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**Exhibit 4.73**

|WHEN RECORDED
      RETURN TO:      | 
|----------------------------------- | 
|                                    | 
|Latham &
      Watkins LLP          | 
|Attn: Jason
      Crowell, Esq.     | 
|600 West Broadway,
      Suite 1800 | 
|San Diego, CA 92101                 | 

(Space Above This Line For Recorders Use Only)

APN NOS.: 005-341-29; 005-341-16; 005-341-23; 005-341-06;
005-341-11; 005-341-18; 005-341-31; and 005-341-36

ASSIGNMENT AND ASSUMPTION OF LEASES

This ASSIGNMENT AND ASSUMPTION OF
LEASES (the Assignment) is made as of October 24, 2007, by and among NEVADA
GEOTHERMAL POWER INC., a corporation registered in British Columbia (NGPI),
and NEVADA GEOTHERMAL POWER COMPANY, a Nevada corporation (NGPC and, together
with NGPI, Assignor), and NGP BLUE MOUNTAIN I LLC, a Delaware limited
liability company (Assignee).

Agreement

For good and valuable
consideration, the receipt and adequacy of which are hereby acknowledged,
Assignor and Assignee mutually agree as follows:

1. Assignment. Assignor
hereby sets over, transfers and assigns unto Assignee, all of Assignors right,
title and interest in and to the leases described on Annex Iand the
leasehold estate created thereby, for the balance of the terms thereof.

2. Assumption. In
consideration of the foregoing assignment, Assignee hereby accepts the foregoing
assignment and assumes and agrees to make all of the payments and to otherwise
observe, keep and perform all the terms, covenants and conditions to be made,
observed, kept and performed by the lessee under the leases described on
Annex I, as fully as though Assignee were originally named as the lessee
under such leases.

3. Intermediate
Assignment. Notwithstanding Sections 1and 2above, the leases
described herein shall be deemed to have been contributed to NGPC (if
applicable) and NGP Blue Mountain Holdco LLC (Holdco) immediately prior to
their assignment to Assignee pursuant to this Assignment, as set fort in the
Contribution Agreement, dated as of September 19, 2007, by and among the parties
hereto and Holdco; provided that the assignments described in Sections 1and 2shall nonetheless be effective simultaneously with the
execution of this Assignment.

4. Third Party Consents.
To the extent consent of a third party is required to assign any of the leases
described on Annex Ior otherwise intended to be subject to this
Assignment, the effectiveness of this Assignment with respect to such lease
shall be conditioned upon and delayed until such time as such consent has been
obtained. The parties hereto agree to complete Annex Iprior to the
initial

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recording of this Assignment and from time to time thereafter
shall update such Annex I upon receipt of additional consents of third
parties necessary to assign the leases contemplated by the Contribution
Agreement, dated as of September 19, 2007 and as amended from time to time
thereafter, among the parties hereto and certain of their affiliates, and, with
respect to each such lease, with such information as may be necessary to place
this Assignment of record with respect to each such lease as such information
becomes available.

| | 5. | Governing Law. This Assignment shall be governed
      by the law of the state of Nevada.
| | -- | -----------------------------------------------------------------------------------------

[remainder of page intentionally left blank]



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IN WITNESS WHEREOF, the parties
hereto have executed this Assignment as of the date first above written.

ASSIGNOR:

| | NEVADA GEOTHERMAL POWER INC.,               
| | --------------------------------------------
| | a corporation registered in British Columbia
| |                                             
| | By:
      /s/ Brian D. Fairbank             
| | Name: Brian D. Fairbank                     
| | Title: President                            

PROVINCE OF BRITISH COLUMBIACITY OF VANCOUVER

This Assignment and Assumption
of Leases was acknowledged before me on ___________October 24_____, 2007,
by ______Brian Fairbank__________________________________, a duly
authorized officer of Nevada Geothermal Power Inc.

|_____________/s/______________________             
|---------------------------------------------------
|NOTARY PUBLIC in and for the Province              
|of British Columbia                                
|                                                   
|                                                   
|                                                   
|                                                   
|(Print or stamp name of Notary)                    
|My Commission Expires: _________n/a_______________.

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ASSIGNOR:

| | NEVADA GEOTHERMAL POWER COMPANY,
| | --------------------------------
| | a Nevada corporation            
| |                                 
| | By:
      /s/ Brian D. Fairbank 
| | Name: Brian D. Fairbank         
| | Title: President                

PROVINCE OF ONTARIOCITY OF TORONTO

This Assignment and Assumption
of Leases was acknowledged before me on ___________October 24_____,2007, by
______Brian Fairbank__________________________________, a duly authorized
officer of Nevada Geothermal Power Company.

