Business and Significant Accounting Policies	9 Months Ended
Sep. 30, 2019
Accounting Policies [Abstract]
Business and Significant Accounting Policies	Business and company formation Solitario Zinc Corp. (“Solitario,” or the “Company”) is an exploration stage company as defined in Industry Guide 7, as issued by the United States Securities and Exchange Commission (“SEC”). Solitario was incorporated in the State of Colorado on November 15, 1984 as a wholly owned subsidiary of Crown Resources Corporation ("Crown"). In July 1994, Solitario became a publicly traded company on the Toronto Stock Exchange (the "TSX") through its initial public offering. Solitario has been actively involved in mineral exploration since 1993. Solitario’s primary business is to acquire exploration mineral properties or royalties and/or discover economic deposits on its mineral properties and advance these deposits, either on its own or through joint ventures, up to the development stage of the project. At that point, or sometime prior to that point, Solitario would likely attempt to sell its mineral properties, pursue their development either on its own, or through a joint venture with a partner that has expertise in mining operations, or create a royalty with a third party that continues to advance the property. Solitario is primarily focused on the acquisition and exploration of zinc-related exploration mineral properties, however Solitario will evaluate and potentially acquire other base and precious metal mineral exploration properties. In addition to focusing on its mineral exploration properties, Solitario also evaluates potential strategic transactions for the acquisition of new precious and base metal properties and assets with exploration potential or business combinations that Solitario determines to be favorable to Solitario. Solitario has recorded revenue in the past from the sale of mineral properties, including the sale of certain mineral royalty properties in January 2019, discussed below, and the sale in June 2018 of its interest in the royalty on the Yanacocha property. Revenues and / or proceeds from the sale or joint venture of properties or assets have not been a consistent annual source of cash and would only occur in the future, if at all, on an infrequent basis. Solitario currently considers its carried interest in the Florida Canyon project and its interest in the Lik project to be its core mineral property assets. Nexa Resources, Ltd. (“Nexa”), Solitario’s joint venture partner, is continuing the exploration and furtherance of the Florida Canyon project and Solitario is monitoring progress at Florida Canyon. Solitario is working with its 50% joint venture partner, Teck American Incorporated, a wholly owned subsidiary of Teck Resources Limited (both companies are referred to as “Teck”), in the Lik deposit to further the exploration of, and to evaluate potential development plans for the Lik project. As of September 30, 2019, Solitario has significant balances of cash and short-term investments that Solitario anticipates using, in part, to further the exploration of the Florida Canyon and Lik projects and to potentially acquire additional mineral property assets. The fluctuations in precious metal and other commodity prices contribute to a challenging environment for mineral exploration and development, which has created opportunities as well as challenges for the potential acquisition of early-stage and advanced mineral exploration projects or other related assets at potentially attractive terms. The accompanying interim condensed consolidated financial statements of Solitario for the three and nine months ended September 30, 2019 are unaudited and are prepared in accordance with accounting principles generally accepted in the United States of America (“generally accepted accounting principles”). They do not include all disclosures required by generally accepted accounting principles for annual financial statements, but in the opinion of management, include all adjustments, consisting only of normal recurring items, necessary for a fair presentation. Interim results are not necessarily indicative of results, which may be achieved in the future or for the full year ending December 31, 2019. These financial statements should be read in conjunction with the financial statements and notes thereto which are included in Solitario’s Annual Report on Form 10-K for the year ended December 31, 2018. The accounting policies set forth in those annual financial statements are the same as the accounting policies utilized in the preparation of these financial statements, except as modified for appropriate interim financial statement presentation. Recent Developments Royalty sale On January 22, 2019, Solitario completed the sale of its interest in certain royalties to SilverStream SEZC, a private Cayman Island royalty and streaming company (“SilverStream”) for Cdn$600,000 (the “Royalty Sale”). The Royalty Sale covered (i) a royalty on the formerly Solitario-owned 125,000-acre polymetallic Pedra Branca palladium, platinum, gold, nickel, cobalt and chrome project in Brazil, (ii) a royalty covering 3,880 acres of non-producing exploration properties in Mexico, and (iii) a purchase option on 11 separate non-producing properties covering over 16,500 acres in Montana. On closing of the Royalty Sale, Solitario received Cdn$250,000 in cash and a convertible note from SilverStream in the principal amount of Cdn$350,000 (the “SilverStream Note”). The SilverStream Note is due December 31, 2019, accrues 5% per annum simple interest, payable on a quarterly basis, and is convertible into common shares of SilverStream, at the discretion of SilverStream, by providing Solitario a notice of conversion. Solitario recorded interest income of $3,000 and $9,000, respectively, from the SilverStream Note during the three and nine months ended September 30, 2019. SilverStream may only provide a notice of conversion if SilverStream has completed an initial public offering during the term of the SilverStream Note for minimum proceeds of Cdn$5,000,000, otherwise the SilverStream Note will be payable in cash at the maturity date. Pursuant to the terms of the SilverStream Note, if SilverStream were to complete an initial public offering and the SilverStream Note was converted, Solitario would receive common shares converted at 85% of the weighted average quoted price of a share of SilverStream