Hello Will
I left this post on the TWG thread but since most of the conversation is happening here I thought I should copy it.
Here is most of that e-mail I previously referred to but edited where repetition with some other posts on this thread has occurred. Kept a few links you have already seen as others on this thread may not.
The following map shows the distribution of known cratons around the world (there are in fact probably as many as 30 as quite a few remnants have been rifted from the larger ones and in some cases accreted to or subducted under one another - the Slave Craton and especially the Superior Craton are an amalgum of different cratons). Note the North American craton extends under Baffin Island.
mountainprovince.com
The next URL discussed the geology of Nunavut. Note the discussion of rock ages in northern Baffin Island under the Archean heading and under the map half way down. Under that map, note the discussion of rifting, grabens faults and dykes:
canadianrockhound.com
See this slide show at:
instruct.uwo.ca
(In particular read slide 28 and last bullet on slide 35)
This URL discusses the significance of grabens:
ac.by
GEOPHYSICS
Belyashov A., Gavrilov A.
Tectonic control over the pipe field location within Belarus (from geophysical data). pp. 113--117
"Abstract: Some hypotheses for the association of pipe fields with certain tectonic conditions are analyzed in the paper. It was noted that the most part of the ancient East European Platform including the region under review corresponds to Clifford's rule about a correlation between diamond kimberlite occurrences in fields of ancient cratons cut by linear fault structures. Recent geophysical investigations and drilling data were used to describe tectonic conditions in the region of the Zhlobin and Uvarovichi field pipes. In was shown that pipe fields are associated with areas of a triple junction of graben-like structures. It was noted that a "hot point" shown as a heat flow anomaly is located at the junction of the Pripyat Trough, Dnieper-Donets Trough and Klintsov Graben. The analysis of geophysical fields has permitted the authors to suggest that the Chashniki fault extends further south. A possibility of discovering pipe fields in southeastern Belarus and neighbouring areas of Russia and Ukraine has been discussed. "
The geology of Lancaster Sound is covered here:
google.com.
[PDF] CHAPTER 6 -EASTERN ARCTIC LANCASTER SOUND BASIN
File Format: PDF/Adobe Acrobat - View as HTML
... in siz e to the Viking Graben in the North Sea . It contains ... oil. Geological Setting
(Figs. 62-64) Lancaster Sound Basin connects the partially drowned ...
www.inac.gc.ca/oil/Pdf/chapter6.pdf - Similar pages
(Note references to: – "partially drowned interior of north american craton & grabens and half-grabens & Lancaster Sound has not been significantly thinned")
CHAPTER 6 -EASTERN ARCTIC
LANCASTER SOUND BASIN
Age........................
Maximum Basin Thickness....
Discoveries.................
Basin Type.................
Depositional Setting.........
Reservoirs ..................
Regional Structure...........
Seals.......................
Source Rocks...............
Depth to Oil Window.......
Seismic Coverage............
Area.......................
Area under Licence..........
Early Cretaceous(?)-Tertiary over Proterozoic to Paleozoic basement 8 km
None Mesozoic rift basin overlying Proterozoic to Paleozoic basin
floor Fluvio-deltaic to marine ?Cretaceous and Paleogene sandstones, ?Palaeozoic sandstones and carbonates, ?Proterozoic sandstones
Block faulting, half-grabens ?Marine shales ?Lower Cretaceous (gas prone) ?Upper Cretaceous, Paleocene marine shales (oil potential)
Unknown
In excess of 60 000 km of marine seismic form an adequate
seismic grid 13,250 km² 931,640 ha (Exploration Licence held under moratorium)
(Water depths reach 800 m, and are generally in excess of 100 m, except within a narrow coastal zone. Ice cover extends from October to late June. Icebergs are common.)
This undrilled basin is a Mesozoic and Cenozoic rift basin comparable in size to the Viking Graben in the North Sea. It contains numerous block faulted structures identified on the basis of an extensive seismic grid. The basin stratigraphy is expected to include Cretaceous and Tertiary reservoir rocks, and mature source rocks for both gas and oil.
