Rio Alto Mining Limited
TSX : RIO
OTCQX : RIOAF
BVL : RIO
FRANKFURT : MS2

Rio Alto Mining Limited

March 05, 2012 04:16 ET

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

VANCOUVER, 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 ID Intercept (m) Copper Grade (%) Gold Grade (g/t)
LA-D11-003 383 0.44 0.26
Including 70 0.60 0.34
47 0.97 0.68
LA-D11-016 824 0.35 0.21
Including 166 0.57 0.37
72 0.66 0.36
LA-D11-017 618 0.48 0.26
Including 76 0.54 0.31
104 0.97 0.55
LA-D11-034 793 0.49 0.27
Including 180 0.73 0.45
198 0.68 0.39

As 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 Results

The 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 ID FROM TO Interval Cu % Au g/t Ag g/t Mo ppm
LA-D11-002 129 458 330 0.29 0.16 0.25 60
Including 264 300 37 0.43 0.26 0.20 30
430 458 28 0.45 0.23 0.38 43
LA-D11-003 101 484 383 0.44 0.26 0.63 44
Including 130 200 70 0.60 0.34 0.63 28
292 339 47 0.97 0.68 2.06 39
LA-D11-016 8 832 824 0.35 0.21 0.61 41
Including 161 218 57 0.38 0.26 0.66 59
264 430 166 0.57 0.37 0.85 30
612 684 72 0.66 0.36 1.65 65
LA-D11-017 12 48 36 0.13 0.11 0.14 42
LA-D11-017 82 700 618 0.48 0.26 0.79 61
Including 151 238 88 0.49 0.26 0.82 42
414 490 76 0.54 0.31 0.63 76
542 646 104 0.97 0.55 2.08 51
681 700 19 0.46 0.22 1.05 137
LA-D11-021 87 839 752 0.31 0.20 0.53 61
Including 346 389 43 0.69 0.66 1.12 18
758 803 45 0.51 0.23 0.32 237
LA-D11-022 8 658 650 0.29 0.17 0.55 91
Including 8 24 16 0.86 0.40 1.07 15
118 424 306 0.34 0.19 0.86 107
LA-D11-023 112 809 697 0.23 0.14 0.64 40
Including 312 406 94 0.31 0.20 1.09 47
508 576 68 0.33 0.15 0.84 50
621 712 91 0.45 0.26 0.82 57
LA-D11-025 30 714 684 0.49 0.37 0.92 49
Including 30 112 82 0.68 0.60 2.03 20
270 298 28 0.59 0.48 0.77 50
348 582 234 0.73 0.52 1.14 31
LA-D11-031 24 160 136 0.82 0.68 2.31 33
LA-D11-031 274 346 72 0.12 0.07 0.40 63
LA-D11-031 374 391 17 0.20 0.15 0.39 112
LA-D11-031 500 916 416 0.39 0.21 1.02 45
Including 604 834 230 0.56 0.33 1.33 68
LA-D11-034 191 984 793 0.49 0.27 0.78 53
Including 242 280 38 0.68 0.36 0.78 26
366 546 180 0.73 0.45 0.89 22
640 838 198 0.68 0.39 1.25 48
LA-R11-023 14 210 196 0.19 0.21 0.33 35
Including 32 44 12 0.55 0.33 0.38 47
LA-R11-023 182 200 18 0.50 0.17 0.66 10
LA-R11-024 98 350 252 0.31 0.21 0.23 34
LA-R11-025 148 258 110 0.22 0.16 0.19 38
Including 188 230 42 0.28 0.20 0.29 35
LA-R11-026 152 188 36 0.13 0.07 0.10 82
LA-R11-026 270 352 82 0.20 0.11 0.16 60
LA-R11-027 312 402 90 0.16 0.09 0.37 88
LA-R11-028 0 118 118 0.17 0.16 0.15 59
Including 0 16 16 0.31 0.18 0.13 76
LA-R11-028 160 402 242 0.16 0.14 0.36 12
LA-R11-029 10 208 198 0.62 0.54 0.85 25
Including 42 156 114 0.85 0.67 1.21 29
LA-R11-030 78 100 22 0.16 0.12 0.12 61
LA-R11-030 140 172 32 0.45 0.48 0.91 88
LA-R11-030 214 402 188 0.22 0.20 0.36 26
LA-R11-030 216 276 60 0.43 0.35 0.86 53
LA-R11-031 6 402 396 0.58 0.51 0.95 79
Including 34 74 40 0.87 0.69 2.38 24
152 402 250 0.64 0.60 0.74 108
LA-R11-032 104 180 76 0.18 0.18 0.20 26
LA-R11-033 Below the Cut Off Grade
LA-R11-034 126 196 70 0.13 0.07 0.25 69
LA-R11-035 52 66 14 0.21 0.08 1.26 5
LA-R11-036 8 402 394 0.36 0.35 0.67 17
Including 242 396 154 0.60 0.58 1.02 16
LA-R11-037 18 402 384 0.37 0.27 0.68 65
Including 168 222 54 0.54 0.45 0.96 99
LA-R11-039 16 402 386 0.18 0.13 0.68 32
LA-R11-040 132 294 162 0.12 0.09 0.20 45
LA-R11-041 48 186 138 0.12 0.07 0.10 25
LA-R11-042 Below the Cut Off Grade

A 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 Assurance

Sampling 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 LIMITED

Alex Black, President & CEO

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