common stock for the most recent 10-day period prior to the notice of conversion. During the nine months ended September 30, 2019, Solitario recorded mineral property revenue of $408,000 for the Royalty Sale, consisting of the fair value of the cash received on the date of the sale of $185,000 and the fair value of the SilverStream Note on the date of the sale of $263,000 less the carrying value of the royalties sold of $40,000. As of September 30, 2019, the approximate fair value of the SilverStream Note, including accrued interest, was $268,000, based upon the current US dollar / Canadian dollar exchange rate, and Solitario recorded a credit to exchange gain and loss of $1,000, included in general and administrative expense during the nine months ended September 30, 2019. Financial reporting The consolidated financial statements include the accounts of Solitario and its wholly owned subsidiaries. All significant intercompany accounts and transactions have been eliminated in consolidation. The consolidated financial statements are prepared in accordance with generally accepted accounting principles and are expressed in U.S. dollars. Revenue recognition Solitario has recorded revenue from the sale of exploration mineral properties and joint venture property payments. Solitario’s policy is to recognize revenue from the sale of its exploration mineral properties (those without reserves) on a property-by-property basis, computed as the cash received and / or expected collectable receivables less any capitalized cost. Payments received for the sale of exploration property interests that are less than the properties cost are recorded as a reduction of the related property's capitalized cost. In addition, Solitario’s policy is to recognize revenue on any receipts of joint venture property payments in excess of its capitalized costs on a property that Solitario may lease to another mining company. Solitario has recognized revenue during the nine months ended September 30, 2019 of $408,000 related to the Royalty Sale, discussed above, in accordance with Accounting Standards Codification (“ASC”) 606. In addition, Solitario recorded revenue during the second quarter of 2018 of $502,000 from the sale of its former Yanacocha exploration mineral property. Solitario expects any property or asset sales in the future to be on an infrequent basis. Prior to the sale of its Yanacocha exploration mineral property, the last proceeds from joint venture property payments was in 2015 and Solitario does not expect to record joint venture property payments on any of its currently held properties for the foreseeable future. Use of estimates The preparation of financial statements in conformity with generally accepted accounting principles requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Some of the more significant estimates included in the preparation of Solitario's financial statements pertain to: (i) Solitario’s carrying value of short-term investments; (ii) the recoverability of mineral properties related to its mineral exploration properties and their future exploration potential; (iii) the fair value of stock option grants to employees, to officers and directors and to others; (iv) the ability of Solitario to realize its deferred tax assets; (v) the collectability of the SilverStream Note; and (vi) Solitario's investment in marketable equity securities. In performing its activities, Solitario has incurred certain costs for mineral properties. The recovery of these costs is ultimately dependent upon the sale of mineral property interests or the development of economically recoverable ore reserves and the ability of Solitario or its joint venture partners to obtain the necessary permits and financing to successfully place the properties into production, and upon future profitable operations, none of which is assured. Cash equivalents Cash equivalents include investments in highly liquid money-market securities with original maturities of three months or less when purchased. As of September 30, 2019, $328,000 of Solitario’s cash and cash equivalents are held in brokerage accounts and foreign banks, which are not covered under the Federal Deposit Insurance Corporation (“FDIC”) rules for the United States. Short-term investments As of September 30, 2019, Solitario has $7,318,000 of its current assets in United States Treasury Securities (“USTS”) with remaining maturities of 30 days to 15 months. The USTS are recorded at their fair value, based upon quoted market prices, and are not covered under the FDIC insurance rules for United States deposits, with increases or decreases in fair market value recorded as interest income in the statement of operation in the period. Solitario’s USTS are highly liquid and may be sold in their entirety at any time at their quoted market price and are classified as a current asset. Mineral properties Solitario expenses all exploration costs incurred on its mineral properties prior to the establishment of proven and probable reserves through the completion of a feasibility study. Initial acquisition costs of its mineral properties are capitalized. Solitario regularly performs evaluations of its investment in mineral properties to assess the recoverability and/or the residual value of its investments in these assets. All long-lived assets are reviewed for impairment whenever events or circumstances change which indicate the carrying amount of an asset may not be recoverable, utilizing established guidelines based upon undiscounted future net cash flows from the asset or upon the determination that certain exploration properties do not have sufficient potential for economic mineralization. Leases Solitario accounts for its leases in accordance with ASC 842, Leases (“ASC 842”) by recognizing right-of-use assets and lease liabilities on the condensed consolidated balance sheet and disclosing key information about lease arrangements. Solitario has elected the practical expedient option to use January 1, 2019, the effective date of adoption of ASC 842, as the initial date of transition and not to restate comparative prior periods and to carry forward historical lease classification. In addition, Solitario has elected the option not to apply the recognition of assets and liabilities provisions of ASC 842 to operating leases of less than one year. See Note 4 “Operating Leases” for more information and disclosures regarding Solitario’s