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UNITED STATESSECURITIES AND EXCHANGE COMMISSIONWashington, D.C.
20549

FORM 40-F/AAmendment No. 1

[   ]REGISTRATION STATEMENT PURSUANT TO
SECTION 12 OF THE SECURITIES EXCHANGE ACT OF 1934

OR

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

|For the fiscal year ended: December 31, 2011 | Commission File Number: 001-35278
|-------------------------------------------- | ---------------------------------

PRIMERO MINING CORP.(Exact name of Registrant as specified in its charter)

|British Columbia, Canada           | 1040                         | Not Applicable     
|---------------------------------- | ---------------------------- | -------------------
|                                   |                              |                    
|(Province or Other Jurisdiction of | (Primary Standard Industrial | (I.R.S. Employer   
|Incorporation or Organization)     | Classification Code)         | Identification No.)

Suite 1640, One Bentall Centre505 Burrard Street,
Box 24Vancouver, British Columbia, Canada( 604) 669
0040(Address and telephone number of Registrants principal
executive offices)

Corporation Service CompanySuite 400, 2711
Centerville RoadWilmington, Delaware 19808(800)
927-9800(Name, address (including zip code) and telephone number
(includingarea code) of agent for service in the United States)

Securities registered or to be registered pursuant to section
12(b) of the Act:

|Title Of Each Class         | Name Of Each Exchange On Which Registered
|--------------------------- | -----------------------------------------
|Common Shares, no par value | New York Stock Exchange                  

Securities registered or to be registered pursuant to Section
12(g) of the Act: None

Securities for which there is a reporting obligation pursuant to
Section 15(d) of the Act: None

For annual reports, indicate by check mark the information filed
with this Form:

|[X]  Annual Information Form | [X]  Audited Annual Financial Statements
|---------------------------- | ----------------------------------------

Indicate the number of outstanding shares of each of the
Companys classes of capital or common stock as of the close of the period
covered by the annual report: 88,259,831 Common Shares as at December 31,
2011

Indicate by check mark whether the Company by filing the information
  contained in this Form is also thereby furnishing the information to the
  Commission pursuant to Rule 12g3-2(b) under the Securities Exchange Act of 1934
  (the Exchange Act). If yes is marked, indicate the file number
  assigned to the Company in connection with such Rule. 
  Yes [ 
   ]     No [X]

Indicate by check mark whether the Company (1) has filed all
reports required to be filed by Section 13 or 15(d) of the Exchange Act during
the preceding 12 months (or for such shorter period that the Company was
required to file such reports), and (2) has been subject to such filing
requirements for the past 90 days. 
  Yes [X]      No [   ]

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Indicate by check mark whether the Company has submitted
electronically and posted on its corporate Web site, if any, every Interactive
Data File required to be submitted and posted pursuant to Rule 405 of Regulation
S-T (§232.405 of this chapter) during the preceding 12 months (or for such
shorter period that the Company was required to submit and post such
files).Yes [   ]     No [   ]

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EXPLANATORY NOTE

Primero Mining Corp. (the Company or Primero)
is filing this Amendment No. 1 to its Annual Report on Form 40-F (the Annual
Report) in order to file with the United States Securities and Exchange
Commission (the SEC) its amended Annual Information Form dated May 15,
2012 (the Amended AIF) filed with Canadian Securities Administrators
via the SEDAR web site on May 23, 2012. The Amended AIF includes updated
scientific and technical information relating to the Companys San Dimas
property (the Property) that was required to be disclosed in the
original Annual Information Form (the Original AIF) but was not
available at the time that the Original AIF was filed with Canadian securities
Administrators via the SEDAR web site on April 3, 2012. The Company was required
to file the Amended AIF pursuant to the decision of the British Columbia
Securities Commission dated April 2, 2012. No other amendments are being made to
the Annual Report as originally filed.

