PolyMet Reports Technical Disclosure Review

HOYT LAKES, MINNESOTA -- (Marketwire) -- 06/14/12 -- PolyMet Mining Corp. (TSX: POM)(NYSE Amex: PLM)(NYSE MKT: PLM) ("PolyMet" or the "Company") today reported that the British Columbia Securities Commission (the "BCSC") has reviewed select matters related to the Company's continuous disclosure record. As a result of that review, the Company received comments from the BCSC identifying certain technical disclosure issues, in particular in the Company's National Instrument 43-101 ("NI 43-101") Technical Report on the NorthMet Deposit, Minnesota, USA, dated September 2007.

In order to address these issues, PolyMet plans to file a new Technical Report under NI 43-101, which will fully support the information set out below. This new Technical Report will be filed on SEDAR upon completion.

PolyMet controls 100% of the development-stage NorthMet copper-nickel-precious metals ore-body and the nearby Erie Plant, located near Hoyt Lakes in the established mining district of the Mesabi Iron Range in northeastern Minnesota.

NorthMet Feasibility Study, Mineral Resources and Mineral Reserves

With publication of the Definitive Feasibility Study ("DFS") in September 2006, summarized in a Technical Report under NI 43-101, PolyMet established SEC-standard mineral reserves. Proven and probable mineral reserves were estimated at 181.7 million short tons grading 0.31% copper, 0.09% nickel and 0.01 ounces per ton ("opt") of precious metals.

In September 2007, PolyMet reported an expansion in these proven and probable mineral reserves to 274.7 million short tons grading 0.28% copper, 0.08% nickel and 0.01 opt of precious metals (palladium, platinum and gold). The expanded reserves were not described in a 43-101-compliant Technical Report.

The reserves lie within measured and indicated mineral resources that were expanded to 638.2 million tons grading 0.27% copper, 0.08% nickel and 0.01 opt of precious metals (palladium, platinum and gold). In addition, inferred mineral resources total 251.6 million tons grading 0.28% copper, 0.08% nickel and 0.01 opt of precious metals. These measured and indicated mineral resources were reported in a Technical Report in September 2007.

The reserves and mineral resources are based on copper at $1.25 per pound, nickel at $5.60 per pound, and precious metal prices of $210, $800, and $400 per ounce respectively for palladium, platinum and gold.

DFS Update

On May 20, 2008 PolyMet reported revised processing plans and cost estimates for construction and operating costs that improve the economics and reduce the operating risks. The mine reserves were unaffected by these changes. The revised plans include:

--  the sale of concentrate during the construction and commissioning of new
    metallurgical facilities resulting in a shorter pre-production
    construction period (12-15 months) and reduced capital costs prior to
    first revenues ($312 million versus $380 million) despite the inclusion
    of an estimated $65 million of additional measures to protect the
    environment;
--  the new metallurgical facilities to be constructed during initial
    production and sales of concentrate. PolyMet anticipates that much of
    the additional $290 million of capital costs (for total project capital
    of $602 million) will be largely funded from cash flow from initial
    operations;
--  mine plans (based on copper at $1.25 per pound) reflect the increase in
    reserves and decrease in stripping ratio reported on September 26, 2007,
    the use of 240-ton trucks, and owner versus contract mine operations,
    and
--  $77 million of mining equipment, which was assumed to be provided by a
    mining contractor in the DFS, has been incorporated as an operating
    lease in updated operating costs.

Project Improvements

On February 2, 2011 the Company announced that it had further simplified the proposed metallurgical process, again with no change to the mine plan, and now plans to build the project in two phases:

--  Phase I: produce and market concentrates containing copper, nickel,
    cobalt and precious metals, and
--  Phase II: process the nickel concentrate through a single autoclave,
    resulting in production and sale of high grade copper concentrate, value
    added nickel-cobalt hydroxide, and precious metals precipitate products.