_____________/s/______________________NOTARY PUBLIC
in and for the Provinceof Ontario

(Print or stamp name of Notary)My Commission Expires:
_________n/a_______________.



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ASSIGNEE:

| | NGP BLUE MOUNTAIN I LLC,            
| | ------------------------------------
| | a Delaware limited liability company
| |                                     
| | By:
      /s/ Brian D. Fairbank     
| | Name: Brian D. Fairbank             
| | Title: President                    

PROVINCE OF ONTARIOCITY OF TORONTO

This Assignment and Assumption
of Leases was acknowledged before me on ___________October 24_____,2007,
by ______Brian Fairbank__________________________________, a duly
authorized officer of Nevada Geothermal Power Inc.

_____________/s/______________________NOTARY PUBLIC
in and for the Province of British Columbia

(Print or stamp name of Notary)My Commission Expires:
_________n/a_______________.



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Annex Ito Assignment and Assumption of Leases

LEASES

|1. | Geothermal Lease Agreement for The DeLong Section 27
      (T36N, R34E) Area, Humboldt County, Nevada, effective as of April 15,
      2006, by and between JHG, LLC, c/o Will DeLong and Nevada Geothermal Power
      Company, a Memorandum of will be recorded in Humboldt County,
    Nevada.
|-- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

|2. | (a) | Geothermal Lease Agreement effective
      as of March 31, 2003 by and between Nevada Land and Resource Company, LLC
      and Nevada Geothermal Power Company, a Nevada corporation (formerly known
      as Noramex Corporation), a Memorandum of which was recorded in Humboldt
      County, Nevada on April 23, 2003 as Instrument No. 2003-2346.                                                                                                                                                                               
|-- | --- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|   |     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|   | (b) | Lease Amendment #189093 dated as of
      November 1, 2005 between Nevada Land and Resource Company, LLC and Nevada
      Geothermal Power Company, a Nevada corporation (formerly known as Noramex
      Corporation).                                                                                                                                                                                                                                                                                                              
|   |     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|   | (c) | Notice of Lease Amendment
      #189093 effective as of February 1, 2006 by and between Nevada Land and
      Resource Company, LLC and Nevada Geothermal Power Company, a Nevada
      corporation.                                                                                                                                                                                                                                                                                                                                 
|
|   |     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|   | (d) | Notice of Lease Amendment
      #189093 effective as of October 3, 2006 between Nevada Land and Resource
      Company, LLC and Nevada Geothermal Power Company, a Nevada corporation.                                                                                                                                                                                                                                                                                                                                               
|
|   |     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|   | (e) | Notice of Lease Amendment #189110
      effective as of February 1, 2007 by and between Nevada Land and Resource
      Company, LLC and Nevada Geothermal Power Company.                                                                                                                                                                                                                                                                                                                                                             
|   |     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|   | (g) | Memorandum of Lease for the Nevada
      Land and Resource Company, LLC Sections 1, 11, 25 and 35 (T36N, R34E)
      Area, Humboldt County, Nevada dated October 24, 2007 by and between Nevada
      Land and Resource Company, LLC and Nevada Geothermal Power Company, a
      Nevada corporation, recorded in Humboldt County, Nevada on ___, 2007 as
      Instrument No. _______________ .                                                                                                                                     
|   |     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|   | (f) | Amendment to Geothermal
      Lease Agreement for the RLF Nevada Properties, LLC Section 13 (T36N, R34E)
      Area, Humboldt County, Nevada dated as of October 24, 2007 by and between
      Nevada Geothermal Power Company and RLF Nevada Properties, LLC, recorded
      in Humboldt County, Nevada on _______________ . ___, 2007 as Instrument
      No.                                                                                                                                                                      
|
|   |     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|1. | (a) | Geothermal Lease dated October 19,
      1993 for the Burlington Northern and Santa Fe Railway Company Sections 15
      and 23 (T36N, R34E) Area, Humboldt County, Nevada by and between The
      Burlington Northern and Santa Fe Railway Company, LLC (successor-
      in-interest to The Atchison, Topeka and Santa Fe Railway Company) and
      Nevada Geothermal Power Company, a Nevada corporation (formerly known as
      Noramex Corporation), a Memorandum of which will be recorded in Humboldt
      County, Nevada.
|   |     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|   | (b) | Exercise of Option to Renew
      Lease No. 187556 effective as of March 1, 2004, by and between The
      Burlington Northern and Santa Fe Railway Company and Nevada Geothermal
      Power Company, a Nevada corporation (formerly known as Noramex
      Corporation), recorded in Humboldt County, Nevada on October 13, 2005 as
      Instrument No. 2005-9318.                                                                                                                                                                
|

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