leases. Fair value ASC 820, Fair Value measurement (“ASC 820”) established a framework for measuring fair value of financial instruments and required disclosures about fair value measurements. For certain of Solitario's financial instruments, including cash and cash equivalents and accounts payable, the carrying amounts approximate fair value due to their short-term maturities. Solitario's short-term investments in USTS, its marketable equity securities, Vendetta Mining Corp. (“Vendetta”) Warrants (defined below in Note 3, “Marketable Equity Securities”) and any covered call options against those marketable equity securities are carried at their estimated fair value based on quoted market prices, and in the case of its Vendetta Warrants, based upon a Black Scholes model. See Note 6, “Fair Value,” below. Marketable equity securities Solitario's investments in marketable equity securities are carried at fair value, which is based upon quoted prices of the securities owned. Solitario records investments in marketable equity securities for investments in publicly traded marketable equity securities for which it does not exercise significant control and where Solitario has no representation on the board of directors of those companies and exercises no control over the management of those companies. The cost of marketable equity securities sold is determined by the specific identification method. Changes in fair value are recorded as unrealized gain or loss in the statement of operations. Derivative instruments Solitario accounts for its derivative instruments in accordance with ASC 815, "Accounting for Derivative Instruments and Hedging Activities" (“ASC 815”). Solitario acquired its investment in Vendetta units, including the Vendetta Warrants during 2019. Solitario recorded the value of the Vendetta Warrants at their fair value as other assets on the consolidated balance sheet. Solitario has sold covered calls from time to time on its investment in Kinross Gold Corporation (“Kinross”) marketable equity securities. Solitario has not designated its sold covered calls as hedging instruments and any changes in the fair value of the sold covered calls and its Vendetta Warrants are recognized in the statement of operations in the period of the change as gain or loss on derivative instruments. Foreign exchange The United States dollar is the functional currency for all of Solitario's foreign subsidiaries. Although Solitario's South American exploration activities during 2018 and the first nine months of 2019 have been conducted primarily in Peru, a portion of the payments under the land, leasehold and exploration agreements of Solitario are denominated in United States dollars. Realized foreign currency gains and losses are included in the results of operations in the period in which they occur. Income taxes Solitario accounts for income taxes in accordance with ASC 740, “Accounting for Income Taxes” (“ASC 740”). Under ASC 740, income taxes are provided for the tax effects of transactions reported in the financial statements and consist of taxes currently due plus deferred taxes related to certain income and expenses recognized in different periods for financial and income tax reporting purposes. Deferred tax assets and liabilities represent the future tax return consequences of those differences, which will either be taxable or deductible when the assets and liabilities are recovered or settled. Deferred taxes are also recognized for operating losses and tax credits that are available to offset future taxable income and income taxes, respectively. A valuation allowance is provided if it is more likely than not that some portion or all of the deferred tax assets will not be realized. Accounting for uncertainty in income taxes ASC 740 clarifies the accounting for uncertainty in income taxes recognized in a company's financial statements. ASC 740 prescribes a recognition threshold and measurement attribute for the financial statement recognition and measurement of a tax position taken or expected to be taken in a tax return. ASC 740 also provides guidance on derecognition, classification, interest and penalties, accounting in interim periods, disclosure, and transition. ASC 740 provides that a company's tax position will be considered settled if the taxing authority has completed its examination, the company does not plan to appeal, and it is remote that the taxing authority would reexamine the tax position in the future. Earnings per share The calculation of basic and diluted earnings (loss) per share is based on the weighted average number of shares of common stock outstanding during the three and nine months ended September 30, 2019 and 2018. Potentially dilutive shares related to outstanding common stock options of 4,373,000 at September 30, 2019 and 4,025,228 at September 30, 2018 for Solitario common shares were excluded from the calculation of diluted earnings (loss) per share because the effects were anti-dilutive. Employee stock compensation and incentive plans Solitario classifies all of its stock options as equity options in accordance with the provisions of ASC 718, “Compensation – Stock Compensation.” Recent accounting pronouncements On January 1, 2019, Solitario adopted Accounting Standards Update No. 2016-02 Leases (“ASU 2016-02”) which requires the application of ASC 842 and the recognition of right-of-use assets and related liabilities associated with all leases that are not short-term in nature. As a result of the adoption of ASU 2016-02 on January 1, 2019, Solitario recorded both an operating lease asset for its Wheat Ridge, Colorado office of $82,000 and an operating lease liability of $82,000 related to the same lease. The adoption of ASU 2016-02 did not require the recording of any other assets or liabilities on our condensed consolidated balance sheets and had an immaterial effect on Solitario’s condensed consolidated statement of operations for the three and nine months ended September 30, 2019, and its condensed consolidated statement of cash flows for the nine months ended September 30, 2019. Solitario has elected the practical expedient option to use January 1, 2019, the effective date of adoption, as the initial date of transition and not to restate comparative prior periods and to carry forward historical lease classification. See Note 4, “Operating Leases” for more information and disclosures regarding Solitario’s leases.

