<PAGE>   1
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549


          [X]       QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d)
                    OF THE SECURITIES EXCHANGE ACT OF 1934

                  FOR THE QUARTERLY PERIOD ENDED MARCH 31, 1999

                                       OR

          [ ]       TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF
                    THE SECURITIES EXCHANGE ACT OF 1934

                         COMMISSION FILE NUMBER 0-20430


                                AZCO MINING INC.


                            (A DELAWARE CORPORATION)

                  IRS EMPLOYER IDENTIFICATION NUMBER 84-1094315

                     2068 Main Street Suite C, P.O. Box 1895
                               Ferndale, WA 98248
                                 (360) 380-4467


Indicate by check mark whether the Registrant (1) has filed all reports required
to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during
the preceding 12 months (or for such shorter period that the Registrant was
required to file such reports), and (2) has been subject to such filing
requirements for the past 90 days.

                               YES [X]   NO [ ]

Indicate the number of shares outstanding of each of the issuer's classes of
common stock, as of the latest practicable date: 29,752,121 shares of the
Company's Common Stock were outstanding as of May 12, 1999.


<PAGE>   2

                           AZCO MINING INC. (DELAWARE)


Statements contained in the quarterly report that are not historical facts are
forward-looking statements as that term is defined in the Private Securities
Litigation Reform Act of 1995. Such forward-looking statements are subject to
risks and uncertainties, which could cause actual results to differ materially
from the estimated results. Such risks and uncertainties are detailed in filings
with the Securities and Exchange Commission.


                          PART I. FINANCIAL INFORMATION


ITEM 1. FINANCIAL STATEMENTS

<TABLE>
<CAPTION>
                                                                            PAGE
                                                                            ----
<S>                                                                         <C>
        Consolidated Balance Sheets                                           3

        Consolidated Statements of Operations                                 4

        Consolidated Statements of Cash Flows                                 5

        Consolidated Statement of Stockholders' Equity                        6

        Notes to Interim Consolidated Financial Statements                  7-10
</TABLE>

                                        2
<PAGE>   3

AZCO MINING INC. (DELAWARE)
CONSOLIDATED BALANCE SHEETS (UNAUDITED)

<TABLE>
<CAPTION>
                ASSETS                                            MARCH, 31              JUNE, 30
                                                                    1999                   1998
<S>                                                             <C>                     <C>
Current assets:
     Cash and cash equivalents                                  $13,709,646             $18,320,882
     Restricted cash                                                 16,165                  16,165
     Prepaids and other                                              90,629                 201,061
     Income tax receivable                                          786,186                 782,000
                                                                -----------             -----------
       Total current assets                                      14,602,626              19,320,108
                                                                -----------             -----------
Property and equipment:
  Mineral properties                                              3,596,374
  Work in progress                                                1,004,682
  Furniture and equipment                                            74,502                  90,440
                                                                -----------              ----------
       Total property and equipment                               4,675,558                  90,440
  Less accumulated depreciation                                     (54,235)                (66,382)
                                                                -----------              ----------
                                                                  4,621,323                  24,058
                                                                -----------              ----------
Investments and advances                                          1,288,347                 134,778
Other assets                                                          7,725                   7,725
                                                                -----------             -----------
                                                                $20,520,021             $19,486,669
                                                                ===========             ============

                      LIABILITIES AND STOCKHOLDERS' EQUITY

Current liabilities:
  Accounts payable and accrued liabilities                          180,715                 299,061
                                                                -----------             -----------
      Total current liabilities                                     180,715                 299,061
Deferred income taxes                                             1,376,378
                                                                -----------             -----------
                                                                  1,557,093                 299,061
                                                                -----------             -----------
Stockholders' equity
  Common stock: $.002 par value, 100,000,000 shares authorized:
  29,752,121 and 25,680,497 shares outstanding as
  of March 31, 1999 and June 30,1998, respectively                   59,504                  51,361
  Additional paid-in capital                                     28,357,979              25,999,733
  Deficit                                                        (9,454,555)             (6,863,486)
                                                                -----------             -----------
                                                                 18,962,928              19,187,608
                                                                -----------             -----------
                                                                $20,520,021             $19,486,669
                                                                ===========             ===========
</TABLE>

Commitments and contingencies

   The accompanying notes are an integral part of these financial statements.


