<PAGE>

                                                                     EXHIBIT 4.4

                                 EXCHANGE AGREEMENT



  EXCHANGE AGREEMENT (this "Agreement") made as of the date set forth on the
signature page hereof between Atlas Corporation, a Delaware corporation (the
"Company"), and the undersigned (the "Holder").


                                 W I T N E S S E T H :
                                 -------------------


  WHEREAS, on November 10, 1995, the Company issued US$10,000,000 principal
amount of its 7% Exchangeable Debentures due October 25, 2000 (the "7%
Debentures") pursuant to an indenture of even date (the "Indenture") between the
Company and The Chase Manhattan Bank (formerly known as Chemical Bank) as
trustee (the "Trustee"), secured by a pledge of 8,474,576 (since reduced to
approximately 8,313,076) shares (such reduced number of pledged shares, as
further reduced by virtue of any subsequent exchanges of 7% Debentures in
accordance with the terms of the 7% Debentures, hereinafter referred to as the
"Pledged Shares") of common stock, no par value per share ("Vista Shares") of
Vista Gold Corp. (as successor by merger to Granges Inc.) under the Indenture
and an escrow and pledge agreement of even date (the "Escrow and Pledge
Agreement") between the Company and the Trustee, as trustee and as escrow agent;

  WHEREAS, the Company and Yorkton Securities, Inc. ("Yorkton"), representing
the holders of all 7% Debentures, have negotiated terms with respect to a
repurchase of the 7% Debentures by the Company;

  WHEREAS, the Holder holds the principal amount of the 7% Debentures indicated
on the signature page hereof (the "Debentures"); and

  WHEREAS, on the terms and conditions set forth herein, the Holder desires to
sell to the Company and the Company desires to purchase from the Holder the
Debentures.

  NOW, THEREFORE, in consideration of the premises and the mutual
representations and covenants hereinafter set forth, the Company and the Holder
do hereby agree as follows:


I.  SALE OF DEBENTURES AND REPRESENTATIONS BY HOLDER
    ------------------------------------------------

  I.1  Sale of Debentures.  (a)  Subject to the terms and conditions hereinafter
       ------------------
set forth, the Holder hereby irrevocably agrees to sell the Debentures to the
Company and waive payment of any interest accrued and unpaid as of the Closing
(as hereinafter defined) in return for (i) a number of Pledged Shares equal to
the product of (A) the number of Pledged Shares and (B) a fraction, the
numerator of which is the principal amount of the Debentures and the denominator
of which is the principal amount of all outstanding 7% Debentures at the time of
the Closing; and (ii) 153 shares of common stock, US$1.00 par value per share,
of the Company (the "Atlas Shares") for each US$1,000 principal amount of the
Debentures (the securities specified in clauses (i) and (ii) above being
collectively referred to herein as the "Securities").  In lieu of fractional
shares resulting from

<PAGE>

the above computations, the Company will make a cash payment equal to the value
of such fractional shares based upon the closing price of the Atlas Shares on
the New York Stock Exchange and of the Vista Shares on the American Stock
Exchange two business days prior to the Closing (as hereinafter defined).

  (b)  The Holder has delivered certificates representing the Debentures to
Yorkton herewith.  The Holder agrees that the certificates representing the
Securities and cash in respect of fractional shares shall be delivered (with
appropriate instruments of transfer endorsed in blank or, in the case of the
Atlas Shares, registered in the name indicated on the signature page hereto) to
Yorkton, as agent for the Holder, at the Closing (as hereinafter defined).  The
Holder agrees that the Company will have no further obligation after making such
delivery to Yorkton, as agent for the Holder, and that Yorkton will thenceforth
be responsible for delivery of the Securities to the Holder.

