HBM HudBay Minerals Inc

The following constitutes Amendment No. 4 to the Schedule 13D filed by the undersigned (“Amendment No. 4”). This Amendment No. 4 amends the Schedule 13D as specifically set forth herein.

Item 3 is hereby amended and restated to read as follows:

The Shares purchased by each of Waterton Mining LP and Waterton Fund II were purchased with working capital (which may, at any given time, include margin loans made by brokerage firms in the ordinary course of business) in open market purchases, except as otherwise noted, as set forth in Schedule A, which is incorporated by reference herein. The aggregate purchase price of the 13,560,625 Shares beneficially owned by Waterton Mining LP is approximately C$84,001,266, excluding brokerage commissions. The aggregate purchase price of the 13,560,631 Shares beneficially owned by Waterton Fund II is approximately C$84,001,303, excluding brokerage commissions.

Item 4 is hereby amended to add the following:

On December 13, 2018, WGRM Inc. and certain of its affiliates (collectively, “Waterton”) issued an open letter to the Issuer’s shareholders announcing that Waterton is finalizing its recruitment of a majority slate of highly qualified, independent director candidates, including a transformational CEO candidate, to nominate for election to the Board of Directors (the “Board”) at the Issuer’s 2019 Annual Meeting of Shareholders (the “Annual Meeting”). Waterton stated that its nominees will possess the collective experience and strategic expertise to drive value at the Issuer and address the challenges and maximize the opportunities facing the Issuer.

In the letter, Waterton reiterated its disappointment with the Issuer’s abysmal performance and the continued destruction of shareholder value under the stewardship of the Issuer’s management team and Board. Specifically, Waterton noted that for the period ending October 4, 2018, the Issuer’s total shareholder return (TSR) versus its peer group ¹ was -106% during the CEO’s tenure and -134% during the Chairman’s tenure. ² Waterton also noted that throughout its efforts to engage in a constructive dialogue with the Issuer, the Board and management team demonstrated a pattern of systemic bad faith and an unwillingness to meaningfully engage with shareholders. Waterton expressed concerns that the Issuer’s behavior stems from a culture of toxic, value-destructive entrenchment at both the Board and C-Suite levels. Waterton further questioned the independence of the Board, noting that 40% of the current Board has been in place for nearly a decade, including Chairman Alan Hibben, who seems to be exerting a troubling level of influence over the Board.

Additionally, in the letter, Waterton withdrew its request to call a Special Meeting relating to shareholder approvals for certain transactions so that Waterton can focus on the urgent need for Board refreshment. A copy of the letter is attached hereto as Exhibit 99.1 and is incorporated herein by reference.

¹ Waterton believes an appropriate peer group for the Issuer should only include companies that (i) have a market capitalization of greater than US$500 million, (ii) have material exposure to the Americas, (iii) have copper comprising greater than 50% of reserves, and (iv) are publicly listed on a major stock exchange, and not the peer group described in the Issuer’s public disclosure.

² Source: Capital IQ

Items 5(a)-(c) are hereby amended and restated to read as follows:

The aggregate percentage of Shares reported owned by each person named herein is based upon 261,272,151 Shares outstanding, as of October 30, 2018, which is the total number of Shares outstanding as reported in Exhibit 99.2 to the Issuer’s Report of foreign issuer on Form 6-K filed with the Securities and Exchange Commission on November 1, 2018.

Percentage: Approximately 5.2%

Percentage: Approximately 5.2%

Percentage: Approximately 5.2%

Percentage: Approximately 5.2%

Percentage: Approximately 5.2%

Percentage: Approximately 10.4%

Percentage: Approximately 10.4%

Item 7 is hereby amended to add the following exhibit:

SIGNATURES

After reasonable inquiry and to the best of his knowledge and belief, each of the undersigned certifies that the information set forth in this statement is true, complete and correct.

Dated: December 17, 2018

SCHEDULE A

Transactions in the Shares Since the Filing of Amendment No. 3 to the Schedule 13D

Waterton Mining Parallel Fund Offshore Master, LP

Waterton Precious Metals Fund II Cayman, LP

^* The price reported is a weighted average price. These shares were purchased in multiple transactions at prices ranging from C$6.14 to C$6.35. The Reporting Persons undertake to provide to the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares purchased at each separate price within the ranges set forth herein.