                                       3
<PAGE>   4

AZCO MINING INC. (DELAWARE)
CONSOLIDATED STATEMENTS OF OPERATIONS (UNAUDITED)

<TABLE>
<CAPTION>
                                                   THREE MONTHS ENDED                NINE MONTHS ENDED
                                                       MARCH 31,                         MARCH 31,
                                                  1999             1998             1999            1998
<S>                                           <C>              <C>               <C>               <C>
INCOME:
    Interest income                            $  215,818      $   240,508       $  719,636        $ 785,522
    Other income                                   11,500            9,852           11,500            9,852
                                               ----------      -----------       ----------       ----------

                                                  227,318          250,360          731,136          795,374
                                               ----------      -----------       ----------       ----------

EXPENSES:
     Salaries and consulting fees                 544,317          213,449          985,022          630,843
     General and administrative                   229,434          254,055          710,476          863,701
     Exploration                                  239,955          652,261        1,467,836        2,076,276
     Accounting and legal                          74,867           81,882          151,780          311,347
     Amortization and depreciation                  3,570            4,666           11,277           15,578
     Legal settlement costs                                                                          400,000
                                               ----------      -----------      -----------      -----------
                                                1,092,143        1,206,313        3,326,391        4,297,745
                                               ----------      -----------      -----------      -----------

Loss before income taxes                          864,825         (955,953)      (2,595,255)      (3,502,371)

     Income Taxes                                  (4,186)        (178,000)          (4,186)      (1,893,237)
                                               ----------      -----------      -----------      -----------
NET LOSS                                       $ (860,639)     $  (777,953)     $(2,591,069)     $(1,609,134)
                                               ==========      ===========      ===========      ============

BASIC LOSS PER COMMON SHARE                    $    (0.03)     $     (0.03)     $     (0.10)     $      (0.06)
                                               ==========      ===========      ===========      ============

DILUTED LOSS PER COMMON SHARE                  $    (0.03)     $     (0.03)     $     (0.10)     $      (0.06)
                                               ==========      ===========      ===========      ============

WEIGHTED AVERAGE COMMON SHARES                 26,402,745       25,678,410       25,828,510        25,520,160
                                               ==========      ===========      ===========      ============
</TABLE>


The accompanying notes are an integral part of these financial statements.

                                       4
<PAGE>   5

AZCO MINING INC. (DELAWARE)
CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED)

<TABLE>
<CAPTION>
                                                                NINE MONTHS ENDED MARCH 31,
                                                               -----------------------------
                                                                   1999             1998
<S>                                                            <C>              <C>
Cash flows from operating activities:
      Net loss                                                 $(2,591,069)     $(1,609,134)
      Adjustments to reconcile net loss to net cash
      Used in operations:
            Stock issued for mineral properties                    234,375           50,000
            Depreciation and amortization                           11,277           15,578
            Stock option compensation expense                      310,000
            Gain on sale of furniture and equipment                 (1,500)
      Changes in assets and liabilities, net:
            Prepaid and other assets                               110,432         (138,914)
            Deposit                                                               4,000,000
            Accounts payable and accrued liabilities              (161,346)        (155,250)
            Income tax receivable                                   (4,186)         (86,272)
                                                               -----------      -----------
Net cash provided by (used for) operating activities            (2,092,017)       2,076,008
                                                               -----------      -----------

Cash flows from investing activities:
      Advances from Indonesian projects                                             244,750
      Investments and advances                                  (1,153,569)
      Work in progress                                            (892,290)
      Purchases of furniture and equipment                          (7,486)          (2,900)
      Proceeds from sale of furniture and equipment                  1,500            5,101
                                                               -----------      -----------
Net cash provided by (used for) investing activities            (2,051,845)         246,951
                                                               -----------      -----------
Cash flows from financing activities:
       Proceeds from sale of common stock                                            54,293
       Purchase of treasury stock                                 (467,374)
                                                               -----------      -----------
Net cash provided by (used for) financing activity:               (467,374)          54,293
                                                               -----------      -----------