Business and Significant Accounting Policies

9 Months Ended

Sep. 30, 2019

Business and Significant Accounting Policies

Business and company formation

Solitario Zinc Corp. (“Solitario,” or the “Company”) is an exploration stage company as defined in Industry Guide 7, as issued by the United States Securities and Exchange Commission (“SEC”). Solitario was incorporated in the State of Colorado on November 15, 1984 as a wholly owned subsidiary of Crown Resources Corporation ("Crown"). In July 1994, Solitario became a publicly traded company on the Toronto Stock Exchange (the "TSX") through its initial public offering. Solitario has been actively involved in mineral exploration since 1993. Solitario’s primary business is to acquire exploration mineral properties or royalties and/or discover economic deposits on its mineral properties and advance these deposits, either on its own or through joint ventures, up to the development stage of the project. At that point, or sometime prior to that point, Solitario would likely attempt to sell its mineral properties, pursue their development either on its own, or through a joint venture with a partner that has expertise in mining operations, or create a royalty with a third party that continues to advance the property. Solitario is primarily focused on the acquisition and exploration of zinc-related exploration mineral properties, however Solitario will evaluate and potentially acquire other base and precious metal mineral exploration properties. In addition to focusing on its mineral exploration properties, Solitario also evaluates potential strategic transactions for the acquisition of new precious and base metal properties and assets with exploration potential or business combinations that Solitario determines to be favorable to Solitario.

Solitario has recorded revenue in the past from the sale of mineral properties, including the sale of certain mineral royalty properties in January 2019, discussed below, and the sale in June 2018 of its interest in the royalty on the Yanacocha property. Revenues and / or proceeds from the sale or joint venture of properties or assets have not been a consistent annual source of cash and would only occur in the future, if at all, on an infrequent basis.

Solitario currently considers its carried interest in the Florida Canyon project and its interest in the Lik project to be its core mineral property assets. Nexa Resources, Ltd. (“Nexa”), Solitario’s joint venture partner, is continuing the exploration and furtherance of the Florida Canyon project and Solitario is monitoring progress at Florida Canyon. Solitario is working with its 50% joint venture partner, Teck American Incorporated, a wholly owned subsidiary of Teck Resources Limited (both companies are referred to as “Teck”), in the Lik deposit to further the exploration of, and to evaluate potential development plans for the Lik project.

