Source: TheNewswire.ca (June 23, 2008 - 1:44 PM EDT)

June 19 2008 - Mainstream Minerals Corporation (TSX.V: MJO) is pleased to announce, subject to regulatory approval, that it has entered into a joint venture earn-in agreement on its Phyllis Lake Project with King's Bay Gold Corporation (TSX.V: KBG). King's Bay can acquire a 50% interest in this Mainstream Minerals project by incurring $500,000.00 of Earn-In Exploration Expenditures within the next 15 months.

Summary of the Phyllis Lake Project

The Phyllis Lake high-grade Molybdenum / Copper / Cobalt Project is comprised of 12 claims totalling 64 claim units (2,560 acres) and is located near the Town of Ignace, Ontario. The property is accessible via the TransCanada Highway and a logging road.

A stripping program carried out by heavy equipment has recently uncovered large zones with impressive widths and strike lengths. Surface sampling has also yielded high-grade results that both companies believe could possibly be the beginning of a large mineral discovery on a new project that has never been explored before.

Surface sampling of this project has yielded results as high as:

0.690 % Molybdenum (Mo), 2.192 % Copper (Cu), 0.415 % Cobalt (Co), 0.393 % Nickel (Ni), 0.100 % Zinc (Zn), 9.60 g/t Silver (Ag), 2.81 g/t Gold (Au), 2.50 g/t Palladium (Pd) and 1.20 g/t Platinum (Pt).

A 3 metre channel sample from a zone with a strike length of approximately 500 metres returned high-grade values of 0.677 % Molybdenum.

Some of these metals are very valuable, for example, and in US dollars:

Moly is currently trading at over $33.00 per pound (lb)

Cobalt at over $48.00/lb

Nickel at over $9.90/lb

Copper at approximately $3.70/lb

Zinc at approximately 0.82/lb

Gold at approximately $900.00 per ounce

Silver at over $17.00 per ounce

Palladium at over $470.00 per ounce

Platinum at over $2,000.00 per ounce

Source: www.kitco.com

Base metals values are reported in percentages. For example, one percent (1.000 %) is equivalent to approximately 22 pounds (lbs) per metric tonne.

East Zone Number 1

Of special interest is a newly uncovered VMS zone with a width of approximately 60 metres with a visible strike length of approximately 500 metres. The main mineralization is Copper, Zinc, and Molybdenum. A 3 metre channel sample taken within this zone returned values of 0.677 % Molybdenum.

The borders of this large zone have not been established as of yet and will need additional stripping to determine the actual width and strike length. A picture of part of this zone can be seen at

http://www.mainstreamminerals.com/ph...

East Zone Number 2

Another area of significant interest is a shear zone that runs for 6 kilometres with a width of approximately 40 metres. Only one grab sample was taken from it to see if it carried gold and it yielded 2.811 g/t Au. This zone will need additional sampling and stripping.

North Zone

The zone is approximately 30 metres wide and the strike length has not been established as of yet. Surface sampling has revealed that the mineralization in this zone consists of Copper, Nickel, Cobalt, Gold, Silver, Platinum and Palladium. Additional stripping and sampling will also be needed.

Central Zone

This zone appears to be a layered intrusive and again is large with a width of 50 metres and a strike length of approximately 700 metres. Surface sampling has revealed that the mineralization consists of Cobalt, Copper, Nickel, and Silver. The borders of this zone have not been established as of yet either.

Both companies are very pleased with the mineral potential of this project. King's Bay, as the new Operator of the project, is planning on commencing an exploration program that will consist of a geophysical survey, sampling, stripping, washing and diamond drilling. Geologist John Archibald is the Qualified Person under National Instrument 43-101.

Both companies are also presently in the middle of a 15,000 metre drilling program at their joint ventured high-grade gold, rare earth elements Bobjo Mine project, Red Lake, ON.

Summary of the Terms of the Phyllis Lake Joint Venture Earn-In Agreement

In accordance with their Joint Venture Earn-In Agreement of June 18th, 2008, Mainstream Minerals granted to King's Bay the right to acquire a fifty percent (50%) interest in the Phyllis Lake property upon King's Bay funding Earn-In Exploration Expenditures in an aggregate amount of $500,000. The Earn-In Exploration Expenditures must be incurred within 15 months from the date of the Joint-Venture Earn-In Agreement.

The scope of this Joint-Venture Earn-In Agreement will also include any and all additionally staked claims by either Mainstream Minerals or King's Bay that come within a 5 kilometre radius of the 64 claim units currently covered under the Phyllis Lake Option Agreement dated May 30th, 2008 between Mainstream Minerals and Falcon Mineral Exploration Limited (the "Vendor"). The Phyllis Lake Option Agreement is subject to a two percent (2%) Net Smelter Return in favour of the Vendor.

Upon King's Bay earning the Earn-in Interest, Mainstream Minerals and King's Bay shall be deemed to have entered into a Joint Venture Agreement in respect of the development, management and further exploration of the Property, and, if deemed warranted, bringing all or a portion of the Property into production by establishing and operating a mine or mines thereon. The respective initial interests of Mainstream Minerals and King's Bay in the Joint Venture will be fifty percent (50%) and fifty percent (50%), subject to the 2% Net Smelter Return interest in favour of the Vendor. King's Bay will be the initial Operator of the Joint Venture during the earn-in period.

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 the prolific Red Lake Gold Camp of Northwestern Ontario. The properties include - (i) 50% of the Bobjo Mine project, (ii) 50 % of the Phyllis Lake project, (iii) 100% of the Dixie Lake North project, and (iv) 50% of the Woman Lake North of South Bay project.

MJO Shares Outstanding: 18,031,087

Mainstream Minerals CorporationNeil SullivanPresident & CEO(204)- 222-0137Email: info@mainstreamminerals.comwww.mains...

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's 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.

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