      I.2  Investor Status.  The Holder makes the representations and warranties
           ---------------
indicated by checkmark below:


     ____  (a)  The Holder represents that: (i) the Holder was not offered
           the Securities in the United States of America, its territories or
           possessions, any state of the United States or the District of
           Columbia (the "United States"),

                (ii)  the Holder is currently, and has been at all times when
                the Securities were offered, outside the United States,


                (iii) the Holder is not a U.S. Person (as hereinafter defined),

                                       2
<PAGE>

  The term "U.S. Person" means:

  (1) any natural person resident in the United States;
  (2) any partnership or corporation organized or incorporated under
      the laws of the United States;
  (3) any estate of which any executor or administrator is a U.S. person;
  (4) any trust of which any trustee is a U.S. Person;
  (5) any agency or branch of a foreign entity located in the United States;
  (6) any non-discretionary account or similar account (other than an estate or
      trust) held by a dealer or other fiduciary for the benefit or account of a
      U.S. person;
  (7) any discretionary account or similar account (other than an estate or
      trust) held by a dealer or other fiduciary organized, incorporated, or (if
      an individual) resident in the United States; and
  (8) partnership or corporation if:
      (i)  organized or incorporated under the laws of any foreign
           jurisdiction; and
      (ii) formed by a U.S. person principally for the purpose of investing in
           securities not registered under the Securities Act of 1933 (the
           "Act"), unless it is organized or incorporated, and owned, by
           accredited investors (as defined in Rule 501(a) under the Act) who
           are not natural persons, estates or trusts.

                                       3
<PAGE>

     Notwithstanding the foregoing definition of "U.S. Person":



          (1)  any discretionary account or similar account (other than an
               estate or trust) held for the benefit or account of a non-U.S.
               person by a dealer or other professional fiduciary organized,
               incorporated, or (if an individual) resident in the United States
               shall not be deemed a U.S. person;
          (2)  any estate of which any professional fiduciary acting as executor
               or administrator is a U.S. person shall not be deemed a U.S.
               person if:
               (i)  an executor or administrator of the estate who is not a U.S.
                    person has sole or shared investment discretion with respect
                    to the assets of the estate; and
               (ii) the estate is governed by foreign law;
          (3)  any trust of which any professional fiduciary acting as trustee
               is a U.S. person shall not be deemed a U.S. person if a trustee
               who is not a U.S. person has sole or shared investment discretion
               with respect to the trust assets, and no beneficiary of the trust
               (and no settlor if the trust is revocable) is a U.S. person;
          (4)  an employee benefit plan established and administered in
               accordance with the law of a country other than the United States
               and customary practices and documentation of such country shall
               not be deemed a U.S. person;
          (5)  any agency or branch of a U.S. person located outside the United
               States shall not be deemed a U.S. person if:
               (i)  the agency or branch operates for valid business reasons;
                    and
               (ii) the agency or branch is engaged in the business of insurance
                    or banking and is subject to substantive insurance or
                    banking

                                       4
<PAGE>

                    regulation, respectively, in the jurisdiction where
                    located;

          (6)  the International Monetary Fund, the International Bank for
               Reconstruction and Development, the Inter-American Development
               Bank, the Asian Development Bank, the African Development Bank,
               the United Nations, and their agencies, affiliates and pension
               plans shall not be deemed U.S. Persons.


  (iv)  If the Holder is a resident of Ontario, the Holder acknowledges that it
has been provided with access to substantially the same information concerning
the Company that a prospectus filed under the Securities Act [Ontario] would
provide and is an investor who, by virtue of net worth and investment experience
or by virtue of consultation with or advice from a person or company who is not
a promoter of the Company and who is a registered adviser or registered dealer,
is able to evaluate this investment on the basis of such information respecting
the investment presented by the Company.



     ____ (b)      (i)  The holder represents that it is (A) a U.S. Person
          or inside the United States and (B) is an "accredited investor" (as
          hereinafter defined).


          The term "accredited investor" means any of the following:


          (1)  any organization described in Section 501(c)(3) of the Internal
          Revenue Code, corporation, Massachusetts or similar business trust, or
          partnership, not formed for the specific purposes of acquiring the
          Securities, with total assets in excess of US$5,000,000;