ANNUAL INFORMATION FORM, AUDITED FINANCIAL STATEMENTS AND
MD&A

The following documents of the Company are filed and
incorporated by reference into this Annual Report:

|Document                                                                                                                                                     | Exhibit No.
|------------------------------------------------------------------------------------------------------------------------------------------------------------ | -----------
|Amended Annual Information Form of the Company for the year
      ended December 31, 2011                                                                    | 99.1 (1)   
|Audited financial statements of the Company for the years ended
      December 31, 2011 and 2010, including the report of auditor with respect
      thereto | 99.2 (2)   
|Management Discussion and Analysis of the Company for the year
      ended December 31, 2011 (the MD&A)                                                    | 99.3 (2)   

|(1) | Filed as an exhibit hereto.                                                                                     
|--- | ----------------------------------------------------------------------------------------------------------------
|    |                                                                                                                 
|(2) | Previously filed as an exhibit to the Companys original
      Annual Report filed with the SEC on April 3, 2012

FORWARD-LOOKING STATEMENTS

This Annual Report, as amended, includes or incorporates by
reference certain statements that constitute forward-looking statements within
the meaning of the United States Private Securities Litigation Reform Act of
1995. These statements appear in a number of places in this Annual Report,
as amended, and documents incorporated by reference herein and include
statements regarding the Companys intent, belief or current expectation and
that of the Companys officers and directors. These forward-looking statements
involve known and unknown risks and uncertainties that may cause the Companys
actual results, performance or achievements to be materially different from any
future results, performance or achievements expressed or implied by such
forward-looking statements. When used in this Annual Report, as amended, or in
documents incorporated by reference in this Annual Report, as amended, words
such as believe, anticipate, estimate, project, intend, expect,
may, will, plan, should, would, contemplate, possible, attempts,
seeks and similar expressions are intended to identify these forward-looking
statements. These forward-looking statements are based on various factors and
were derived utilizing numerous assumptions that could cause the Companys
actual results to differ materially from those in the forward-looking
statements. Accordingly, readers are cautioned not to put undue reliance on
these forward-looking statements.

Forward-looking statements include, among others, statements
regarding:

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- the ability of the Company to expand production at the San Dimas Mine (as
  defined in the AIF, as amended,);
- the ability of the Company to successfully operate the San Dimas Mine;
- the ability of the Company to identify appropriate acquisition
  opportunities, or if an opportunity is identified, to conclude a transaction
  on satisfactory terms;
- the expected results of exploration activities;
- the recording of revenue under the Amended and Restated Silver Purchase
  Agreement (as defined in the AIF, as amended,) at the fixed price realization
  and the recording of taxes on this basis;
- the identification of potential taxes as a contingent liability and
  retaining access to sufficient cash to satisfy such contingent liability;
- increased delineation at the San Dimas Mine that will lead to better grade
  control and the attainment of more consistent production targets in the
  future;
- the expected results of reclamation activities at the San Dimas Mine;
- the estimation or realization of Minerals Reserves (as defined in the AIF,
  as amended,) and Mineral Resources (as defined in the AIF, as amended,) and
  the realization of Mineral Reserve estimates (including all assumptions),
- the ability to identify new Mineral Resources and convert Mineral Resources
  into Mineral Reserves;
- the impact of new estimation methodologies on mine and production planning;
- the timing and success of exploration activities;
- the timing and the ability to expand the mill;
- intentions to become an intermediate gold producer;
- the timing and amount of estimated future production;
- the ability to generate cash flows that exceed capital requirements;
- capital expenditures and costs, including forecasted cash costs;
- the timing of the development of new mineral deposits;
- the sufficiency of future cash flows;
- requirements for additional capital and ability to complete future
  financings to raise additional capital for exploration, development and
  operational activities and for acquisitions;
- projected gold and silver production;
- expected ore grades, recovery rates and throughput;
- the ability of the Company to comply with environmental, safety and other
  regulatory requirements;

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- expected or proposed development or construction activities, including
  additional tunnels, plant expansion, tailings improvements and hydro-electric
  improvements, and the expected costs thereof;
- expected environmental capital expenditures;
- expectations regarding currency fluctuations;
- future prices of precious and base metals;
- the ability of the Company to achieve a favourable advance ruling on its
  restructuring plan from Mexican tax authorities;
- the ability of the Company to obtain government approvals or permits in
  connection with the continued operation and development of the San Dimas
  Mines;
- the timing and results of union contract negotiations;
- the resolution of title disputes relating to the Companys properties; and
- the timing and possible outcome of pending litigation.

