Analytical Package Metadata

Reconciliation of picked, probed and confirmed indicator mineral grain counts (ODM)

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Download analytical data for this package in one of three formats, depending on the desired convention for treating values below the lower detection limit:

Analytical Package Description

Laboratory: No laboratory was required

Kimberlite indicator mineral grain counts reported by Overburden Drilling Management are presented alongside the number of grains analysed by microprobe, and the mineral identifications assigned based on the microprobe analysis.

Indicator mineral identification typically involves an initial picking phase, using a binocular microscope, followed by electron microprobe analysis to confirm the identification and gain additional data on the mineral chemistry.  The picked grains are often referred to as “potential” indicator minerals, prior to confirmation by microprobe.  In order to evaluate the data quality, it is useful to know how many of the picked grains were analysed by microprobe, and how many were confirmed to correspond to what was picked.

In general, reports do not explicitly include this information, but it may be possible to deduce it, subject to the following caveats:

  • The list of grains that were searched for by the picking laboratory should be known.  Grains may be searched for, but not found, and hence not reported.  This is commonly the case for diamond – always looked for, but very rarely found.  Ideally, detailed criteria for the searching should be known.  For example, when searching for garnets, what are the criteria for discriminating based on colour (e.g. did the lab distinguish between purple and red garnets?).  In a typical kimberlite indicator mineral picking, only six or seven different kinds of grains will be picked (peridotitic (purple) garnet, eclogitic (orange) garnet, chrome diopside (green), ilmenite, chromite, forsterite, diamond).  Other kinds of indicator mineral picking may yield a much greater variety of picked grains.
  • The picked grains are usually mounted in epoxy on 25 mm diameter lucite disks, with several hundred grains on a single disk.  A “map” is created by the mounting laboratory, referencing the original grain ID with its position on the mount.  The map is needed to link the picked grain to the probe analysis.  In practice, these maps are very rarely published, making it impossible to unequivocally associate a specific picked grain with a probe analysis.
  • The microprobe analysis returns a “complete” analysis of major oxides in the grain, which should sum to almost 100% for most minerals.  It is then possible to make a good guess about the identity of the mineral.  It is sometimes difficult to make a positive identification because (a) many minerals form complex solid solutions, and (b) some components (e.g. carbonate, phosphate) cannot be analysed by electron microprobe.
  • Classification of mineral identities may vary according to the requirements of the study.  For example, what are the chromium concentrations that separate low-chrome-diopside from chrome diopside from high-chrome diopside?  Should low-chrome diopside be considered a KIM?

This package corresponds to the standard ODM set of six picked grains, namely “purple garnet”, “orange garnet”, chrome diopside, chromite, ilmenite, and forsterite.

Analytical Suites:

1  Reconciliation of picked, probed and confirmed indicator mineral grain counts (Overburden Drilling Management). ( Picked grains )
2  Reconciliation of picked, probed and confirmed indicator mineral grain counts (Overburden Drilling Management). ( Probed grains )
3  Reconciliation of picked, probed and confirmed indicator mineral grain counts (Overburden Drilling Management). ( Confirmed grains )

Analytical Methods:

IndexColumn NameSuite OrderMethod OrderSuite RepeatQuantityUnitsDetermination Limit
1  GP_1    KIM GP  count  
2  GO_1    KIM GO  count  
3  DC_1    KIM DC  count  
4  IL_1    KIM IM  count  
5  CR_1    KIM CR  count  
6  OL_1    Ol  count  
7  GP_2    KIM GP  count  
8  GO_2    KIM GO  count  
9  DC_2    KIM DC  count  
10  IL_2    KIM IM  count  
11  CR_2    KIM CR  count  
12  OL_2    Ol  count  
13  GP_3    KIM GP  count  
14  GO_3    KIM GO  count  
15  DC_3    KIM DC  count  
16  IL_3    KIM IM  count  
17  CR_3    KIM CR  count  
18  OL_3    Ol  count  

Associated Analytical Sample Bundles:

IndexBundle IDBundle NameYear
1  310004     C-NGO 2005/2007 Boothia Peninsula HMC samples: Picked Grain Probe Checks   2008
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