Cover [Abstract] Document Information [Table] Class of Stock [Axis] Class of Stock [Domain] Represents the Common shares, without par value. Common Shares, without par value Represents the Redeemable warrants, each whole warrant exercisable for one Common Share, each at an exercise price of $11.50 per share. Redeemable warrants, each whole warrant exercisable for one Common Share, each at an exercise price of $11.50 per share Document Information [Line Items] Document Type Document Type Entity Registrant Name Entity Registrant Name Document Period End Date Document Quarterly Report Document Transition Report Entity File Number Entity Incorporation, State or Country Code Entity Tax Identification Number Entity Address, Address Line One Entity Address, City or Town Entity Address, State or Province Entity Address, Postal Zip Code City Area Code Local Phone Number Entity Current Reporting Status Entity Interactive Data Current Title of 12(b) Security Trading Symbol Security Exchange Name Entity Filer Category Entity Filer Category Entity Small Business Entity Small Business Entity Emerging Growth Company Entity Emerging Growth Company Entity Ex Transition Period Entity Ex Transition Period Entity Shell Company Entity Common Stock, Shares Outstanding Entity Central Index Key Entity Central Index Key Current Fiscal Year End Date Document Fiscal Year Focus Document Fiscal Period Focus Amendment Flag Amendment Flag Condensed Consolidated Balance Sheets Statement [Table] Statement [Line Items] Assets [Abstract] ASSETS Assets, Current [Abstract] Current Cash and Cash Equivalents, at Carrying Value Cash and cash equivalents - end of period Cash and cash equivalents - beginning of period Cash and cash equivalents Amount of receivables and prepayments. Receivables And Prepayments Current Receivables and prepayments Assets, Current Total current assets Assets, Noncurrent [Abstract] Non-current Amount of exploration licenses. Exploration Licenses Noncurrent Exploration contracts Exploration contracts (Note 6) Property, Plant and Equipment, Net Equipment Assets, Noncurrent Total non-current assets Assets TOTAL ASSETS Liabilities [Abstract] LIABILITIES Liabilities, Current [Abstract] Current Accounts Payable and Accrued Liabilities, Current Accounts payable and accrued liabilities Amount of deferred acquisition costs. Deferred Acquisitions Costs Deferred acquisition costs Liabilities, Current Total current liabilities Liabilities, Noncurrent [Abstract] Non-current Deferred Income Tax Liabilities, Net Deferred tax liability(1) Deferred tax liability Amount of Warrant Liability. Warrant Liability Warrant liability Liabilities Total Liabilities TOTAL LIABILITIES Stockholders' Equity Attributable to Parent [Abstract] EQUITY Common Stock, Value, Issued Common shares (unlimited shares, no par value - issued: 224,385,324 (December 31, 2020 - 189,493,593)) Total value Preferred Stock, Value, Issued Preferred shares (unlimited share, no par value - issued: nil (December 31, 2020 - 509,459)) Additional Paid in Capital. Additional Paid in Capital Accumulated Other Comprehensive Income (Loss), Net of Tax Accumulated other comprehensive loss Retained Earnings (Accumulated Deficit) Deficit Stockholders' Equity Attributable to Parent Total Shareholders' equity TOTAL EQUITY Liabilities and Equity TOTAL LIABILITIES AND EQUITY Represents information pertaining to Class A Special Shares. Class A special shares Represents information pertaining to Class B Special Shares. Class B special shares Represents information pertaining to Class C Special Shares. Class C special shares Represents information pertaining to Class D Special Shares. Class D special shares Represents information pertaining to Class E Special Shares. Class E special shares Represents information pertaining to Class F Special Shares. Class F special shares Represents information pertaining to Class G Special Shares. Class G special shares Represents information pertaining to Class H Special Shares. Class H special shares Represents information pertaining to Class I Special Shares. Class I special shares Represents information pertaining to Class J Special Shares. Class J special shares Common Stock, No Par Value Common shares, no par value Common Stock, Shares, Issued Number of ending balance Number of beginning balance Ordinary shares, issued Preferred Stock, No Par Value Preferred shares, no par value Preferred Stock, Shares Issued Preference shares, shares issued Condensed Consolidated Statements of Loss and Comprehensive Loss Operating Expenses [Abstract] Operating expenses Exploration Expense Exploration expenses Marine vessel cost recognized General and Administrative Expense General and administrative expenses Operating Income (Loss) Operating loss Operating loss Other Items [Abstract] Other items Fair Value Adjustment of Warrants Change in fair value of warrant liability Foreign Currency Transaction Gain (Loss), before