The above forward-looking information is necessarily based upon
a number of factors and assumptions that, while considered reasonable by the
Company as of the date of such statements, are inherently subject to significant
business, economic and competitive uncertainties and contingencies. Key
assumptions upon which the Companys forward-looking statements are based
include the following:

- the specific assumptions set forth in the AIF, as amended, and the
  MD&A;
- the expectations and beliefs of management;
- assumptions relating to the existence of companies that may wish to dispose
  of producing or near-term producing precious metals assets;
- that there are no significant disruptions affecting operations, whether due
  to labour disruptions, supply disruptions, damage to or loss of equipment,
  whether as a result of natural occurrences including flooding, political
  changes, title issues, intervention by local landowners, loss of permits, or
  environmental concerns or otherwise;
- that there are no disruptions in the supply of power from the Las Truchas
  power generation facility, whether as a result of damage to the facility or
  unusually limited amounts of precipitation;
- that development and expansion at the San Dimas Mine proceeds on a basis
  consistent with current expectations and the Company does not change its
  development and exploration plans;
- that the exchange rate between the Canadian dollar, Mexican peso and the
  United States dollar remains consistent with current levels or as set out in
  the AIF, as amended,;
- that prices for gold and silver remain consistent with the Companys
  expectations;
- that prices for key mining supplies, including labour costs and
  consumables, remain consistent with the Companys current expectations;
- that production meets expectations and is consistent with estimates;

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- that plant, equipment and processes will operate as anticipated;
- that the Companys current estimates of Mineral Reserves, Mineral
  Resources, mineral grades and mineral recovery are accurate;
- that the Company identifies higher grade veins in sufficient quantifies of
  minable ore in the Central Block and Sinaloa Graben;
- that the geology and vein structures in the Sinaloa Graben are as expected;
- that the Company completes the proposed tunnels and access routes;
- that the ratio of gold to silver price is maintained in accordance with the
  Companys expectations;
- that there are no material variations in the current tax and regulatory
  environment or the tax positions taken by the Company;
- that the Company will maintain access to surface rights;
- that the Company will be able to obtain and maintain government approvals
  or permits in connection with the continued operation and development of the
  San Dimas Mine;
- that the Company will be able to repay its indebtedness under the
  Promissory Note and Convertible Promissory Note (as defined in the AIF, as
  amended,);
- that the Company can access financing, appropriate equipment and sufficient
  labour; and
- that the political environment within Mexico will continue to support the
  development of environmentally safe mining projects.

No assurance can be given that these assumptions will prove to
be correct. These assumptions should be considered carefully by readers. Readers
are cautioned not to place undue reliance on the forward-looking information and
statements or the assumptions on which the Companys forward-looking information
and statements are based.

Forward-looking information is subject to a variety of risks
and uncertainties which could cause actual events or results to differ from
those reflected in the forward-looking statements. Such risks include, but are
not limited to:

- the specific risks set forth in the AIF, as amended, and the MD&A;
- Mexican tax authorities may not provide a favourable advance ruling
  supporting the Companys restructuring plan;
- if the Company is required to revert to paying taxes based on the market
  price of silver for all sales under the Amended and Restated Silver Purchase
  Agreement to SW Caymans (as defined in the AIF, as amended, under Acquisition
  of San Dimas Mine), the Company may be required to pay higher taxes with
  higher silver prices, and the adverse tax consequences to the Company may,
  depending on the annual production of silver, increase in severity and the
  Companys cash flow may not be sufficient to fund its obligations, there may
  be an impairment loss and a write down of the San Dimas Mine and the Company
  could be forced to discontinue production and may lose its interest in, or may
  be forced to sell, some of its properties;
- the ability of the Company to achieve projected gold and silver production
  and, gold and silver grades;
- projected cash costs of production and capital expenditures may be greater
  than anticipated;