                                       5
<PAGE>

     (2)  any bank as defined in Section 3(a)(2) of the Act, or any savings and
          loan association or other institution as defined in Section 3(a)(5)(A)
          of the Act whether acting in its individual or fiduciary capacity; any
          broker or dealer registered pursuant to Section 15 of the Securities
          Exchange Act of 1934 (the "1934 Act"); any insurance company as
          defined in Section 2(13) of the Act; any investment company registered
          under the Investment Company Act of 1940 or a business development
          company as defined in Section 2(a)(48) of that act; any Small Business
          Investment Company licensed by the U.S. Small Business Administration
          under Section 301(c) or (d) of the Small Business Investment Act of
          1958; any plan established and maintained by a state of the United
          States, such state's political subdivisions, or any agency or
          instrumentality of a state of the United States or such state's
          political subdivisions for the benefit of its employees, if such plan
          has total assets in excess of US$5,000,000; any employee benefit plan
          within the meaning of the Employee Retirement Income Security Act of
          1974 if the investment decision is made by a plan fiduciary, as
          defined in Section 3(21) of such act, which is either a bank, savings
          and loan association, insurance company, or registered investment
          adviser, or if the employee benefit plan has total assets in excess of
          US$5,000,000 or, if a self-directed plan, with investment decisions
          made solely by persons that are accredited investors;

     (3)  any private business development company as defined in Section
          202(a)(22) of the Investment Advisers Act of 1940;

     (4)  any natural person whose individual net worth, or joint net worth with
          that

                                       6
<PAGE>

          person's spouse, at the time of his purchase exceeds
          US$1,000,000;


     (5)  any natural person who had an individual income in excess of
          US$200,000 in each of the two most recent years or joint income with
          that person's spouse in excess of US$300,000 in each of those years
          and has a reasonable expectation of reaching the same income level in
          the current year;



     (6)  Any trust, with total assets in excess of US$5,000,000, not formed for
          the specific purpose of acquiring the Securities, whose purchase is
          directed by a person who, either alone or with his purchaser
          representative(s) has such knowledge and experience in financial and
          business matters that he is capable of evaluating the merits and risks
          of an investment in the Securities; or


      (7) any entity in which all of the equity owners are accredited investors.


          (ii)  The Holder hereby represents that the Holder is acquiring the
Securities for the Holder's own account for investment and not with a view
toward the resale or distribution to others.

          (iii) The Holder hereby represents that it is not an affiliate (as
hereinafter defined) of Vista Gold Corp. and has not been such an affiliate
during the preceding three months.  For the purposes of the preceding sentence,
the term "affiliate" shall mean a person that directly, or indirectly through
one or more intermediaries, controls, or is controlled by, or is under common
control with, Vista Gold Corp.

                                       7
<PAGE>

The Holder is a "Reg S Purchaser" if it checks subsection (a) above and is a
"Reg D Purchaser" if it checks subsection (b) above.

  I.3  (a)  The Holder acknowledges that the Securities have not been registered
under the Act and may not be offered or sold in the United States unless so
registered or if an exemption from such registration is available.  The Holder
further acknowledges that the Company is under no obligation to register any of
the Securities under the Act or any state securities or "blue sky" laws.  The
Holder agrees to hold the Company and its directors, officers, employees,
controlling persons and agents (including Yorkton and its officers, directors,
employees, counsel, controlling persons and agents) and their respective heirs,
representatives, successors and assigns harmless and to indemnify them against
all liabilities, costs and expenses incurred by them as a result of, (i) any
misrepresentation made by the Holder contained in this Agreement, (ii) any sale
or distribution by the Holder in violation of the Act or any applicable state
securities or "blue sky" laws or (iii) any untrue statement of a material fact
made by the Holder and contained herein.

       (b)  If the Holder is a "Reg D Purchaser", the Holder consents to the
placement of a legend on any certificate or other document evidencing the Atlas
Shares that such securities have not been registered under the Act or any state
securities or "blue sky" laws and setting forth or referring to the restrictions
on transferability and sale thereof contained in this Agreement.

  The Company and the Holder anticipate that Vista Gold Corp. will permit the
removal of all restrictive legends on the Vista Shares upon the acquisition
thereof by a Reg D Purchaser pursuant to the terms hereof, and will allow the
Vista Shares to be resold by a Reg D Purchaser without registration under the
Act pursuant to Rule 144(k) under the Act without any holding period or

                                       8
<PAGE>

volume restrictions provided that any such sales are made in accordance with
Rule 144(f) in "brokers' transactions" (as defined in the Act) or directly with
a "market maker" (as defined in the Securities Exchange Act of 1934, as amended)
and further provided that, at the time of such sales, such Holder is not an
"affiliate" (as defined in Rule 144) of Vista Gold Corp. and has not been an
affiliate in the preceding three months (a "144(k) sale").

