6-K

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form 6-K

REPORT OF FOREIGN PRIVATE ISSUER PURSUANTTO RULE 13a-16 OR 15d-16 UNDER THE SECURITIES EXCHANGE ACT OF 1934

For the month of October 2025

Commission File Number 001-35297

Fortuna Mining Corp.

(Translation of registrant’s name into English)

1111 Melville Street, Suite 820, Vancouver, British Columbia, Canada V6E 3V6

(Address of principal executive office)

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F.

FORM 20-F   ¨ FORM 40-F  þ

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, thereunto duly authorized.

Exhibits:

Exhibit 99.1

NEWS RELEASE

Fortuna expandsWest African presence, forms exploration alliance in Guinea with DeSoto Resources

Vancouver,October 2, 2025: Fortuna Mining Corp. (NYSE: FSM | TSX: FVI) is pleased to announce it has executed a binding Heads of Agreement (HOA) with DeSoto Resources Limited, an Australian-listed gold exploration company, to establish an exploration alliance and joint venture across the highly prospective Siguiri Basin in Guinea.

New ExplorationFront

Paul Weedon, Senior Vice President of Exploration at Fortuna, commented, “Guinea’s Siguiri Basin has demonstrated potential to host multi-million-ounce gold deposits in a country with a long mining history. This agreement with DeSoto provides Fortuna with an excellent entry into this highly prospective region, alongside a highly qualified and experienced team with a proven track record of discovery across West Africa.”

Key AgreementTerms

About DeSotoResources Limited

DeSoto Resources Limited is an Australian-listed gold exploration company focused on exploration and project generation in Guinea. DeSoto´s founders and management team have a demonstrated track record of success in West African exploration, including credit for the discovery of Predictive Discovery’s 5.4-million-ounce Bankan Gold Project.

About FortunaMining Corp.

Fortuna Mining Corp. is a Canadian precious metals mining company with three operating mines and a portfolio of exploration projects in Argentina, Côte d’Ivoire, Mexico, and Peru, as well as the Diamba Sud Gold Project in Senegal. Sustainability is at the core of our operations and stakeholder relationships. We produce gold and silver while creating long-term shared value through efficient production, environmental stewardship, and social responsibility. For more information, please visit our website at www.fortunamining.com

ON BEHALF OF THE BOARD

Jorge A. Ganoza

President, CEO, and Director

Fortuna Mining Corp.

Investor Relations:

CarlosBaca | info@fmcmail.com | fortunamining.com | X | LinkedIn

| YouTube

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Forward looking Statements

This news releasecontains forward-looking statements which constitute “forward-looking information” within the meaning of applicable Canadiansecurities legislation and “forward-looking statements” within the meaning of the “safe harbor” provisions ofthe Private Securities Litigation Reform Act of 1995 (collectively, “Forward-looking Statements”). All statements includedherein, other than statements of historical fact, are Forward-looking Statements and are subject to a variety of known and unknown risksand uncertainties which could cause actual events or results to differ materially from those reflected in the Forward-looking Statements.The Forward-looking Statements in this news release include, without limitation, statements regarding the potential of Guinea’sSiguiri Basin to host multi-million-ounce gold deposits; the ability of JVCo to acquire new mining permits; statements pertaining toidentification of Go Projects and the formation of a joint venture; and the Company’s business strategy, plans and outlook. Often,but not always, these Forward-looking Statements can be identified by the use of words such as “estimated”, “potential”, “open”, “future”, “assumed”, “projected”, “used”, “detailed”, “has been”, “gain”, “planned”, “reflecting”, “will”, “containing”, “remaining”, “to be”, or statements that events, “could” or “should” occur or be achievedand similar expressions, including negative variations.

Forward-lookingStatements involve known and unknown risks, uncertainties and other factors which may cause the actual results, performance or achievementsof the Company to be materially different from any results, performance or achievements expressed or implied by the Forward-looking Statements.Such uncertainties and factors include, among others, changes in general economic conditions and financial markets; changes in pricesfor gold, silver, and other metals; the timing and success of the Company’s proposed exploration programs; technological and operationalhazards in Fortuna’s mining and mine development activities; risks inherent in mineral exploration; fluctuations in prices forenergy, labor, materials, supplies and services; fluctuations in currencies; uncertainties inherent in the estimation of mineral reserves,mineral resources, and metal recoveries; the Company’s ability to obtain all necessary permits, licenses and regulatory approvalsin a timely manner; governmental and other approvals; political unrest or instability in countries where Fortuna is active; labor relationsissues; as well as those factors discussed under “Risk Factors” in the Company's Annual Information Form for the financialyear ended December 31, 2024. Although the Company has attempted to identify important factors that could cause actual actions,events or results to differ materially from those described in Forward-looking Statements, there may be other factors that cause actions,events or results to differ from those anticipated, estimated or intended.

Forward-lookingStatements contained herein are based on the assumptions, beliefs, expectations and opinions of management, including but not limitedto, expected trends in mineral prices and currency exchange rates; that the Company’s activities will be in accordance with theCompany’s public statements and stated goals; that there will be no material adverse change affecting the Company or its properties;that all required approvals will be obtained; that there will be no significant disruptions affecting operations and such other assumptionsas set out herein.

Forward-lookingStatements are made as of the date hereof and the Company disclaims any obligation to update any Forward-looking Statements, whetheras a result of new information, future events or results or otherwise, except as required by law. There can be no assurance that Forward-lookingStatements will prove to be accurate, as actual results and future events could differ materially from those anticipated in such statements.Accordingly, investors should not place undue reliance on Forward-looking Statements

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