As of September 30, 2019, Solitario has significant balances of cash and short-term investments that Solitario anticipates using, in part, to further the exploration of the Florida Canyon and Lik projects and to potentially acquire additional mineral property assets. The fluctuations in precious metal and other commodity prices contribute to a challenging environment for mineral exploration and development, which has created opportunities as well as challenges for the potential acquisition of early-stage and advanced mineral exploration projects or other related assets at potentially attractive terms.

The accompanying interim condensed consolidated financial statements of Solitario for the three and nine months ended September 30, 2019 are unaudited and are prepared in accordance with accounting principles generally accepted in the United States of America (“generally accepted accounting principles”). They do not include all disclosures required by generally accepted accounting principles for annual financial statements, but in the opinion of management, include all adjustments, consisting only of normal recurring items, necessary for a fair presentation. Interim results are not necessarily indicative of results, which may be achieved in the future or for the full year ending December 31, 2019.

These financial statements should be read in conjunction with the financial statements and notes thereto which are included in Solitario’s Annual Report on Form 10-K for the year ended December 31, 2018. The accounting policies set forth in those annual financial statements are the same as the accounting policies utilized in the preparation of these financial statements, except as modified for appropriate interim financial statement presentation.

Recent Developments

Royalty sale

On January 22, 2019, Solitario completed the sale of its interest in certain royalties to SilverStream SEZC, a private Cayman Island royalty and streaming company (“SilverStream”) for Cdn$600,000 (the “Royalty Sale”). The Royalty Sale covered (i) a royalty on the formerly Solitario-owned 125,000-acre polymetallic Pedra Branca palladium, platinum, gold, nickel, cobalt and chrome project in Brazil, (ii) a royalty covering 3,880 acres of non-producing exploration properties in Mexico, and (iii) a purchase option on 11 separate non-producing properties covering over 16,500 acres in Montana. On closing of the Royalty Sale, Solitario received Cdn$250,000 in cash and a convertible note from SilverStream in the principal amount of Cdn$350,000 (the “SilverStream Note”). The SilverStream Note is due December 31, 2019, accrues 5% per annum simple interest, payable on a quarterly basis, and is convertible into common shares of SilverStream, at the discretion of SilverStream, by providing Solitario a notice of conversion. Solitario recorded interest income of $3,000 and $9,000, respectively, from the SilverStream Note during the three and nine months ended September 30, 2019. SilverStream may only provide a notice of conversion if SilverStream has completed an initial public offering during the term of the SilverStream Note for minimum proceeds of Cdn$5,000,000, otherwise the SilverStream Note will be payable in cash at the maturity date. Pursuant to the terms of the SilverStream Note, if SilverStream were to complete an initial public offering and the SilverStream Note was converted, Solitario would receive common shares converted at 85% of the weighted average quoted price of a share of SilverStream common stock for the most recent 10-day period prior to the notice of conversion. During the nine months ended September 30, 2019, Solitario recorded mineral property revenue of $408,000 for the Royalty Sale, consisting of the fair value of the cash received on the date of the sale of $185,000 and the fair value of the SilverStream Note on the date of the sale of $263,000 less the carrying value of the royalties sold of $40,000. As of September 30, 2019, the approximate fair value of the SilverStream Note, including accrued interest, was $268,000, based upon the current US dollar / Canadian dollar exchange rate, and Solitario recorded a credit to exchange gain and loss of $1,000, included in general and administrative expense during the nine months ended September 30, 2019.

Financial reporting

The consolidated financial statements include the accounts of Solitario and its wholly owned subsidiaries. All significant intercompany accounts and transactions have been eliminated in consolidation. The consolidated financial statements are prepared in accordance with generally accepted accounting principles and are expressed in U.S. dollars.

Revenue recognition

Solitario has recorded revenue from the sale of exploration mineral properties and joint venture property payments. Solitario’s policy is to recognize revenue from the sale of its exploration mineral properties (those without reserves) on a property-by-property basis, computed as the cash received and / or expected collectable receivables less any capitalized cost. Payments received for the sale of exploration property interests that are less than the properties cost are recorded as a reduction of the related property's capitalized cost. In addition, Solitario’s policy is to recognize revenue on any receipts of joint venture property payments in excess of its capitalized costs on a property that Solitario may lease to another mining company.