Net increase (decrease) in cash and cash equivalents            (4,611,236)       2,377,252

Cash and cash equivalents at  beginning of period               18,320,882       17,080,260
                                                               -----------      -----------
Cash and cash equivalents at end of period                     $13,709,646      $19,457,512
                                                               ===========      ===========
</TABLE>


   The accompanying notes are an integral part of these financial statements


                                        5
<PAGE>   6

 AZCO MINING INC.
 (DELAWARE)
 CONSOLIDATED STATEMENT OF STOCKHOLDERS' EQUITY (UNAUDITED)

<TABLE>
<CAPTION>
                                                Common                  Additional
                                                 Stock                    Paid-In
                                        Shares           Amount           Capital          Deficit
<S>                                    <C>              <C>            <C>              <C>          
 Balance, June 30, 1998                25,680,497       $ 51,361       $ 25,999,733     $ (6,863,486)

   Shares issued:
     Property payments                    375,000            750            233,625
     Acquisition of AMPI                4,500,000          9,000          2,280,388

   Shares purchased:
     Treasury stock                      (803,376)        (1,607)          (465,767)

    Stock option compensation                                               310,000

 Net Loss                                                                                 (2,591,069)
                                       ----------       --------      -------------    ------------- 

 Balance March 31, 1999                29,752,121       $ 59,504      $  28,357,979    $  (9,454,555)
                                       ==========       ========      =============    ============= 
</TABLE>


        The accompanying notes are an integral part of the financial statements.


                                       6
<PAGE>   7

AZCO MINING INC. (DELAWARE)
NOTES TO INTERIM CONSOLIDATED FINANCIAL STATEMENTS (UNAUDITED)


NOTE 1. BASIS OF PRESENTATION

In the opinion of management, the accompanying interim financial statements
contain all material adjustments consisting only of normal recurring adjustments
necessary to present fairly the financial position, the results of operations
and the cash flows of the Company and its consolidated subsidiaries for the
interim period. Users of financial information produced for interim periods are
encouraged to refer to the footnotes contained in the Annual Report on Form 10-K
when reviewing interim financial results.

AZCO Mining Inc. (Delaware) (the "Company") was formed on July 13, 1988 to
acquire mining properties and either develop or sell them. The Company will
consider properties of merit in almost any geographical location.


NOTE 2. PIEDRAS VERDES PROJECT (MEXICO)

The Company announced in November of 1998 that it had received a pre-feasibility
study on the Piedras Verdes project from its 70% project partner Phelps Dodge
Corporation. The study, assuming a copper price of $1.00/ lb. estimates project
operating costs below $0.50 per pound, over a 10-year life with annual copper
production of 130 million pounds. A $3.6 million work budget advancing the
project towards a bankable feasibility study over the next 18 months has been
approved and is being initiated by Phelps Dodge Corporation. The Company will be
responsible for the funding of its 30% portion of the work budget.


NOTE 3. MALI PROJECT (NORTHWESTERN AFRICA)

During the nine-month period ended March 31, 1999 the Company expensed $403,650
against its Mali Project. Included in project operating costs was $234,375 that
represented 375,000 shares of the Company's stock issued under the terms of the
Lines Overseas Management Agreement of April 6, 1998. The operating costs are
included in exploration costs in the accompanying statement of operations. The
Company, as of March 31, 1999, had advanced to the Mali Project a total of
$5,240,639.

The Company announced on January 21, 1999 that it had concluded a joint venture
agreement with Randgold Resources Limited ("Randgold"), whereby Randgold
acquired the right to earn up to 75% of the Company's interest in West Africa
Gold and Exploration S.A.