5

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- the volatility of prices of gold, silver and other metals;
- the ratio between the market prices of gold and silver;
- uncertainty of Mineral Reserves, Mineral Resources, exploration potential,
  mineral grades and mineral recovery estimates;
- uncertainty of future production, delays in completion of the mill
  expansion, exploration and development plans;
- insufficient capital to complete mill expansion, development and
  exploration plans;
- inability to maintain or acquire attractive mining properties on terms it
  considers acceptable or at all, and other risks inherent with acquisitions;
- potentially unknown liabilities associated with the acquisition of the San
  Dimas Assets (as defined in the AIF, as amended, under Corporate Structure)
  and the shares of Silver Trading (as defined in the AIF, as amended, under
  Corporate Structure);
- delays in obtaining governmental approvals, permits or financing or in the
  completion of development or construction activities;
- the Companys ability to repay its indebtedness under the Promissory Note
  and Convertible Promissory Note and the Companys limited ability to incur
  additional indebtedness;
- the possibility that the Mexican government will contest the entitlement of
  the Company to a credit against federal tax payable;
- currency fluctuations;
- limitations on insurance coverage;
- financing of additional capital requirements;
- commercial viability of mineral deposits;
- cost of exploration and development programs;
- inability to complete the proposed tunnels, access routes or other
  development, for whatever reason;
- risks associated with having adequate infrastructure, including unexpected
  interruptions in power supply from the hydroelectric project;
- mining risks, including unexpected formations and cave-ins, which delay
  operations or prevent extraction of material;
- risks associated with competition in the mining industry;
- risks associated with the ability to retain key executives and certain
  operating personnel;
- risks associated with conflicting legal obligations of directors and
  officers of the Company who are directors and/or officers of other companies;
- risks associated with foreign operations;

6

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- adverse changes to in labour relations legislation or in the relationship
  between the Company with its employees and unions at the San Dimas Mine;
- title disputes or claims;
- changes in governmental and environmental regulation that results in
  increased costs;
- cost of environmental expenditures and potential environmental liabilities;
- landowner dissatisfaction and disputes;
- failure of plant, equipment or processes to operate as anticipated;
- accidents, labour disputes and road blocks; and
- risks associated with having a significant shareholder.

Should one or more of these risks and uncertainties
materialize, or should underlying assumptions prove incorrect, actual results
may vary materially from those described in forward-looking statements.

Investors are advised to carefully review and consider the risk
factors identified in the AIF, as amended, under the heading Risk Factors for
a discussion of the factors that could cause the Companys actual results,
performance and achievements to be materially different from any anticipated
future results, performance or achievements expressed or implied by the
forward-looking statements. Readers are further cautioned that the foregoing
list of assumptions and risk factors is not exhaustive and it is recommended
that prospective investors consult the more complete discussion of the Companys
business, financial condition and prospects that is included in the AIF, as
amended, and the MD&A. Although the Company believes that the assumptions on
which the forward-looking statements are made are reasonable, based on the
information available to the Company on the date such statements were made, no
assurances can be given as to whether these assumptions will prove to be
correct. Accordingly, readers should not place undue reliance on forward-looking
information. The forward-looking information and statements contained in this
AIF, as amended, and the MD&A are made as of the date thereof and,
accordingly, are subject to change after such date. The Company does not
undertake to update any forward-looking information, except as, and to the
extent, required by applicable securities laws, including applicable United
States federal securities laws. The forward-looking statements contained herein
are expressly qualified by this cautionary statement.

CAUTIONARY NOTE TO UNITED STATES INVESTORS
CONCERNINGESTIMATES OF MEASURED, INDICATED AND INFERRED RESOURCES

The disclosure in this Annual Report, as amended, including the
documents incorporated by reference herein, uses terms that comply with
reporting standards in Canada and certain estimates are made in accordance with
Canadian National Instrument 43-101 Standards of Disclosure for Mineral
Projects (NI 43-101). NI 43-101 is a rule developed by the Canadian
Securities Administrators that establishes standards for all public disclosure
an issuer makes of scientific and technical information concerning mineral
projects. Unless otherwise indicated, all reserve and resource estimates
contained in or incorporated by reference in this Annual Report, as amended,
have been prepared in accordance with NI 43-101. These standards differ
significantly from the requirements of the SEC, and reserve and resource
information contained herein and incorporated by reference herein may not be
comparable to similar information disclosed by U.S. companies.

