Rio Alto Mining Limited

Rio Alto Mining Limited

July 20, 2011 09:20 ET

Rio Alto Drills 238 Metres of 1.06 Grams of Gold Per Tonne

VANCOUVER, BRITISH COLUMBIA--(Marketwire - July 20, 2011) - Rio Alto Mining Limited ("Rio Alto" or the "Company") (TSX VENTURE:RIO)(OTCQX:RIOAF)(BVLAC:RIO)(DBFrankfurt:MS2) is pleased to report assay results from 18 reverse circulation ("RC") drill holes within and around the Calaorco Pit at the Company's La Arena Gold Oxide Mine ("Oxide Mine") located in La Libertad, northern Peru.

Significant intercepts were:

Hole Intercept (mts) Gold Grade (g/t)
CA-R11-038 158 0.58
CA-R11-039 200 0.46
CA-R11-047 238 1.06
CA-R11-049 148 0.65
CA-R11-050 104 1.72
CA-R11-050 158 0.51

The following results are from the last 18 RC holes drilled at Calaorco with 15 out of the 18 holes intersecting gold mineralization above the mining cutoff grade. These drill holes were within ("Inside") and extended outside or below ("Below") the current design of the Calaorco Pit.

A total of 13,674 metres of RC drilling in 50 holes has been completed at the Calaorco Pit and this drill program is complete for this year. The Company's geologists are interpreting the data generated by these 50 holes to calculate an updated resource estimate for the Calaorco Pit. Management expects that this drilling program will result in positive changes to the resource block classification; define new resource blocks; and given that the deposit is open to the northwest and southeast identify new areas to test in order to increase resources. The updated resource estimate for the Calaorco Pit is planned for release in Q4 2011.

Drill Results

References to "Pit Location" in the following table refer to intercepts within ("Inside") the Calaorco Pit or drill hole intercepts that extended outside or below ("Below") the Calaorco Pit. A map illustrating drill hole locations and selected drill hole cross sections related to this press release may be accessed by following this link:

Hole ID From To Interval Au g/t Ag g/t Pit
RC33 240 286 46 0.28 0.42 Inside
RC34 Below the cut off grade
RC35 180 226 46 0.20 0.37 Inside
RC36 Below the cut off grade
RC37 Below the cut off grade
RC38 4 162 158 0.58 0.33 Inside
Including 52 64 12 1.87 0.33 Inside
Including 92 148 56 0.76 0.49 Inside
RC39 30 230 200 0.46 0.41 Inside
Including 66 84 18 2.23 0.83 Inside
RC40 124 142 18 0.78 0.52 Inside
RC40 278 296 18 0.59 0.32 Below
RC41 0 22 22 0.43 0.20 Inside
RC41 220 238 18 0.38 0.81 Below
RC42 76 146 70 0.21 0.47 Inside
RC42 180 218 38 0.12 0.25 Below
RC42 246 291 45 0.32 0.47 Below
RC43 0 30 30 0.52 0.42 Inside
RC44 84 146 62 0.37 0.65 Inside
RC44 244 300 56 0.22 0.35 Below
RC45 66 134 68 0.28 0.61 Inside
RC45 204 210 6 0.54 1.47 Below
RC46 20 34 14 0.51 0.33 Inside
RC47 0 238 238 1.06 0.44 Below
Including 18 90 72 1.36 0.59 Inside
Including 160 168 8 8.33 0.83 Inside
Including 220 238 18 1.54 0.32 Below
RC48 0 92 92 0.97 0.26 Inside
RC48 128 166 38 0.86 0.45 Inside
RC49 0 148 148 0.65 0.68 Inside
Including 36 72 36 2.10 1.49 Inside
RC49 186 236 50 0.13 0.29 Below
RC49 256 274 18 0.24 0.40 Below
RC50 0 104 104 1.72 0.38 Below
Including 56 98 42 2.61 0.61 Below
RC50 142 300 158 0.51 0.60 Below
Including 144 180 36 1.32 0.76 Below

Sulphide Drilling Program

The drilling program at the La Arena Copper/Gold sulphide project started this week. The Company has three diamond core drilling rigs on site with a fourth due in August. The current program involves drilling 55 diamond core holes for a total of 32,330 metres. Drilling depth will vary between 400 to 750 m in order to: upgrade the category of resource blocks from inferred to indicated; define new resource blocks; and identify new areas to test in order to increase resources. During the past 6 months, in preparation for the sulphide drilling program, the Company´s geological team has reinterpreted the mineral distribution, structures, lithology and alteration of the pre-existing geological model. This reinterpretation will be tested by the planned 55 holes.

Astrid Prospect (Oxides)

On June 15, 2011, the Company announced that the Astrid Prospect, a gold oxide exploration target, located approximately 500 metres north of the Calaorco Pit had been identified by surface mapping and geochemical sampling. This target has the same geological and geochemical characteristics as Calaorco and contains gold mineralization hosted in oxidized brecciated sandstone. The current surface footprint of the Astrid Prospect is 500 metres by 200 metres, over which the Company is conducting a 14 Km IP (induced polarization) and Ground Magnetic survey. The Company plans to start a first pass RC drilling program at Astrid in late August.

Quality Control and Assurance

Sampling of the reverse circulation drilling and sample preparation were performed by Rio Alto personnel and were carried out under strict protocols recommended in the NI 43-101 Technical Report dated July 31, 2010 prepared by Coffey Mining Pty Ltd for the Company (the "Report"). Samples were taken every 2m and split in half to yield seven to ten kilogram samples. Drill sample recovery was generally in excess of 90%. Rio Alto has 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. Samples were shipped to CIMM-Peru in Lima where they were dried, crushed, pulverized, and assayed. All gold assays were obtained by standard 50g fire assaying with AA finish. All silver assays reported in the press release were obtained by Aqua-Regia dissolution followed by ICP measurement. CIMM-Peru is an ISO 9001:2000 certified laboratory.

Enrique Garay, M Sc. P. Geo. (AIG Member), Vice President Geology of Rio Alto is the Qualified Person responsible for the management of the exploration program and disclosure of the drill results as defined by National Instrument 43-101. Mr. Garay has read and approved the scientific and technical information in this news release. For additional information regarding the Oxide Mine and the sulphide project please refer to the Report, a copy of which is available under Rio Alto's SEDAR profile at

This news release contains certain forward-looking information including statements concerning the expected timing for the arrival of drills at La Arena, the timing of a new resource estimate for the Calaorco Pit and the timing and scope of exploration programs at the Company´s sulphide project and Astrid prospect. 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 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: or Rio Alto's SEDAR profile at


Alex Black, President & COO

Neither TSX Venture Exchange nor its Regulation Services Provider (as that term is defined in the policies of the TSX Venture Exchange) accepts the responsibility for the adequacy or accuracy of this release.

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