Material Event (Form 8-K)

As previously announced, on January 25, 2026, Gold Resource Corporation (the "Company") entered into an Arrangement Agreement and Plan of Merger, as amended by that certain First Amendment to Arrangement Agreement dated May 15, 2026 (the "Arrangement Agreement"), with Goldgroup Mining Inc., a corporation incorporated under the laws of the province of British Columbia ("Goldgroup"), and Goldgroup Merger Sub Inc., a Colorado corporation and direct, wholly owned subsidiary of Goldgroup ("Purchaser Sub"). The Arrangement Agreement provides that, among other things and subject to the terms and conditions of the Arrangement Agreement, Purchaser Sub will merge with and into the Company, with the Company surviving and continuing as the surviving corporation as a direct, wholly owned subsidiary of Goldgroup (such transaction, the "Merger").

In connection with the Merger, the Company filed a definitive proxy statement (the "Proxy Statement") with the U.S. Securities and Exchange Commission (the "SEC") on May 29, 2026. As is common in transactions of this type, multiple lawsuits have been threatened by purported shareholders of the Company, challenging the completeness and accuracy of the disclosure in the Proxy Statement.

The supplemental disclosures below should be read in conjunction with the Proxy Statement, available on the SEC's website at https://www.sec.gov, along with periodic reports and other information the Company files with the SEC. To the extent information herein differs from or updates information contained in the Proxy Statement, the information set forth herein shall supersede or supplement the information in the Proxy Statement. All page references are to the Proxy Statement, and terms used but not defined below have the meanings set forth in the Proxy Statement.

The Company and Goldgroup believe the claims in the threatened lawsuits are without merit and that no supplemental disclosures are required under applicable law. However, to eliminate the burden, expense, and uncertainties inherent in such litigation, and without admitting any liability or wrongdoing, the Company is voluntarily making the supplemental disclosures set forth below. Nothing herein shall be deemed an admission of the legal necessity or materiality of any of these disclosures. The Company and Goldgroup specifically deny all allegations in the threatened lawsuits, including that any additional disclosure was or is required.

Supplemental Proxy Statement Disclosures

The following changes, shown in strikethrough (for deletions) and underline (for additions) text, are made to the second sentence under the heading "Who is entitled to vote at the Special Meeting?" on page 8

As of the record date, there were approximately 161,889,776163,392,909 Company Shares outstanding, with one vote per share.

The following disclosure is added immediately following the first sentence in the sixth paragraph on page 33

None of these agreements contained a "don't ask, don't waive" provision that would prevent the counterparty from making a proposal to acquire the Company.

The following disclosure is added immediately following the second sentence of the second full paragraph on page 43

The projections provided to ATB Cormark were subject to the assumptions and limitations set forth in the section entitled "-Certain Prospective Financial and Operating Information" beginning on page 49 of this Proxy Statement.

The following disclosure is added to the top of page 49

Certain Prospective Financial and Operating Information

The Company does not, as a matter of course, make public projections as to future performance, earnings, or other results due to the inherent unpredictability of projections and their underlying assumptions and estimates. However, the Company provided to Goldgroup, in connection with its due diligence review, certain non-public unaudited financial and operating projections on a stand-alone basis, without giving effect to the Merger, for the period from 2026 through 2030 (the "Company Projections for Gold Resource"). The Company prepared similar financial and operating projections for Goldgroup for the period from 2026 through 2031 based, in part, on Goldgroup's management model and certain estimates of the Company's management (the "Company Projections for Goldgroup" and, together with the Company Projections for Gold Resource, are referred to as the "Projections" herein); Goldgroup management was not involved in the preparation of the Company Projections for Goldgroup aside from providing the Company with Goldgroup's management model. In addition, the Company provided the Projections to ATB Cormark in connection with the preparation of its valuation analyses and fairness opinion, as described in, and subject to the assumptions and limitations as set forth in, the section entitled "-Opinion of Our Financial Advisor."