible evaluation, development and mining of minerals within the
       Property. For the purposes of these Heads of Agreement and the Joint
       Venture Agreement, the "Property" shall consist of the mineral rights and
       concessions or parts thereof listed in Schedule 1.1-A and the location of
       which are approximately shown on the map in Schedule 1.1-B of these Heads
       of Agreement.

1.2    While these Heads of Agreement and the Joint Venture Agreement remain
       current, the parties agree to make available, for the benefit of their
       joint undertaking described herein and the Joint Venture, any
       prospecting, exploration or mining rights held or applied for by them or
       their affiliates (including such rights as are held at the date of this
       letter) within the outermost boundaries of the Property.

1.3    Areas of Interest

       1.3.1   While these Heads of Agreement and the Joint Venture Agreement
               remain current, the parties agree that if either of them acquires
               an interest in the two concessions known as the Tanon
               concessions - those being concessions nos. 01/32 and 01/33 - or
               to any other from of mineral right within the area of the Tanon
               concessions, those acquired rights shall be included under the
               terms of this agreement.

       1.3.2   While these Heads of Agreement and the Joint Venture Agreement
               remain current Guyanor hereby grants Rio Tinto a right of first
               offer in respect of that part of Permis A no 75/99 lying outside
               the Property. That right of first offer will be as per the
               definition of Right of First Offer in Clause 11.1 hereunder
               except that where that Clause 11.1 reads "Property" it shall
               refer to the area referred to in this Clause 1.3.3 for the
               purpose of the first right of offer referred to in this Clause
               1.3.3.

1.4    For avoidance of doubt, nothing contained in these Heads of Agreement or
       the Joint Venture Agreement shall restrict the ability of the parties to
       engage in and receive the full

                                                                    Page 2 of 17
<PAGE>

       benefit of their business activities outside the Property except as
       provided for in Clause 1.3.

2.     Rio Tinto Earn-In rights

2.1    Rio Tinto's undivided beneficial interest in the Property and its
       participating interest in the Joint Venture (collectively a
       "Participating Interest") shall be zero percent until it has fulfilled
       the requirements set out herein to acquire its 40% Participating Interest
       and until that time Guyanor's Participating Interest shall be 100%.

2.2    Rio Tinto shall have the right, but not the obligation, to acquire a 40%
       Participating Interest by sole funding work expenditures within the
       Property up to a total of US$2,250,000 before the third anniversary of
       this Heads of Agreement.

2.3    Upon completion of US$2,250,000 in work expenditures funded by Rio Tinto
       within the Property before the third anniversary hereof, Rio Tinto shall
       have earned a 40% Participating Interest free and clear of all
       encumbrances other than proportionate responsibility for the 2.5% Net
       Profits Interest that may become payable to La Source. Rio Tinto may then
       elect at its sole option to earn a further 30% Participating Interest in
       the Joint Venture by sole funding a further US$6,750,000 in work
       expenditures by the fifth anniversary of these Heads of Agreement.

2.4    For the avoidance of doubt, during any period during which Rio Tinto
       shall be earning in a Participating Interest in the Joint Venture, be it
       40% or the additional 30%, Guyanor shall be carried by Rio Tinto and
       therefore shall not be required to contribute to any program and budget
       of the Joint Venture nor shall Guyanor's Participating Interest be
       diluted during such period. If Rio Tinto has elected to earn the
       additional 30%, its interest shall only increase from 40% if it completes
       the additional US$6,750,000 of work expenditures required to earn the
       additional 30%.

2.5    Promptly after having earned either a 40% Participating Interest or a 70%
       Participating Interest in the Joint Venture, Rio Tinto shall notify
       Guyanor in writing of the fact that it now holds a 40% or a 70%
       Participating Interest.

2.6    Upon receiving notice in writing from Rio Tinto that Rio Tinto has earned
       a 70% Participating Interest, Guyanor shall elect either:

       (a)  to fund its 30% Participating Interest and consequently thereafter
            the parties shall contribute to the funding of Joint Venture
            operations in proportion to their respective Participating Interests
            or otherwise have their Participating Interests adjusted as provided
            for in Clause 6 below, or

       (b)  to request that Rio Tinto continue sole funding 100% of the costs
            and expenses of the Joint Venture until the commencement of
            commercial production of the first mine within the Property. If
            Guyanor makes this election, Rio Tinto's Participating Interest
            shall be increased by 10% from 70% to 80% by sole funding all of the
            Joint Venture's work programs and budgets until the commencement of
            commercial production of a mine within the Property. Rio Tinto's
            additional 10% Participating Interest in the Joint Venture shall
            vest upon commencement of commercial production of a mine within the
            Property.

