Twin has compared some of their geochemistry with other pipes in their 2000 annual report. As I stumble on others I will send them along.
At Lakefield Research, heavy mineral concentrates
were produced from representative 8 to 10 kg
samples of kimberlite from ten sites in the
Jackson Inlet cluster, through a combination of
staged crushing, wet screening and dense media
(DMS) separation. Minerals were picked from
riffled aliquots of concentrates using a binocular
microscope. The riffled samples were of sufficient
size to contain from 60 to 120 grains of chromite
and from 90 to 125 grains of garnet. Chromite
and garnet grains were mounted in epoxy and
analysed for major and minor element contents
by electron microprobe (JEOL 733 Superprobe)
under standard operating conditions. The data
was interpreted using industry-standard bi-variate
plots and data classification schemes published
by, Sobolev (1973), Dawson and Stephens
(1975), Gurney (1985), Fipke et al. (1995)
and Schulze (1997). The majority of grains selected have either a
peridotitic or eclogitic parentage. Interpretation of the chromite data shows that for
the ten sample sites, between 14% and 68% of
the chromite compositions plot within the compo-
sitional field of world-wide chromite inclusions in
diamond, with an average of about 46%. Interpretation of the garnet data shows that
between 9% and 56% (ave. 28%) of the garnets
are classified as sub-calcic, G10 Cr-pyrope and
between 0% and 12% (ave. 5%) as high pressure
eclogitic garnet, both of which are similar to the
compositions of garnet inclusions in diamond as
determined from a world-wide database.
This data compares very favourably with kimberlite
pipes under development elsewhere in Canada.
For example, Diavik's A154S pipe which grades
approximately 4.5 ct/t, contains about 28% dia-
mond-inclusion chromite and 23.5% sub-calcic,
G10 Cr-pyrope. In addition, A154N (~2.2 ct/t),
A21 (~2.7 ct/t) and A418 (~4.0 ct/t), three other
pipes in Diavik's mining plan contain 23.6%,
15.9% and 10.2% sub-calcic, G10 Cr-pyrope,
respectively. Data for the proportion of high-
pressure eclogite and chromite have not been
published for these kimberlites. In South Africa, mineral concentrates produced
from kimberlite at the Finsch (~ 0.9 ct/t),
Premier (0.3 ct/t) and Newlands (0.65 ct/t)
Mines contain 42.2%, 18.9% and 23.8%,
sub-calcic, G10 Cr-pyrope, respectively. |
