Summary of Significant Accounting Policies and Business Operations (Policies)	3 Months Ended
Mar. 31, 2025
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Business Operations [Policy Text Block]	Business Operations Thunder Mountain Gold, Inc. ("Thunder Mountain", "THMG", or "the Company") was originally incorporated under the laws of the State of Idaho on November 9, 1935, under the name of Montgomery Mines, Inc. In April 1978, the Montgomery Mines Corporation was obtained by a group of the Thunder Mountain property holders and changed its name to Thunder Mountain Gold, Inc., with the primary goal to further develop their holdings in the Thunder Mountain Mining District, located in Valley County, Idaho. Thunder Mountain Gold, Inc. takes its name from the Thunder Mountain Mining District, where its principal lode mining claims were located. For several years, the Company's activities were restricted to maintaining its property position and exploration activities. During 2005, the Company sold its holdings in the Thunder Mountain Mining District. During 2007, the Company acquired the South Mountain Mines property in southwest Idaho and initiated exploration activities on that property, which continue today.
Basis of Presentation and Going Concern [Policy Text Block]	Basis of Presentation and Going Concern The condensed consolidated financial statements accompanying this report show an accumulated deficit of $8,340,019 at March 31, 2025 which raises substantial doubt about the Company's ability to continue as a going concern. The Company's ability to secure capital for exploration and working capital needs is crucial, given the absence of recurring revenue streams. Long-term strategies involve financing through stock or debt sales and eventual profitability from mining operations. Capital raising efforts are hindered by current capital market conditions and the broader economic climate in the United States. Company management is actively seeking additional funds through various means, including public offerings, private placements, mergers, option agreements, and external debt, to ensure the Company's viability. The condensed consolidated financial statements do not include any adjustments that might be necessary should the Company be unable to continue as a going concern. If the going concern basis was not appropriate for these financial statements, adjustments would be necessary in the carrying value of assets and liabilities, the reported expenses and the balance sheet classifications used.
Principles of Consolidation [Policy Text Block]	Principles of Consolidation The condensed consolidated financial statements include the accounts of the Company; its wholly owned subsidiaries, Thunder Mountain Resources, Inc. ("TMRI") and South Mountain Mines, Inc. ("SMMI"); and a company in which the Company owns 75% and has majority control, Owyhee Gold Trust, LLC ("OGT"). The Company's consolidated financial statements reflect the other investor's 25% noncontrolling, capped interest in OGT. Intercompany accounts are eliminated in consolidation.
Accounting Estimates [Policy Text Block]	Accounting Estimates The preparation of the condensed consolidated financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. The more significant areas requiring the use of management estimates and assumptions include the carrying value of properties and mineral interests, environmental remediation liabilities, deferred tax assets, and stock-based compensation. Management's estimates and assumptions are based on historical experience and other assumptions believed to be reasonable under the circumstances. Actual results could differ from those estimates.
Income Taxes [Policy Text Block]	Income Taxes The Company recognizes deferred income tax liabilities or assets at the end of each period using the tax rate expected to be in effect when the taxes are actually paid or recovered. A valuation allowance is recognized on deferred tax assets when it is more likely than not that some or all of the deferred tax assets will not be realized.
Cash and Cash Equivalents [Policy Text Block]	Cash and Cash Equivalents For the purposes of the balance sheet and statement of cash flows, the Company considers all highly liquid investments with a maturity of three months or less when purchased to be a cash equivalent.
Fair Value Measurements [Policy Text Block]	Fair Value Measurements When required to measure assets or liabilities at fair value, the Company uses a fair value hierarchy based on the level of independent, objective evidence surrounding the inputs used. The Company determines the level within the fair value hierarchy in which the fair value measurements in their entirety fall. The categorization within the fair value hierarchy is based upon the lowest level of input that is significant to the fair value measurement. Level 1 uses quoted prices in active markets for identical assets or liabilities, Level 2 uses significant other observable inputs, and Level 3 uses significant unobservable inputs. The amount of the total gains or losses for the period are included in earnings that are attributable to the change in unrealized gains or losses relating to those assets and liabilities still held at the reporting date. The Company has no financial liabilities that are adjusted to fair value on a recurring basis.
