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Twinning Drill Holes (6 replies)

Dizzy Flores
8 months ago
Dizzy Flores 8 months ago

Twinning Drill holes - often suggested to verify existing mineralisation, for example for resource due diligence.Since mineralization is often heterogeneous, it seems to me that we are testing short range variability and not "twinning" the existing drill hole as such. I would like to provoke some comments by suggesting that the practice of twinning is only going to verify if mineralization exists at all and that we should not expect to verify actual grades/widths by a handful of manually selected twins which is what often gets done.

8 months ago
Obergruppenfuhrer 8 months ago

We use twins to check the mineralization and the litho logical intervals, especially for the high grade areas. Biased twins could give you indications that you have a problem with your drilling method and/or procedure or your legacy data (if you twin old collars) or the way you log the data. There is a good article about twinned holes written by Marat Abzalov there: http://is.gd/VDZno2

Bill Fraser
8 months ago
Bill Fraser 8 months ago

I totally agree with you (by the way would you have the full PDF of the article? I am no member of http://is.gd/ONJspU), but I would just add twin can also be useful to validate a different drilling method, for example after drilling several holes with Diamond, a few RC twins may validate or invalidate the RC method for such a deposit environment. For example you may realize in some cases that your RC holes show contamination, or do not represent high grade areas, or over-evaluate grades because of loss of fines, etc. Same applies for other drilling methods (small diameter DD, AC, RAB, etc.)

I don't think twin hole contribute to variogram modeling for short distances, it hardly ever gives interesting results, I prefer a good old variogram cross!

Carmen Ibanz
8 months ago
Carmen Ibanz 8 months ago

If you really want to spice up your testing of how heterogeneous your mineralization is try scissor holes. Scissor holes may show sample bias as a result of direction drilled to address JORC 2012 Sample representivity orientation of data in relation to geological structure. Can also lead to confusion demonstrating how heterogeneous it is.

If the purpose of twinned holes is to confirm legacy drill sampling quality then need to consider how many drilling campaigns. In Kalgoorlie region in Australia legacy drilling could be over a long period 20-30 yrs by different companies and different campaigns and differently equipped drill rigs and analytical processes.

Twinning of diamond hole to establish the adequacy of RC the holes are normally drilled close by parallel to the original hole as the purpose is to test the quality of drilling rather than establish geological heterogeneity best established by a variographic drill pattern either a cross or rectilinear or staggered grid pattern reflecting known expected geological continuity for each domain to establish the critical variogram short ranges for resource modeling.

8 months ago
Gruppen 8 months ago

Twinning can also be used to understand the variation between different drilling campaigns - to ensure the validity of results for campaigns of different eras and / or different companies (i.e. the same type of drilling and sampling technique would be used in the later drilled borehole).

Twinning in the sense it has been commented upon in this discussion is particularly important for understanding the potential performance of coal washing: selected borehole sites will have HQ (wire line or conventional core diameter), 100mm core and 200mm in order to crush to different top sizes then obtain wash ability test results on the samples.

The general rule of thumb is a top size that is 1/4 of the core diameter. This is important as it leads to an understanding of the wash ability distribution across the float fractions in combination with top size and fines generated when crushing to that top size.

Twinning therefore can tie and validate previous work or it can be used to understand the results of different processes used in the handling and processing of a mineral.

John Koenig
8 months ago
John Koenig 8 months ago

I would also add that twinning an RC hole with a diamond hole can be very useful for confirming structural orientations- more specifically a lot of geologists have a tendency to wireframe ore perpendicular to the drill hole orientations. This can obviously lead to very nasty things when mining begins and it turns out there are multiple east dipping veins instead of a thick west dipping vein as modeled. This is obviously best done with oriented core (such as Reflex ACT III) and a good downhole survey.

Ace Levy
8 months ago
Ace Levy 8 months ago

Tele-viewers can be inserted into RC holes and measures structural information. Diamond drill core is best if you can afford it.