THUNDER MOUNTAIN GOLD INC

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-K

☒ ANNUAL REPORT PURSUANT TO SECTION 13 OR 15 (d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the fiscal year ended**December 31,2025 **

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

For the transition period from to

Commission file number: 001-08429

THUNDER MOUNTAIN GOLD, INC.

(Exact Name of Registrant as Specified in its Charter)

11770 W. President Dr., Ste. F, Boise Idaho 83713

(Address of principal executive offices) (zip code)

(208)658-1037

(Registrant's Telephone Number, including Area Code)

SECURITIES REGISTERED UNDER SECTION 12(g) OF THE EXCHANGE ACT:

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. Yes ☐No ☒

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Act. Yes ☐No ☒

Indicate by checkmark 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 ☒ No ☐

Indicate by check mark whether the Registrant 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 (§ 229.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files). Yes ☐No ☒

Indicate by checkmark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K is not contained herein, and will not be contained, to the best of the registrant's knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to the Form 10-K. ☒

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company or an emerging growth company. See definitions of "large accelerated filer," "accelerated filer," "smaller reporting company," and "emerging growth company" in Rule 12b-2 of the Exchange Act. (Check one):

Large Accelerated Filer ☐ Accelerated Filer ☐Non-Accelerated Filer ☒ Smaller Reporting Company☒ Emerging Growth Company☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. [ ]

Indicate by check mark whether the registrant has filed a report on and attestation to its management's assessment of the effectiveness of its internal control over financial reporting under Section 404(b) of the Sarbanes-Oxley Act (15 U.S.C. 7262(b) by the registered public accounting firm that prepared or issued its audit report.☐

If securities are registered pursuant to Section 12(b) of the Act, indicate by check mark whether the financial statements of the registrant included in the filing reflect the correction of an error to previously issued financial statements.☐

Indicate by check mark whether any of those error corrections are restatements that required a recovery analysis of incentive-based compensation received by any of the registrant's executive officers during the relevant recovery period pursuant to §240.10D-1(b). ☐

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Act). Yes ☐ No☒

The aggregate market value of the voting and non-voting common equity held by non-affiliates was $16,238,799 as of June 30, 2025

The number of shares of the Registrant's Common Stock outstanding as of March 23, 2026, was 93,505,579.

THUNDER MOUNTAIN GOLD, INC.

Form 10-K

December 31, 2025

Table of Contents

CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS

This Annual Report on Form 10-K and the exhibits attached hereto contain "forward-looking statements" within the meaning of the Private Securities Litigation Reform Act of 1995, as amended. All statements other than statements of historical fact are forward-looking statements for purposes of federal and state securities laws, including statements about anticipated future operating and financial performance, financial position and liquidity, growth opportunities and growth rates, pricing plans, acquisition and divestiture opportunities, business prospects, strategic alternatives, business strategies, regulatory and competitive outlook, investment and expenditure plans, financing needs and availability and other similar forecasts and statements of expectation and statements of assumptions underlying any of the foregoing. The words "aims," "anticipates," "believes," "could," "estimates," "expects," "intends," "may," "plans," "projects," "seeks," "should" and variations of these words and similar expressions are generally intended to identify these forward-looking statements. These forward-looking statements are inherently subject to significant business, economic and competitive uncertainties and contingencies, many of which are beyond our control. In addition, these forward-looking statements are subject to assumptions with respect to future business strategies and decisions that are subject to change.

Forward-looking statements by us are based on estimates, projections, beliefs and assumptions of management and are not guarantees of future performance. Such forward-looking statements may be contained in this Annual Report on Form 10-K underItem 1 Description of the Business,Item 1A Risk Factors, andItem 7 Management's Discussion and Analysis of Financial Conditions and Results of Operations, or in our Current Reports on Form 8-K, among other places. Some of other risk factors include, but are not limited to, the following:

• adverse effects of climate changes or natural disasters;

• adverse effects of global or regional pandemic disease spread or other crises;

• global economic and capital market uncertainties;

• the speculative nature of minerals or mineral exploration, including risks of diminishing quantities or grades;

• operational or technical difficulties in connection with exploration, processing or mining activities;

• costs, hazards and uncertainties associated mineral exploration, resource development, and economic feasibility;

• contests over title to our properties;

• potential dilution to our shareholders from our stock issuances, recapitalization and balance sheet restructuring activities;

• potential inability to comply with applicable government regulations or law;

• adoption of or changes in legislation or regulations adversely affecting our businesses;

• permitting constraints or delays;

• changes in the United States or other monetary or fiscal policies or regulations;

• interruptions in our production capabilities due to capital constraints;

• equipment failures;

• fluctuation of prices for certain commodities;

• changes in generally accepted accounting principles;

• adverse effects of war, mass shooting, terrorism and geopolitical events;

• potential inability to implement our business strategies;

• potential inability to produce revenues;

• potential inability to attract and retain key personnel;

• assertion of claims, lawsuits and proceedings against us;

• potential inability to satisfy debt and lease obligations; and

• potential inability to maintain an effective system of internal controls over financial reporting.

