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Exhibit 4.18 

FIRST AMENDMENT TO MINING CONTRACT 

This FIRST AMENDMENT TO MINING CONTRACT, dated as ofApril 5, 2005 (this "Amendment"), is entered into by and between Minera SanXavier, S.A. de C.V., a Mexican corporation ("Owner"), and Washington GroupLatin America, Inc., a Delaware, U.S.A. corporation ("Contractor"). Owner andContractor are referred to in this Amendment individually as a "Party" andtogether as the "Parties." 

RECITALS 

WHEREAS, Owner owns and operates theCerro San Pedro Mine located in Cerro de San Pedro, Mexico (the "Mine"); 

WHERAS, the Parties to this Amendmentare Parties to the Mining Contract, effective as of December 30, 2003 (the"Mining Contract"), in which Owner engaged Contractor to, among other things,perform drilling, blasting, excavating, mining, hauling and construction-relatedservices at the Mine; 

WHEREAS, in consideration for Ownerreimbursing Contractor for certain standby charges of Contractor during the timeperiod between May 12, 2004 and February 28, 2005, Contractor has agreed to thedevelopment of a new termination provision in the event that the Owner mustterminate the Mining Contract due to an Event of Force Majeure; and 

WHEREAS, the Parties desire to enterinto this Amendment to formalize their verbal agreements and to update thedesignation of persons to receive notice. 

NOW THEREFORE, in consideration of themutual promises set forth in this Amendment and for other good and valuableconsideration, the receipt and sufficiency of which are hereby acknowledged, theParties to this Amendment, intending to be legally bound, agree as follows:

AGREEMENT 

> 
1.  Unless otherwise defined in this Amendment, all capitalized terms used herein  that are defined in the Mining Contract shall have the respective meanings  given to such terms in the Mining Contract. 

2. The second sentence of the fourth  paragraph of Article 13 shall be deleted in its entirety and the following  sentences shall be substituted therefor: 

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In the event of such termination,  Owner shall pay Contractor the same amounts as would be paid, under Section  12.2.1(a) through 12.2.1(e). Contractor shall also be entitled to a One  Million Dollar ($1,000,000) break fee; *provided that*,  in the event Owner or any of Owner's direct or indirect affiliates recommences  the Project within one year from the date in which Owner or Contractor  terminates the Agreement due to an Event of Force Majeure, Contractor shall  credit Owner $500,000 towards the remobilization of Contractor's Equipment and  personnel to the Project. 
3.In Article 14 of the  Mining Contract 
A.Change the recipient    for primary copy of notice to Owner to the "General Manager" instead of the    "Mine Manager"; 
B.Change the recipient    of the copy of any notice to Owner to "Richard J.  Hall, President and    Chief Executive Office" instead of "Fred H. Lightner, Sr. Vice President and    Chief Operating Officer"; 
C.Add the following    provision immediately following Contractor's official notice information:    
With a copy to:Washington Group    International, Inc.
 Attn: Brian Best
 Regional Managing    Attorney
 7800 E. Union    Avenue, Suite 100
 Denver, CO 80237
 U.S.A.
 Phone: (303)    843-2855
 Fax: (303)    343-2266
4.*Exhibit K* of the Mining Contract is deleted in its entirety and the  revised *Exhibit K*  attached hereto is substituted therefor. 
5.Except as expressly  modified pursuant to this Amendment, all other provisions of the Mining  Contract are unaffected, remain in full force and effect with no other  amendments or modifications and are ratified and confirmed in all respects.  
6.This Amendment shall  be governed by the laws of the State of Colorado, excluding any provisions or  principles thereof, which would require the application of the laws of a  different jurisdiction. 
7.This Amendment may be  executed in any number of counterparts, all of which taken together shall  constitute a single and complete agreement. 
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IN WITNESS WHEREOF and intending to belegally bound, the Parties have executed this Amendment on this 5 day of April,2005. 
**Minera San Xavier, S.A. de C.V.**Washington Group    Latin America,**
 **Inc.**
  
By:            /s/ Richard J. HallBy:         /s/ LeRoy E. Wilkes
Name:           Richard J. HallName:          LeRoy E. Wilkes
Title:             DirectorTitle:            President Mining Business Unit
                      Washington Group International,
                       Inc. Attorney-in-Fact
                       Washington Group Latin America, Inc.
 

 

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**EXHIBIT K 

PERMIT CONDITIONS 

(*See Attached)*
 

 

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