                                       7
<PAGE>   8

AZCO MINING INC. (DELAWARE)
NOTES TO INTERIM CONSOLIDATED FINANCIAL STATEMENTS (UNAUDITED)
(CONTINUED)


("WAG"). To earn this consideration Randgold has agreed, over the next 36
months, to conduct exploration on the WAG concessions at a minimum cost of $2
million, with the aim of establishing whether there is a viable economic gold
deposit of at least one million ounces. Thereafter Randgold shall prepare a
Bankable Feasibility Study on any such deposit for WAG within a further 12
months in order to earn its interest therein.


NOTE 4. PONGKOR PROJECT (INDONESIA)

The Company has completed a geologic evaluation of the Pongkor properties and
has compiled an extensive report that is currently being disseminated to a
number of companies, which have expressed an interest in joint-venturing the
properties.


NOTE 5. BENITOITE PROJECT (SAN BENITO COUNTY, CALIFORNIA)

On March 18, 1999 the Company announced that it had paid $20,000 for an
extension, to January 1, 2000, on its option to acquire the Benitoite Gem Mine
in San Benito County, California.

The Company has staked additional ground in the area of the Gem Mine and has
entered into a letter of agreement with a third party whereby the Company would
sell its option to acquire the Gem Mine and the additional claims.


NOTE 6. LA ADELITA PROPERTY (MEXICO)

On July 21, 1998, the Company entered into an option agreement with Minera
Cortez whereby the Company was granted an option to earn up to a 70% interest in
the La Adelita property in Sonora, Mexico under the following terms:

  i. by subscribing for 100,000 common shares of Cortez at Cdn. $0.25 per share

 ii. by making option payments and paying finder's fees on behalf of Cortez
     totaling $165,000 over the next five years

iii. By incurring exploration expenditures on the property totaling $500,000
     over the next three years.

During the nine-month period ended March 31, 1999 the Company has expended
$88,228 on the La Adelita property and thus completed its first year's
commitment to the property.

                                       8
<PAGE>   9

AZCO MINING INC. (DELAWARE)
NOTES TO INTERIM CONSOLIDATED FINANCIAL STATEMENTS (UNAUDITED)
(CONTINUED)


NOTE 7. BLACK CANYON MICA PROJECT

On March 10, 1999 the Company announced that it had acquired Arizona Mica
Properties, Inc. ("AMPI") through a merger with the Company's subsidiary,
Sanchez Mining Inc. AMPI is the owner of the Black Canyon Mica Project, a
significant source of high-quality mica and a pilot processing plant situated
near Phoenix, Arizona.

The acquisition has been accounted for by the purchase method, and the results
of AMPI have been reflected in the Company's results of operations from March
10, 1999. The Company issued to the principals of AMPI 4,500,000 shares of the
Company's common stock (subject to certain trading and voting trust
restrictions) with a value of $2,289,388, in exchange for all the outstanding
shares of AMPI. Details of the net assets acquired are as follows:

<TABLE>
<CAPTION>
               Net assets acquired:

<S>                                                             <C>
                        Mineral properties                       3,596,374

                        Work in progress                           112,392

                        Lease obligation                           (43,000)

                        Deferred income taxes                   (1,376,378)
                                                                ----------
                                                                 2,289,388
                                                                ==========
</TABLE>


The issuance of the Company's shares to acquire shares of AMPI is a non-cash
investing and financing activity, and accordingly, the transaction is not
reflected in the Consolidated Statement of Cash Flows.

The acquisition was completed following a 3-month due diligence period which
included confirmatory diamond drilling, concentration test work, a marketing
study, environmental audit, legal title work and significant development work.
The Company has expensed as exploration expense $293,387 of due diligence work
on the Black Canyon Mica Project through March 31, 1999.

                                       9
<PAGE>   10

AZCO MINING INC. (DELAWARE)
NOTES TO INTERIM CONSOLIDATED FINANCIAL STATEMENTS (UNAUDITED)
(CONTINUED)


The acquisition includes the plant site, pilot facilities and 43 claims. An
additional 226 adjacent claims have been staked and recorded by the Company.
Substantial development and construction has been completed and further work is
continuing to complete a production facility with an estimated capacity of
10,000 tones per annum. Through March 31, 1999 the Company has expended $892,290
on the development and construction of the Mica project, which has been recorded
as work in progress.


