Structural Geology from oriented drill core

Structural observations on a small sample of drill core helps understanding the structural setting. SJS has a long history of involvement with oriented core and our staff bring years of experience in this area.

It is important to collect structural data as accurately as possible. Below are three different instruments commonly used to measure planar and linear structures in drill core. We present here a critical analysis of the methods.


Coremap

  • Does not require separate compass or clinometer

  • Works on magnetic rocks.

  • Because readings are internal to the device, does not require to be aligned with drill hole  - But aligning encourages on-site thinking, holistic interpretation and if necessary re-design of next hole.
  • Accurate measurement of planar and linear features.
  • Planar elements – Use flat plate to define plane and adjust frame edges into parallelism.
  • Linear elements - Penetrative and non-penetrative can be measured-  Hold bar on lineation and adjust frame edges into parallelism.
  • Encourages careful readings.
  • Slow relative to some other methods.

          

         

       




Rocket Launcher

  • Readings taken as in outcrop with a compass-clinometer.
  • Planar elements – Use flat plate to define plane and adjust frame edges into parallelism.
  • Linear elements - Penetrative and non-penetrative can be measured- Hold bar on lineation and measure with compass clinometer.
  • Need non-magnetic environment.
  • Not suitable for magnetic drill core





Core Protractor

  • Planar features - α angle to core axis, β clockwise down core to dip direction.
  • Linear features - γ lineation to core axis, δ measured clockwise angle from TOH reference line to lineation.   
  • Need to use stereonet or computer program to convert to strike and dip.
  • Errors in β very large as α -> 90





Critical Comparison of Instruments


      Coremap™   
 Rocket Launcher  Core Protractor 
   Planar readings
 

***
 
** 
***  but * when
alpha ->90'
 
Movement of core

* 
 *
 ***

 Penetrative linear


***
 
** 
 * manual processing 

 Non-penetrative linear

*** 
*** 

 Survey timing

 *
 ***

 Half core


 ***

**
 
 X

Magnetic rocks

 
 ***
*** 
 
Thinking and interpretation 

*** 
*** 

 Vergence

*** 
 ***
 X

 Computer entry


 Separate task
Separate task 
Essential unless use
manual stereonet
with each reading 
 
Cost (approximate)

Please ask for
a quote
A$700 
 Kenometer A$340
each or
A$75 or less
 
Error setting up device


<1 degree 
< 5 degrees 
 
Error placing core in device


 <2 degrees
 <10 degrees
5 degrees 

Error on readings
 
 <2 degrees <5 degrees  <5 degrees, but increases
to <25 degrees for beta
as alpha -> 90degrees  
* ok    ** good   ***excellent



  • Potential errors in using oriented drill core are plentiful and if not constrained make the exercise worthless.
  • Coremap, rocket launcher and core protractors can all provide satisfactory planar readings.
  • SJS Resource Management prefers the Coremap, which slows-down readings and encourages collection of quality data, picture building and thinking.

 

Julian Vearncombe

For more about core orientation, structural geology and training please contact info@sjsresource.com.au




Julian Vearncombe 20-Aug-2013
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Julian Vearncombe

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