  The Company notes that Rule 144 under the Act would currently allow resales of
Atlas Shares by Reg D Purchasers without registration under the Act after one
year, subject to volume and certain other restrictions or after two years in a
144(k) sale.

          (c)  If the Holder is a "Reg S Purchaser", the Holder consents to the
placement of a legend, for so long as required by law, on any certificate or
other document evidencing the Atlas Shares as required by Regulation S under the
Act.  The Company will remove any such legends 40 days after issuance unless, in
the opinion of counsel to the Company, such legends must be retained by virtue
of a change of applicable law.

  The Company and the Holder intend that the Vista Shares being transferred to
the Holder will be transferred to each Reg S Purchaser pursuant to Rule 904 of
Regulation S under the Act and, accordingly, it is anticipated that Vista Gold
Corp. will permit the removal of all restrictive legends on the Vista Shares
upon the acquisition thereof by a Reg S Purchaser pursuant to the terms hereof,
and will allow the Vista Shares to be resold by a Reg S Purchaser without
registration under the Act pursuant to Rule 904 under the Act.

          (d)  The Holder is aware that the Company will make a notation in its
appropriate records with respect to the restrictions on the transferability of
the Atlas Shares and will refuse to

                                       9
<PAGE>

register any transfers of Atlas Shares not made in accordance with the Act.

  I.4  The Holder represents that (i) the Holder was contacted regarding the
offer of the Securities by Yorkton (or an authorized agent or representative
thereof with whom the Holder had a prior substantial pre-existing relationship)
and (ii) no Securities were offered or sold to it by means of any form of
general solicitation or general advertising, and in connection therewith the
Holder did not: (A) receive or review any advertisement, article, notice or
other communication published in a newspaper or magazine or similar media or
broadcast over television or radio, whether closed circuit or generally
available, in connection with the sale of Securities by the Company or (B)
attend any seminar meeting or industry investor conference whose attendees were
invited by any general solicitation or general advertising.

  I.5  (a)  The Holder hereby acknowledges and represents that (i) the Holder
has prior investment experience, including investment in unregistered
securities, or the Holder has employed the services of an investment advisor,
attorney and/or accountant experienced in evaluating such investments to read
all of the documents furnished or made available by the Company to the Holder
and to evaluate the merits and risks of such an investment on the Holder's
behalf; and (ii) the Holder is able to bear the economic risk which the Holder
hereby assumes.

  (b)  To the extent necessary, the Holder has retained, at the expense of the
Holder, and relied upon appropriate professional advice regarding the
investment, tax and legal merits and consequences of this Agreement, its sale of
the Debentures and its purchase of the Securities hereunder.

  I.6  The Holder represents that the Holder has full power and authority
(corporate,

                                       10
<PAGE>

statutory and otherwise) to execute and deliver this Agreement, to sell the
Debentures and to purchase the Securities. This Agreement constitutes the legal,
valid and binding obligation of the Holder, enforceable against the Holder in
accordance with its terms.

  I.7  No Conflict, Governmental and Other Consents.  The execution and delivery
       --------------------------------------------
by the Holder of this Agreement and the consummation of the transactions
contemplated hereby will not result in the violation of any law, statute, rule,
regulation, order, writ, injunction, judgment or decree of any court or
governmental authority to or by which the Holder is bound, or of any provision
of the constitutive documents of the Holder.

  I.8  The Holder owns the Debentures free and clear of any claim or lien of any
nature whatsoever and has not transferred or assigned any rights in or to the
Debentures including, without limitation, any pledge, option, warrant or puts
and will deliver the Debentures free and clear of any such claims or liens.

  I.9   The Holder acknowledges that upon Closing Yorkton will receive a
commission from the Company of 2.5% of the principal amount of the Debentures,
payable in cash and shares of the Company.

II.  REPRESENTATIONS BY AND COVENANTS OF THE COMPANY
     -----------------------------------------------

     The Company hereby represents and warrants to the Holder that:

     II.1  Organization and Good Standing and Qualification.  The Company is a
           ------------------------------------------------
corporation duly organized, validly existing and in good standing under the laws
of the state of Delaware.