NOTE 8. SHARE REPURCHASE

On August 6, 1998 the Company approved the repurchase of up to 1,284,024 shares
of its issued and outstanding common stock on the American Stock Exchange
commencing August 13, 1998 and continuing through August 13, 1999. The maximum
authorized repurchase price is $1.50 per common share. The Company repurchased
803,376 shares through March 31, 1999.


NOTE 9. INVESTMENTS AND ADVANCES

On May 22, 1998 the Company entered into an agreement to purchase a $1,500,000
convertible debenture of Oro Argentina Limited (OAL) for the purpose of
financing the first phase of the Chiqua White Bentonite Project. At March 31,
1999, $1,159,390 has been drawn against the debenture by OAL and the Company
accrued $78,369 in interest on the debenture.

The debenture bears interest at 12% per annum and is due on September 1, 2000.
During this term, the Company can convert the debenture into shares of OAL at
$0.50 per unit, where each unit consists of one common share and one warrant,
convertible into common shares within two years of issue at $0.60 per share.

The ultimate recovery of the debenture is dependent on the ability of OAL to
realize its exploration and development assets, which are subject to the
measurement uncertainty inherent in such assets.


NOTE 10. OUTSTANDING OPTIONS

At March 31, 1999 the Company had 3,564,500 options outstanding which are
exercisable between $0.47 and $3.00 per common share at varying dates through
2004.

                                       10
<PAGE>   11

AZCO MINING INC. (DELAWARE)


ITEM 2. MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS
        OF OPERATIONS

RESULTS OF OPERATIONS

GENERAL

The Company was formed on July 13, 1988. On December 21, 1995 the Company
announced that it had completed the sale of its Sanchez Project and a 70%
interest in its Mexican Project, the Piedras Verdes, to Phelps Dodge Corporation
for $40 million. All material revenues since the sale have been a result of
interest earned on the proceeds of the sale of assets to Phelps Dodge
Corporation.

The Company is currently in the development and construction stage of its newly
acquired Black Canyon Mica Project and is evaluating a number of other
opportunities in the mining industry for the purpose of merger, acquisition,
joint venture or project development.

NINE MONTHS ENDED MARCH 31, 1999 COMPARED TO NINE MONTHS ENDED MARCH 31, 1998.

The net loss for the nine months ended March 31, 1999 was $2,591,069 compared to
a net loss of $1,609,134 for the nine months ended March 31, 1998. The increase
in the current period net loss is the result of the accrual of a $1,893,237
federal income tax refund during the nine months ended March 31, 1998 off set by
legal settlement costs of $400,000 for the same period.

Salaries and consulting fees expense was $985.022 for the nine months ended
March 31, 1999 compared to $630.843 for the nine months ended March 31, 1998.
The increase in salaries and consulting fees expense in the current period is
due to the recording of $310,000 in compensation expense recognized on stock
options granted to non-employees during the current period.

Accounting and legal expense was $151,780 for the nine months ended March 31,
1999 compared to $311,347 for the nine months ended March 31, 1998. The decrease
in accounting and legal expense as well as legal settlement costs was the result
of the full and final settlement of all matters and claims with AIOC
Corporation.

Exploration expense was $1,467,836 for the nine months ended March 31, 1999
compared to $2,076,276 for the nine months ended March 31, 1998. The decrease in
exploration expense is due to decreased activity on the Piedras Verdes Project
during the current period.


                                       11
<PAGE>   12

AZCO MINING INC. (DELAWARE)
RESULTS OF OPERATIONS 
(CONTINUED)


THREE MONTHS ENDED MARCH 31, 1999 COMPARED TO THREE MONTHS ENDED MARCH 31, 1998.

Net loss for the three months ended March 31, 1999 was $860,639 compared to the
net loss of $777,953 for the three months ended March 31, 1998.

Salaries and consulting fees expense was $544,317 for the three months ended
March 31, 1999 compared to $213,449 for the three months ended March 31, 1998.
The increase in salaries and consulting fees expense is due to the recording of
$310,000 in compensation expense recognized on stock options granted to
non-employees during the current period.