Financial Instruments [Policy Text Block]	Financial Instruments The Company's financial instruments include cash and cash equivalents.
Investments [Policy Text Block]	Investments The Company determines the appropriate classification of investments at the time of acquisition and re-evaluates such determinations at each reporting date. Equity securities that have a readily determined fair value are carried at fair value determined using Level 1 fair value measurement inputs with the change in fair value recognized as unrealized gain (loss) in the condensed consolidated statement of operations each reporting period. Gains and losses on the sale of securities are recognized on a specific identification basis.
Mineral Interests [Policy Text Block]	Mineral Interests The Company capitalizes costs for acquiring mineral interests, and expenses costs to maintain mineral rights and leases as incurred. Exploration costs are expensed in the period in which they are incurred. Should a property reach the production stage, these capitalized costs would be amortized using the units-of-production method based on periodic estimates of ore reserves. Mineral interests are periodically assessed for impairment of value and any subsequent losses are charged to operations at the time of impairment. If a mineral interest is abandoned or sold, its capitalized costs are charged to operations. Consideration received by the Company pursuant to joint ventures or purchase option agreements is applied against the carrying value of the related mineral interest. When and if payments received exceed the carrying value, the excess amount is recognized as a gain in the condensed consolidated statement of operations in the period the consideration is received. In November 2024, the FASB issued ASU 2024-03, Income Statement - Reporting Comprehensive Income - Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses, which requires disclosure about the types of costs and expenses included in certain expense captions presented on the income statement. The new disclosure requirements are effective for the Company's annual periods for fiscal years beginning after December 15, 2026, and interim periods within fiscal years beginning after December 15, 2027, with early adoption permitted, and may be applied either prospectively or retrospectively. We are currently evaluating the ASU to determine its impact on our consolidated financial statements and disclosures.
Leases [Policy Text Block]	Leases Arrangements meeting the definition of a lease are classified as operating or financing leases and are recorded on the condensed consolidated balance sheet as both a right-of-use asset and lease liability, calculated by discounting fixed lease payments over the lease term at the rate implicit in the lease or the Company's incremental borrowing rate. Lease liabilities are increased by interest and reduced by payments each period, and the right-of-use asset is amortized over the lease term. For operating leases, interest on the lease liability and the amortization of the right-of-use asset result in straight-line rent expense over the lease term. For finance leases, interest on the lease liability and the amortization of the right-of-use asset results in front-loaded expense over the lease term. Variable lease expenses are recorded when incurred.
Investments in Joint Ventures [Policy Text Block]	Investments in Joint Ventures For companies and joint ventures (JVs) where the Company holds more than 50% of the voting interests, but less than 100%, and has significant influence, the company or joint venture is consolidated, and other investor interests are presented as noncontrolling. In determining whether significant influence exists, the Company considers its participation in policy-making decisions and its representation on the venture's management committee. For JVs in which the Company does not have joint control or significant influence, the cost method is used. For those JVs in which there is joint control between the parties, the equity method is utilized whereby the Company's share of the ventures' earnings and losses is included in the statement of operations as earnings in JVs and its investments therein are adjusted by a similar amount. The Company periodically assesses its investments in JVs for impairment. If management determines that a decline in fair value is other than temporary it will write-down the investment and charge the impairment against operations.
Reclamation and Remediation [Policy Text Block]	Reclamation and Remediation The Company's operations have been, and are subject to, standards for mine reclamation that have been established by various governmental agencies. The Company would record the fair value of an asset retirement obligation as a liability in the period in which the Company incurred a legal obligation for the retirement of tangible long-lived assets. A corresponding asset would also be recorded and depreciated over the life of the asset. For non-operating properties, the Company accrues costs associated with environmental remediation obligations when it is probable that such costs will be incurred, and they are reasonably estimable. Such costs are based on management's estimate of amounts expected to be incurred when the remediation work is performed. The Company had accrued $81,250 at March 31, 2025 and, December 31, 2024, respectively, on its condensed consolidated balance sheets relating to estimated mine closure and reclamation costs on its South Mountain Mines property.