                                       11
<PAGE>

  II.2  Securities Validly Issued, Fully Paid and Nonassessable.  The Atlas
        -------------------------------------------------------
Shares have been duly and validly authorized and, when issued and paid for
pursuant to this Agreement, will be validly issued, fully paid and
nonassessable.  The Vista Shares are, to the Company's best knowledge, validly
issued, fully paid and nonassessable.

  II.3  Authorization, Enforceability.  The Company has all corporate right,
        -----------------------------
power and authority to enter into this Agreement and to consummate the
transactions contemplated hereby.  All corporate action on the part of the
Company, its directors and stockholders necessary for the authorization,
execution, delivery and performance of this Agreement by the Company, the
authorization, sale, issuance and delivery of the Securities contemplated hereby
and the performance of the Company's obligations hereunder has been taken.  This
Agreement, when countersigned by the Company, will be duly executed and
delivered by the Company and constitute a legal, valid and binding obligation of
the Company, enforceable against the Company in accordance with its terms.

  II.4  No Conflict, Governmental and Other Consents.  The execution and
        --------------------------------------------
delivery by the Company of this Agreement and the consummation of the
transactions contemplated hereby will not result in the violation of any law,
statute, rule, regulation, order, writ, injunction, judgment or decree of any
court or governmental authority to or by which the Company is bound, or of any
provision of the Certificate of Incorporation or Bylaws of the Company.

                                       12
<PAGE>

III.  TERMS OF SALE
      -------------

  III.1  Closing.  On or about June 15, 1997, or such other date as agreed upon
         -------
between the Company and Yorkton but in no event later than July 4, 1997, the
Company will deliver the Securities to Yorkton and Yorkton will deliver the
Debentures to the Company (the "Closing").  The Company shall have no obligation
to deliver the Securities or to proceed to Closing unless the holders 80% in
principal amount of outstanding 7% Debentures enter into identical Agreements
with the Company.  Notwithstanding the foregoing two sentences, the Company may,
in its sole discretion, proceed to Closing and deliver the Securities and this
Agreement shall be valid and binding in all respects as between the Company and
the Holder.

  If Vista Gold Corp. does not provide its transfer agent an opinion of counsel
with respect to removal of legends on the Vista Shares as contemplated by
Section 0 hereof, the Holder may elect not to close, provided, however, that if
holders of more than 20% in principal amount of outstanding 7% Debentures  so
elect, the Company may elect not to close with any other holder, including the
Holder.

  III.2 Amendment of Indenture and Escrow and Pledge Agreement. (a) The Holder
        ------------------------------------------------------
hereby consents to and approves any number of supplemental indentures pursuant
to Section 802 of the Indenture, and any number of supplements or amendments to
the Escrow and Pledge Agreement pursuant to Section 17 thereof, necessary or
convenient to evidence this Agreement (including Section hereof) and accomplish
the transactions contemplated hereby. The Holder acknowledges that the Company
intends to discharge the Debentures and the Indenture as soon as practicable
after the Closing and that such supplements and amendments will be formalized
and reduced to writing only if the Company, the Trustee or

                                       13
<PAGE>

their respective counsels consider it necessary or advisable in order to
discharge the Debentures and the Indenture. Such supplements and amendments
shall be deemed to have been made and entered into and shall be binding upon the
Holder, its successors and assigns, regardless of whether so formalized or
reduced to writing and regardless of whether holders of a majority in principal
amount of outstanding 7% Debenture delivers similar consents and approvals to
the Company.

IV.  MISCELLANEOUS
     -------------

     IV.1  Any notice or other communication given hereunder shall be deemed
sufficient if in writing and sent by registered or certified mail, return
receipt requested, or delivered by hand against written receipt therefor,
addressed to the Company at 370 Seventeenth Street, suite 3050, Denver, Colorado
80202, Attention: Senior Vice President, Legal Affairs, and to the Holder at the
Holder's address indicated on the signature page of this Agreement.  Notices
shall be deemed to have been given or delivered on the date of mailing, except
notices of change of address, which shall be deemed to have been given or
delivered when received.

