Excelsior Advances Prefeasibility & Provides Positive Metallurgy Test Results at Gunnison

VANCOUVER, BRITISH COLUMBIA--(Marketwired - Sep 10, 2013) - Excelsior Mining Corp. (TSX VENTURE:MIN)(FRANKFURT:3XS)(OTCQX:EXMGF) ("Excelsior" or the "Company") is pleased to announce an update on the Company's prefeasibility study as well as all the results from the most recent metallurgical test program from its North Star deposit, part of Excelsior's Gunnison Copper project, located in southeastern Arizona.

Prefeasibility Study Update

The Company has engaged M3 Engineering & Technology Corporation ("M3") of Tucson, Arizona to support the Company in the completion of a prefeasibility study on the Gunnison Copper project. M3 is a global full-service engineering design firm that provides expertise in engineering and construction management services. The firm has a long history of supporting base metal mining projects.

"M3's professionalism and direct experience with in-situ copper recovery projects, including our Gunnison project, makes them the best choice to help Excelsior complete the prefeasibility study; we look forward to releasing the results later this year," said Stephen Twyerould, President and CEO of Excelsior Mining.

Metallurgy Test Results at Gunnison Continue to Validate In-Situ Recovery Potential

A total of 13 submerged leach tests have been completed and the final results are presented in the table below. Previously, the Company released the results from five tests from the Lower Abrigo rock formation (see February 14, 2013 news release: http://www.excelsiormining.com/index.php/news/news-2013/392-metallurgy-tests-return-favourable-results-for-in-situ-recovery-at-gunnison); these test results have been updated. In general, higher acid concentrations generated faster recovery rates while longer leach times generated higher total recoveries.

"Once again we have procured technical results that underscore the viability of in-situ recovery at Gunnison," stated Stephen Twyerould. "These metallurgical results, when combined with previous results, will be used for the preparation of a prefeasibility study."

Submerged leach tests details

Submerged leach testing employs a protocol similar to column leach testing, but modified to more closely reflect conditions during in-situ leaching. These tests were designed to be repeatable, and to evaluate the response of mineralization to in-situ leaching at different flow rates and acid concentrations.

The assay procedure for determining "acid soluble copper" does not typically include copper present in the form of secondary copper sulfides which are soluble under typical leaching conditions, including submerged leach tests. Should the ore being tested contain some copper as secondary copper sulfides, this copper will solubilize and as a consequent the calculated acid soluble copper recovery may exceed 100 percent. This is the case in samples from the Abrigo formation. Based on the sequential head assays, and given sufficient time and acid concentration, it can be expected that copper recoveries could reach 105% to 115% of the acid soluble copper content for the Abrigo Formation and 100% for the Martin Formation.

The submerged leach tests were conducted by the independent laboratory, SGS Metcon of Tucson, Arizona under the supervision of Dr. Ronald J. Roman, an independent consultant who is a Qualified Person as defined by NI 43-101. Dr. Roman has reviewed and approved the technical information disclosed in this news release. Dr. Roman has verified the data underlying the test results by designing the test procedure, supervising the test work, obtaining all the analytical data over the life of the experiment and performing the calculations presented below.

1. Calculated head grade: Cu (total) = total copper, Cu (AS) = acid soluble copper, SI = solubility index Cu (AS) / Cu (total)
2. Flow rate: litres per hour of leach solution applied per cross-sectional square metre
3. Acid Content: acid concentration of the leach solution in grams per litre of free acid
4. Days leached includes periods of post leach rinsing
5. Adjusted Acid Consumption: test acid consumption in pounds of acid consumed per pound of copper recovered adjusted by a factor of 0.5 to compensate for overestimation due to the test protocol

The recovery/time curves for each formation can be found on the Excelsior website at: http://www.excelsiormining.com/index.php/projects

To view the graphs accompanying this press release, click on the following link: http://media3.marketwire.com/docs/graph910.pdf

Due to the nature of the copper oxide mineralization at North Star, combined with standard metallurgical testing procedures on drill core, more of the un-mineralized rock known as "gangue" is inadvertently exposed to the acid solution than would be expected during normal in-situ mining conditions. This overexposure results in inflated acid consumption rates from metallurgical testing compared to those expected during actual in-situ operational conditions. Previous acid consumption tests described in Excelsior's February 14, 2013 news release indicated over estimation is in the order of 40% to 80%. As such, acid consumption numbers presented in the table above represent test acid consumption numbers multiplied by a factor of 0.5.

Further information concerning these metallurgical tests can be found on the Excelsior website at: http://excelsiormining.com/index.php/projects.

Project Summary

The Gunnison Copper Project is located in a remote section of Cochise County in southeastern Arizona. The focus of the project is the North Star deposit, which currently has a total Measured and Indicated mineral resource of 3.21 billion pounds of oxide copper (498 M tons at 0.32%) and an Inferred mineral resource of 0.83 billion pounds of oxide copper (156 M tons at 0.27%). This oxide mineral resource has the potential to be mined using in-situ recovery methods. Mineral resources which are not mineral reserves do not have demonstrated economic viability.

