Mainstream Minerals Corp. - Initial Public Offering Completed and Upcoming Listing on the TSX Venture Exchange Winnipeg, Manitoba – June 12th, 2007 – Mainstream Minerals Corporation (TSX.V: MJO) is pleased to announce that it has completed its Initial Public Offering (IPO) and attained the maximum aggregate subscription proceeds under the prospectus offering of $1,000,000.08. An aggregate of 1,851,852 flow-through shares were issued at a price of $0.27 per unit ($500,000.04) and 1,851,852 non-flow-through units were issued at a price of $0.27 per unit ($500,000.04). Each non-flow-through unit is comprised of one common share and one half (1/2) common share purchase warrant. Each common share purchase warrant can be exercised into one common share upon payment of $0.45 on or before 18 months from the date of issue. Wellington West Capital Inc. acted as the Agent for this IPO and shall receive as compensation a commission equal to 9 % of the aggregate subscription proceeds of the Offering. The Agent shall also be entitled to receive such number of Agents’ Warrants enabling it to purchase that number of common shares which is equal to 10 % of the flow-through shares and non-flow-through units sold under the offering. The TSX Venture Exchange recently approved the listing of the common shares of Mainstream Minerals Corporation. The Company’s common shares are anticipated to start trading on the Exchange on Wednesday June 13th, 2007 under the trading symbol MJO. ABOUT MAINSTREAM MINERALS Mainstream Minerals Corporation is a mineral exploration and development company focused on precious metal mining properties with economic potential, with the aim of bringing such properties to commercial production. The Company’s portfolio of properties is primarily located in northwestern Ontario’s prolific Red Lake Gold Camp. On December 11th, 2006, the Corporation, along with its 50 / 50 joint-venture partner King’s Bay Gold Corporation (TSX.V: KBG), announced the discovery of high-grade gold bearing veins at the Bobjo Mine, Earngey Township, Red Lake District, Ontario. Surface grab samples from a vein, with a width of up to 6 metres, returned high-grade gold values of up to 2,942.7 g/t (85.84 oz/t) and 806.9 g/t (23.54 oz/t). Other veins and stringers also returned high-grade gold values including 55.34 g/t (1.61 oz/t), 49.54 g/t (1.55 oz/t), 42.65 g/t (1.24 oz/t), 42.37 g/t (1.23 oz/t), 36.89 g/t (1.07 oz/t), and 36.23 g/t (1.05 oz/t). The Bobjo Mine property is located between the former South Bay and Uchi Lake gold mines. It is comprised of a total of 9 patented and 86 unpatented claim units (3,800 acres) with a power transmission line passing through the southern part of the property. The area has a history of gold and base metal production dating back 80 years and the work presently being carried out by the partners represents the commencement of the first modern, systematic exploration of this property. Further results and updates will be released as they become available. The Board of Directors of Mainstream Minerals Corporation is composed of: Michael A. Dehn B.Sc. – Chairman, Chief Operating Officer Gerald Colborne B.Sc., M.Sc., P.Eng., P.Geol., F.G.A.C., M.C.I.M. – Director, President & Chief Executive Officer Raymond Préfontaine B.A. (Economics), B.Comm. (Hons.) – Chief Financial Officer Neil Sullivan B.A. (Economics), LLB – Director Richard Rivet – Director Kyle Picard – Director Jean Rivet – Director Mike Wallace - Director The Officers of Mainstream Minerals Corporation are: Michael A. Dehn B.Sc. – As the Company’s Chief Operating Officer, Mr. Dehn has been actively involved in financings, marketing and project management related to exploring for precious metals, base metals, diamonds and industrial minerals since 1994. For 10 years, he was a senior geologist with Goldcorp Inc. in Red Lake, Ontario. As such, he has extensive knowledge and experience with the intricacies of the Red Lake Gold Camp, where the majority of Mainstream Minerals Corporation’s exploration and development activities are located. Mr. Dehn graduated from the University of Waterloo with a B.Sc. in Earth Sciences in 1993, and on the technical side has worked extensively with new regional exploration technologies including remote sensing, computer modeling, geophysics and geochemistry. Gerald Colborne B.Sc., M.Sc., P.Eng., P.Geol., F.G.A.C., M.C.I.M. – Mr. Colborne has a long and extensive career in the minerals exploration and mining industry. As the Company’s President and Chief Executive Officer, Mr. Colborne brings over 40 years of experience at the senior executive level in both the private and public sectors (notably with primary resources, industry, finance and government). Mr. Colborne is a registered Professional Engineer in the Provinces of Saskatchewan, Alberta, Manitoba and Ontario, and was once licensed in New Brunswick and Newfoundland. He is a member of the Canadian Institute of Mining and Metallurgy, Society of Mining Engineers of the American Institute of Mining and Petroleum Engineers, a Fellow of the Geological Association of Canada, Canadian Association of Petroleum Geologists, and a past VicePresident and Director of the Prospectors and Developers Association of Canada. Mr. Colborne enrolled at the University of Alberta where he obtained both his B.Sc. and M.Sc. degrees in Geology. He later became and is still a registered Professional Engineer and Professional Geologist. During his career, Mr. Colborne worked extensively throughout Canada and the Americas in his chosen field and was successful in bringing several exploration properties forward into becoming productive and profitable mining operations. This success in turn allowed him to progress in his career as a senior manager and corporate executive where he later became the Director of the Royal Bank of Canada’s Mining Industry Department, the Deputy Minister for the Province of Saskatchewan’s Department of Industry and Commerce, a consultant to the Bank of British Columbia – Mining Act Revision Committee, a field geologist with both the Alberta Research Council and the Federal Geological Survey of Canada, as well having undertaken several consulting assignments with the United Nations. Mr. Colborne has served on the boards of directors of many public corporations, written many publications, and was awarded the Centennial Medal for services to the nation of Canada and the Dr. Bell Memorial Medallion for his overall contribution to the mining industry in Canada. Raymond Préfontaine B.A. (Economics), B.Comm. (Hons.) – As the Company’s Chief Financial Officer, Mr. Préfontaine brings with him 20 years of experience in both managerial and directorship roles in the financial services industry. Throughout his career, as a senior management professional, he has demonstrated an ability to execute and implement effective decisions regarding new business development, marketing, corporate finance, commercial banking, accounting, credit management and in the structuring and directing of investments, both in the private sector and in the capital markets. Mr. Préfontaine is a graduate of the University of Manitoba where he obtained a Bachelor of Arts (Economics) and a Bachelor of Commerce (Honours). During his university years, he earned a Queen’s Commission and served his country as a naval officer in the Canadian Armed Forces Reserve – Maritime Command. He has successfully completed several securities industry courses as provided by the Canadian Securities Institute and the Investment Funds Institute of Canada. He is also currently the Chair and a Director of the Saint-Boniface General Hospital Auxiliary Inc. Subsequent to the closing of the IPO Offering, the Company has 12,816,224 common shares issued and outstanding and has cash resources on hand of approximately $1.6 million. Mainstream Minerals Corporation Gerald Colborne President & CEO (204) 222-0137 info@mainstreamminerals.com www.mainstreamminerals.com The TSX Venture Exchange has not reviewed and does not accept responsibility for the adequacy or accuracy of this release. Some of the statements contained in this release are forward-looking statements, such as estimates and statements that describe MJO's future plans, objectives or goals, including words to the effect that MJO or management expects a stated condition or result to occur. Since forward-looking statements address future events and conditions, by their very nature, they involve inherent risks and uncertainties.