Occurrence of such events or circumstances could have a material adverse effect on our business, financial condition, results of operations or cash flows, or the market price of our securities. All subsequent written and oral forward-looking statements by or attributable to us or persons acting on our behalf are expressly qualified in their entirety by these factors. Should one or more of these risks or uncertainties materialize, or should underlying assumptions prove incorrect, actual results may vary materially from those anticipated, believed, estimated, or expected. We caution readers not to place undue reliance on any such forward-looking statements, which speak only as of the date made. Except as may be required by securities or other law, we undertake no obligation to publicly update or revise any forward-looking statements, whether as a result of new information, future events, or otherwise.

We qualify all the forward-looking statements contained in this Annual Report by the foregoing cautionary statements.

CAUTIONARY NOTE TO U.S. RESIDENTS CONCERNING DISCLOSURE OF MINERAL RESOURCES

Thunder Mountain Gold, Inc. ("Thunder Mountain," "we," "us," "our" or the "Company") is a U.S. domestic issuer for U.S. Securities and Exchange Commission ("SEC") purposes; it is required to report its financial results under U.S. Generally Accepted Accounting Principles ("U.S. GAAP"), and its shares of common stock trade on the TSX Venture Exchange (the "TSX-V") and the OTCQB Venture Market tier of the OTC Markets. However, certain prior regulatory filings made in Canada contain or incorporate by reference therein certain disclosure that satisfies the additional requirements of Canadian securities laws, which differ from the requirements of United States' securities laws. Unless otherwise indicated, all resource estimates included in those Canadian filings, and in the documents incorporated by reference therein, had been prepared in accordance with Canadian National Instrument 43-101 -Standards of Disclosure for Mineral Projects ("NI 43-101") and the Canadian Institute of Mining, Metallurgy and Petroleum ("CIM") classification system. 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.

Canadian standards, including NI 43-101, may differ from the requirements of Subpart 1300 of Regulation S-K ("S-K 1300"). Thus, resource information contained, or incorporated by reference, in the Company's Canadian filings, and in the documents incorporated by reference therein, may not be comparable to similar information disclosed by companies reporting mineral reserve and mineral resource information under S-K 1300.

The terms "mineral reserve," "proven mineral reserve" and "probable mineral reserve" are Canadian mining terms as defined in accordance with NI 43-101 and CIM standards. Pursuant to S-K 1300, the SEC now recognizes estimates of "measured mineral resources," "indicated mineral resources" and "inferred mineral resources." In addition, the SEC has amended its definitions of "proven mineral reserves" and "probably mineral reserves" to be substantially similar to the corresponding standards of the CIM.

Investors are cautioned that while terms are substantially similar to CIM standards, there are differences in the definitions and standards under S-K 1300 and the CIM standards. Accordingly, there is no assurance any mineral reserves or mineral resources that the Company may report as "proven reserves," "probable reserves," "measured mineral resources," "indicated mineral resources" and "inferred mineral resources" under NI 43-101 will be the same as the reserve or resource estimates prepared under the standards adopted under S-K 1300.

Investors are also cautioned that while the SEC now recognizes "measured mineral resources," "indicated mineral resources" and "inferred mineral resources," investors should not assume that any part or all of mineral deposits in these categories will ever be converted into mineral reserves.

Mineralization described using these terms has a great amount of uncertainty as to their existence, and great uncertainty as to their economic and legal feasibility. It cannot be assumed that all or any part of an "measured mineral resource," "indicated mineral resource" or "inferred mineral resource" will ever be upgraded to a higher category. Under Canadian rules, estimates of inferred mineral resources may not form the basis of feasibility or pre-feasibility studies, except in rare cases. Investors are cautioned not to assume that all or any part of an inferred mineral resource exists or is economically or legally mineable. Disclosure of "contained ounces" in a resource is permitted disclosure under Canadian regulations; however, the SEC normally only permits issuers to report mineralization that does not constitute "reserves" by SEC standards as in place tonnage and grade without reference to unit measures.