About Excelsior

Excelsior is a mineral exploration and development company that is advancing the Gunnison Copper Project. The Excelsior management team consists of experienced professionals with proven track records of advancing mining projects into production.

Excelsior's exploration work on the Gunnison Property is supervised by Dr. Stephen Twyerould, Fellow of AUSIMM, President and CEO of Excelsior, and a Qualified Person as defined by NI 43-101. Dr. Twyerould has reviewed and approved the technical information disclosed in the "Project Summary" and "About Excelsior" sections of this news release.

Further details about Excelsior can be found at: http://www.excelsiormining.com. Further information about the Gunnison Copper Project can be found in the technical report filed on SEDAR at www.sedar.com entitled: "Gunnison Copper Project Preliminary Economic Assessment, NI 43-101 Technical Report" dated November 18, 2011.

ON BEHALF OF THE EXCELSIOR BOARD

Stephen Twyerould, President & CEO

Cautionary Note Regarding Forward-Looking Information

This news release contains "forward-looking information" concerning anticipated developments and events that may occur in the future. Forward looking information contained in this news release includes, but is not limited to, statements with respect to: (i) the estimation of inferred and indicated mineral resources; (ii) the future implications of the metallurgical test results; (iii) production from the Gunnison Project; (iv) the completion of a pre-feasibility study; (v) expected acid consumption rates and; (vi) the ability to mine Gunnison using in-situ recovery mining techniques are forward-looking statements.

In certain cases, forward-looking information can be identified by the use of words such as "plans", "expects" or "does not expect", "is expected", "budget", "scheduled", "estimates", "forecasts", "intends", "anticipates" or "does not anticipate", or "believes", or variations of such words and phrases or state that certain actions, events or results "may", "could", "would", "might" or "will be taken", "occur" or "be achieved" suggesting future outcomes, or other expectations, beliefs, plans, objectives, assumptions, intentions or statements about future events or performance. Forward-looking information contained in this news release is based on certain factors and assumptions regarding, among other things, the estimation of mineral resources, the realization of resource estimates, copper and other metal prices, the timing and amount of future exploration and development expenditures, the estimation of initial and sustaining capital requirements, the estimation of labour and operating costs, the availability of necessary financing and materials to continue to explore and develop the Gunnison Project in the short and long-term, the progress of exploration and development activities, the receipt of necessary regulatory approvals, the completion of the environmental assessment process, the estimation of insurance coverage, and assumptions with respect to currency fluctuations, environmental risks, title disputes or claims, and other similar matters. While the Company considers these assumptions to be reasonable based on information currently available to it, they may prove to be incorrect.

Forward-looking information involves known and unknown risks, uncertainties and other factors which may cause the actual results, performance or achievements of the Company to be materially different from any future results, performance or achievements expressed or implied by the forward-looking information. Such factors include risks inherent in the exploration and development of mineral deposits, including risks relating to changes in project parameters as plans continue to be redefined including the possibility that mining operations may not commence at the Gunnison Project, risks relating to variations in mineral resources, grade or recovery rates resulting from current exploration and development activities, risks relating to the ability to access infrastructure, risks relating to changes in copper and other commodity prices and the worldwide demand for and supply of copper and related products, risks related to increased competition in the market for copper and related products and in the mining industry generally, risks related to current global financial conditions, uncertainties inherent in the estimation of mineral resources, access and supply risks, reliance on key personnel, operational risks inherent in the conduct of mining activities, including the risk of accidents, labour disputes, increases in capital and operating costs and the risk of delays or increased costs that might be encountered during the development process, regulatory risks, including risks relating to the acquisition of the necessary licenses and permits, financing, capitalization and liquidity risks, including the risk that the financing necessary to fund the exploration and development activities at the Gunnison Project may not be available on satisfactory terms, or at all, risks related to disputes concerning property titles and interest, environmental risks and the additional risks identified in the "Risk Factors" section of the Company's reports and filings with applicable Canadian securities regulators.

Although the Company has attempted to identify important factors that could cause actual actions, events or results to differ materially from those described in forward-looking information, there may be other factors that cause actions, events or results not to be as anticipated, estimated or intended. Accordingly, readers should not place undue reliance on forward-looking information. The forward-looking information is made as of the date of this news release. Except as required by applicable securities laws, the Company does not undertake any obligation to publicly update or revise any forward-looking information.

Neither the TSX Venture Exchange nor its Regulation Services Provider (as that term is defined in the policies of the TSX Venture Exchange) accepts responsibility for the adequacy or accuracy of this release, and no securities regulatory authority has either approved or disapproved of the contents of this release.