Tax Foreign exchange loss Interest Income (Expense), Net Interest expense (income) Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Loss and comprehensive loss for the period Loss and comprehensive loss for the period Earnings Per Share, Basic and Diluted [Abstract] Loss per share Earnings Per Share, Basic and Diluted Loss per share Basic and diluted Weighted Average Number of Shares Outstanding, Basic and Diluted Weighted average number of common shares outstanding - basic and diluted Condensed Consolidated Statements of Changes in Shareholders' Equity Equity Components [Axis] Equity Component [Domain] Common shares Preferred shares Represents the Special shares. Special Shares Additional Paid in Capital Accumulated Other Comprehensive Loss Deficit Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Balance Balance Shares, Outstanding Balance (in Shares) Balance (in Shares) Stock Issued During Period, Value, Stock Options Exercised Amount of Exercise of stock options Exercise of stock options (Note 10) Amount related to common shares to be issued for exploration expenses. Common Shares To Be Issued For Exploration Expenses Common shares to be issued for exploration expenses (Note 6) Stock Issued During Period, Value, Conversion of Convertible Securities Conversion of debentures (Note 7) Amount related to private placement. Shares Issued During Period Private Placement Private placements (net of financing costs) Amount of private placement Shares issued during shares period private placement. Shares Issued During Shares Period Private Placement Private placements (net of financing costs) (in shares) Amount related to financing cost. Stock Issued During Period Value Financing Cost Financing cost Amount of financing cost incurred - Cash Stock issued during period shares financing cost. Stock Issued During Period Shares Financing Cost Financing cost (in shares) Common shares issued for acquisition of Tonga Offshore Minerals Limited. Common Shares Issued For Acquisition Of Tonga Offshore Minerals Limited Common shares issued for acquisition of Tonga Offshore Minerals Limited (Note 5) Stock issued during period shares for acquisition of Tonga Offshore Minerals Limited. Stock Issued During Period Shares For Acquisition Of Tonga Offshore Minerals Limited Common shares issued for acquisition of Tonga Offshore Minerals Limited (Note 5) (in shares) Shares Issued, Value, Share-based Payment Arrangement, after Forfeiture Common share options-payments (Note 10) Stock-based Compensation Expenses Stock Issued During Period, Value, Issued for Services Common shares issued for services Stock Issued During Period, Value, Acquisitions Amount of Issued in Business Combination Net equity from Business Combination (Note 4) Value of stock issued during the period upon the conversion of preferred shares. Conversion of Preferred Shares to Common Stock Conversion of preferred shares to common shares Amount of conversion of preferred shares to common shares Net Income (Loss) Attributable to Parent Loss for the period Loss for the period Condensed Consolidated Statements of Cash Flows Net Cash Provided by (Used in) Operating Activities [Abstract] Cash resources provided by (used in) Operating Activities: Items Not Affecting Cash Abstract Items not affecting cash: Amortization Amortization Share-based Payment Arrangement, Noncash Expense Expenses settled in share-based payments Increase (Decrease) in Interest Payable, Net Interest on convertible debentures Foreign Currency Transaction Gain (Loss), Unrealized Unrealized foreign exchange Increase (Decrease) in Operating Capital [Abstract] Changes in working capital: The increase (decrease) during the reporting period in amount due within one year (or one business cycle) from customers for the credit sale of goods and services and prepaid expenses. Increase (Decrease) in Receivables and Prepaid Expense Receivables and prepayments Increase (Decrease) in Accounts Payable and Accrued Liabilities Accounts payable and accrued liabilities Net Cash Provided by (Used in) Operating Activities Net cash used in operating activities Net Cash Provided by (Used in) Investing Activities [Abstract] Cash resources provided by (used in) Investing activities Payments to Acquire Mining Assets Acquisition of exploration contract Application fee Payments to Acquire Machinery and Equipment Acquisition of equipment Net Cash Provided by (Used in) Investing Activities Net cash used in investing activities Net Cash Provided by (Used in) Financing Activities [Abstract] Cash resources provided by (used in) Financing Activities: Proceeds from Stock Options Exercised Proceeds from stock option exercised Exercise of stock options Proceeds from Convertible Debt Proceeds from issuance of convertible debentures Proceeds from Issuance of Common Stock Total proceeds Proceeds from issuance of common shares (net of fees and other costs) Proceeds from net contributions