                                                                    Page 3 of 17
<PAGE>

            For purposes of these Heads of Agreement, "commencement of
            commercial production" means the last day of the first period of 90
            consecutive days (excluding days, if any, where mining operations
            are legally required to be suspended) during which mining operations
            have been conducted pursuant to the feasibility study upon which the
            decision to develop the mine was based at 70% of the planned
            operating capacity of the processing facilities.

            Upon commencement of commercial production within the Property, 20%
            of all the expenditures incurred by Rio Tinto between the date of
            Guyanor's election hereunder and the commencement of commercial
            production within the Property shall be payable on a priority basis
            to Rio Tinto out of 80% of all the amounts distributable by the
            Joint Venture to Guyanor and the balance, ie 20%, shall be
            immediately distributed to Guyanor. The unpaid balance of all
            principal amounts repayable to Rio Tinto under this paragraph shall
            bear interest from the date the expenditures were made at a simple
            rate per annum (i.e., shall not be compounded) equal to 3% plus 12
            month LIBOR as in effect from time to time.

2.7    Upon receiving notice in writing from Rio Tinto that Rio Tinto has earned
       a 40% Participating Interest and does not elect to earn the additional
       30% Participating Interest, Guyanor shall thereafter fund its 60%
       Participating Interest and Rio Tinto shall fund its 40% Participating
       Interest and consequently thereafter the parties shall contribute to the
       funding of the Joint Venture operations in proportion to their respective
       Participating Interests or otherwise have them adjusted as provided in
       Clause 6 below.

2.8.   If Guyanor does not make the election referred to in paragraph 2.6(b),
       Guyanor shall thereafter fund its 30% Participating Interest and Rio
       Tinto shall fund its 70% Participating Interest and consequently
       thereafter the parties shall contribute to the funding of the Joint
       Venture operations in proportion to their respective Participating
       Interests or otherwise have them adjusted as provided in Clause 6 below.

2.9    In order to maintain its option under these Heads of Agreement, Rio Tinto
       shall fulfil the following conditions:

       (a)  in the period being one year from the date on which these Heads of
            Agreement are signed, Rio Tinto shall sole fund work expenditures on
            the Property of at least US$750,000 (the "Minimum Expenditure").
            This Minimum Expenditure shall be funded by means of Guyanor as
            Operator using US$750,000 of the proceeds of a US$1,000,000 private
            placement taken by Rio Tinto (or an affiliate) in shares of Golden
            Star Resources Ltd. This US$750,000 shall be in addition to the
            US$2,250,000 of work expenditures required to be spent by Rio Tinto
            before the third anniversary to earn a 40% Participating Interest.

       (b)  in order for Rio Tinto to maintain its option to earn a 40% interest
            in the Property, for each calendar year commencing 1 January 2002
            and while these Heads of Agreement or the Joint Venture Agreement,
            as the case may be, remains current, Rio Tinto must incur work
            expenditures on the Property of at least US$500,000.

            Except for the Minimum Expenditure the making of any work
            expenditure under these Heads of Agreement or the Joint Venture, as
            the case may be up to the time Rio Tinto has earned its 40%
            Participating Interest, shall be in the sole

                                                                    Page 4 of 17
<PAGE>

            discretion of Rio Tinto and the sole remedy of Guyanor in the event
            that Rio Tinto does not meet any of its work expenditure
            requirements hereunder, up to the time Rio Tinto has earned its 40%
            Participating Interest excepting force majeure, shall be termination
            of this Agreement. If any of the expenditure conditions herein up to
            the time Rio Tinto has earned its 40% Participating Interest are not
            met, except for reason of force majeure, Rio Tinto shall be deemed
            to have withdrawn from this Agreement and the parties shall have no
            further obligation to each other except as may be otherwise provided
            in clause 3 of this Heads of Agreement.

       (c)  after Rio Tinto has earned its 40% interest in the Property, in
            order for it to maintain its option to earn a further 30% interest
            in the Property, for each 12 month period between anniversaries of
            Rio Tinto vesting at 40%, Rio Tinto must incur work expenditures on
            the Property of at least US$500,000 or pay in cash to Guyanor within
            30 days after the relevant anniversary the shortfall between actual
            lesser expenditures and US$500,000- such shortfall expenditure shall
            be deemed to be work expenditure for purposes of these Heads of
            Agreement. If Rio Tinto has not incurred this level of work
            expenditure in any given 12 month period after vesting at 40%,
            Guyanor shall have the right, but not the obligation, to become
            manager and operator of the Joint Venture and the provisions in
            Clause 6 shall apply thereafter.

