<PAGE>   1

                                                                   Exhibit 10.15

                              MANAGEMENT AGREEMENT


This agreement dated August 15, 1994 by and between AZCO Mining Inc., a Delaware
corporation (the "Company") and Alan P. Lindsay, the corporate officer, (the
"officer").

Whereas the officer has rendered valuable services to the Company and the
Company desires to be assured that the executive will continue rendering such
services to the Company;

Whereas the officer is willing to continue to serve the Company but desires
assurance that he will be protected in the event of any change in control;

Now therefore, in consideration of the mutual covenants and promises herein, the
parties agree as follows.

The Company agrees that if

1.         there is a change of control of the Company, and

2.         the officer leaves the employment of the Company, for whatever reason
           (other than discharge for cause, death or disability) within six
           months after such acquisition of control

a.         the officer shall receive as a lump sum, a cash payment in the amount
           not to exceed 299% of the base amount as defined in IRC Section 280G
           (b) (3); provided, that in any event, the amount payable under this
           clause (a) shall not exceed the maximum amount payable to the officer
           without the imposition of any excise taxes under the provisions of
           Section 4999 of the Internal Revenue Code as that section may be
           amended from time to time.

b.         the officer will continue to be covered by all of the Company's
           medical, health, life and dental plans for 24 months after such
           change of control.

The amounts paid to the officer hereunder shall be considered severance pay in
consideration of the past services he has rendered to the Company and in
consideration of his continued service from the date hereof to his entitlement
to those payments. The officer shall have no duty to mitigate his damages by
seeking other employment. Should the officer actually receive other payments
from any such other employment, the payments called for hereunder shall not be
reduced or offset by any future earnings.

as used herein, the term "change in control" shall mean either

1.         the acquisition of (whether direct or indirect) shares in excess of
           20 percent of the outstanding shares of common stock of the Company
           by a person or group of persons,


<PAGE>   2



           other than through a public equity offering by the Company, or

2.         the occurrence of any transaction relating to the Company required to
           be described pursuant to the requirements of item 6 (e) of schedule
           14A of the Securities and Exchange Commission under the Securities
           and Exchange Act of 1934, or

3.         any change in the composition of the board of directors of the
           Company resulting in a majority of the present directors not
           constituting a majority provided, that in making such determination
           directors who were elected by, or on the recommendation of, such
           present majority, shall be excluded.

The arrangements called for by this agreement are not intended to have any
effect on the officer's participation in any other benefits available to
executive personnel or to preclude other compensation or additional benefits as
may be authorized by the board of directors from time to time.

This agreement shall be binding and shall inure to the benefit of the respective
successors, assigns, legal representatives and heirs to the parties hereto.

This agreement shall terminate, even though prior to the acquisition of any
control of the Company as defined here, if the officer shall voluntarily resign,
retire, become permanently and totally disabled, voluntarily take another
position requiring a substantial portion of his time, or die. This agreement
shall also terminate if the executive's employment as an officer of the Company
shall have been terminated for any reason by the board of directors of the
Company as constituted prior to any acquisition of control of the Company as
defined herein.

In witness whereof, the parties have signed this agreement this 15th day of
August, 1994.




-------------------         -------         -----------------           -------
Officer's Signature           Date           AZCO Mining Inc.             Date


<PAGE>   3

                              MANAGEMENT AGREEMENT



This agreement dated August 15, 1994 by and between AZCO Mining Inc., a Delaware
corporation (the "Company") and Anthony R. Harvey, the corporate officer, (the
"officer").

Whereas the officer has rendered valuable services to the Company and the
Company desires to be assured that the executive will continue rendering such
services to the Company;

Whereas the officer is willing to continue to serve the Company but desires
assurance that he will be protected in the event of any change in control;

Now therefore, in consideration of the mutual covenants and promises herein, the
parties agree as follows.