Solitario has recognized revenue during the nine months ended September 30, 2019 of $408,000 related to the Royalty Sale, discussed above, in accordance with Accounting Standards Codification (“ASC”) 606. In addition, Solitario recorded revenue during the second quarter of 2018 of $502,000 from the sale of its former Yanacocha exploration mineral property. Solitario expects any property or asset sales in the future to be on an infrequent basis. Prior to the sale of its Yanacocha exploration mineral property, the last proceeds from joint venture property payments was in 2015 and Solitario does not expect to record joint venture property payments on any of its currently held properties for the foreseeable future.

Use of estimates

The preparation of financial statements in conformity with generally accepted accounting principles requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Some of the more significant estimates included in the preparation of Solitario's financial statements pertain to: (i) Solitario’s carrying value of short-term investments; (ii) the recoverability of mineral properties related to its mineral exploration properties and their future exploration potential; (iii) the fair value of stock option grants to employees, to officers and directors and to others; (iv) the ability of Solitario to realize its deferred tax assets; (v) the collectability of the SilverStream Note; and (vi) Solitario's investment in marketable equity securities.

In performing its activities, Solitario has incurred certain costs for mineral properties. The recovery of these costs is ultimately dependent upon the sale of mineral property interests or the development of economically recoverable ore reserves and the ability of Solitario or its joint venture partners to obtain the necessary permits and financing to successfully place the properties into production, and upon future profitable operations, none of which is assured.

Cash equivalents

Cash equivalents include investments in highly liquid money-market securities with original maturities of three months or less when purchased. As of September 30, 2019, $328,000 of Solitario’s cash and cash equivalents are held in brokerage accounts and foreign banks, which are not covered under the Federal Deposit Insurance Corporation (“FDIC”) rules for the United States.

Short-term investments

As of September 30, 2019, Solitario has $7,318,000 of its current assets in United States Treasury Securities (“USTS”) with remaining maturities of 30 days to 15 months. The USTS are recorded at their fair value, based upon quoted market prices, and are not covered under the FDIC insurance rules for United States deposits, with increases or decreases in fair market value recorded as interest income in the statement of operation in the period. Solitario’s USTS are highly liquid and may be sold in their entirety at any time at their quoted market price and are classified as a current asset.

Mineral properties

Solitario expenses all exploration costs incurred on its mineral properties prior to the establishment of proven and probable reserves through the completion of a feasibility study. Initial acquisition costs of its mineral properties are capitalized. Solitario regularly performs evaluations of its investment in mineral properties to assess the recoverability and/or the residual value of its investments in these assets. All long-lived assets are reviewed for impairment whenever events or circumstances change which indicate the carrying amount of an asset may not be recoverable, utilizing established guidelines based upon undiscounted future net cash flows from the asset or upon the determination that certain exploration properties do not have sufficient potential for economic mineralization.

Leases

Solitario accounts for its leases in accordance with ASC 842, Leases (“ASC 842”) by recognizing right-of-use assets and lease liabilities on the condensed consolidated balance sheet and disclosing key information about lease arrangements. Solitario has elected the practical expedient option to use January 1, 2019, the effective date of adoption of ASC 842, as the initial date of transition and not to restate comparative prior periods and to carry forward historical lease classification. In addition, Solitario has elected the option not to apply the recognition of assets and liabilities provisions of ASC 842 to operating leases of less than one year. See Note 4 “Operating Leases” for more information and disclosures regarding Solitario’s leases.

Fair value

ASC 820, Fair Value measurement (“ASC 820”) established a framework for measuring fair value of financial instruments and required disclosures about fair value measurements. For certain of Solitario's financial instruments, including cash and cash equivalents and accounts payable, the carrying amounts approximate fair value due to their short-term maturities. Solitario's short-term investments in USTS, its marketable equity securities, Vendetta Mining Corp. (“Vendetta”) Warrants (defined below in Note 3, “Marketable Equity Securities”) and any covered call options against those marketable equity securities are carried at their estimated fair value based on quoted market prices, and in the case of its Vendetta Warrants, based upon a Black Scholes model. See Note 6, “Fair Value,” below.

