Rio Alto Mining Limited
TSX VENTURE : RIO
FRANKFURT : MS2
BVLAC : RIO
OTCQX : RIOAF
PINK SHEETS : RIOAF

Rio Alto Mining Limited

May 20, 2010 09:23 ET

Rio Alto Completes First Tranche of Private Placement for $7.5 Million

CALGARY, ALBERTA--(Marketwire - May 20, 2010) - Rio Alto Mining Limited ("Rio Alto") (TSX VENTURE:RIO)(BVLAC:RIO)(DBFrankfurt:MS2)(OTCQX:RIOAF)(PINK SHEETS:RIOAF) is pleased to announce that has closed the first tranche of a private placement of common shares for gross proceeds of C$7,510,000 (US$7,270,000). At this closing 10,097,162 common shares were sold at the issue price of $0.75 (US$0.72) per share. One or more additional tranches of the private placement may be completed.

The net proceeds of the private placement will be used by Rio Alto for the development of La Arena Gold Oxide Project and for general corporate purposes. The common shares issued pursuant to the private placement are subject to a statutory resale restriction period of four months and a day expiring on September 20, 2010. The completion of the private placement is subject to final approval from the TSX Venture Exchange.

Rio Alto will pay finders' fees in connection with the first tranche of the private placement of US$510,000.

Rio Alto plans to bring La Arena Gold Oxide Project into production during 2010 and to use cash flow from production to further develop its assets in Peru. To learn more about Rio Alto, please visit Rio Alto's website or Rio Alto's profile on SEDAR at www.sedar.com.

Reader Advisory

Certain statements contained herein constitute forward-looking statements, including the use of proceeds of the private placement and development of La Arena Gold Oxide Project. All statements included herein, other than statements of historical fact, are forward-looking information and such information involves various risks and uncertainties. Rio Alto believes the expectations reflected in these forward looking statements are reasonable but no assurance can be given that these expectations will prove to be correct and such forward-looking statements in this press release should not be unduly relied upon. 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. Forward-looking statements included in this press release are made as of the date of this press release and Rio Alto disclaims any intention or obligation to update or revise any forward-looking statements, whether as a result of new information, future events or otherwise, except as expressly required by applicable securities legislation.

To learn more about Rio Alto Mining Limited, please visit: www.rioaltomining.com.

ON BEHALF OF THE BOARD OF

RIO ALTO MINING LIMITED

Feisal Somji, President and CEO

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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