       If Rio Tinto is prevented by force majeure from incurring work
       expenditures necessary to maintain or exercise its option then it shall
       have additional time to incur such work expenditures as is equal to the
       duration of the force majeure condition.

2.10   Guyanor undertakes to do all acts and to execute all documents as shall
       be necessary to enable Rio Tinto to earn, hold and protect its right to
       acquire the Participating Interests herein provided for.

2.11   Guyanor further undertakes that from the date hereof and for as long as
       Rio Tinto is the manager and/or operator of the Joint Venture, it will
       not make any representation, statement or commitment to any governmental
       or state authority relating to the level of work expenditures to be made
       on any properties within the Area of Interest without first obtaining Rio
       Tinto's written consent.

3.     Withdrawal

3.1    Any party may withdraw from these Heads of Agreement or the Joint Venture
       Agreement after Rio Tinto has ceased sole funding by giving not less than
       60 days prior written notice to the other party of its intention to do
       so.

3.2    Upon withdrawal the withdrawing party shall at the request of the other
       party transfer to the non-withdrawing party all its right, title and
       interest to any prospecting, exploration, development, or other form of
       mineral right that are the subject of the Joint Venture Agreement and
       until such time as such transfer is made the withdrawing party shall hold
       such rights for and on behalf of the non-withdrawing party. The
       withdrawing party shall continue to be liable, to the extent of its
       Participating Interest prior to its withdrawal, for any liabilities or
       obligations that arose out of operations or activities prior to the date
       of its withdrawal, including, without limitation, in the case of Rio
       Tinto any amount due under section 2.5 hereof.

                                                                    Page 5 of 17
<PAGE>

3.3    If Rio Tinto withdraws from these Heads of Agreement, it shall:

       (a)  meet the percentage which corresponds to its percentage
            Participating Interest (which for the purposes of this clause 3.3(a)
            shall be deemed to be 100% during the period prior to Rio Tinto
            earning its 40% Participating Interest) of the costs of any
            environmental or rehabilitation liabilities which arise under French
            law as a consequence of the activities or operations undertaken on
            the Property according to work programmes specified by the
            Management Committee after the date of these Heads of Agreement and
            prior to its withdrawal, provided that such liabilities arise either
            from Rio Tinto's conduct as Operator or from the prudent conduct of
            Guyanor in accordance with Clause 5.6 hereunder and are not the
            result of any gross negligent or wilful reckless act or omission by
            Guyanor; and

       (b)  meet the percentage which corresponds to its percentage
            Participating Interest (which for the purposes of this clause 3.3(b)
            shall be deemed to be 100% during the period prior to Rio Tinto
            earning its 40% Participating Interest) of any costs which might be
            incurred by Guyanor under French labour law with respect to work
            force reductions that are specifically caused by Rio Tinto's
            withdrawal and which relate solely and exclusively to the period
            after the date hereof and have been approved by the Management
            Committee (including the layoff of any employee employed by Guyanor
            before and at the date hereof), and the direct field demobilisation
            costs specifically arising from Rio Tinto's decision to withdraw
            provided such costs were incurred exclusively as a result of Rio
            Tinto's entry into this agreement and any amount due under section
            2.5(a) above. For greater clarity, if the total of such costs as are
            referred to in this paragraph that are incurred by Guyanor as a
            result of Rio Tinto's decision to withdraw comprise amounts in
            respect of periods before and after the date hereof, only that part
            relating to after the date hereof shall be borne by Rio Tinto.

3.4    Subject to the provisions of Clause 3.2 above, where a party has
       withdrawn from the Joint Venture, the other party shall do all things and
       execute all documents to ensure that the withdrawing party's name is
       removed from any register pertaining the exploration and/or mining rights
       held by the Joint Venture.

4.     Work Programmes and Management Committee

4.1    No later than 30 days after the date hereof, the parties shall establish
       a Management Committee to determine the annual work programmes and
       budgets and to generally oversee exploration, evaluation and development
       activities within the Property. Each party shall be entitled to appoint
       two members to the Management Committee. A quorum shall be deemed formed
       if there is at least one member present from each party. In lieu of
       physical meetings, the Management Committee may hold telephone
       conferences, so long as decisions are immediately confirmed in writing
       and signed by the parties.

4.2    (i)   During such period as Rio Tinto is sole funding work expenditures,
             it shall determine all decisions of the Management Committee. (For
             avoidance of doubt this provision shall also apply during the
             period that the Minimum Expenditure is being made).

