HMC <0.25 mm fraction (post-heavy liquid)

Keyword Definition

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


Category: Sample preparation procedures

Keywords corresponding to sample preparation procedures. Taken from the “Sample_Preparation_Methodss_SHARED” database table.

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