ABBREVIATIONS AND TERMS OF REFERENCE

GLOSSARY OF SIGNIFICANT MINING TERMS

Alluvial - Adjectivally used to identify rocks or minerals deposited over time by moving water.

Arsenopyrite - An iron-arsenic sulfide. Common constituent of gold mineralization.

Bedrock - Solid rock underlying overburden.

Dip - Angle made by an inclined surface with the horizontal, measured perpendicular to strike.

Deposit-A mineral deposit is a mineralized body that has been intersected by sufficient closely-spaced drill holes or underground sampling to support sufficient tonnage and average grade(s) of metal(s) to warrant further exploration or development activities.

Drift - A horizontal mine opening driven on the vein. Driving is a term used to describe the excavation of a mine passageway.

Exploration Stage Issuer - As defined by Subpart 1300 of Regulation S-K - is an issuer that has no material property with mineral reserves disclosed.

Exploration Stage Property - As defined by Subpart 1300 of Regulation S-K - is a property that has no mineral reserves disclosed.

Fault - A fracture in the earth's crust accompanied by a displacement of one side of the fracture with respect to the other and in a direction parallel to the fracture.

Flotation - A physiochemical process for the separation of finely divided solids from one another. Separation of these (dissimilar) discrete solids from each other is affected by the selective attachment of the particle surface to gas bubbles.

GPT - grams per metric tonne.

Galena - A lead sulfide mineral.

Indicated Mineral Resource (or "Indicated") - is that part of a mineral resource for which quantity and grade or quality are estimated on the basis of adequate geological evidence and sampling. The level of geological certainty associated with an indicated mineral resource is sufficient to allow a qualified person to apply modifying factors in sufficient detail to support mine planning and evaluation of the economic viability of the deposit. Because an indicated mineral resource has a lower level of confidence than the level of confidence of a measured mineral resource, an indicated mineral resource may only be converted to a probable mineral reserve.

Inferred Mineral Resource (or "Inferred") - has the meaning defined by Subpart 1300 of Regulation S-K - is that part of a mineral resource for which quantity and grade or quality are estimated on the basis of limited geological evidence and sampling. The level of geological uncertainty associated with an inferred mineral resource is too high to apply relevant technical and economic factors likely to influence the prospects of economic extraction in a manner useful for evaluation of economic viability. Because an inferred mineral resource has the lowest level of geological confidence of all mineral resources, which prevents the application of the modifying factors in a manner useful for evaluation of economic viability, an inferred mineral resource may not be considered when assessing the economic viability of a mining project and may not be converted to a mineral reserve.

Measured Mineral Resource (or "Measured") - has the meaning defined by Subpart 1300 of Regulation S-K - is that part of a mineral resource for which quantity and grade or quality are estimated on the basis of conclusive geological evidence and sampling. The level of geological certainty associated with a measured mineral resource is sufficient to allow a qualified person to apply modifying factors, as defined in this section, in sufficient detail to support detailed mine planning and final evaluation of the economic viability of the deposit. Because a measured mineral resource has a higher level of confidence than the level of confidence of either an indicated mineral resource or an inferred mineral resource, a measured mineral resource may be converted to a proven mineral reserve or to a probable mineral reserve.

Mill - A general term used to denote a mineral processing plant.

Mineralization - The presence of minerals, usually of potential economic significance, in a specific area or geologic formation.

Mineral Resource - has the meaning defined by Subpart 1300 of Regulation S-K - is a concentration or occurrence of material of economic interest in or on the Earth's crust in such form, grade or quality, and quantity that there are reasonable prospects for economic extraction. A mineral resource is a reasonable estimate of mineralization, taking into account relevant factors such as cut-off grade, likely mining dimensions, location or continuity, that, with the assumed and justifiable technical and economic conditions, is likely to, in whole or in part, become economically extractable. It is not merely an inventory of all mineralization drilled or sampled.

Mineral Reserve - has the meaning defined by Subpart 1300 of Regulation S-K - An estimate of tonnage and grade or quality of indicated and measured mineral resources that, in the opinion of the qualified person, can be the basis of an economically viable project. More specifically, it is the economically mineable part of a measured or indicated mineral resource, which includes diluting materials and allowances for losses that may occur when the material is mined or extracted.