                                                                    Page 6 of 17
<PAGE>

       (ii)  Thereafter, subject to the terms of paragraph (iii) of this clause,
             each party shall have a vote on the Management Committee in
             proportion to its Participating Interest, and decisions of the
             Management Committee shall, subject to Clause 4.3 hereunder, be
             decided by a simple majority of votes.

       (iii) If Rio Tinto holds a majority Participating Interest greater than
             51% but has ceased to be manager and operator - other than in the
             case it has appointed a third party or affiliate as manager and
             operator - the decisions of the Management Committee shall be
             determined by Guyanor as if it held a 51% Participating Interest
             until such time as Guyanor has earned a 51% or greater
             Participating Interest, in which case the terms of paragraph (ii)
             of this clause shall prevail.

       Throughout the term of this Heads of Agreement and the Joint Venture
       Agreement, but only after Rio Tinto has earned its 40% Participating
       Interest, the Management Committee may determine to surrender mineral
       rights that are subject to this agreement, but the Operator shall not
       proceed with such surrender before giving the other party the opportunity
       to adopt such mineral rights in its name - any such transfer being free
       of consideration (but the transferee shall bear the costs of such
       transfer).

The Management Committee shall convene at least once every three months in a
location to be agreed between the parties, failing which, it shall meet in
Cayenne, French Guiana.

4.3    The following matters shall require votes representing at least 90% of
       the Participating Interests in the Joint Venture:

       (a)  surrender or abandonment of any part of the Property;

       (b)  re-negotiation of the terms under which the Property is held;

       (c)  the sale, encumbrance or disposal of Assets of the joint venture
            other than in the ordinary course of business or as expressly
            provided for in these Heads of the Joint Venture Agreement.

       (d)  Debt financing arrangements for the Joint Venture (as opposed to the
            participants) with affiliates of the parties;

       (e)  Capital expansion programs within five years following commencement
            of commercial production;

       (f)  Forward selling and hedging programs;

       (g)  Declarations of force majeure;

       (h)  Any changes in policies on accounting (including any changes in
            administrative charges) and on dividends and distribution of profit
            of the Joint Venture.

4.4    The full Joint Venture Agreement shall contain a mutually agreed policies
       on accounting and on dividends and distribution of profit.

4.5    If the party that is Operator under these Heads of Agreement or under the
       Joint Venture Agreement or the party that controls the decisions of the
       Management Committee

                                                                    Page 7 of 17
<PAGE>

       engages an affiliate to provide goods, services or financing to the joint
       venture, it shall do so on terms no less favourable than those available
       from independent third parties on arm's length terms.

5.     Operator

5.1    Guyanor shall be appointed the first Operator of operations to be
       undertaken under these Heads of Agreement and the Joint Venture
       Agreement.

5.2    During the period of this Agreement the Operator shall provide the other
       party monthly reports of exploration progress and expenditure in such
       reasonable detail and according to such reasonable schedule as the other
       party may request.

5.3    The Operator undertakes to promptly inform the non-operator of any
       occurrence or non occurrence that may affect the validity of good
       standing of the Property or any part of it.

5.4    The Operator undertakes to promptly inform the non-operator of any
       adverse environmental, health, safety or community relations event or
       issue arising out of or in relation to work performed under this Heads of
       Agreement or the Joint Venture Agreement.

5.5    During the period in which Guyanor is Operator, unless provided in an
       approved programme and budget, it shall seek Rio Tinto's consent to the
       making of any commitment of duration longer than the then current work
       programme and budget or calendar year whichever is the shorter.

5.6    Following completion of the Minimum Expenditure in accordance with
       paragraph 2.7(a), or in the event of the insolvency of Guyanor, or
       default by it in performance of its obligations hereunder, Rio Tinto (or
       its nominated affiliate) may elect, and shall have the right upon making
       such election, to be appointed the Operator of operations to replace
       Guyanor. Rio Tinto shall meet any reasonable employee cost that may be
       incurred by Guyanor in respect of liabilities created after the date
       hereto under French law with respect to work force reductions that are
       specifically caused by Rio Tinto replacing Guyanor as Operator.

5.7    Any party appointed Operator under these Heads of Agreement or the Joint
       Venture Agreement shall manage, direct and conduct operations within the
       Property in accordance with all Management Committee decisions.

5.8    The Operator shall conduct all operations in an efficient and workmanlike
       manner, in accordance with the highest standards of safety and sound
       mining industry practice, and in compliance with all applicable laws and
       the provisions of any exploration or mining titles held for the benefit
       of the Joint Venture and shall make best efforts to preserve the title to
       the Property in good standing, free from liens or encumbrances, and pay
       all taxes, filing fees, third-party costs and employee wages as and when
       due. In no event shall standards of environmental, health, safety and
       community relations care and management be less than those required by
       Rio Tinto corporate policy.

