Results Support Ongoing Resource and Reserve Uplift Efforts and Continue to Reinforce the Geological Confidence in the Elk Creek Deposit

NioCorp Developments Ltd. (NASDAQ:NB), a leading U.S. critical minerals developer, today announced the final assay results from its completed 2025 drilling campaign at the Elk Creek Critical Minerals Project in southeast Nebraska.

The assay results reported are consistent with the Company’s expectations and reinforce confidence in the continuity and grade of mineralization within the targeted areas of the Elk Creek deposit. The drilling program focused on areas of the deposit where additional data density was required to support higher confidence classifications under applicable reporting standards. The results are being used to update the Elk Creek Project’s Mineral Resource and Mineral Reserve.

“These results reflect an excellent job by our colleagues at Dahrouge in targeting the drillholes to intercept the correct geologic units in the ore zone,” said Scott Honan, President and Chief Operating Officer of NioCorp. “The highlighted intervals are a further reflection of the robustness and large size of the Elk Creek deposit.”

“I am very pleased to see the completion of the assay analyses of the more than 7,000 drill core samples that our Department of War-funded infill drilling campaign produced,” said NioCorp CEO and Chairman Mark A. Smith.  “The results we are seeing are very encouraging.  The team is now working diligently to incorporate these results into an updated mineral resource and reserve and mine plan, which is a key component of the updated Feasibility Study that will help the Export-Import Bank of the U.S. complete its diligence of our pending debt financing application.”

Mr. Smith added:  “I am also proud of the fact that NioCorp follows the highest technical standards in conducting this work so that we can meet the compliance requirements of both the Securities and Exchange Commission’s SK 1300 and Canada’s NI 43-101 reporting requirements.  Very few critical minerals projects in the U.S. operate with this level of rigor and regulatory compliance, and that fact sets the Elk Creek Project apart from many other projects because it reduces risk and allows investors to have greater confidence in our data and projected financial returns.”

Table 1: Interval Highlights – Nb₂O₅

Table 2: Interval Highlights – Sc

Table 3: Interval Highlights – TiO₂

Table 4: Interval Highlights – TREO

Figure 1: 2025 Resource Drill Hole Location Map – Elk Creek Project, Southeast Nebraska

Supporting cross sections for the drill results reported herein are available on the Company’s website here: https://www.niocorp.com/niocorp-2025-infill-drill-cross-sections.

Table 5: Summary of Significant DDH Results

The table below shows highlights from the remaining resource drillholes completed during the 2025 program that have not previously been publicly released. These results will be utilized in updating the mineral resource and mineral reserve for the project.

Table 6: Summary of Drill Hole Coordinates

Sampling, Analytical Methods and QA/QC Protocols

All drilling was completed using a Boart Longyear LF160 diamond drill rig with HQ size core. Drill core samples from Phase I of the program were shipped to SGS Analytical’s preparation facility in Denver, Colorado for standard sample preparation which includes weighing, drying, crush (< 4 kg) up to 75% passing 2 mm, rifle split (250 g) and pulverize (Cr steel) to 90% passing 75 µm. The samples were subsequently analyzed using GE-ICM91A50 (sodium peroxide fusion with subsequent analysis by ICP and ICP/MS), GO_XRF72+GC_XRF76V (Nb₂O₅ and Ta₂O₅).

All Phase II samples were shipped to ActLabs preparation facility in Ancaster, Ontario for standard sample preparation (RX1) which includes weighing, drying, crush (<7kg) up to 80% passing 2mm, rifle split (250 g) and pulverize (mild steel) up to 90% passing 105 µm. The samples were subsequently analyzed using 8-REE (lithium metaborate/tetraborate fusion), 8-Nb2O5 & Ta2O5 XRF (lithium metaborate/tetraborate fusion).

The drill core was saw-cut into half-core with one half being sent for geochemical analysis and the other half-core remaining in the core box onsite. A quality assurance/quality control protocol was incorporated into the drilling program and included the insertion of certified reference material, silica blanks, duplicate quarters, pulps and rejects all at a rate of approximately 5% respectively.

The assay results discussed in this press release are not measures of reserves or resources as defined in Subpart 1300 of Regulation S-K promulgated by the SEC or National Instrument 43-101. The conversion of assay results in this news release into reserve or resource estimates in compliance with S-K 1300 and NI 43-101 requires additional technical work and analysis that remains ongoing. In addition, the assay results discussed in this press release may not be indicative of future assay results, and may not be indicative of our ability to uplift any of the Elk Creek Project’s Indicated Mineral Resources into Measured Mineral Resources or the subsequent uplift of any of its Probable Mineral Reserves into Proven Mineral Reserves. As such, the conversion of reported mineral resources to mineral reserves should not be assumed, and the reclassification of reported mineral resources or mineral reserves from lower to higher levels of geological confidence should not be assumed.

Qualified Persons:

Trevor Mills, P.G., SME-RM, Principal Geologist / US Operations Manager of Dahrouge Geological Consulting USA Ltd., a Qualified Person as defined by NI 43-101, has reviewed and approved the technical information and verified the data contained within the news release. Mr. Mills has verified all scientific and technical data disclosed in this news release including the sampling and QA/QC results, and certified analytical data underlying the technical information disclosed herein. Mr. Mills noted no errors or omissions during the data verification process. The Company and Mr. Mills do not recognize any factors of sampling or recovery that could materially affect the accuracy or reliability of the assay data disclosed in this news release.