Previous plans included a second autoclave and a copper solvent extraction/electro-winning ("SX-EW") circuit to produce copper metal along with value added nickel-cobalt hydroxide and precious metals precipitate products. The changes reflect continued metallurgical process and other project improvements as well as improved environmental controls that are being incorporated into the environmental review process. The advantages, compared with the earlier plan, include a better return on capital investment, reduced financial risk, lower energy consumption, and reduced waste disposal and emissions at site. Approximately $127 million of the total $602 million capital costs estimated in the May 2008 DFS Update will not be incurred in this revised plan.

Throughout these changes in 2008 and 2011, there has been no material change in the mine plan.

About PolyMet

PolyMet Mining Corp. (www.polymetmining.com) is a publicly-traded mine development company that controls 100% of the NorthMet copper-nickel-precious metals ore body through a long-term lease and owns 100% of the Erie Plant, a large processing facility located approximately six miles from the ore body in the established mining district of the Mesabi Range in northeastern Minnesota. PolyMet Mining Corp. has completed its Definitive Feasibility Study and is seeking environmental and operating permits to enable it to commence production. The NorthMet project is expected to require approximately one-and-a-quarter million hours of construction labor and create approximately 360 long-term jobs, a level of activity that will have a significant multiplier effect in the local economy.

POLYMET MINING CORP.

Joe Scipioni, CEO

This news release contains certain forward-looking statements concerning anticipated developments in PolyMet's operations in the future. Forward-looking statements are frequently, but not always, identified by words such as "expects", "anticipates", "believes", "intends", "estimates", "potential", "possible", "projects", "plans", and similar expressions, or statements that events, conditions or results "will", "may", "could", or "should" occur or be achieved or their negatives or other comparable words. These forward-looking statements may include statements regarding our beliefs related to the ability and timing for filing a new Technical Report, exploration results and budgets, reserve estimates, mineral resource estimates, work programs, capital expenditures, actions by government authorities, including changes in government regulation, the market price of natural resources, costs, ability to receive environmental and operating permits, job creation, or other statements that are not a statement of fact. Forward-looking statements address future events and conditions and therefore involve inherent known and unknown risks and uncertainties. Actual results may differ materially from those in the forward-looking statements due to risks facing PolyMet or due to actual facts differing from the assumptions underlying its predictions.

In connection with the forward-looking information contained in this news release, PolyMet has made numerous assumptions, regarding, among other things: the geological, metallurgical, engineering, financial and economic advice that PolyMet has received is reliable, and is based upon practices and methodologies which are consistent with industry standards. While PolyMet considers these assumptions to be reasonable, these assumptions are inherently subject to significant uncertainties and contingencies.

PolyMet's forward-looking statements are based on the beliefs, expectations and opinions of management on the date the statements are made, and PolyMet does not assume any obligation to update forward-looking statements if circumstances or management's beliefs, expectations and opinions should change.

Specific reference is made to PolyMet's most recent Annual Report on Form 20-F for the fiscal year ended January 31, 2012 and in our other filings with Canadian securities authorities and the U.S. Securities and Exchange Commission, including our Report on Form 6-K providing information with respect to our operations for the year ended January 31, 2012 for a discussion of some of the risk factors and other considerations underlying forward-looking statements.

The TSX has not reviewed and does not accept responsibility for the adequacy or accuracy of this release.

Contacts:

PolyMet Mining Corp. - Corporate

Douglas Newby

Chief Financial Officer

+1 (212) 867-1834
dnewby@polymetmining.com


PolyMet Mining Corp. - Media

LaTisha Gietzen

VP Public, Gov't & Environmental Affairs

+1 (218) 225-4417
lgietzen@polymetmining.com


PolyMet Mining Corp. - Investors

Crystal Agresti

+1 (845) 742-8153
cagresti@polymetmining.com


PolyMet Mining Corp.

Alex Macdougall

+1 (226) 663-3000
amacdougall@polymetmining.com
www.polymetmining.com