5.9    Either party may call a meeting of the Management Committee upon giving
       reasonable written notice to the other. A notice of five working days in
       French Guiana shall be deemed to constitute reasonable notice hereunder.

                                                                    Page 8 of 17
<PAGE>

5.10   Where Guyanor is Operator, Rio Tinto shall have the right to second or
       contract a geologist to Guyanor, to evaluate and assist with the
       implementation of the approved programmes. The costs of that secondment
       shall be expenditures hereunder. Likewise, where Rio Tinto is the
       Operator, Guyanor shall have the right to second or contract a geologist
       to Rio Tinto, to evaluate and assist with the implementation of the
       approved programmes. The costs of that secondment shall be part of the
       work program and budget of the Joint Venture.

5.11   During the period in which Guyanor is Operator, subject to the approval
       of the Management Committee, Rio Tinto may charge to its earn-in under
       the option the reasonable costs of its technical and other support given
       to the programme.

5.12   The Operator shall undertake activities in accordance with approved
       programmes and budgets. To the extent that the costs incurred for such
       activities exceed an approved budget by up to 10%, such costs shall be
       deemed approved; to the extent that costs incurred exceed 10% over
       budget, the excess over 10% shall be for the sole account of the Operator
       unless the Management Committee has agreed a revision to the budget.

5.13   The Operator shall have the right to be reimbursed for the costs of the
       work it performs including administrative and office overhead expenses
       directly resulting from work carried out hereunder. When Rio Tinto is
       sole-funding and Guyanor is the Operator, these expenses shall be charged
       to Rio Tinto's earn-in. That reimbursement shall be no greater than what
       is necessary to recoup, on a cost-accounting basis, the costs it incurs
       in performing its obligations hereunder. Any transactions or agreements
       entered into by the Operator with any of its affiliate or associate
       companies shall be on an arms length basis.

5.14   The Operator shall make cash calls on a calendar monthly basis. Such cash
       calls shall be sufficient to fund the next month's exploration
       expenditures that shall have been forecast by the Operator at the
       beginning of the calendar year in a monthly budget phasing. The cash call
       may exceed the next month's exploration expenditure to the extent
       necessary to maintain no less than two weeks' and no more than four
       weeks' excess funding balance in the bank account designated for funding
       work expenditures hereunder. Unless otherwise provided elsewhere in these
       Heads of Agreement, upon termination of these joint venture arrangements
       the unspent balance of joint venture funds shall be appropriately
       reimbursed to the parties. Monies received by the Operator will be held
       in trust for the Joint Venture.

       The Operator agrees to meet all reasonable requests from the Management
       Committee to perform its obligations to such standards as are required by
       this Clause 5. The non operator shall at all reasonable times and at its
       expense have access to Operator's operations hereunder upon reasonable
       notice and the right to audit at its cost the Operator's internal
       procedures and both parties accept to make all reasonable changes to
       these as may be requested by the other party hereunder.

                                                                    Page 9 of 17
<PAGE>

6.     Dilution, default and elimination of minority interests

6.1    If any party elects to not contribute to the funding of Joint Venture
       operations in proportion to its Participating Interest, then its
       Participating Interest shall be diluted at a standard straight-line rate.

6.2    If any party fails, after having made an election to do so, to contribute
       to the funding of Joint Venture operations in proportion to its
       Participating Interest, then its Participating Interest shall be diluted
       in an accelerated manner at 25% above the standard rate.

6.3    If any party is diluted below a 10% Participating Interest, it shall be
       deemed to have withdrawn from the Joint Venture and shall relinquish its
       Participating Interest. In lieu of its former Participating Interest, the
       withdrawing party shall be entitled to receive a 2.5% Net Profit Interest
       from the continuing party's operations in the Property.

7.     Marketing

7.1    If diamonds or other non metallic minerals (and for greater certainty
       excluding gold which is a metallic mineral) are produced under the Joint
       Venture, Guyanor appoints Rio Tinto (or Rio Tinto's nominated affiliate)
       as its sole and exclusive agent to market and sell all diamonds and non
       metallic minerals produced by the Joint Venture from the Property on its
       behalf as long as Rio Tinto has an interest greater than 50%. If at any
       time operations in the Property are being conducted by a joint venture
       company, the parties appoint Rio Tinto (or its nominated affiliate) as
       the sole and exclusive agent to market and sell such diamonds and non
       metallic minerals as the joint venture company shall be entitled to.

