Northern Orion Resources Inc.

Northern Orion Resources Inc.

August 15, 2005 15:15 ET

Northern Orion Reports Further Extension of Mineral Reserves and Plans to Increase Production at Alumbrera

VANCOUVER, BRITISH COLUMBIA--(CCNMatthews - Aug. 15, 2005) - Northern Orion Resources Inc. (TSX:NNO)(AMEX:NTO) is pleased to announce that Mineral Reserves at Alumbrera have increased by more than 10%, and US$15.5 million (Northern Orion share - US$1.9 million) will be spent on an expansion of the concentrator at the mine.

The expansion, which is projected to increase mill throughput by 8% to 40 million tonnes per annum, is scheduled for commissioning in December 2006 and should result in an increase in production levels.

Alumbrera has recently confirmed 40 million tonnes of additional Mineral Reserves from its on-going ore delineation drilling program, undertaken both within the existing ore envelope and from extensions at depth, plus improvements in the ultimate pit slopes design. This equates to an additional 375 million pounds of contained copper (Northern Orion share - 46.9 million pounds) and 500,000 ounces of gold (Northern Orion share - 62,500 ounces) over the life of the mine, and is a further increase to the 80 million tonnes of Mineral Reserves Alumbrera announced in June 2004. The mine plan has been re-optimized based on a new geological model with this additional mineralization. Alumbrera plans to continue with in-pit resource definition in the second half of 2005 in hopes of adding further Mineral Reserves.

As a consequence of the announced increase, current Mineral Reserves and Resources are (on a 100% basis, of which Northern Orion owns 12.5%):

Mineral Reserves(i) Mineral Resources(i)
------------------------------- ------------------------------
Proved 370 Mt @0.47%Cu & Measured 390 Mt @0.47%Cu &
0.52 gpt Au 0.51 gpt Au
------------------------------- ------------------------------
Probable 24 Mt @0.42%Cu & Indicated 28 Mt @0.42%Cu &
0.43 gpt Au 0.43 gpt Au
------------------------------- ------------------------------
Total 390 Mt @0.47%Cu & Total 420 Mt @0.47%Cu &
0.51 gpt Au 0.50 gpt Au
------------------------------- ------------------------------

(i) The information in this press release which relates to Mineral
Resources and Reserves is based on information verified by
Alumbrera's internal lab facilities and compiled by Mr. Luis Rivera
who is a member of the Australasian Institute of Mining and
Metallurgy and who is a Qualified Person as defined by National
Instrument 43-101. Mr. Rivera is a full-time employee of Minera
Alumbrera Limited. Ore Reserves have been calculated in accordance
with the recommendations of the Australian Institute of Mining and
Metallurgy - Joint Ore Reserve Committee (the "JORC" code),where the
Measured and Indicated Mineral Resources are inclusive of those
Mineral Resources modified to produce the Mineral Reserves.

David Cohen, President and CEO

Except for the statements of historical fact contained herein, certain information presented constitutes "forward-looking statements" within the meaning of the United States Private Securities Litigation Reform Act of 1995. Such forward-looking statements, including but not limited to, those with respect to the price of molybdenum, gold, silver and copper, the timing and amount of estimated future production, the potential and/or projected cash flow generated from production, costs of production, reserve determination and reserve conversion rates, and the potential for further equity dilution involve known and unknown risks, uncertainties and other factors which may cause the actual results, performance or achievement of Northern Orion to be materially different from any future results, performance or achievements expressed or implied by such forward-looking statements. Such factors include, among others, risks related to international operations, risks related to joint venture operations, the actual results of current exploration activities, actual results of current reclamation activities, conclusions of economic evaluations, uncertainty in the estimation of ore reserves and mineral resources, changes in project parameters as plans continue to be refined, future prices of gold, silver and copper, economic and political instability in Argentina, environmental risks and hazards, increased infrastructure and/or operating costs, labor and employment matters, and government regulation as well as those factors discussed in the section entitled "Risk Factors" in Northern Orion's Renewal Annual Information form attached to Northern Orion's latest Form 40-F on file with the United States Securities and Exchange Commission in Washington, D.C. Although Northern Orion has attempted to identify important factors that could cause actual results to differ materially, there may be other factors that cause results not to be as anticipated, estimated or intended. There can be no assurance that such statements will prove to be accurate as actual results and future events could differ materially from those anticipated in such statements. Northern Orion disclaims any intention or obligation to update or revise any forward-looking statements, whether as a result of new information, future events or otherwise. Accordingly, readers should not place undue reliance on forward-looking statements.

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