Upsize of Brokered Private Placement up to C$20M

NOT FOR DISTRIBUTION TO U.S. NEWS WIRE SERVICES OR DISSEMINATION IN THE UNITED STATES.

Toronto, September 18, 2025. Orosur Mining Inc. ("Orosur" or the "Company") (TSX-V/AIM:OMI) is pleased to announce that as a result of strong investor demand, the Company has increased the size of its previously announced "best efforts" private placement (the "Base Offering") from gross proceeds of up to C$15,000,000 to gross proceeds of up to C$18,000,000. Pursuant to the upsized Base Offering, the Company will sell up to 52,941,177 common shares of the Company (the "New Common Shares") at a price of C$0.34 (being approximately GBP £0.1809 at an exchange rate of GBP £1.88 to CAD) per New Common Share (the "Offering Price"). Red Cloud Securities Inc. ("Red Cloud") is acting as lead agent and sole bookrunner on behalf of a syndicate of agents (collectively, the "Agents"), together with U.K. corporate brokers Turner Pope Investments (TPI) Ltd. and with Greenwood Capital Partners Limited (together, the "U.K. Brokers") under the Offering.

The Company has also granted the Agents the option, exercisable in full or in part, up to 48 hours prior to the Closing Date, to sell up to an additional 5,882,353 New Common Shares at the Offering Price for up to an additional C$2,000,000 in gross proceeds (the "Agents' Option", and together with the Base Offering, the "Offering"). The New Common Shares issued pursuant to the Base Offering together with any New Common Shares which may be issued pursuant to the Agents' Option to be referred to as the "Offer Shares".

The Offering is scheduled to close on or around September 30, 2025 (the "Closing Date"), or such other date as the Company and Red Cloud may agree (being no later than October 17, 2025) and is subject to certain conditions including, but not limited to, receipt of all necessary approvals including the approval of the TSX Venture Exchange ("TSX-V") and admission to the AIM Market of London Stock Exchange plc ("AIM").

The Offering will allow the Company to make use of its joint listing on the TSX-V and AIM to broaden its shareholder base, including institutional investors in Canada, the UK and certain other foreign jurisdictions, and is expected to improve the liquidity of the Company's common shares.

There is an amended offering document (the "Amended Offering Document") related to the Offering in Canada that can be accessed under the Company's profile at www.sedarplus.ca and on the Company's website at www.orosur.ca. Prospective investors in Canada should read the Amended Offering Document before making an investment decision.

The UK Placing

The element of the Offering which shall be undertaken by the UK Brokers in the UK, shall be carried out by way of a placing ("Placing") to institutional and other eligible investors. The Company and the UK Brokers entered into a placing agreement with the Company on September 17, 2025, under which, on the terms and subject to the conditions set out in the placing agreement, the UK Brokers, as agents for and on behalf of the Company, agreed to use their respective reasonable endeavours to procure placees in the UK for the Offer Shares at the Offering Price. The Placing is not being underwritten by the UK Brokers or any other person.

The timing of the closing of the book and allocations are at the discretion of the UK Brokers and the Agents, in consultation with the Company. Details of the total number of Offer Shares will be announced as soon as practicable after the close of the Offering via the Result of Placing Announcement.