Share-Based Compensation [Policy Text Block]	Share-Based Compensation Share-based payments to employees and directors, including grants of employee stock options, are measured at fair value and expensed in the condensed consolidated statements of operations over the vesting period.
Segment Policy [Policy Text Block]	Segment Policy The Chief Executive Officer of Thunder Mountain Gold Inc. serves as the Company's Chief Operating Decision Maker ("CODM"). The Company operates as a single business segment, focused primarily on the exploration and development of the South Mountain Project. As a single-segment entity, the Company complies with ASC 280-10-50-20, reporting segment profit or loss, significant expenses, and other segment items. Given our status as a mineral exploration company with no revenue, financial activities were minimal, primarily consisting of essential corporate expenditure and limited exploration. Since our single segment represents the entire entity, certain financial information may be referenced in the primary financial statements instead of duplicated in segment disclosures.
Investments in Equity Securities [Policy Text Block]	Investments in Equity Securities Investments in equity securities are generally measured at fair value. Unrealized gains and losses for equity securities resulting from changes in fair value are recognized in current earnings. If an equity security does not have a readily determinable fair value, we may elect to measure the security at its cost minus impairment, if any, plus or minus changes resulting from observable price changes in orderly transactions for an identical or similar investment in the same issuer. At the end of each reporting period, we reassess whether an equity investment security without a readily determinable fair value qualifies to be measured at cost, less impairment, consider whether impairment indicators exist to evaluate if an equity investment security is impaired and, if so, record an impairment loss. At the end of each reporting period, unrealized gains and losses resulting from changes in fair value are recognized in current earnings. Upon sale of an equity security, the realized gain or loss is recognized in current earnings.
Recent Accounting Pronouncements [Policy Text Block]	Recent Accounting Pronouncements Accounting Standards Updates In August 2023, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2023-05, Business Combinations-Joint Venture Formations (Subtopic 805-60): Recognition and Initial Measurement, which clarifies the business combination accounting for joint venture formations. The amendments in the ASU seek to reduce diversity in practice that has resulted from a lack of authoritative guidance regarding the accounting for the formation of joint ventures in separate financial statements. The amendments also seek to clarify the initial measurement of joint venture net assets, including businesses contributed to a joint venture. The guidance is applicable to all entities involved in the formation of a joint venture. The amendments are effective for all joint venture formations with a formation date on or after January 1, 2025. Early adoption and retrospective application of the amendments are permitted. Adoption of the new guidance did not have a material impact on our consolidated financial statements and disclosures. In December 2023, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2023-09 Income Taxes (Topic 740): Improvements to Income Tax Disclosures. This update requires companies to report on an annual basis, specific categories in the rate reconciliation and additional information on reconciling items greater than 5% of the taxable income or loss. The update also requires disclosure of income taxes paid to Federal, state and foreign jurisdictions along with other municipal and local jurisdictions representing 5% or more of total income taxes paid. This update is effective for annual periods beginning after December 15, 2024, with early adoption permitted. The Company is currently evaluating the impact of adopting this standard on its consolidated financial statements.
Net Income (Loss) Per Share [Policy Text Block]	Net Income (Loss) Per Share The Company is required to have dual presentation of basic earnings per share ("EPS") and diluted EPS. The Company calculates basic earnings (loss) per share by dividing net income or loss available to common stockholders by the weighted average number of common shares outstanding. Diluted earnings per share reflect potentially dilutive common stock equivalents, including options and warrants that could share in our earnings through the conversion to common shares, except where their inclusion would be anti-dilutive. For the quarters ended March 31, 2025 and 2024 outstanding common stock options of 4,865,000 and 3,450,000, respectively were excluded from the calculation of diluted earnings per share as their effect would have been anti-dilutive due to the net loss for the period.

