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SHAREHOLDERS' EQUITY (Details) - USD ($) |  |  |  |  |  |  |  |  |  | 3 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Feb. 09, 2021 | Jan. 29, 2021 | Dec. 31, 2020 | Sep. 10, 2020 | Jun. 25, 2020 | Nov. 20, 2019 | May 23, 2019 | Mar. 29, 2019 | Nov. 08, 2018 | Mar. 31, 2019 | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019 | Jun. 30, 2021 | Jun. 29, 2021 | Dec. 31, 2018
Common stock, shares authorized |  |  |  |  |  |  |  |  |  |  |  |  |  | 675,000,000 | 500,000,000 |
Number of units issued |  |  |  |  |  |  | 1,935,484 |  |  |  |  |  |  |  |  |
Net proceeds |  |  |  |  |  |  | $ 2,600,000 |  |  |  |  |  | $ 1,851,000 |  |  |
Issuance costs |  |  |  |  |  |  | $ 400,000 |  |  |  |  |  |  |  |  |
Sale of common stock for cash, net of issuance costs |  |  |  |  |  |  |  |  |  |  | $ 29,875,000 |  | $ 69,467,000 |  |  |
Weighted average exercise price of stock options (in dollars per share) |  |  |  |  |  |  |  |  |  |  |  | $ 1.02 | $ 1.01 |  |  |
Outstanding options (in shares) |  |  | 7,012,334 |  |  |  |  |  |  |  | 6,171,167 | 7,012,334 | 5,269,000 |  |  | 4,243,000
Stock options exercised (in shares) |  |  |  |  |  |  |  |  |  |  |  | 135,000 | 535,000 |  |  |
Stock options issued (in shares) |  |  |  |  |  |  |  |  |  |  | 950,000 | 5,097,000 | 3,050,000 |  |  |
Acquisition of Mineral Property Interests |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shares issued in connection with acquisitions (in shares) |  |  |  |  |  |  |  |  |  |  |  | 53,600 | 353,570 |  |  |
Shares issued in connection with acquisitions |  |  |  |  |  |  |  |  |  |  |  | $ 100,000 |  |  |  |
November 2019 Offering |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of units issued |  |  |  |  |  | 37,750,000 |  |  |  |  |  |  |  |  |  |
Price per unit |  |  |  |  |  | $ 1.325 |  |  |  |  |  |  |  |  |  |
Net proceeds |  |  |  |  |  | $ 46,600,000 |  |  |  |  |  |  |  |  |  |
Warrant expiration term |  |  |  |  |  | 5 years |  |  |  |  |  |  |  |  |  |
Issuance costs |  |  |  |  |  | $ 3,500,000 |  |  |  |  |  |  |  |  |  |
Outstanding warrants |  |  |  |  |  |  |  |  |  |  | $ 21,706,250 |  |  |  |  |
June 2020 Amended and Restated Credit Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of units issued |  |  |  |  | 2,091,700 |  |  |  |  |  |  |  |  |  |  |
Net proceeds |  |  |  |  | $ 1,900,000 |  |  |  |  |  |  |  |  |  |  |
March 2019 Offering |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of units issued |  |  |  |  |  |  |  | 14,193,548 |  |  |  |  |  |  |  |
Price per unit |  |  |  |  |  |  |  | $ 1.55 |  |  |  |  |  |  |  |
Net proceeds |  |  |  |  |  |  |  | $ 20,300,000 |  |  |  |  |  |  |  |
Number of shares of common stock |  |  |  |  |  |  |  | 1 |  |  |  |  |  |  |  |
Number of warrants received for each share of common stock share sold |  |  |  |  |  |  |  | 0.50 |  |  |  |  |  |  |  |
Issuance costs |  |  |  |  |  |  |  | $ 1,700,000 |  |  |  |  |  |  |  |
Equity Incentive Plan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Weighted average exercise price of stock options (in dollars per share) |  |  |  |  |  |  |  |  |  |  |  | $ 1.02 |  |  |  |
Stock options exercised (in shares) |  |  |  |  |  |  |  |  |  |  | 0 |  |  |  |  |
Stock options issued (in shares) |  |  |  |  |  |  |  |  |  |  | 0 | 135,000 |  |  |  |
Officers Directors And Certain Employees |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock options granted |  |  |  |  |  |  |  |  |  |  | $ 950,000 |  |  |  |  |
Weighted average exercise price of stock options (in dollars per share) |  |  |  |  |  |  |  |  |  |  | $ 1.22 |  |  |  |  |
Equity Financing In February 2021 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of units issued | 30,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Price per unit | $ 1.05 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gross proceeds | $ 31,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net proceeds | 29,900,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Issuance costs | $ 1,700,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity Financing In February 2021 | Canadian Development Expenses |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gross proceeds |  |  |  |  |  |  |  |  |  |  | $ 31,500,000 |  |  |  |  |
