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Excelsior’s Preliminary Metallurgical Tests Fully Consistent with Prefeasibility Results


May 20, 2015                                                        

Excelsior Mining Corp. (TSX-V: MIN) (Frankfurt: 3XS) (OTCQX: EXMGF) ("Excelsior" or the “Company”) is pleased to announce interim results from ten “fracture simulation” leach tests at the Gunnison Copper Project in Arizona.

The tests demonstrate copper recovery from the fractured rocks occurs rapidly and relatively uniformly across all rock types. The tests have also allowed for detailed and quantitative acid consumption measurements. To date, the results of recovery and acid consumption are entirely consistent with the metallurgical parameters used in the 2014 Prefeasibility Study (PFS).

On September 15, 2014, Excelsior announced that it had commenced a metallurgical drilling and testing program at the Gunnison Copper Project. The drilling program consisted of ten (10) diamond-drill holes totalling 5,899 feet (11,306 feet in total drilling). The drilling program generated new samples, representing a variety of structures and rock types, which were then submitted for extensive metallurgical testing. The results of the metallurgical tests will be used to determine copper extraction rates, acid consumption rates, and rinsing procedures and rates. Results will be used for both the permit application process and the Feasibility Study.

A total of ten “fracture simulation” leach tests have been ongoing as part of the metallurgical program. Fracture simulation boxes #1 and #2 have been completed after 199 and 166 days of respective leaching. Box #3 is still leaching after 170 days and the remaining seven boxes have been leaching for approximately 80 days. Highlights of the preliminary results are set out in Table 1 below.

Commenting on these results, Stephen Twyerould, President and C.E.O. said, “The fracture simulation boxes offer us the best lab-scale testing of expected underground leach conditions to date. We are pleased to see that across all rock types, these initial results mirror the industry-leading outcomes from our 2014 Prefeasibility Study in terms of acid consumption and copper recoveries. Once again, Excelsior has returned results that highlight the viability of an in-situ recovery operation at Gunnison.”

Final metallurgical test results are expected to be released in July, 2015. In addition, Excelsior has also been undertaking a hydrology program that involved drilling 26 hydrological test wells. Extensive geophysical logging and pump testing is currently being conducted on these holes to define the hydrological properties that control fluid movement through the naturally fractured, mineralized, bedrock. The results of the hydrological program are also expected to be available in July 2015.

Details Regarding Metallurgical Tests

The fracture simulation leach tests were designed to simulate the leaching of copper from a fracture surface as would occur during in-situ recovery operations at the Gunnison Copper Project. Natural, mineralized, fracture surfaces were taken from drill core representing the major rock and mineralization types found in the deposit. Samples were then embedded in acid resistant epoxy such that all un-natural surfaces of the core were covered by epoxy and the natural, mineralized, fracture, surfaces were left exposed to the leach solution. The samples were placed in an approximately 9 foot long by 10 inch wide clear Perspex box with the un-coated mineralized fracture surfaces facing upwards, and the rest of the sample surrounded by epoxy, thereby restricting the leaching process to the fracture surface. A clear Perspex lid was placed on top of each box with minimal void space between the lid and the fracture surface (Figures 1 and 2). Mature raffinate, at 15 grams per litre acid concentration, was delivered at one end of the box, fully saturating the core, and moving across the fracture surface in a controlled manner, thereby producing copper-rich leach solution that was collected and sampled at the other end of the box (Figure 3).

Figures 1, 2, and 3 can be viewed via the following link:
http://www.excelsiormining.com/index.php/projects

Results indicate copper is leaching rapidly and relatively uniformly across all rock types. Recoveries reported in Table 1 include copper leached from typical copper oxide minerals (e.g. chrysocolla), that report to the acid soluble assay, as well as slow leaching and transitional copper minerals that do not typically report to the acid soluble copper assay.

One of the key deliverables from these tests is quantitative acid consumption numbers (see Table 1). These results are consistent with the numbers used in Excelsior’s Prefeasibility Study.

Table 1. Interim results from fracture simulation leach testing.

Ore Core Tray At 80 days At 160 days
Recovery*
%
Acid Consumption
(lbs/lb Cu)
Recovery*
%
Acid Consumption
(lbs/lb Cu)
Lower Abrigo 1 59.9 5.5 76.9 6.2
10 73.9 4.1    
Middle Abrigo 6 62.8 5.0    
9 61.9 5.8    
Upper Abrigo 2 59.7 3.7 78.8 4.5
5 64.7 7.4    
Martin 3 43.7 4.6 71.3 5.9
4 59.1 11.7    
7 62.7 8.3    
8 58.0 3.2    

*The Recovery percentage is expressed as the percentage of leachable copper, which includes typical acid soluble minerals as well as slow leaching oxides and transitional sulfides.

Leaching of boxes 4 to 10 will continue over the next several weeks. The data collected from these boxes will be used to develop recovery and acid consumption models to be used in Excelsior’s Feasibility Study.

Metallurgical testing is being conducted by the independent laboratory, MAG (Minerals Advisory Group) of Tucson, Arizona under the supervision of Dr. Ronald J. Roman, an independent consultant who is a Qualified Person as defined by National Instrument 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 above.

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. 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, NI 43-101 Technical Report, Prefeasibility Study” dated February 14, 2014.

For more information on Excelsior, please visit our website at www.excelsiormining.com.

ON BEHALF OF THE EXCELSIOR BOARD

"Mark J. Morabito"
Executive Chairman

For further information regarding this press release please contact:

Excelsior Mining Corp.
JJ Jennex, Vice President, Corporate Affairs
T: 604-681-8030 x240
E: info@excelsiormining.com
www.excelsiormining.com

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) acid consumption and copper recoveries; (ii) the preparation of a feasibility study model; (iii) the timing of final metallurgical program and hydrology program results and (iv) the advancement of the Gunnison Project.

Such forward-looking information can be identified by the use of the word “will”. Forward-looking information contained in this news release is based on certain factors and assumptions regarding, among other things, the estimation of mineral resources and mineral reserves, the realization of resource and reserve 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 permitting 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 and reserves, 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.