The Company agrees that if

1.         there is a change of control of the Company, and

2.         the officer leaves the employment of the Company, for whatever reason
           (other than discharge for cause, death or disability) within six
           months after such acquisition of control

a.         the officer shall receive as a lump sum, a cash payment in the amount
           not to exceed 299% of the base amount as defined in IRC Section 280G
           (b) (3); provided, that in any event, the amount payable under this
           clause (a) shall not exceed the maximum amount payable to the officer
           without the imposition of any excise taxes under the provisions of
           Section 4999 of the Internal Revenue Code as that section may be
           amended from time to time.

b.         the officer will continue to be covered by all of the Company's
           medical, health, life and dental plans for 24 months after such
           change of control.

The amounts paid to the officer hereunder shall be considered severance pay in
consideration of the past services he has rendered to the Company and in
consideration of his continued service from the date hereof to his entitlement
to those payments. The officer shall have no duty to mitigate his damages by
seeking other employment. Should the officer actually receive other payments
from any such other employment, the payments called for hereunder shall not be
reduced or offset by any future earnings.

as used herein, the term "change in control" shall mean either

1.         the acquisition of (whether direct or indirect) shares in excess of
           20 percent of the outstanding shares of common stock of the Company
           by a person or group of persons,


<PAGE>   4

           other than through a public equity offering by the Company, or

2.         the occurrence of any transaction relating to the Company required to
           be described pursuant to the requirements of item 6 (e) of schedule
           14A of the Securities and Exchange Commission under the Securities
           and Exchange Act of 1934, or

3.         any change in the composition of the board of directors of the
           Company resulting in a majority of the present directors not
           constituting a majority provided, that in making such determination
           directors who were elected by, or on the recommendation of, such
           present majority, shall be excluded.

The arrangements called for by this agreement are not intended to have any
effect on the officer's participation in any other benefits available to
executive personnel or to preclude other compensation or additional benefits as
may be authorized by the board of directors from time to time.

This agreement shall be binding and shall inure to the benefit of the respective
successors, assigns, legal representatives and heirs to the parties hereto.

This agreement shall terminate, even though prior to the acquisition of any
control of the Company as defined here, if the officer shall voluntarily resign,
retire, become permanently and totally disabled, voluntarily take another
position requiring a substantial portion of his time, or die. This agreement
shall also terminate if the executive's employment as an officer of the Company
shall have been terminated for any reason by the board of directors of the
Company as constituted prior to any acquisition of control of the Company as
defined herein.

In witness whereof, the parties have signed this agreement this 15th day of
August, 1994.




-------------------         -------         -----------------           -------
Officer's Signature           Date           AZCO Mining Inc.             Date



<PAGE>   5

                              MANAGEMENT AGREEMENT



This agreement dated November 19, 1996, by and between AZCO Mining Inc., a
Delaware corporation (the "Company") and Ryan A. Modesto, the corporate officer,
(the "officer").

Whereas the officer has rendered valuable services to the Company and the
Company desires to be assured that the executive will continue rendering such
services to the Company;

Whereas the officer is willing to continue to serve the Company but desires
assurance that he will be protected in the event of any change in control;

Now therefore, in consideration of the mutual covenants and promises herein, the
parties agree as follows.

The Company agrees that if

1.         there is a change of control of the Company, and

2.         the officer leaves the employment of the Company, for whatever reason
           (other than discharge for cause, death or disability) within six
           months after such acquisition of control

a.         the officer shall receive as a lump sum, a cash payment in the amount
           not to exceed 299% of the base amount as defined in IRC Section 280G
           (b) (3); provided, that in any event, the amount payable under this
           clause (a) shall not exceed the maximum amount payable to the officer
           without the imposition of any excise taxes under the provisions of
           Section 4999 of the Internal Revenue Code as that section may be
           amended from time to time.

b.         the officer will continue to be covered by all of the Company's
           medical, health, life and dental plans for 24 months after such
           change of control.