from business combination. Net contributions from Business Combination Proceeds from Business Combination (net of fees and other costs) Net contributions from Business Combination Net Cash Provided by (Used in) Financing Activities Net cash provided by financing activities Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect Net change in cash and cash equivalents Effect of Exchange Rate on Cash and Cash Equivalents Impact of exchange rate changes on cash and cash equivalents Nature of Operations Nature of Operations. Nature of Operations Restatement of Previously Issued Quarterly Financial Statements Error Correction [Text Block] Restatement of Previously Issued Quarterly Financial Statements Summary of Significant Accounting Policies Significant Accounting Policies [Text Block] Summary of Significant Accounting Policies Business Combination Business Combination Disclosure [Text Block] Business Combination TOML Acquisition Asset Acquisition [Text Block] TOML Acquisition Exploration Contracts. No definition available. Explorations Licenses [TextBlock] Exploration Contracts Convertible Debentures Debt Disclosure [Text Block] Convertible Debentures The disclosure of Warrant liability abstract. Warrant Liability. The entire disclosure of warrant liability. Warrants Liability [Text Block] Warrant Liability Common Shares Stockholders' Equity Note Disclosure [Text Block] Common Shares Share-based compensation Share-based Payment Arrangement [Text Block] Share-based compensation Loss per share Earnings Per Share [Text Block] Loss per share Related Party Transactions Related Party Transactions Disclosure [Text Block] Related Party Transactions Commitments Commitments and Contingencies Disclosure [Text Block] Commitments Supplemental Cash Flow Information Cash Flow, Supplemental Disclosures [Text Block] Supplemental Cash Flow Information Segmented Information Segment Reporting Disclosure [Text Block] Segmented Information Subsequent Events Subsequent Events [Text Block] Subsequent Events Basis of Accounting, Policy [Policy Text Block] Basis of Presentation No definition available. Basis Of Measurements, Policy [Policy Text Block] Basis of Measurement Use of Estimates, Policy [Policy Text Block] Use of Estimates Fair Value of Financial Instruments, Policy [Policy Text Block] Fair Value of Financial Instruments Derivatives, Policy [Policy Text Block] Warrant Liabilities New Accounting Pronouncements, Policy [Policy Text Block] Recent Accounting Pronouncements Issued and Adopted Schedule of Error Corrections and Prior Period Adjustments [Table Text Block] Schedule of Restatement of Previously Issued Quarterly Financial Statements The tabular disclosure of the Special Shares and their respective vesting thresholds, assuming the full amount of Special Shares from Rollover Options are issued. Schedule Of The Special Shares And Their Respective Vesting Thresholds, Assuming The Full Amount Of Special Shares From Rollover Options Are Issued [Table Text Block] Summary of the Special Shares and their respective vesting thresholds, assuming the full amount of Special Shares from Rollover Options are issued The tabular disclosure of reconciliation of elements of Business Combination to consolidated statement of cash flows. Schedule Of Reconciliation Of Elements Of Business Combination To Consolidated Statement Of Cash Flows [Table Text Block] Summary of reconciliation of cash proceeds from the Business Combination The tabular disclosure of number of shares of TMC common stock issued immediately following the consummation of the Business Combination. Schedule Of Number Of Shares Of Tmc Common Stock Issued Immediately Following The Consummation Of The Business Combination [Table Text Block] Summary of number of shares of TMC common shares issued immediately following the consummation of the Business Combination Schedule of Business Acquisitions, by Acquisition [Table Text Block] Schedule of net assets acquired as part of the TOML acquisition No definition available. Schedule Of Common Share Transactions [Table Text Block] Schedule of common shares transactions No definition available. Schedule Of Break Down Of Explorations Expenses [Table Text Block] Schedule of breakdown of exploration expenses Schedule of Derivative Liabilities at Fair Value [Table Text Block] Schedule of changes in the fair value of warrant liabilities Fair Value, Concentration of Risk [Table Text Block] Schedule of provides quantitative information regarding Level 3 fair value measurements Schedule of Stock by Class [Table Text Block] Schedule of authorized and issued & outstanding common shares and special shares Schedule of Common Stock Outstanding Roll Forward [Table Text Block] Schedule of common shares Stock Options (Tables) [Table] Award Type [Axis] Award Type [Domain] Restricted Stock Units (RSUs) [Member] Restricted Stock Units ("RSUs") No definition available. Short Term Incentive Plans [Member]