John, Byron

I finally had some time this weekend to revisit the resistivity surveys.

Jim Conley sent me a well log, conleyWellLog.txt,  from his well adjacent to our EW dipole-dipoles survey, conleyEWdipole.jpg.  Stratigraphically, this area is in the Tertiary Poison Canyon formation described as buff arkosic conglomerates and sandstone, yellow siltstone and shale.  This description fits Jim's well log.  I haven't seen any outcrops of the Poison Canyon, but I suspect the shale occurs as stringers.  Jim is producing water at 313'-348'.  The resistivity survey shows a shallower low resistivity zone.  I noticed a hydrant while we were doing the survey.  I'll go down to the court house and see if I can find any more drilling records.

For the Fischer resistivity survey, I took at look at the Silver Spurs regional gravity survey, gravity.doc, along the road adjacent to the dipole-dipole survey to see if there might be any correlation.  The gravity.doc contains free air, Bouguer and complete Bouguer for stations 302-309.  These locations are marked with respect to the resistivity survey in resistivityGravity.jpg.  The resistivity station numbers can be correlated with the resistivity cross section, fischerNSdipole.jpg,  by multiplying the station number by 100.

There is quite a bit of topographic relief so the complete Bouguer is probably the most meaningful.  No regionals have been removed.  Gravity values are relative readings in mgal.  As you can see from the Bouguer, there appears to be a small basin centered around gravity station 304 which correlates with an x of 1500' on the resistivity section.  The resistivity indicates a south dipping feature to at least an x of 1000' or gravity station 306.  The complete Bouguer gravity trend doesn't support this dipping feature.

The gravity survey was done on a shoe string budget.  I was not able to use an RTK GPS base station.  Elevations were pulled off a 30m DEM from XYs that are probably +/- 20 feet at best. I was mostly interested in regional gravity anomalies.  We have about 60' of elevation change from gravity station 304-309.  Assuming an elevation error +/- 10 feet gives a Bouguer error of +/- 2 mgal.  Any relevant anomaly could be obscured in the uncertainty.

Best regards, 

Wes