7.2    Upon Rio Tinto's request, Guyanor and Rio Tinto shall negotiate and
       execute one or more Marketing Agreements to give effect to the above
       appointment in clause 7.1. The Marketing Agreement(s) shall provide that
       Rio Tinto or the relevant affiliate of Rio Tinto (as the case may be)
       shall be entitled, as agent, to deduct expenses incurred in each sale and
       to charge a marketing and sales commission equal to 3% of the gross sale
       proceeds accruing to the parties or the joint venture company (as the
       case may be).

7.3    The appointment of Rio Tinto (and its affiliates) as agent shall be
       subject to the applicable laws or orders of government agencies in force
       from time to time in French Guiana in relation to the marketing of
       minerals extracted or produced in French Guiana. The parties agree at Rio
       Tinto's cost to do all acts and execute all documents as are reasonably
       necessary to give effect to Rio Tinto's appointment, or the appointment
       of an affiliate of Rio Tinto, as agent under this paragraph 7.

8.     Title to exploration and mining rights

8.1    While these Heads of Agreement and the Joint Venture Agreement remain
       current, the title to any prospecting, exploration or mining rights
       relating to the Area of Interest held by either party shall be held for
       the benefit of the other party and the Joint Venture to the extent
       provided for in this Heads of Agreement.

8.2    Upon Rio Tinto completing US$2,250,000 in work expenditures, it shall be
       entitled to request that all prospecting, exploration or mining rights
       held by Guyanor for the benefit of the Joint Venture be transferred into
       the name of a newly formed corporate entity

                                                                   Page 10 of 17
<PAGE>

       "Newco" in which the parties will hold shares in accordance with their
       Participating Interests. Guyanor shall do all acts and execute all
       documents to give effect to that transfer. The costs of such transfer
       shall be borne by the parties in proportion to their percentage interest
       in the Joint Venture at the time of the transfer unless the transfer is
       financially adverse to Guyanor in which case the costs shall be borne by
       Rio Tinto. Newco shall hold those rights for the benefit of the parties
       in accordance with their rights under the Joint Venture Agreement. If by
       reason of any legal restriction in French Guiana, Newco is not permitted
       to hold such rights, then Guyanor shall hold those rights for the benefit
       of the parties jointly, until such time as they can be transferred to
       Newco to be so held. As an alternative to the foregoing, if it is more
       effective for both Rio Tinto and Guyanor, for tax or other reasons to
       hold the rights referred to in this paragraph in either or both of the
       entities comprising Guyanor as defined herein, the ownership, operation
       and management of such entity or entities shall be amended to reflect the
       terms of these Heads of Agreement and the Joint Venture Agreement.

8.3    In the event that Rio Tinto withdraws from these Heads of Agreement or
       the Joint Venture Agreement, or otherwise fails to earn a Participating
       Interest, it shall immediately, and at its sole cost, provide transfers
       to Guyanor free of consideration of any right, title and interest it
       holds in any of the shares of Newco.

9.     Representations and Warranties

9.1    Guyanor Resources and SOTRAPMAG represent and warrant to Rio Tinto that:

       (a)  each of them is a company duly incorporated and in good standing in
            its place of incorporation and that it is qualified to do business
            in those jurisdictions where necessary in order to carry out this
            Agreement;

       (b)  neither of them will breach any other agreement or arrangement by
            entering into or performing this Agreement;

       (c)  the only surviving third party right under the La Source JVA is the
            right of La Source to receive a 2.5% Net Profit Interest from future
            production from the Project Area (as defined in the La Source's
            JVA);

       (d)  the applicable governmental agency granted the Property to Guyanor
            and, to the best of its knowledge after due enquiry, it holds the
            properties free and clear of all encumbrances, liens, options or
            other third party rights;

       (e)  all fees in respect of any Property have been paid and other filings
            required to maintain the Property in good standing have been
            properly and timely recorded or filed with every applicable
            governmental agency except for those fees and filings the non-
            payment or absence of filing of which would not have a material
            adverse effect on the Property;

       (f)  neither of them has received any claim or notice of violation
            alleging any violation of any law, rule, regulation or permit,
            including without limitation, any environmental law, rule,
            regulation or permit, in connection with the Property from any
            governmental or regulatory authority, and to the best of its
            knowledge, there are no pending or threatened actions, suits, claims
            or proceedings that may affect the Property;

                                                                   Page 11 of 17
<PAGE>

       (g)  each of them has delivered or made available to Rio Tinto all
            material information, whether technical or of other nature,
            concerning the Property in its possession or control including, for
            the avoidance of doubt, details of all contracts or permissions to
            work, whether formal or informal, given to small miners in respect
            of the Property;