Summary of Significant Accounting Policies and Business Operations (Policies)

3 Months Ended

Mar. 31, 2025

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Business Operations

Thunder Mountain Gold, Inc. ("Thunder Mountain", "THMG", or "the Company") was originally incorporated under the laws of the State of Idaho on November 9, 1935, under the name of Montgomery Mines, Inc. In April 1978, the Montgomery Mines Corporation was obtained by a group of the Thunder Mountain property holders and changed its name to Thunder Mountain Gold, Inc., with the primary goal to further develop their holdings in the Thunder Mountain Mining District, located in Valley County, Idaho. Thunder Mountain Gold, Inc. takes its name from the Thunder Mountain Mining District, where its principal lode mining claims were located. For several years, the Company's activities were restricted to maintaining its property position and exploration activities. During 2005, the Company sold its holdings in the Thunder Mountain Mining District. During 2007, the Company acquired the South Mountain Mines property in southwest Idaho and initiated exploration activities on that property, which continue today.

Basis of Presentation and Going Concern [Policy Text Block]

Basis of Presentation and Going Concern

The condensed consolidated financial statements accompanying this report show an accumulated deficit of $8,340,019 at March 31, 2025 which raises substantial doubt about the Company's ability to continue as a going concern.

The Company's ability to secure capital for exploration and working capital needs is crucial, given the absence of recurring revenue streams. Long-term strategies involve financing through stock or debt sales and eventual profitability from mining operations. Capital raising efforts are hindered by current capital market conditions and the broader economic climate in the United States. Company management is actively seeking additional funds through various means, including public offerings, private placements, mergers, option agreements, and external debt, to ensure the Company's viability.

The condensed consolidated financial statements do not include any adjustments that might be necessary should the Company be unable to continue as a going concern. If the going concern basis was not appropriate for these financial statements, adjustments would be necessary in the carrying value of assets and liabilities, the reported expenses and the balance sheet classifications used.

Principles of Consolidation [Policy Text Block]

Principles of Consolidation

The condensed consolidated financial statements include the accounts of the Company; its wholly owned subsidiaries, Thunder Mountain Resources, Inc. ("TMRI") and South Mountain Mines, Inc. ("SMMI"); and a company in which the Company owns 75% and has majority control, Owyhee Gold Trust, LLC ("OGT"). The Company's consolidated financial statements reflect the other investor's 25% noncontrolling, capped interest in OGT. Intercompany accounts are eliminated in consolidation.

Accounting Estimates [Policy Text Block]

Accounting Estimates

The preparation of the condensed consolidated financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. The more significant areas requiring the use of management estimates and assumptions include the carrying value of properties and mineral interests, environmental remediation liabilities, deferred tax assets, and stock-based compensation. Management's estimates and assumptions are based on historical experience and other assumptions believed to be reasonable under the circumstances. Actual results could differ from those estimates.

Income Taxes [Policy Text Block]

Income Taxes

The Company recognizes deferred income tax liabilities or assets at the end of each period using the tax rate expected to be in effect when the taxes are actually paid or recovered. A valuation allowance is recognized on deferred tax assets when it is more likely than not that some or all of the deferred tax assets will not be realized.

Cash and Cash Equivalents [Policy Text Block]

Cash and Cash Equivalents

For the purposes of the balance sheet and statement of cash flows, the Company considers all highly liquid investments with a maturity of three months or less when purchased to be a cash equivalent.

Fair Value Measurements [Policy Text Block]

Fair Value Measurements

When required to measure assets or liabilities at fair value, the Company uses a fair value hierarchy based on the level of independent, objective evidence surrounding the inputs used. The Company determines the level within the fair value hierarchy in which the fair value measurements in their entirety fall. The categorization within the fair value hierarchy is based upon the lowest level of input that is significant to the fair value measurement. Level 1 uses quoted prices in active markets for identical assets or liabilities, Level 2 uses significant other observable inputs, and Level 3 uses significant unobservable inputs. The amount of the total gains or losses for the period are included in earnings that are attributable to the change in unrealized gains or losses relating to those assets and liabilities still held at the reporting date. The Company has no financial liabilities that are adjusted to fair value on a recurring basis.