Geological Setting (Figs. 62-64)
Lancaster Sound Basin connects the partially drowned interior of the North American craton - the Canadian Arctic Islands - with Baffin Bay and the North Atlantic.
The basin originated as a rift at the northwestern end of Baffin Bay. Unlike Baffin Bay, the continental crust in Lancaster Sound has not been significantly thinned and no sea-floor spreading has taken place. The fill of the basin consists of Mesozoic, Tertiary and Quaternary sediments and is bordered to the north and south by Proterozoic and lower Paleozoic rocks exposed on Devon Island to the north and on Bylot Island and the Borden Peninsula of Baffin Island to the south. In cross-section, the basin is a half-graben with the basin axis adjacent to the Devon Fault. The displacement of several thousand metres on this fault throws Proterozoic
rocks exposed on Devon island against Mesozoic to Tertiary basin-fill. The basin shallows to the west into Barrow Strait and also to the east across the Sherrard Ridge, which acts as a sill separating Lancaster Sound
and Baffin Bay basins."
Regarding erosion see:
sts.gsc.nrcan.gc.ca
Note: "Glacial erosion has been negligible, leaving the old features largely intact."
Preglacial plateau and gorges, northern Brodeur Peninsula.
This broad flat plateau covers much of northern Baffin Island (and parts of adjacent areas). It is a relic of a regionally extensive erosion surface (or peneplain) which was cut down to near sea level before the glacial period. The deep river gorges were cut into it as it was lifted to its present level. These drainage systems are thought to have been cut before the inter-island channels were formed. Glacial erosion has been negligible, leaving the old features largely intact.
Several of the abstracts I posted on SI discuss the geochemistry under Sommerset Island 100km to the northwest of Jackson Inlet across Lancaster Sound (which is a graben). It shows the the Somerset kimberlites have the same basic geochemistry as Group 1 kimberlites from the southern Kaapvall Craton.
See the abstracts I left on the SUF SI thread especially:
"The Age of Two cratons: A PGE and Os-Isotopic study of peridotite xenoliths from the Jericho kimberlite (Slave Craton) and the Somerset Island kimberlite field (Churchill Province) G. J. Irvine 1, D. G. Pearson 1 , M. G. Kopylova 2, R. W. Carlson 3, B. A. Kjarsgaard 4, G. Dreibus 5"
Note the following quote:
"1) There is clear evidence of Archean ages for the lithosphere beneath Jericho [17] and Somerset Island. At Jericho both spinel and garnet facies peridotites give Archean model ages. The oldest TRD ages for Somerset Island peridotites are late Archean suggesting the existence of some cratonic lithospheric material beneath this region."
Also see:
instruct.uwo.ca
"Kimberlite Fields of Nunavut
John Armstrong District Geologist, DIAND NWT Geology Division"
Which contains the following quote:
"Somerset/Brodeur
A minimum of 36 kimberlites are known to occur on Somerset Island and have been the topic of numerous published papers, additional kimberlites occur on the Brodeur Peninsula and more recently have been discovered on north Baffin bringing the total number of occurrences so greater tan 40. The majority of these pipes were discovered by Diapros and Cominco in the period 1973-1975. Diapros established a 1-ton/hr processing facility in the vicinity of the Batty kimberlites (n = 21) in the summer of l974,a total of 262.3 tons of kimberlite were sampled and and 215.1 tonns were processed from the Diapron, Batty. Nord, Oucat, Ham. and Elwin kimberlites. Diamonds were recovered from the Nord (0.142 et): Diapros (total etws of 0.0015); and Batty-KI (0.024 and 0.129 et). Kimberlites are typically hypabyssal or diatreme facies and range in age from 105Ma to 88Ma. Studies conducted on mantle xenoliths define a geotherm of approximately 44 mW/m^2 (Kiaragased and Peterson, 1992:
Sebmidheger and Francis, 1999). The transition from lithosphere to asthenosphere at depths of 140 kilometres beneath Somerset Island is suggested by an inflection in the temperature and pressure array defined by mantle peridotites (Selansidherger and Francis, 1999). The presence of diamonds also indicates that kimberlites tapped lithosphere within the diamond stability field, although the lithospheric root is thinner under Somerset Island than in the central Slave craton. Preliminary Re-Os dating of mantle xenoliths have returned some model Arebean dates for material sampled (Irvine et at., 1999)."