       (h)  to the best of their knowledge, all activities on or in relation to
            the Property carried out by either of them and the parties to the La
            Source JVA up to the date on which this Agreement has been signed
            have been carried out in accordance with all applicable laws,
            regulations and permits, including without limitation those for the
            protection of the environment and no conditions exist which could
            give rise to the making of a remediation order or similar order in
            respect of the Property; and

       (i)  more generally, to the best of their knowledge, all activities
            carried out by either of them and the parties to the LA Source JVA
            within the Area of Interest up to the date which this Agreement has
            been signed have been carried out in accordance with all applicable
            laws, regulations and permits and none has been subject to any legal
            or regulatory action against it regarding such activities.

9.2    The representations and warranties shall not be limited by any knowledge
       held by Rio Tinto.

9.3    The representations and warranties given under paragraph 9.1 shall
       continue in force and shall be repeated during the term of these Heads of
       Agreement.

9.4    Rio Tinto's commitment to the Minimum Expenditure shall be contingent
       upon Guyanor's representations and warranties being materially correct.

9.5    Each of Guyanor and Rio Tinto hereby covenant and agree that:

       (a)  it will give prompt notice to the other of any notice of default,
            lawsuit, proceeding, action or damage of which it becomes aware and
            which might affect the Property; and

       (b)  it will not sell or otherwise transfer the Property or put any
            encumbrance or lien on the Property.

10. Governing Law

This Heads of Agreement shall be governed by and interpreted in accordance with
the laws of British Columbia, Canada, except with respect to real property and
mining law, in which case the laws of French Guiana shall apply.

11.    Miscellaneous

The Joint Venture Agreement shall also contain provisions that give effect to
the following:

11.1   Each party shall be free from time to time to transfer its Participating
       Interest, or its interest in these Heads of Agreement or the Joint
       Venture Agreement, to an associated

                                                                   Page 12 of 17
<PAGE>

       company or affiliate. Further, a party may transfer its Participating
       Interest to a third party, but subject to a "Right of First Offer" to the
       other party to acquire the Participating Interest on the same terms and
       conditions.

       Under the Right of First Offer if a party, the "Offeror":

       (i)  plans to offer to any third party, or receives from any third party
            an unsolicited offer that it intends to accept containing the
            specific terms of a possible participation of any type, form or
            extent in the Property ("Participation"), then it shall provide to
            the other party the proposed terms. The other party shall have 45
            days from the receipt of such information to notify the Offeror that
            it agrees to match the applicable offer on the same terms or on
            terms no less favourable to the Offeror. If the other party fails to
            provide such notice within the 45 days, the Offeror will have 180
            days from the expiration of the 45 days to sign binding agreements
            for Participation with any third party on the same terms or on terms
            no less favourable to the Offeror. If not signed within this time,
            the rights of first offer herein shall revive; or

       (ii) plans to solicit from any third party offers for the specific terms
            of a Participation (without having complied with the provisions of
            subsection (i) above), it shall first request in writing that the
            other party submits an offer for Participation. The other party
            shall have 45 days from receipt of the written request to submit an
            offer for Participation to the Offeror. If the other party does not
            provide such offer or if the Offeror does not accept the offer
            proposed by the other party, it shall be free for the next 180 days
            to solicit offers and to accept offers for Participation on terms no
            less favourable to it than those offered by the other party. If the
            Offeror accepts such offer from a third party, binding documents for
            Participation must be signed within this 180 days or the rights of
            first offer herein shall revive.

11.2   The Joint Venture Agreement shall contain a mutually agreed Accounting
       Procedure.

11.3   The parties agree to be bound by obligations of confidentiality in
       respect of their operations in the Property and any data produced
       therefrom. There shall be exclusions from these obligations that reflect
       standard industry practice. In addition, Guyanor shall have the right to
       make public disclosures of information pertaining to operations under
       these Heads of Agreement in the Property and Area of Interest, provided
       it first obtains Rio Tinto's written consent to the timing and content of
       such disclosure (such consent not to be unreasonably withheld). The
       refusal by Rio Tinto to let Guyanor make a press release it is required
       by law or the rules and regulations of a stock exchange to make shall be
       deemed unreasonable.

11.4   Each party shall give appropriate representations and warranties as to
       its capacity to enter into the Joint Venture Agreement. In addition,
       Guyanor shall give appropriate representations and warranties as to its
       title to any prospecting, exploration or mineral rights held by it and
       the terms and good standing of those rights.