Marketable equity securities

Solitario's investments in marketable equity securities are carried at fair value, which is based upon quoted prices of the securities owned. Solitario records investments in marketable equity securities for investments in publicly traded marketable equity securities for which it does not exercise significant control and where Solitario has no representation on the board of directors of those companies and exercises no control over the management of those companies. The cost of marketable equity securities sold is determined by the specific identification method. Changes in fair value are recorded as unrealized gain or loss in the statement of operations.

Derivative instruments

Solitario accounts for its derivative instruments in accordance with ASC 815, "Accounting for Derivative Instruments and Hedging Activities" (“ASC 815”). Solitario acquired its investment in Vendetta units, including the Vendetta Warrants during 2019. Solitario recorded the value of the Vendetta Warrants at their fair value as other assets on the consolidated balance sheet. Solitario has sold covered calls from time to time on its investment in Kinross Gold Corporation (“Kinross”) marketable equity securities. Solitario has not designated its sold covered calls as hedging instruments and any changes in the fair value of the sold covered calls and its Vendetta Warrants are recognized in the statement of operations in the period of the change as gain or loss on derivative instruments.

Foreign exchange

The United States dollar is the functional currency for all of Solitario's foreign subsidiaries. Although Solitario's South American exploration activities during 2018 and the first nine months of 2019 have been conducted primarily in Peru, a portion of the payments under the land, leasehold and exploration agreements of Solitario are denominated in United States dollars. Realized foreign currency gains and losses are included in the results of operations in the period in which they occur.

Income taxes

Solitario accounts for income taxes in accordance with ASC 740, “Accounting for Income Taxes” (“ASC 740”). Under ASC 740, income taxes are provided for the tax effects of transactions reported in the financial statements and consist of taxes currently due plus deferred taxes related to certain income and expenses recognized in different periods for financial and income tax reporting purposes. Deferred tax assets and liabilities represent the future tax return consequences of those differences, which will either be taxable or deductible when the assets and liabilities are recovered or settled. Deferred taxes are also recognized for operating losses and tax credits that are available to offset future taxable income and income taxes, respectively. A valuation allowance is provided if it is more likely than not that some portion or all of the deferred tax assets will not be realized.

Accounting for uncertainty in income taxes

ASC 740 clarifies the accounting for uncertainty in income taxes recognized in a company's financial statements. ASC 740 prescribes a recognition threshold and measurement attribute for the financial statement recognition and measurement of a tax position taken or expected to be taken in a tax return. ASC 740 also provides guidance on derecognition, classification, interest and penalties, accounting in interim periods, disclosure, and transition. ASC 740 provides that a company's tax position will be considered settled if the taxing authority has completed its examination, the company does not plan to appeal, and it is remote that the taxing authority would reexamine the tax position in the future.

Earnings per share

The calculation of basic and diluted earnings (loss) per share is based on the weighted average number of shares of common stock outstanding during the three and nine months ended September 30, 2019 and 2018. Potentially dilutive shares related to outstanding common stock options of 4,373,000 at September 30, 2019 and 4,025,228 at September 30, 2018 for Solitario common shares were excluded from the calculation of diluted earnings (loss) per share because the effects were anti-dilutive.

Employee stock compensation and incentive plans

Solitario classifies all of its stock options as equity options in accordance with the provisions of ASC 718, “Compensation – Stock Compensation.”

Recent accounting pronouncements

On January 1, 2019, Solitario adopted Accounting Standards Update No. 2016-02 Leases (“ASU 2016-02”) which requires the application of ASC 842 and the recognition of right-of-use assets and related liabilities associated with all leases that are not short-term in nature. As a result of the adoption of ASU 2016-02 on January 1, 2019, Solitario recorded both an operating lease asset for its Wheat Ridge, Colorado office of $82,000 and an operating lease liability of $82,000 related to the same lease. The adoption of ASU 2016-02 did not require the recording of any other assets or liabilities on our condensed consolidated balance sheets and had an immaterial effect on Solitario’s condensed consolidated statement of operations for the three and nine months ended September 30, 2019, and its condensed consolidated statement of cash flows for the nine months ended September 30, 2019. Solitario has elected the practical expedient option to use January 1, 2019, the effective date of adoption, as the initial date of transition and not to restate comparative prior periods and to carry forward historical lease classification. See Note 4, “Operating Leases” for more information and disclosures regarding Solitario’s leases.