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v3.25.2

COMMON SHARES (Details 11) - Note Warrant [Member] - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Jun. 30, 2025 | Jun. 30, 2024
Subsidiary, Sale of Stock [Line Items] |  |
Initial valuation, at begining | $ 1,353 | $ 3,279
Change in valuation | 1,661 | $ (1,926)
Exchange of 2023 Private Warrants for 2023 Public Warrants | (482) |
Ending balance | $ 2,532 |

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- Definition The element represents changes in fair value of initial valuation. + References No definition available. + Details
Name: | niobf_ChangesInFairValueOfInitialValuation
Namespace Prefix: | niobf_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition The element represents changes in fair value of initial valuation1. + References No definition available. + Details
Name: | niobf_ChangesInFairValueOfInitialValuation1
Namespace Prefix: | niobf_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition The element represents exchange of private warrants for public warrants. + References No definition available. + Details
Name: | niobf_ExchangeOfPrivateWarrantsForPublicWarrants
Namespace Prefix: | niobf_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition The element represents servicing assets at fair value changes in fair value resulting from changes in valuation inputs. + References No definition available. + Details
Name: | niobf_ServicingAssetsAtFairValueChangesInFairValueResultingFromChangesInValuationInputs
Namespace Prefix: | niobf_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_SubsidiarySaleOfStockLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_SubsidiarySaleOfStockAxis=us-gaap_NoteWarrantMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |