Summary of Significant Accounting Policies and Business Operations (Policies)	9 Months Ended
Sep. 30, 2023
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. On December 30, 2022, Thunder Mountain Gold, Inc. by and through its subsidiaries Thunder Mountain Resources, Inc., a Nevada Corporation, and South Mountain Mines, Inc., an Idaho Corporation ("SMMI") (collectively the "Company", "THMG", or "We", "Our" or "Us") agreed to terminate an Option Agreement, (the "BeMetals Option Agreement") with BeMetals Corporation, a British Columbia corporation, and BeMetals USA Corporation, a Delaware corporation ("BeMetals or BMET"). The "BeMetals Option Agreement was entered into on February 27, 2019, the original terms of the Option Agreement, BeMetals provided the funding to SMMI for project expenses including Management Services Income. The Company has 8 million common shares of BMET USA with a market value of $769,344, and the Company had cash and cash equivalents of $209,529 for the nine months ended September 30, 2023. See Note 3 for further information.
Basis of Presentation and Going Concern [Policy Text Block]	Basis of Presentation and Going Concern The accompanying condensed consolidated financial statements have been prepared under the assumption that the Company will continue as a going concern. The Company has historically incurred losses, however, the Company has cash reserves and available marketable securities sufficient to cover normal operating expenses. If necessary, the Company continues to have the ability to raise additional capital in order to fund its future exploration and working capital requirements.
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 condensed consolidated financial statements reflect the other investor's 25% non-controlling, capped interest in OGT. Intercompany accounts are eliminated in consolidation.
Accounting Estimates [Policy Text Block]	Accounting Estimates The preparation of 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.
Revenue Recognition [Policy Text Block]	Revenue Recognition Management service revenue is recognized when the Company has satisfied its performance obligation required under its management contract with BeMetals. Such an obligation is satisfied over time as work is performed and the Company has a contractual right to payment.
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. At September 30, 2023, the Company has one financial asset, investment in equity security, that is adjusted to fair value on a recurring basis for which the fair value is determined based on Level 1 inputs as the equity security is traded on a stock exchange. 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, and the investment in BeMetal's equity securities, the carrying value of which approximates fair value based on the nature of those instruments.
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.
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 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. See Note 3 regarding the Company's investment in Owyhee Gold Trust. Joint ventures in which the Company has the ability to exercise significant influence, but does not control, are accounted for under the equity method of accounting.
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 September 30, 2023 and December 31, 2022, 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.
Recent Accounting Pronouncements [Policy Text Block]	Recent Accounting Pronouncements Accounting Standards Updates In June 2022, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") No. 2022-03 Fair Value Measurement (Topic 820): Fair Value Measurement of Equity Securities Subject to Contractual Resale Restrictions. This update is to clarify that a contractual restriction on the sale of an equity security is not considered part of the unit of account of the equity security and, therefore, is not considered in measuring fair value. This update is effective for the fiscal year beginning after December 15, 2023, with early adoption permitted. The Company is currently evaluating the impact of adopting this standard on its consolidated financial statements. Accounting Standards Adopted In August 2020, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") No. 2020-06 Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging-Contracts in Entity's Own Equity (Subtopic 815-40): Accounting for Convertible Instruments and Contracts in an Entity's Own Equity. The update is to address issues identified because of the complexity associated with applying generally accepted accounting principles for certain financial instruments with characteristics of liabilities and equity. The update is effective for fiscal years beginning after December 15, 2021, including interim periods within those fiscal years and with early adoption permitted. The adoption of this standard did not impact the Company's consolidated financial statements. Other accounting standards that have been issued or proposed by FASB that do not require adoption until a future date are not expected to have a material impact on the financial statements upon adoption.
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 three and nine months ended September 30, 2023 and September 30, 2022, outstanding common stock equivalents 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)

9 Months Ended

Sep. 30, 2023

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.

On December 30, 2022, Thunder Mountain Gold, Inc. by and through its subsidiaries Thunder Mountain Resources, Inc., a Nevada Corporation, and South Mountain Mines, Inc., an Idaho Corporation ("SMMI") (collectively the "Company", "THMG", or "We", "Our" or "Us") agreed to terminate an Option Agreement, (the "BeMetals Option Agreement") with BeMetals Corporation, a British Columbia corporation, and BeMetals USA Corporation, a Delaware corporation ("BeMetals or BMET").

The "BeMetals Option Agreement was entered into on February 27, 2019, the original terms of the Option Agreement, BeMetals provided the funding to SMMI for project expenses including Management Services Income. The Company has 8 million common shares of BMET USA with a market value of $769,344, and the Company had cash and cash equivalents of $209,529 for the nine months ended September 30, 2023. See Note 3 for further information.

Basis of Presentation and Going Concern [Policy Text Block]

Basis of Presentation and Going Concern

The accompanying condensed consolidated financial statements have been prepared under the assumption that the Company will continue as a going concern. The Company has historically incurred losses, however, the Company has cash reserves and available marketable securities sufficient to cover normal operating expenses. If necessary, the Company continues to have the ability to raise additional capital in order to fund its future exploration and working capital requirements.

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 condensed consolidated financial statements reflect the other investor's 25% non-controlling, capped interest in OGT. Intercompany accounts are eliminated in consolidation.

Accounting Estimates [Policy Text Block]

Accounting Estimates

The preparation of 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.

Revenue Recognition [Policy Text Block]

Revenue Recognition

Management service revenue is recognized when the Company has satisfied its performance obligation required under its management contract with BeMetals. Such an obligation is satisfied over time as work is performed and the Company has a contractual right to payment.

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. At September 30, 2023, the Company has one financial asset, investment in equity security, that is adjusted to fair value on a recurring basis for which the fair value is determined based on Level 1 inputs as the equity security is traded on a stock exchange. 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, and the investment in BeMetal's equity securities, the carrying value of which approximates fair value based on the nature of those instruments.

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.

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 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. See Note 3 regarding the Company's investment in Owyhee Gold Trust. Joint ventures in which the Company has the ability to exercise significant influence, but does not control, are accounted for under the equity method of accounting.

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 September 30, 2023 and December 31, 2022, 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.

Recent Accounting Pronouncements [Policy Text Block]

Recent Accounting Pronouncements

Accounting Standards Updates

In June 2022, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") No. 2022-03 Fair Value Measurement (Topic 820): Fair Value Measurement of Equity Securities Subject to Contractual Resale Restrictions. This update is to clarify that a contractual restriction on the sale of an equity security is not considered part of the unit of account of the equity security and, therefore, is not considered in measuring fair value. This update is effective for the fiscal year beginning after December 15, 2023, with early adoption permitted. The Company is currently evaluating the impact of adopting this standard on its consolidated financial statements.

Accounting Standards Adopted

In August 2020, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") No. 2020-06 Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging-Contracts in Entity's Own Equity (Subtopic 815-40): Accounting for Convertible Instruments and Contracts in an Entity's Own Equity. The update is to address issues identified because of the complexity associated with applying generally accepted accounting principles for certain financial instruments with characteristics of liabilities and equity. The update is effective for fiscal years beginning after December 15, 2021, including interim periods within those fiscal years and with early adoption permitted. The adoption of this standard did not impact the Company's consolidated financial statements.

Other accounting standards that have been issued or proposed by FASB that do not require adoption until a future date are not expected to have a material impact on the financial statements upon adoption.

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 three and nine months ended September 30, 2023 and September 30, 2022, outstanding common stock equivalents 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.