Exploration expense was $239,955 for the three months ended March 31, 1999
compared to $652,261 for the three months ended March 31, 1998. The decrease in
exploration expense is due to decreased activity on the Piedras Verdes Project
in the current period.

During the three month period ended March 31, 1999 the Company advanced an
additional $43,296 against the OAL debenture. Through March 31, 1999 the Company
has advanced $1,159,390 to OAL and accrued $78,369 in interest under the May 22,
1998 debenture agreement.

FINANCIAL CONDITION

As of March 31,1999 the Company had cash and cash equivalents of $13,709,646.

The Company believes that for the current fiscal year ended June 30, 1999 all
capital requirements will be funded with present cash and cash equivalents.


ITEM 3: QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK 

Not applicable.


PART II. OTHER INFORMATION

ITEM 1: LEGAL PROCEEDINGS

On January 22, 1999 the trustee ("Petitioner") in bankruptcy proceedings against
Eagle River International Ltd. ("Eagle") served a petition, in the Quebec
Superior Court, District of Hull, upon the Company in order to recuperate assets
from the Company.


                                       12
<PAGE>   13

                           AZCO MINING INC. (DELAWARE)


It is the understanding of the Company and its Canadian legal counsel that the
Petitioner alleges that, through the Company's involvement with Eagle in the
Mali Project, the Company is guilty of contractual breaches in excess of
$3,400,000.

It is the position of the Company and its Canadian legal counsel that it is very
unlikely that the Company committed the alleged contractual breaches and both
are of the impression that the damages claimed are grossly exaggerated.

Currently, the Company has presented a motion to transfer the proceedings to a
British Columbia Bankruptcy Court and the Court has taken the matter under
advisement.


ITEM 2: CHANGES IN SECURITIES AND USE OF PROCEEDS

     SALE OF UNREGISTERED SECURITIES

     On March 9, 1999 the Company consummated the acquisition of Arizona Mica
Properties, Inc., (AMPI) an Arizona corporation, that owned the rights to
develop 43 unpatented lode-mining claims located in Yavapai County, Arizona.
This acquisition was accomplished through the merger of AMPI with and into the
Company's wholly owned subsidiary, Sanchez Mining Inc., a Delaware corporation
("Sanchez"), with Sanchez being the surviving corporation in the merger. In
connection with the merger, the Company issued an aggregate of 4,500,000 shares
(the "Shares") of its Common stock to the three shareholders of AMPI, Messieurs.
Lawrence G. Olson, John O. Rud and Floyd R. Bleak, with each such shareholder
receiving 1,500,000 shares of the Company's Common Stock. The shares were issued
as "restricted securities" as that term is defined in Rule 144 promulgated under
the United States Securities Act of 1933, as amended (the "Act"), and the
certificates representing the shares bear a restrictive legend permitting
transfer only pursuant to registration or applicable exemption under the Act.
The securities were issued in reliance upon the exemption from registration
provided under Section 4 (2) of the securities act of 1933.


ITEMS 3-4: NOT APPLICABLE

ITEM 5: OTHER INFORMATION

     None.


                                       13
<PAGE>   14

                           AZCO MINING INC. (DELAWARE)


ITEM 6: EXHIBITS AND REPORTS ON FORM 8-K

(a)  EXHIBITS:

     None.

(b)  REPORTS ON FORM 8-K

     The Company filed a report on Form 8-K dated March 9, 1999 reporting the
     Company's acquisition of AMPI. Included in the report were AMPI financial
     statements as at November 30, 1998.



                                   SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the
Registrant has duly caused this report to be signed on its behalf by the
undersigned thereunder duly authorized.



Date: May 14, 1999                       BY: /s/ Alan P. Lindsay
                                             -----------------------------------
                                             Alan P. Lindsay
                                             CEO, President and Chairman


Date: May 14, 1999                       BY: /s/ Ryan A. Modesto
                                             -----------------------------------
                                             Ryan A. Modesto
                                             Vice President of Finance


                                       14