Financial Instruments [Policy Text Block]

Financial Instruments

The Company's financial instruments include cash and cash equivalents.

Investments [Policy Text Block]

Investments

The Company determines the appropriate classification of investments at the time of acquisition and re-evaluates such determinations at each reporting date. Equity securities that have a readily determined fair value are carried at fair value determined using Level 1 fair value measurement inputs with the change in fair value recognized as unrealized gain (loss) in the condensed consolidated statement of operations each reporting period. Gains and losses on the sale of securities are recognized on a specific identification basis.

Mineral Interests [Policy Text Block]

Mineral Interests

The Company capitalizes costs for acquiring mineral interests, and expenses costs to maintain mineral rights and leases as incurred. Exploration costs are expensed in the period in which they are incurred. Should a property reach the production stage, these capitalized costs would be amortized using the units-of-production method based on periodic estimates of ore reserves. Mineral interests are periodically assessed for impairment of value and any subsequent losses are charged to operations at the time of impairment.

If a mineral interest is abandoned or sold, its capitalized costs are charged to operations. Consideration received by the Company pursuant to joint ventures or purchase option agreements is applied against the carrying value of the related mineral interest. When and if payments received exceed the carrying value, the excess amount is recognized as a gain in the condensed consolidated statement of operations in the period the consideration is received.

In November 2024, the FASB issued ASU 2024-03, Income Statement - Reporting Comprehensive Income - Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses, which requires disclosure about the types of costs and expenses included in certain expense captions presented on the income statement. The new disclosure requirements are effective for the Company's annual periods for fiscal years beginning after December 15, 2026, and interim periods within fiscal years beginning after December 15, 2027, with early adoption permitted, and may be applied either prospectively or retrospectively. We are currently evaluating the ASU to determine its impact on our consolidated financial statements and disclosures.

Leases [Policy Text Block]

Leases

Arrangements meeting the definition of a lease are classified as operating or financing leases and are recorded on the condensed consolidated balance sheet as both a right-of-use asset and lease liability, calculated by discounting fixed lease payments over the lease term at the rate implicit in the lease or the Company's incremental borrowing rate. Lease liabilities are increased by interest and reduced by payments each period, and the right-of-use asset is amortized over the lease term. For operating leases, interest on the lease liability and the amortization of the right-of-use asset result in straight-line rent expense over the lease term. For finance leases, interest on the lease liability and the amortization of the right-of-use asset results in front-loaded expense over the lease term. Variable lease expenses are recorded when incurred.

Investments in Joint Ventures [Policy Text Block]

Investments in Joint Ventures

For companies and joint ventures (JVs) where the Company holds more than 50% of the voting interests, but less than 100%, and has significant influence, the company or joint venture is consolidated, and other investor interests are presented as noncontrolling. In determining whether significant influence exists, the Company considers its participation in policy-making decisions and its representation on the venture's management committee.

For JVs in which the Company does not have joint control or significant influence, the cost method is used. For those JVs in which there is joint control between the parties, the equity method is utilized whereby the Company's share of the ventures' earnings and losses is included in the statement of operations as earnings in JVs and its investments therein are adjusted by a similar amount. The Company periodically assesses its investments in JVs for impairment. If management determines that a decline in fair value is other than temporary it will write-down the investment and charge the impairment against operations.

Reclamation and Remediation [Policy Text Block]

Reclamation and Remediation

The Company's operations have been, and are subject to, standards for mine reclamation that have been established by various governmental agencies. The Company would record the fair value of an asset retirement obligation as a liability in the period in which the Company incurred a legal obligation for the retirement of tangible long-lived assets. A corresponding asset would also be recorded and depreciated over the life of the asset.