11.5   The parties shall make available to each other all the data and
       information in their possession relating to the Area of Interest.

11.6   The right of La Source to receive a 2.5% Net Profit Interest from future
       production from the Project Area (as defined in the La Source's JVA)
       shall be fulfilled by the Joint Venture and, for avoidance of doubt, not
       by any one or more individual parties to it.

                                                                   Page 13 of 17
<PAGE>

11.7   Rio Tinto's rights and obligations hereunder shall be subject to the
       closing of the Share Subscription Agreement (the "Share Subscription
       Agreement") of the date hereof under which an affiliate of Rio Tinto
       agrees to take a US$1,000,000 private placement in the stock of Golden
       Star Resources, US$750,000 of the proceeds of which shall be advanced by
       Golden Star Resources to Guyanor for the purpose of funding the Minimum
       Expenditure referred to herein.

11.8   A condition precedent to this Heads of Agreement becoming effective is
       the Board of Directors of Golden Star Resources giving its express
       approval to the transactions contemplated by the Share Subscription
       Agreement, including the terms of this Heads of Agreement; unless
       otherwise agreed by the parties hereto, if this approval has not been
       given by close of business 8 January 2001 this Agreement shall
       automatically terminate and shall be without any force or effect and
       neither party shall have any right or obligation arising from this
       Agreement.

To indicate your acceptance of the terms of these Heads of Agreement please sign
below.

Yours faithfully

for RIO TINTO MINING AND EXPLORATION LIMITED
6 St James's Square, London, SW1Y 4LD, United Kingdom

Signature: /s/ K. H. Haddow

Name: K. H. Haddow

Title: General Manager Commercial


for Guyanor Resources S.A.

Signature: /s/ Carlos H. Bertoni

Name: Carlos H. Bertoni

Title: President

for SOCIETE DE TRAVAUX PUBLICS ET DE MINES AURIFERES EN GUYANE SARL

Signature: /s/ Carlos H. Bertoni

Name: Carlos H. Bertoni

Title: Managing director

                                                                   Page 14 of 17
<PAGE>

SCHEDULE 1.1-A

       List of Mineral Rights and parts thereof comprising the "PROPERTY"


GUYANOR title :

That part of Permis A No 75/99 previously covered by the Concession miniere
06/95 and to the west of a north-south line drawn parallel to the western
boundary of Concession miniere 06/95 along 176000E.

SOTRAPMAG titles :

Concessions minieres nos. C01/48, C02/48, C03/48, C01/19, C01/46, C02/46, C03/46
and C02/24.

Authorisations given for alluvial mining titles by third parties (primary
mineralization rights held by Guyanor and SOTRAPMAG):

Compagnie Miniere Esperance SA- 3 ((Autorisation d'Exploitation))
Gold Mining SARL - 3 ((Autorisations d'Exploitation)
Compagnie Miniere des Anciens Placers SARL - 3 (Autorisations d'Exploitation))
Antoine Leveille - 1 ((Autorisation d'Exploitation ))
ATENOR SARL - 2 ((Autorisation d'Exploitation))
Ange Leveille - 1 ((Autorisation d'Exploitation))
AGELOR SARL - 2 ((Autorisation d'Exploitation))
Orizon SARL - 1 ((Autorisation d'Exploitation))
MEXAUR SARL  - 1 ((Autorisation d'Exploitation))
Societe d'Exploitation Miniere Antilles Guyane SARL - 3 ((Autorisations
d'Exploitation))
Compagnie des Travaux Miniers de Guyane SARL - 1 Convention d'Exploitation
Compagnie Miniere Valdecente SARL - 2 ((Autorisation d'Exploitation))
Societe Miniere McMahon SARL - 3 (Autorisation d'Exploitation))
Compagnie Aurifere Amazonienne SARL - 3 ((Autorisation d'Exploitation))
Mr. Jose Constable - 1 ((Autorisation d'Exploitation))
Mr. Reginaldo Bonaretto - 1 ((Autorisation d'Exploitation))
Mr. F. Achille - 1 ((Autorisation d'Exploitation))
Mr. J. Labrana -1 ((Autorisation d'Exploitation

                                                                   Page 15 of 17
<PAGE>

                                 SCHEDULE 1.1-B

                              MAP OF THE PROPERTY

                               See map next page

                                                                   Page 16 of 17
<PAGE>

Page 17 is a map.  Its description is:

A black and white map of portions of French Guiana where in the Paul-Isnard
mineral rights are located.  Each of the Permits, Concessions and Permis
included in the agreement are outlined by a black line and each area is labeled
by its concession number, or permis name.


                                                                   Page 17 of 17