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Press release from Marketwire

Rio Alto Drills 104 Meters Grading 0.97% Cu and 0.55 g/t Au

Monday, March 05, 2012

Rio Alto Drills 104 Meters Grading 0.97% Cu and 0.55 g/t Au04:16 EST Monday, March 05, 2012VANCOUVER, BRITISH COLUMBIA--(Marketwire - March 5, 2012) - Rio Alto Mining Limited ("Rio Alto" or the "Company") (TSX VENTURE:RIO)(OTCQX:RIOAF)(BVL:RIO)(DBFrankfurt:MS2) is pleased to report assay results from 20 reverse circulation ("RC") drill holes and 10 diamond drill ("DD") holes completed after September 30, 2011 as part of the Company's ongoing feasibility study for La Arena sulphide deposit at the Company´s La Arena Project located in La Libertad Region in northern Peru.Significant intercepts from this drilling were:HOLE IDIntercept (m)Copper Grade (%)Gold Grade (g/t)LA-D11-0033830.440.26Including700.600.34470.970.68LA-D11-0168240.350.21Including1660.570.37720.660.36LA-D11-0176180.480.26Including760.540.311040.970.55LA-D11-0347930.490.27Including1800.730.451980.680.39As part of the feasibility study for La Arena sulphide deposit, the Company expects to drill an additional 60,000 meters of DD drilling that will complete the database for the sulphide feasibility study resource estimate which is due to be updated in Q3, 2012. The drilling program is expected to be completed in August 2012.Updated mineral resource estimates for the oxide and sulphide deposits comprising La Arena Project are described in the Company's recently filed Technical Report (the "2011 Report") with an effective date of September 30, 2011 prepared on behalf of the Company by Kirk Mining Consultants Pty Ltd. For additional information regarding the La Arena sulphide project and the updated mineral resource estimates please refer to Company's January 5, 2012 news release and the 2011 Report, copies of which may be referenced within Rio Alto's SEDAR profile at www.sedar.com.Sulphide Drilling ResultsThe results of the additional 10 DD holes (7,578 meters) and 20 RC holes (5,892 meters) of drilling completed by Rio Alto since the September 30, 2011 effective date for the current updated sulphide mineral resource are as follows:HOLE IDFROMTOIntervalCu %Au g/tAg g/tMo ppmLA-D11-0021294583300.290.160.2560Including264300370.430.260.2030430458280.450.230.3843LA-D11-0031014843830.440.260.6344Including130200700.600.340.6328292339470.970.682.0639LA-D11-01688328240.350.210.6141Including161218570.380.260.66592644301660.570.370.8530612684720.660.361.6565LA-D11-0171248360.130.110.1442LA-D11-017827006180.480.260.7961Including151238880.490.260.8242414490760.540.310.63765426461040.970.552.0851681700190.460.221.05137LA-D11-021878397520.310.200.5361Including346389430.690.661.1218758803450.510.230.32237LA-D11-02286586500.290.170.5591Including824160.860.401.07151184243060.340.190.86107LA-D11-0231128096970.230.140.6440Including312406940.310.201.0947508576680.330.150.8450621712910.450.260.8257LA-D11-025307146840.490.370.9249Including30112820.680.602.0320270298280.590.480.77503485822340.730.521.1431LA-D11-031241601360.820.682.3133LA-D11-031274346720.120.070.4063LA-D11-031374391170.200.150.39112LA-D11-0315009164160.390.211.0245Including6048342300.560.331.3368LA-D11-0341919847930.490.270.7853Including242280380.680.360.78263665461800.730.450.89226408381980.680.391.2548LA-R11-023142101960.190.210.3335Including3244120.550.330.3847LA-R11-023182200180.500.170.6610LA-R11-024983502520.310.210.2334LA-R11-0251482581100.220.160.1938Including188230420.280.200.2935LA-R11-026152188360.130.070.1082LA-R11-026270352820.200.110.1660LA-R11-027312402900.160.090.3788LA-R11-02801181180.170.160.1559Including016160.310.180.1376LA-R11-0281604022420.160.140.3612LA-R11-029102081980.620.540.8525Including421561140.850.671.2129LA-R11-03078100220.160.120.1261LA-R11-030140172320.450.480.9188LA-R11-0302144021880.220.200.3626LA-R11-030216276600.430.350.8653LA-R11-03164023960.580.510.9579Including3474400.870.692.38241524022500.640.600.74108LA-R11-032104180760.180.180.2026LA-R11-033Below the Cut Off GradeLA-R11-034126196700.130.070.2569LA-R11-0355266140.210.081.265LA-R11-03684023940.360.350.6717Including2423961540.600.581.0216LA-R11-037184023840.370.270.6865Including168222540.540.450.9699LA-R11-039164023860.180.130.6832LA-R11-0401322941620.120.090.2045LA-R11-041481861380.120.070.1025LA-R11-042Below the Cut Off GradeA map of drill hole locations and selected drill hole cross sections related to this press release may be viewed at the following link: http://file.marketwire.com/release/rio305_Figs.pdf.The Company will release assay results for additional and future drill holes once the results have been compiled. The sulphide mineral resource is open at depth and in all directions. In addition to completing the sulphide feasibility study drill program, the Company intends to begin testing the extension of the sulphide mineralization at La Arena.Quality Control and AssuranceSampling of RC drilling and sample preparation for holes drilled by the Company were performed by Rio Alto personnel and carried out under strict protocols recommended in the Technical Report on the La Arena Project, Peru prepared on behalf of the Company by Coffey Mining Pty Ltd with an effective date of July 31, 2010 ("July 2010 Report"). Samples were taken every two meters and split in half to yield seven to ten kilogram samples. Drill sample recovery was generally in excess of 90%. Sampling of DD holes and sample preparation for holes drilled by the Company were performed by Rio Alto personnel. In the case of each DD hole, an average depth of 450 to 500 meters was drilled with a HQ bit (63.5 mm core size), and the remainder of the hole drilled with a NQ bit (47.6 mm core size). Drill core sample recovery was generally in excess of 90%. The core boxes were washed and photographed. The sample intervals are every two meters, except where sampling is broken up on specific geological contacts. The core is split in half using a rock saw with half of the core sent for laboratory analysis and half of the core remaining in storage. The QA/QC procedures employed for sampling and assaying of holes drilled by the Previous Owners is described in the July 2010 Report and was considered satisfactory. There is a rigorous QA/QC program over the chain-of-custody of samples and the insertion of blanks, duplicates and certified reference standards in each batch of samples. This procedure was implemented based on a recommended protocol from Coffey Mining in 2011. Samples were shipped to CERTIMIN, in Lima, where they were processed and assayed. All gold assays were obtained by standard 50g fire assaying with AAS finish. All silver assays were obtained by Aqua-Regia dissolution followed by ICP measurement. All Cu and Mo assays were obtained by Aqua-Regia dissolution followed by ICP. Cu values over 10,000 ppm are assayed by Atomic Absorption. The Induced Coupled Plasma (ICP) technique provides assays for 35 elements. CERTIMIN is an ISO 9001:2008 certified laboratory.Mr. Enrique Garay, M Sc. P. Geo (AIG Member), Vice President Geology of Rio Alto, is the Qualified Person (as defined by NI 43-101) responsible for managing the Company's exploration programs and disclosure of drilling results. Mr. Ian Dreyer, B.App. Sc.(AUSIMM 305241,CP), a Qualified Person (as defined by NI 43-101), formerly of Coffey Mining Pty Ltd, designed and reviewed the Quality Control and Assurance Program of the Company prepared the updated resource estimates set out in the 2011 Report. Mr. Garay and Mr. Dreyer have read and verified the scientific and technical information in this press release.This news release contains certain forward-looking information including statements concerning the expected timing for the release of resource estimates and future exploration programs. All statements included herein, other than statements of historical fact, are forward-looking information and such information involves various risks and uncertainties. There can be no assurance that such information will prove to be accurate and actual results and future events could differ materially from those anticipated in such information. A description of assumptions used to develop such forward-looking information and a description of risk factors that may cause actual results to differ materially from forward-looking information can be found in Rio Alto's disclosure documents on the SEDAR website at www.sedar.com. Rio Alto does not undertake to update any forward-looking information except in accordance with applicable securities laws.To learn more about Rio Alto Mining Limited, please visit: www.rioaltomining.com or Rio Alto's SEDAR profile at www.sedar.com.ON BEHALF OF THE BOARD OF RIO ALTO MINING LIMITEDAlex Black, President & CEOFOR FURTHER INFORMATION PLEASE CONTACT: Alex BlackRio Alto Mining LimitedPresident & CEO+51 1 625 9900 or +51 99279 4655alexb@rioaltomining.comORAlejandra GomezRio Alto Mining LimitedInvestor Relations+1 604 628 1401+1 866 393 4493 (FAX)alejandrag@rioaltomining.comwww.rioaltomining.com