This Annual Report, as amended, includes estimates of mineral
reserves (Mineral Reserves) that have been calculated in accordance
with NI 43-101, as required by Canadian securities regulatory authorities. For
United States reporting purposes, SEC Industry Guide 7 under the Exchange Act,
as interpreted by Staff of the SEC, applies different standards in order to
classify mineralization as a reserve. As a result, the definitions of proven and
probable reserves used in NI 43-101 differ from the definitions in the SEC
Industry Guide 7. Under SEC standards, mineralization may not be classified as a
"reserve" unless the determination has been made that the mineralization could be economically and legally produced or extracted at the
time the reserve determination is made. Among other things, all necessary
permits would be required to be in hand or issuance imminent in order to
classify mineralized material as reserves under the SEC standards. Accordingly,
mineral reserve estimates contained in this Annual Report, as amended, may not
qualify as reserves under SEC standards.

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In addition, this Annual Report, as amended, uses the terms
measured mineral resources, indicated mineral resources and inferred
mineral resources (together Mineral Resources) to comply with the
reporting standards in Canada. The Company advises United States investors that
while those terms are recognized and required by Canadian regulations, the SEC
does not recognize them. United States investors are cautioned not to assume
that any part or all of the mineral deposits in these categories will ever be
converted into mineral reserves. These terms have a great amount of uncertainty
as to their existence, and great uncertainty as to their economic and legal
feasibility.

Further, inferred mineral resources have a great amount of
uncertainty as to their existence and as to whether they can be mined legally or
economically. Therefore, United States investors are also cautioned not to
assume that all or any part of the inferred resources exist. In accordance
with Canadian securities laws, estimates of inferred resources cannot form the
basis of feasibility or other economic studies.

It cannot be assumed that all or any part of measured mineral
resources, indicated mineral resources, or inferred mineral resources will
ever be upgraded to a higher category. Investors are cautioned not to assume
that any part of the reported measured mineral resources, indicated mineral
resources, or inferred mineral resources in this Annual Report, as amended,
is economically or legally mineable.

NI 43-101 also permits the inclusion of disclosure regarding
the potential quantity and grade, expressed as ranges, of a target for further
exploration provided that the disclosure (i) states with equal prominence that
the potential quantity and grade is conceptual in nature, that there has been
insufficient exploration to define a mineral resource and that it is uncertain
if further exploration will result in the target being delineated as a mineral
resources, and (ii) states the basis on which the disclosed potential quantity
and grade has been determined. Disclosure regarding exploration potential has
been included in the Companys AIF, as amended, that is incorporated into this
Annual Report, as amended,. United States investors are cautioned that
disclosure of such exploration potential is conceptual in nature by definition
and there is no assurance that exploration of the mineral potential identified
will result in any category of NI 43-101 Mineral Resources being identified.

In addition, disclosure of contained ounces is permitted
disclosure under Canadian securities laws; however, the SEC only permits issuers
to report mineralization as in place tonnage and grade without reference to unit
measures.

For the above reasons, information contained in this Annual
Report, as amended, and the documents incorporated by reference herein
containing descriptions of the Companys mineral deposits may not be comparable
to similar information made public by U.S. companies subject to the reporting
and disclosure requirements under the United States federal securities laws and
the rules and regulations thereunder.

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UNDERTAKING AND CONSENT TO SERVICE OF PROCESS

Undertaking

The Company undertakes to make available, in person or by
telephone, representatives to respond to inquiries made by the Commission staff,
and to furnish promptly, when requested to do so by the Commission staff,
information relating to:

- the securities registered pursuant to Form 40-F;
- the securities in relation to which the obligation to file an annual report
  on Form 40-F arises; or
- transactions in said securities.

Consent to Service of Process

Concurrently with the filing of its Registration Statement on
Form 40-F with the SEC on August 11, 2011, the Company filed an Appointment of
Agent for Service of Process and Undertaking on Form F-X signed by the Company
and its agent for service of process with respect to the class of securities in
relation to which the obligation to file this Annual Report on Form 40-F arises.