     IV.2  This Agreement shall not be changed, modified or amended except by a
writing signed by the parties to be charged, and this Agreement may not be
discharged except by performance in accordance with its terms or by a writing
signed by the party to be charged.

     IV.3  This Agreement shall be binding upon and inure to the benefit of the
parties hereto and to their respective heirs, legal representatives, successors
and assigns.  This Agreement sets forth the entire agreement and understanding
between the parties as to the subject matter hereof and merges and supersedes
all prior discussions, agreements and understandings of any and every nature
among them.

                                       14
<PAGE>

  IV.4  Upon the execution and delivery of this Agreement by the Holder, this
Agreement shall become a binding obligation of the Holder with respect to the
purchase of the Securities as herein provided.

  IV.5  NOTWITHSTANDING THE PLACE WHERE THIS AGREEMENT MAY BE EXECUTED BY ANY OF
THE PARTIES HERETO, THE PARTIES EXPRESSLY AGREE THAT ALL THE TERMS AND
PROVISIONS HEREOF SHALL BE CONSTRUED IN ACCORDANCE WITH AND GOVERNED BY THE LAWS
OF THE STATE OF NEW YORK WITHOUT REGARD TO PRINCIPLES OF CONFLICTS OF LAW.  IN
THE EVENT THAT A JUDICIAL PROCEEDING IS NECESSARY, THE SOLE FORUM FOR RESOLVING
DISPUTES ARISING OUT OF OR RELATING TO THIS AGREEMENT IS THE SUPREME COURT OF
THE STATE OF NEW YORK IN AND FOR THE COUNTY OF NEW YORK OR THE FEDERAL COURTS
FOR SUCH STATE AND COUNTY, AND RELATED APPELLATE COURTS.  THE PARTIES HEREBY
IRREVOCABLY CONSENT TO THE JURISDICTION OF SUCH COURTS AND AGREE TO SAID VENUE.

  IV.6  In order to discourage frivolous claims the parties agree that unless a
claimant in any proceeding arising out of this Agreement succeeds in
establishing his claim and recovering a judgment against another party
(regardless of whether such claimant succeeds against one of the other parties
to the action), then the other party shall be entitled to recover from such
claimant all of its reasonable legal costs and expenses relating to such
proceeding or incurred in preparation therefor.

  IV.7  The holding of any provision of this Agreement to be invalid or
unenforceable by a

                                       15
<PAGE>

court of competent jurisdiction shall not affect any other provision of this
Agreement, which shall remain in full force and effect. If any provision of this
Agreement shall be declared by a court of competent jurisdiction to be invalid,
illegal or incapable of being enforced in whole or in part, such provision shall
be interpreted so as to remain enforceable to the maximum extent permissible
consistent with applicable law and the remaining conditions and provisions or
portions thereof shall nevertheless remain in full force and effect and
enforceable to the extent they are valid, legal and enforceable, and no
provisions shall be deemed dependent upon any other covenant or provision unless
so expressed herein.

  IV.8  It is agreed that a waiver by either party of a breach of any provision
of this Agreement shall not operate, or be construed, as a waiver of any
subsequent breach by that same party.

  IV.9  The parties agree to execute and deliver all such further documents,
agreements and instruments and take such other and further action as may be
necessary or appropriate to carry out the purposes and intent of this Agreement.

  IV.10  This Agreement may be executed in two or more counterparts, each of
which shall be deemed an original, but all of which shall together constitute
one and the same instrument.

  IV.11  The Holder represents and warrants that it has not engaged, consented
to nor authorized any broker, finder or intermediary to act on its behalf,
directly or indirectly, as a broker, finder or intermediary in connection with
the transactions contemplated by this Agreement.  The Holder hereby agrees to
indemnify and hold harmless the Company from and against all fees, commissions
or other payments owing to any such person or firm acting on behalf of such
Holder

                                       16
<PAGE>

hereunder.

  IV.12   Nothing in this Agreement shall create or be deemed to create any
rights in any person or entity not a party to this Agreement.

