NioCorp Developments Ltd美股招股说明书(2026-02-24版)

Filed Pursuant to Rule 424(b)(2)Registration No.: 333-290837 Preliminary Prospectus Supplement(to Prospectus dated October 10, 2025) Common SharesPre-Funded Warrants to PurchaseCommon Shares We are offeringof our common shares, without par value (“Common Shares”), and, in lieu of Common Shares to certain investors that sochoose,pre-funded Warrants (as defined herein) to purchase an aggregate ofCommon Shares (the “Pre-Funded Warrants”). The purchase price of each Pre-Funded Warrant will equal the price per share at which each Common Share is sold to the public in this offering, minus $0.0001, which is the exercise price of each Pre-Funded Warrant. The Pre-Funded Warrants will not have an expiration date and will be immediately exercisable. The offering price for each Common Share is $.This prospectus supplement also relates to the offering of Common Shares issuable upon exercise of the Pre-Funded Warrants. The Common Shares and Pre-Funded Warrants are being sold on a “reasonable best efforts” basis. See “Plan of Distribution.” Our Common Shares trade on the Nasdaq Global Market under the symbol “NB.” On February 23, 2026, the last reported sale price of ourCommon Shares on the Nasdaq Global Market was $5.55 per Common Share. There is no established trading market for the Pre-Funded Warrantsand we do not expect a market to develop. In addition, we do not intend to list the Pre-Funded Warrants on any national securities exchange or anyother nationally recognized trading system. Investing in our securities involves a high degree of risk. See “Risk Factors” beginning on page S-4 of this prospectus supplement and onpage 2 of the accompanying prospectus, and the documents incorporated by reference herein and therein. Neither the Securities and Exchange Commission (the “SEC”) nor any state securities commission has approved or disapproved of thesesecurities or determined if this prospectus supplement or the accompanying prospectus is truthful or complete. Any representation to thecontrary is a criminal offense. We have engaged Maxim Group LLC (the “Placement Agent”) to act as our exclusive placement agent in connection with this offering. ThePlacement Agent has agreed to use its reasonable best efforts to solicit offers for the securities offered by this prospectus supplement andaccompanying prospectus. The Placement Agent does not have any obligation to sell any specific number or dollar amount of the securities beingoffered hereby, nor are we requiring any minimum purchase or sale of any specific number of securities in order for us to consummate this offeringand there are no arrangements to place the funds in an escrow, trust, or similar account. The Placement Agent is not purchasing or selling any of thesecurities we are offering. We have agreed to pay the Placement Agent the commissions set forth in the table below. See “Plan of Distribution”beginning on page S-31 of this prospectus supplement for more information regarding these arrangements. (1) We have agreed to pay the Placement Agent a cash placement commission equal to 6.00% of the aggregate proceeds from the sale of the CommonShares and the Pre-Funded Warrants sold in this offering to the investors. The Company has agreed to reimburse the Placement Agent for certainexpenses incurred in connection with this offering. See “Plan of Distribution” for additional disclosure regarding the Placement Agent’scompensation.(2) Reflects actual amounts. The securities are expected to be delivered on or about, 2026, subject to satisfaction of customary closing conditions. Sole Placement Agent Maxim Group LLC The date of this prospectus supplement is, 2026. Prospectus Supplement About This Prospectus SupplementS-iiWhere You Can Find More InformationS-iiiIncorporation of Documents by ReferenceS-iiiProspectus Supplement SummaryS-1Risk FactorsS-4Cautionary Note Regarding Forward-Looking StatementsS-9Use of ProceedsS-10DilutionS-11Description of SecuritiesS-12Certain United States Federal Income Tax ConsiderationsS-20Certain Canadian Federal Income Tax Considerations for U.S. ResidentsS-28Plan of DistributionS-30Legal MattersS-35ExpertsS-35 Prospectus Page ABOUT THIS PROSPECTUSIIWHERE YOU CAN FIND MORE INFORMATIONIIIINFORMATION INCORPORATED BY REFERENCEIVSUMMARY1RISK FACTORS2CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS3USE OF PROCEEDS5DESCRIPTION OF CAPITAL STOCK6DESCRIPTION OF WARRANTS11DESCRIPTION OF DEBT SECURITIES13DESCRIPTION OF UNITS21PLAN OF DISTRIBUTION22LEGAL MATTERS23EXPERTS24 ABOUT THIS PROSPECTUS SUPPLEMENT This prospectus supplement and the accompanying prospectus are part of a registration statement on Form S-3 that we filedwith the SEC on October 10, 2025 using a “shelf” registration process. This prospectus supplement describes the specific terms of the securities we are offering and adds to, and updates,information in the accompanying prospectus and the documents incorporated by reference herein and therein. If there is a confli