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ODM IM grain separation (NGR modified procedure)

ODM grain separation.  The sample is separated into several size and magnetic fractions, as a precursor to mineral grain identification.  The procedure corresponds to the standard ODM flow chart, with one exception – the dry sieving step prior to heavy liquid separation is NOT performed.

General Methodology:

The bulk sample was weighed on receipt at the laboratory1. The weight is typically about 15 kg. A 500 gram sample was removed and archived2. The remaining sample3 was wet-sieved, to remove the size fraction greater than 2 mm, which was archived4. The size fraction below 2 mm5 was separated using a Deister Diagonal-Deck Concentrating Table, model no. 15S, with a deck cover and riffles custom-built by ODM. The silt-sized gold grains were cleanly separated from the other material at this stage, by virtue of their size and density. If the sample contained more than 5-10 gold grains, it was re-tabled, to ensure a more complete recovery of the gold grains.  The table reject was re-tabled to ensure a more complete recovery of kimberlite indicator minerals (KIMs) and magmatic massive sulphide indicator minerals (MMSIMs). The gold grains were counted and classified according to angularity, and then added back into the table concentrate. The light fraction from the table separation was stored6.

[The table concentrate was NOT sieved to remove the fraction below 0.25 mm, suitable for geochemical analysis7.]  The entire table concentrate from both tabling runs was separated in methylene iodide diluted with acetone to S.G. 3.20 to recover heavy minerals. The light fraction was stored8. A hand-held magnet was used to separate the ferromagnetic fraction from the heavy fraction9. The non-ferromagnetic fraction10 was sieved to remove the <0.25mm fraction, for geochemical analysis11, thus leaving any natural oxidation in the sample for analysis. The >0.25 mm fraction was washed with oxalic acid (C2H2O4), to remove any oxidized coatings). The sample was sieved again and the washed-off material was stored12. The remaining material was sieved into three size fractions (0.25-0.5 mm, 0.5-1.0mm and 1.0-2.0 mm) 13,14,15. The 0.25-0.5 mm size fraction was then separated using a high intensity lift-type induced roll separator (Carpco Model MLH (13) 111-5). The strongly paramagnetic fraction was removed first (current set to 0.6 Amp) 16, then the moderately paramagnetic fraction (0.8 Amp) 17, and finally the weakly paramagnetic fraction (1.0 Amp) 18, leaving behind the non-paramagnetic fraction19. The different paramagnetic fractions were visually inspected, and major mineralogical components (>15%) were identified for the strongly paramagnetic and non-paramagnetic fractions. These were recorded as the “input assemblage” for indicator mineral identification.


Sample List:

1. Bulk Received

2. Character sample

3. Table Split

4. Oversize fraction (>2 mm clasts)

5. Table Feed

6. Light fraction (table)

7. < 0.25 mm fraction (pre heavy liquid)

8. Light fraction (heavy liquid)

9. Ferromagnetic fraction

10. Non-ferromagnetic fraction

11. < 0.25 mm fraction (post heavy liquid)

12. < 0.25 mm fraction (wash)

13. 0.25-0.5 mm fraction

14. 0.5-1.0 mm fraction

15. 1.0-2.0 mm fraction

16. < 0.6 Amp fraction

17. 0.6-0.8 Amp fraction

18. 0.8-1.0 Amp fraction

19. >1.0 Amp fraction


Instrument: unstated

Sample material: solid

Sample weight: unstated

Analytical Technique:

Hierarchical classification

Technique >> Physical techniques >> Mineral grain separation



Analytical Decomposition:

Hierarchical classification

Decomposition >> None



Analytical Methods:

IndexMethod OrderMethod IDQuantityDetection Limit
1  6001     Wt_BulkRec 
2  6002     Wt_CharSmp 
3  6003     Wt_TblSplt 
4  6004     Wt_OvrSize 
5  6005     Wt_TblFeed 
6  6006     Wt_LgtFrac 
7  6007     Wt_Fn_Pre 
8  6008     Wt_Lght_HL 
9  6009     Wt_Ferr 
10  10  6010     Wt_NonFerr 
11  11  6011     Wt_Fn_Post 
12  12  6012     Wt_Fn_Wash 
13  13  6013     Wt_25_50 
14  14  6014     Wt_50_100 
15  15  6015     Wt_100_200 

Associated Analytical Packages:

IndexPackage IDPackage Name
1  1     ODM IM processing (NGR: modified procedure)
2  182     ODM IM processing (standard KIM and MMSIM procedure), plus 100 grain count
3  232     ODM HMC processing and Indicator Mineral Identification (NGR KIM + MMSIM)
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