                                       17
<PAGE>

                                 [Signature Page]



--------------------------------------------------------------------------------
Signature

--------------------------------------------------------------------------------
Name Typed or Printed

--------------------------------------------------------------------------------
Entity Name

--------------------------------------------------------------------------------
Address

--------------------------------------------------------------------------------
City, State and Zip Code



Principal amount of 7% Debentures  __________.


Name in which Securities should be issued:
___________________________________________________________

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


                                       18
<PAGE>

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

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

          This Exchange Agreement is agreed to and accepted as of ____________,
1997.

                              ATLAS CORPORATION


                         By:
_______________________________________________________________
                              Name:
                              Title:

                                       19
<PAGE>

                                 CONSENT OF BENEFICIAL OWNER



     The undersigned
______________________________________________________________________ (the
"Holder"):

     1.   Certifies that the Holder is the beneficial owner of US$ ___________
principal amount of 7% Exchangeable Debentures due October 25, 2000 (the
"Debentures") of Atlas Corporation (the "Company") registered in the name of
______________________________ ;

     2.   Acknowledges that the Company has not yet made payment of the
installment of interest on the Debentures that became due on May 1, 1997;

     3.   Agrees to suspend all interest payments now or heretofore payable
under the Debentures or the related Indenture (the "Indenture") dated as of
November 10, 1995 between the Company and The Chase Manhattan Bank (formerly
known as Chemical Bank) as trustee (the "Trustee") until the closing (the
"Closing") under the Agreement to be entered into between the Company and the
Holder relating to the exchange of the Debentures for common shares of Vista
Gold Corp. and common stock of the Company and during the period of such
suspension no default, Event of Default (as defined in the Indenture) or claim
of the Holder or the Trustee shall arise or exist by reason of non-payment of
any such interest, provided, that such suspension shall not continue beyond 30
days from the date hereof unless the Holder consents to such continuance in
another writing;

     4.   Further acknowledges that the foregoing suspension shall be valid and
binding as to the Holder, its successors and assigns, regardless of whether
Closing occurs;

     5.   Agrees to provide any transferee of the Debentures a copy of this
consent;

     6.   Consents to and approves any number of supplemental indentures and
supplements or amendments to the Escrow and Pledge Agreement, dated as of
November 10, 1995 between the Company and The Chase Manhattan Bank (formerly
known as Chemical Bank) as trustee and as escrow agent, necessary or convenient
to effect or evidence this consent.


     IN WITNESS WHEREOF, I have set my hand this____ day of ____________, 1997.



--------------------------------------------------------------------------------
                                Name:
                                Title:

                                       20
<PAGE>

                          CONSENT OF REGISTERED OWNER



     The undersigned
______________________________________________________________________ (the
"Holder"), the registered owner of US$ ___________ principal amount of 7%
Exchangeable Debentures due October 25, 2000 (the "Debentures") of Atlas
Corporation (the "Company"):

     1.   Acknowledges that the Company has not yet made payment of the
installment of interest on the Debentures that became due on May 1, 1997;

     2.   Agrees to suspend all interest payments now or heretofore payable
under the Debentures or the related Indenture (the "Indenture") dated as of
November 10, 1995 between the Company and The Chase Manhattan Bank (formerly
known as Chemical Bank) as trustee (the "Trustee") until the closing (the
"Closing") under the Agreement to be entered into between the Company and the
Holder relating to the exchange of the Debentures for common shares of Vista
Gold Corp. and common stock of the Company and during the period of such
suspension no default, Event of Default (as defined in the Indenture) or claim
of the Holder or the Trustee shall arise or exist by reason of non-payment of
any such interest, provided, that such suspension shall not continue beyond 30
days from the date hereof unless the Holder consents to such continuance in
another writing;

     3.   Further acknowledges that the foregoing suspension shall be valid and
binding as to the Holder, its successors and assigns, regardless of whether
Closing occurs;

     4.   Agrees to provide any transferee of the Debentures a copy of this
consent;

     5.   Consents to and approves any number of supplemental indentures and
supplements or amendments to the Escrow and Pledge Agreement, dated as of
November 10, 1995 between the Company and The Chase Manhattan Bank (formerly
known as Chemical Bank) as trustee and as escrow agent, necessary or convenient
to effect or evidence this consent.


     IN WITNESS WHEREOF, I have set my hand this____ day of ____________, 1997.



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