The amounts paid to the officer hereunder shall be considered severance pay in
consideration of the past services he has rendered to the Company and in
consideration of his continued service from the date hereof to his entitlement
to those payments. The officer shall have no duty to mitigate his damages by
seeking other employment. Should the officer actually receive other payments
from any such other employment, the payments called for hereunder shall not be
reduced or offset by any future earnings.

as used herein, the term "change in control" shall mean either

1.         the acquisition of (whether direct or indirect) shares in excess of
           20 percent of the outstanding shares of common stock of the Company
           by a person or group of persons, other than through a public equity
           offering by the Company, or


<PAGE>   6




2.         the occurrence of any transaction relating to the Company required to
           be described pursuant to the requirements of item 6 (e) of schedule
           14A of the Securities and Exchange Commission under the Securities
           and Exchange Act of 1934, or

3.         any change in the composition of the board of directors of the
           Company resulting in a majority of the present directors not
           constituting a majority provided, that in making such determination
           directors who were elected by, or on the recommendation of, such
           present majority, shall be excluded.

The arrangements called for by this agreement are not intended to have any
effect on the officer's participation in any other benefits available to
executive personnel or to preclude other compensation or additional benefits as
may be authorized by the board of directors from time to time.

This agreement shall be binding and shall inure to the benefit of the respective
successors, assigns, legal representatives and heirs to the parties hereto.

This agreement shall terminate, even though prior to the acquisition of any
control of the Company as defined here, if the officer shall voluntarily resign,
retire, become permanently and totally disabled, voluntarily take another
position requiring a substantial portion of his time, or die. This agreement
shall also terminate if the executive's employment as an officer of the Company
shall have been terminated for any reason by the board of directors of the
Company as constituted prior to any acquisition of control of the Company as
defined herein.

In witness whereof, the parties have signed this agreement this 19th day of
November, 1996.





-------------------         -------         -----------------           -------
Officer's Signature           Date           AZCO Mining Inc.             Date


<PAGE>   7


                              MANAGEMENT AGREEMENT



This agreement dated October 7, 1997 by and between AZCO Mining Inc., a Delaware
corporation (the "Company") and Nick Badham, the corporate officer, (the
"officer").

Whereas the officer has rendered valuable services to the Company and the
Company desires to be assured that the executive will continue rendering such
services to the Company;

Whereas the officer is willing to continue to serve the Company but desires
assurance that he will be protected in the event of any change in control;

Now therefore, in consideration of the mutual covenants and promises herein, the
parties agree as follows.

The Company agrees that if

1.         there is a change of control of the Company, and

2.         the officer leaves the employment of the Company, for whatever reason
           (other than discharge for cause, death or disability) within six
           months after such acquisition of control

a.         the officer shall receive as a lump sum, a cash payment in the amount
           not to exceed 299% of the base amount as defined in IRC Section 280G
           (b) (3); provided, that in any event, the amount payable under this
           clause (a) shall not exceed the maximum amount payable to the officer
           without the imposition of any excise taxes under the provisions of
           Section 4999 of the Internal Revenue Code as that section may be
           amended from time to time.

b.         the officer will continue to be covered by all of the Company's
           medical, health, life and dental plans for 24 months after such
           change of control.

The amounts paid to the officer hereunder shall be considered severance pay in
consideration of the past services he has rendered to the Company and in
consideration of his continued service from the date hereof to his entitlement
to those payments. The officer shall have no duty to mitigate his damages by
seeking other employment. Should the officer actually receive other payments
from any such other employment, the payments called for hereunder shall not be
reduced or offset by any future earnings.

as used herein, the term "change in control" shall mean either

1.         the acquisition of (whether direct or indirect) shares in excess of
           20 percent of the outstanding shares of common stock of the Company
           by a person or group of persons,


<PAGE>   8

           other than through a public equity offering by the Company, or

2.         the occurrence of any transaction relating to the Company required to
           be described pursuant to the requirements of item 6 (e) of schedule
           14A of the Securities and Exchange Commission under the Securities
           and Exchange Act of 1934, or

3.         any change in the composition of the board of directors of the
           Company resulting in a majority of the present directors not
           constituting a majority provided, that in making such determination
           directors who were elected by, or on the recommendation of, such
           present majority, shall be excluded.