Any change to the name or address of the Companys agent for
service shall be communicated promptly to the Commission by amendment to Form
F-X referencing the file number of the Company.

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SIGNATURES

Pursuant to the requirements of the Exchange Act, the
Registrant certifies that it meets all of the requirements for filing on Form
40-F and has duly caused this annual report to be signed on its behalf by the
undersigned, thereto duly authorized.

|Date: May 23, 2012 | PRIMERO MINING CORP.
|------------------ | --------------------
|                   |                     
|                   |                     
|                   |                     
|                   | By:                 
|                   |                     
|                   |                     

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EXHIBIT INDEX

|Exhibit Number | Exhibit Description                                                                                                                                                                                                           
|-------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|               |                                                                                                                                                                                                                               
|Principal      |                                                                                                                                                                                                                               
|Documents      |                                                                                                                                                                                                                               
|               |                                                                                                                                                                                                                               
|99.1           | Amended Annual
        Information Form of the Company for the year ended December 31, 2011 (2)                                                                                                                               
|               |                                                                                                                                                                                                                               
|99.2           | Audited financial
        statements of the Company and the notes thereto for the fiscal year ended
        December 31, 2011 and 2010 together with the report of the auditors thereon
        (1)                           
|               |                                                                                                                                                                                                                               
|99.3           | Managements Discussion
        and Analysis of the Company for the year ended December 31, 2011 (1)                                                                                                                           
|               |                                                                                                                                                                                                                               
|Certifications |                                                                                                                                                                                                                               
|               |                                                                                                                                                                                                                               
|99.4           | Certification
        of Chief Executive Officer pursuant to Rule 13a-14(a) of the Exchange
        Act (2)                                                                                                                   
|               |                                                                                                                                                                                                                               
|99.5           | Certification
        of Chief Financial Officer pursuant to Rule 13a-14(a) of the Exchange
        Act (2)                                                                                                                   
|               |                                                                                                                                                                                                                               
|99.6           | Certification
        of Chief Executive Officer pursuant to Rule 13a-14(b) of the Exchange
        Act and 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of
        the Sarbanes-Oxley Act of 2002 (2)          
|               |                                                                                                                                                                                                                               
|99.7           | Certification
        of Chief Financial Officer pursuant to Rule 13a-14(b) of the Exchange
        Act and 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of
        the Sarbanes-Oxley Act of 2002 (2)          
|               |                                                                                                                                                                                                                               
|Consents       |                                                                                                                                                                                                                               
|               |                                                                                                                                                                                                                               
|99.8           | Consent of Deloitte
        & Touche LLP dated April 2, 2012 relating to their audit report dated
        March 27, 2012 on the financial statements of the Company for the years
        ended December 31, 2011 and 2010 (1)
|               |                                                                                                                                                                                                                               
|99.9           | Consent of Gordon
        Watts dated April 2, 2012 (1)                                                                                                                                                                       
|               |                                                                                                                                                                                                                               
|99.10          | Consent of Velasquez
        Spring dated April 2, 2012 (1)                                                                                                                                                                   
|               |                                                                                                                                                                                                                               
|99.11          | Consent
        of Herbert A. Smith dated May 23, 2012 (2)                                                                                                                                                                    
|               |                                                                                                                                                                                                                               
|99.12          | Consent
        of J. Morton Shannon dated May 23, 2012 (2)                                                                                                                                                                   
|               |                                                                                                                                                                                                                               
|99.13          | Consent
        of Rodney Webster dated May 23, 2012 (2)                                                                                                                                                                      
|               |                                                                                                                                                                                                                               
|99.14          | Consent
        of Alan Riles dated May 23, 2012 (2)                                                                                                                                                                          

(1)              
Previously filed as an exhibit to the Annual Report on Form 40-F of the Company
for the year ended December 31, 2011 filed on April 3, 2012.

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(2)          
    Filed as an exhibit to this Amendment No. 1 to Annual Report
on Form 40-F of the Company for the year ended December 31, 2011.

2

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