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THERMONIC LOCATION OF WATER-WELL SITES IN A BURIED   FLUVIAL CHANNEL IN THE JURASSIC MORRISON   FORMATION, MCKINLEY COUNTY, NEW MEXICO, U.S.A.   

William M. Turner, Ph.D. 
 

INTRODUCTION  

AGW scientists completed a major project for the Sohio Uranium Company on its L-Bar uranium property using its proprietary Thermonic geophysical methods.  The location of the property is shown in Figure 1.  The objectives of the project were to:  

• Locate optimal well sites for a well field to supply a uranium mill; and,  
• Determine if Thermonics is a useful uranium-exploration method. 
 

GEOLOGIC SETTING 

The project area lies in the New Mexico uranium belt on the southern edge of the San Juan Basin about 50 miles (80 km) west of Albuquerque, New Mexico.

Uranium is concentrated in organic material entrained in sandstone of the Jackpile Channel-Sand Member of the Morrison Formation of Jurassic age.  The channel sands are overlain by 600 to 1,500 feet (180 to 450 m) of Cretaceous marine sandstone and shale.  The Jackpile Channel Sand is the primary channel sand underlying the L-Bar property.  The Jackpile Channel Sand ranges in thickness from feather edges to about 85 feet (26 m) in the center of the channel.  Tributaries to the main Jackpile Channel were expected by Sohio but could not be located by drilling.
 

PROCEDURE  

AGW scientists measured temperature in both the saturated and unsaturated parts of more than 90 40-foot (121 m) deep uranium-exploration bore holes.  We made temperature measurements in lines of bore holes perpendicular to the axis of the ore body in other areas. We also measured water-level measurements in each bore hole.   

We processed the temperature data using our proprietary methods to remove effects of downward solar-heat propagation and variable thermal properties of the rocks.  We plotted corrected heat-flow data from a depth of 95 feet (30 m).   We contoured the data using AGW's proprietary "valley mapping function" because of the inability of commercial contouring software to consider subsurface temperature distributions caused by moving ground water.
 

RESULTS 

We successfully traced the axis of the Jackpile Sand Channel and identified and traced several tributaries.  The main channel sand was about 400 feet (122 m) wide.  Later mining found the tributary channel to be about 25 feet (8 m) wide. 

    Furthermore:

    • Uranium mineralization follows the Jackpile Channel Sand and its  tributaries. 
    • The axial zone of the Jackpile channel sand is the zone of greatest aquifer transmissivity,  maximum mass rate of ground-water flow, and the best site for water production wells.

CONCLUSIONS   

    We conclude that:

    • Data from 50 feet beneath the land surface  provides the same information as data from greater depths.
    • Despite the use of drilling mud and a mud cake in the bore holes, fluid levels return to their pre-drilling level within a few days of drilling. 
    • Control of mine water is easiest with wells located in the channel.. 
    • Thermonics can trace uranium-bearing paleo-stream channels and is a useful uranium exploration method for these types of deposits. 
    • Thermonics can trace buried stream channels and is a valuable ground-water exploration and well-site location method.

     

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