Subscription Receipts | Officers Directors And Certain Employees |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of units issued |  |  |  |  |  |  |  | 1,935,484 |  |  |  |  |  |  |  |
Price per unit |  |  |  |  |  |  |  | $ 1.55 |  |  |  |  |  |  |  |
Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of units issued |  |  |  |  |  |  |  |  |  |  |  |  | 1,010,000 |  |  |
Net proceeds |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,851,000 |  |  |
Shares issued for acquisition of mineral property interests (in shares) |  |  |  |  |  |  |  |  |  |  |  | 53,000 | 354,000 |  |  |
Stock options exercised (in shares) |  |  |  |  |  |  |  |  |  |  |  | 135,000 | 535,000 |  |  |
Common Stock [Member] | November 2019 Offering |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net proceeds |  |  |  |  |  | 37,300,000 |  |  |  |  |  |  |  |  |  |
Warrant | November 2019 Offering |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net proceeds |  |  |  |  |  | $ 9,300,000 |  |  |  |  |  |  |  |  |  |
Number of shares of common stock |  |  |  |  |  | 1 |  |  |  |  |  |  |  |  |  |
Number of warrants received for each share of common stock share sold |  |  |  |  |  | 0.50 |  |  |  |  |  |  |  |  |  |
Warrant | March 2019 Offering |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Warrant expiration term |  |  |  |  |  |  |  | 3 years |  |  |  |  |  |  |  |
Price per common share for each warrant |  |  |  |  |  |  |  | $ 2.00 |  |  |  |  |  |  |  |
Warrant at Second Stock Price | November 2019 Offering |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares of common stock |  |  |  |  |  | 1 |  |  |  |  |  |  |  |  |  |
Price per common share for each warrant |  |  |  |  |  | $ 1.7225 |  |  |  |  |  |  |  |  |  |
Flow Through Common Shares | Canadian Development Expenses |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of units issued |  | 12,600,600 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Price per unit |  | $ 1.01 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gross proceeds |  | $ 12,700,000 |  |  |  |  |  |  |  |  | 12,700,000 |  |  |  |  |
Net proceeds |  | 12,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Issuance costs |  | 700,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net proceeds allocated to the sale of tax benefits |  | 1,200,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sale of common stock for cash, net of issuance costs |  | $ 10,800,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Exploration expenditures |  |  |  |  |  |  |  |  |  |  | 12,700,000 |  |  |  |  |
Flow Through Common Shares | Canadian Exploration Expenditures |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of units issued |  |  | 7,669,900 | 6,298,166 |  |  |  |  |  |  |  |  |  |  |  |
Price per unit |  |  | $ 1.28 | $ 1.65 |  |  |  |  |  |  |  | $ 1.28 |  |  |  |
Gross proceeds |  |  |  | $ 10,400,000 |  |  |  |  |  |  |  |  |  |  |  |
Net proceeds |  |  | $ 9,800,000 | 9,800,000 |  |  |  |  |  |  |  |  |  |  |  |
Issuance costs |  |  | 0 | 600,000 |  |  |  |  |  |  |  |  |  |  |  |
Net proceeds allocated to the sale of tax benefits |  |  | 2,100,000 | 2,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |
Sale of common stock for cash, net of issuance costs |  |  | $ 7,700,000 | $ 7,800,000 |  |  |  |  |  |  |  |  |  |  |  |
Exploration expenditures |  |  |  |  |  |  |  |  |  |  | $ 12,700,000 |  |  |  |  |
At-the-market ("ATM") |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of units issued |  |  |  |  |  |  |  |  |  | 1,010,545 |  |  |  |  |  |
Sale of common stock for cash, net of issuance costs |  |  |  |  |  |  |  |  |  | $ 1,900,000 |  |  |  |  |  |
Aggregate offering price |  |  |  |  |  |  |  |  | $ 90,000,000.0 |  |  |  |  |  |  |

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