For non-operating properties, the Company accrues costs associated with environmental remediation obligations when it is probable that such costs will be incurred, and they are reasonably estimable. Such costs are based on management's estimate of amounts expected to be incurred when the remediation work is performed. The Company had accrued $81,250 at March 31, 2025 and, December 31, 2024, respectively, on its condensed consolidated balance sheets relating to estimated mine closure and reclamation costs on its South Mountain Mines property.

Share-Based Compensation [Policy Text Block]

Share-Based Compensation

Share-based payments to employees and directors, including grants of employee stock options, are measured at fair value and expensed in the condensed consolidated statements of operations over the vesting period.

Segment Policy [Policy Text Block]

Segment Policy

The Chief Executive Officer of Thunder Mountain Gold Inc. serves as the Company's Chief Operating Decision Maker ("CODM"). The Company operates as a single business segment, focused primarily on the exploration and development of the South Mountain Project.

As a single-segment entity, the Company complies with ASC 280-10-50-20, reporting segment profit or loss, significant expenses, and other segment items. Given our status as a mineral exploration company with no revenue, financial activities were minimal, primarily consisting of essential corporate expenditure and limited exploration.

Since our single segment represents the entire entity, certain financial information may be referenced in the primary financial statements instead of duplicated in segment disclosures.

Investments in Equity Securities [Policy Text Block]

Investments in Equity Securities

Investments in equity securities are generally measured at fair value. Unrealized gains and losses for equity securities resulting from changes in fair value are recognized in current earnings. If an equity security does not have a readily determinable fair value, we may elect to measure the security at its cost minus impairment, if any, plus or minus changes resulting from observable price changes in orderly transactions for an identical or similar investment in the same issuer. At the end of each reporting period, we reassess whether an equity investment security without a readily determinable fair value qualifies to be measured at cost, less impairment, consider whether impairment indicators exist to evaluate if an equity investment security is impaired and, if so, record an impairment loss. At the end of each reporting period, unrealized gains and losses resulting from changes in fair value are recognized in current earnings. Upon sale of an equity security, the realized gain or loss is recognized in current earnings.

Recent Accounting Pronouncements [Policy Text Block]

Recent Accounting Pronouncements

Accounting Standards Updates

In August 2023, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2023-05, Business Combinations-Joint Venture Formations (Subtopic 805-60): Recognition and Initial Measurement, which clarifies the business combination accounting for joint venture formations. The amendments in the ASU seek to reduce diversity in practice that has resulted from a lack of authoritative guidance regarding the accounting for the formation of joint ventures in separate financial statements. The amendments also seek to clarify the initial measurement of joint venture net assets, including businesses contributed to a joint venture. The guidance is applicable to all entities involved in the formation of a joint venture. The amendments are effective for all joint venture formations with a formation date on or after January 1, 2025. Early adoption and retrospective application of the amendments are permitted. Adoption of the new guidance did not have a material impact on our consolidated financial statements and disclosures.

In December 2023, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2023-09 Income Taxes (Topic 740): Improvements to Income Tax Disclosures. This update requires companies to report on an annual basis, specific categories in the rate reconciliation and additional information on reconciling items greater than 5% of the taxable income or loss. The update also requires disclosure of income taxes paid to Federal, state and foreign jurisdictions along with other municipal and local jurisdictions representing 5% or more of total income taxes paid. This update is effective for annual periods beginning after December 15, 2024, with early adoption permitted. The Company is currently evaluating the impact of adopting this standard on its consolidated financial statements.

Net Income (Loss) Per Share [Policy Text Block]

Net Income (Loss) Per Share

The Company is required to have dual presentation of basic earnings per share ("EPS") and diluted EPS. The Company calculates basic earnings (loss) per share by dividing net income or loss available to common stockholders by the weighted average number of common shares outstanding. Diluted earnings per share reflect potentially dilutive common stock equivalents, including options and warrants that could share in our earnings through the conversion to common shares, except where their inclusion would be anti-dilutive. For the quarters ended March 31, 2025 and 2024 outstanding common stock options of 4,865,000 and 3,450,000, respectively were excluded from the calculation of diluted earnings per share as their effect would have been anti-dilutive due to the net loss for the period.