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                                                                       EXHIBIT 4

               OPTION TO PURCHASE AND ROYALTY AMENDMENT AGREEMENT

        This Option to Purchase and Royalty Amendment Agreement is made as of
this 26th day of September, 2002 between CENTRAL MINERA CORP., a company
organized under the laws of the Yukon Territory and having an office at 1040 -
885 West Georgia Street, Vancouver, B.C. V6C 3E8 (the "Vendor") and ISLAND ARC
EXPLORATION INC., a company duly incorporated under the laws of the Province of
British Columbia, having an office at Suite 611-675 West Hastings Street,
Vancouver, B.C. V6B 1N2 ("Island Arc").

                                    RECITALS

         The Vendor and Island Arc are parties to an Option to Purchase and
Royalty Agreement made as of November 13, 2001 (the "Original Agreement"),
pursuant to which the Vendor agreed to grant Island Arc an option to purchase
all of the Vendor's right, title and interest to certain Claims, as defined
therein. Among other things, Island Arc covenanted in the Original Agreement
that (i) on or before the Approval Date, as defined in the Original Agreement,
it would make a cash payment to the Vendor of $10,000 (the "Initial Cash
Consideration") and (ii) on the Approval Date it would deliver 100,000 Shares
(the "Initial Share Consideration"), as defined in the Original Agreement, to
the Vendor. Although the Approval Date, within the meaning of the Original
Agreement, was December 27, 2001, Island Arc has not paid the Initial Cash
Consideration and has not delivered the Initial Share Consideration.

                                    AGREEMENT

         In consideration of the foregoing, of the mutual agreements hereinafter
contained and of other good and valuable consideration, the receipt and
sufficiency of which is hereby acknowledged, the Vendor and Island Arc have
agreed to modify the terms of the Original Agreement as follows:

1.       Section 3.1 of the Original Agreement is deleted and the following
substituted:

3.1      (a)      In consideration for:

                  (i)      a cash payment of $5,000 on execution of this
                           Amendment Agreement; and

                  (ii)     a cash payment of $5,000 on or before the first
                           anniversary of the Approval Date; and

                  (iii)    the allotment and issue of 100,000 Shares and
                           delivery of certificates therefor to the Vendor on
                           execution of this Amendment Agreement,

                  the Vendor hereby gives and grants to Island Arc the sole and
                  exclusive right and option (the "Option") to acquire an
                  undivided 100% of the right, title and interest of the Vendor
                  in and to the Claims, subject only to the Vendor receiving the
                  Royalty, in accordance with the terms of this Agreement.


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         (b)      The Option may be exercised by:

                  (i)      paying $15,000 in cash and allotting and issuing and
                           delivering certificates for 100,000 Shares on or
                           before the first anniversary of the Approval Date;

                  (ii)     paying $20,000 in cash and allotting and issuing and
                           delivering certificates for 100,000 Shares on or
                           before the second anniversary of the Approval Date;
                           and

                  (iii)    paying $30,000 in cash and allotting and issuing and
                           delivering certificates for 100,000 Shares on or
                           before the third anniversary of the Approval Date.

         (c)      Subject to Section 14, Island Arc may let the Option lapse by
                  failing to make the payments or deliver the Shares specified
                  in paragraph (b) of this section 3.1 on or before the dates
                  specified therein.

2.       Section 5.1 of the Original Agreement is deleted and the following
substituted:

5.1      This Agreement and the Option will terminate:

         (a)      forthwith following execution of this Amendment Agreement if
                  Island Arc does not upon execution thereof make the cash
                  payment provided for in section 3.1 (a) (i) and deliver the
                  Shares provided for in section 3.1 (a) (iii);

         (b)      subject to section 19.1:

                  (i)      on the first anniversary of the Approval Date unless
                           Island Arc has made the cash payment provided for in
                           section 3.1 (a) (ii) and made the cash payment and
                           delivered the Shares provided for in section 3.1 (b)
                           (i);

                  (ii)     on the second anniversary of the Approval Date unless
                           Island Arc has made the cash payment and delivered
                           the Shares provided for in section 3.1 (b) (ii);

                  (iii)    on the third anniversary of the Approval Date unless
                           Island Arc has made the cash payment and delivered
                           the Shares provided for in section 3.1 (b) (iii).

3.       The Original Agreement is amended by adding, as Section 14.2, the
following:

                  If Island Arc abandons its interest in the Claims in
                  accordance with Section 14.1 or this Agreement and the Option
                  otherwise terminate, Island Arc shall ensure that the Claims
                  are in at least the same state concerning environmental and
                  hazardous conditions as they were on the date of the Original
                  Agreement and shall forthwith undertake such reclamation work
                  as is necessary to comply with all requirements of law,
                  environmental, health or safety legislation, regulations,
                  rules, ordinances, policies, orders,

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                  approvals, notices, licences, directives or permits of any
                  federal, provincial or local judicial, regulatory or
                  administrative agency, board or governmental authority
                  including, but not limited to, those relating to (i) pollution
                  or protection of the air, surface water, ground water or land,
                  (ii) solid, gaseous or liquid waste generation, handling,
                  treatment, storage, disposal or transportation, (iii) exposure
                  to hazardous or toxic substances, or (iv) the closure,
                  decommissioning, dismantling or abandonment of an facilities,
                  mines or workings and the reclamation or restoration of lands.

4.       Section 25.1 of the Original Agreement is deleted and the following
substituted:

                  This Agreement provides for an option only, and except for the
                  cash payments and the Shares provided for in section 3.1 (a)
                  hereof (both of which are firm commitments), nothing herein
                  contained shall be construed as obligating Island Arc to do
                  any acts or make any payment hereunder and any act or acts or
                  payment or payments as shall be made hereunder shall not be
                  construed as obligating Island Arc to do any further act or
                  make any further payment.

IN WITNESS WHEREOF the parties, intending to be legally bound, have executed
this Agreement.


CENTRAL MINERA CORP.

PER:  "Michael Cytrynbaum"
      --------------------------
       Authorized Signatory



ISLAND ARC EXPLORATION INC.

PER:   "Lawrence D. Barr"
      --------------------------
        Authorized Signatory