The arrangements called for by this agreement are not intended to have any
effect on the officer's participation in any other benefits available to
executive personnel or to preclude other compensation or additional benefits as
may be authorized by the board of directors from time to time.

This agreement shall be binding and shall inure to the benefit of the respective
successors, assigns, legal representatives and heirs to the parties hereto.

This agreement shall terminate, even though prior to the acquisition of any
control of the Company as defined here, if the officer shall voluntarily resign,
retire, become permanently and totally disabled, voluntarily take another
position requiring a substantial portion of his time, or die. This agreement
shall also terminate if the executive's employment as an officer of the Company
shall have been terminated for any reason by the board of directors of the
Company as constituted prior to any acquisition of control of the Company as
defined herein.

In witness whereof, the parties have signed this agreement this 7th day of
October, 1997.





-------------------         -------         -----------------           -------
Officer's Signature           Date           AZCO Mining Inc.             Date



<PAGE>   9


                              MANAGEMENT AGREEMENT



This agreement dated October 7, 1997 by and between AZCO Mining Inc., a Delaware
corporation (the "Company") and Doug Ramshaw, the corporate officer, (the
"officer").

Whereas the officer has rendered valuable services to the Company and the
Company desires to be assured that the executive will continue rendering such
services to the Company;

Whereas the officer is willing to continue to serve the Company but desires
assurance that he will be protected in the event of any change in control;

Now therefore, in consideration of the mutual covenants and promises herein, the
parties agree as follows.

The Company agrees that if

1.         there is a change of control of the Company, and

2.         the officer leaves the employment of the Company, for whatever reason
           (other than discharge for cause, death or disability) within six
           months after such acquisition of control

a.         the officer shall receive as a lump sum, a cash payment in the amount
           not to exceed 299% of the base amount as defined in IRC Section 280G
           (b) (3); provided, that in any event, the amount payable under this
           clause (a) shall not exceed the maximum amount payable to the officer
           without the imposition of any excise taxes under the provisions of
           Section 4999 of the Internal Revenue Code as that section may be
           amended from time to time.

b.         the officer will continue to be covered by all of the Company's
           medical, health, life and dental plans for 24 months after such
           change of control.

The amounts paid to the officer hereunder shall be considered severance pay in
consideration of the past services he has rendered to the Company and in
consideration of his continued service from the date hereof to his entitlement
to those payments. The officer shall have no duty to mitigate his damages by
seeking other employment. Should the officer actually receive other payments
from any such other employment, the payments called for hereunder shall not be
reduced or offset by any future earnings.

as used herein, the term "change in control" shall mean either

1.         the acquisition of (whether direct or indirect) shares in excess of
           20 percent of the outstanding shares of common stock of the Company
           by a person or group of persons,


<PAGE>   10



           other than through a public equity offering by the Company, or

2.         the occurrence of any transaction relating to the Company required to
           be described pursuant to the requirements of item 6 (e) of schedule
           14A of the Securities and Exchange Commission under the Securities
           and Exchange Act of 1934, or

3.         any change in the composition of the board of directors of the
           Company resulting in a majority of the present directors not
           constituting a majority provided, that in making such determination
           directors who were elected by, or on the recommendation of, such
           present majority, shall be excluded.

The arrangements called for by this agreement are not intended to have any
effect on the officer's participation in any other benefits available to
executive personnel or to preclude other compensation or additional benefits as
may be authorized by the board of directors from time to time.

This agreement shall be binding and shall inure to the benefit of the respective
successors, assigns, legal representatives and heirs to the parties hereto.

This agreement shall terminate, even though prior to the acquisition of any
control of the Company as defined here, if the officer shall voluntarily resign,
retire, become permanently and totally disabled, voluntarily take another
position requiring a substantial portion of his time, or die. This agreement
shall also terminate if the executive's employment as an officer of the Company
shall have been terminated for any reason by the board of directors of the
Company as constituted prior to any acquisition of control of the Company as
defined herein.

In witness whereof, the parties have signed this agreement this 7th day of
October, 1997.




-------------------         -------         -----------------           -------
Officer's Signature           Date           AZCO Mining Inc.             Date