Note: TWG's kimberlites must be different (younger or at least less eroded) than those on Somerset Island and else where on the Brodeur Peninsula as they are described in this abstract as "typically hypabyssal or diatreme facies and range in age from 105Ma to 88 Ma" where as the Jackson Inlet kimberlites are largely unerroded tuffascious and diatreme pipes.
These are a few of the Kaapvaal Craton Group 1 kimberlites that Somerset Island kimberlite geochemistry is similar to:
MINE SIZE (at surface) PRODUCTION (to 1993)
Kimberley 3.7 ha 32.7 million carats
Dutoitspan 10.6 ha 21.3 million carats
Bultfontein 9.7 ha 36.2 million carats
Wesselton 8.7 ha 33.6 million carats
De Beers 5.1 ha 36.4 million carats
Mine Dumps - 11.4 million carats
TOTAL 37.8 ha 171.6 million carats
Note: Even at a very modest .22 cpt these smallish Kaapvaal mines were highly profitable due presumably to high stone values.
The following are exerpts from the NM Aug 27, 2001 article (copy attached):
"On the Brodeur Peninsula of Baffin Island, 100 km east of Somerset Island, Twin Mining (TWG-T) has made an extraordinary find at its Jackson Inlet property. Numerous commercial-size gem stones were recovered from surface sampling of the Freightrain kimberlite body. What makes the find extraordinary -- even puzzling -- is that unlike the kimberlites being mined at Lac de Gras and elsewhere in the world, the Jackson Inlet diamonds are reported to differ in their "total absence of boart, rejections, coated and cubes, which are low-grade and low-yield diamonds." No explanation was given for this phenomenon, which is highly unusual, given current geological evidence on diamond distribution."
"The 86 stones were examined by Antwerp-based Diamond Trading N.V., which stated that Freightrain diamonds are "similar to high-quality South African diamonds, but without having their characteristic yellow colouring." In comparison, the Lac de Gras diamonds from the Ekati and Diavik projects are "generally octahedrons with higher occurrences of black piques [impurities] and maccles [intergrown diamond crystals]."
"Twin Mining has recovered a total of 869 stones to date, including microdiamonds, from limited surface sampling on Freightrain. Derbuch told The Northern Miner, during a recent site visit, that no boarts occur in the micros either, though there have been a few cubes.
Derbuch also said there is definitely a bias toward larger stones. Richard Roy, project manager and consultant, concurs that almost half of the +1-mm diamonds are greater than 2 mm. The percentage of large diamonds is unusual, almost double that of known producers in the world.
There also is an apparent gap in the plotting of the size distribution of the microdiamonds recovered last year. "There are two populations of diamonds," Davis explained, "either on an aggregate basis or an individual-sample basis. The micros don't match the macros. There has been a sampling of two sources [by the kimberlite]."
He added that there is a population of small stones (up to the 0.6-mm size fraction) that are separated from a population of larger +1-mm stones by three size fractions where only a sparse number of diamonds have been recovered. While it is possible in a single kimberlite to find multiple populations of diamond sizes, it's unusual for the populations not to overlap."
"Lakefield Research produced heavy mineral concentrates from 8-to-10-kg samples of kimberlite taken from 10 sites on the Freightrain body. The riffled samples contained anywhere from 60 to 120 grains of chromite and 90-125 grains of garnet. The grains were then probed. An average of 28% of the garnets are classified as sub-calcic, G10 chromium pyrope, whereas an average of 5% are high-pressure eclogitic garnets. An interpretation of the chromite data by Lakefield shows that an average of 46% of the chromites fall within the diamond inclusion field."
This quote is from TWG's 2000 AR which quotes Lakefield Research's heavy mineral analylical results from Freighttrain:
"The majority of grains selected have either a peridotitic or eclogitic parantage."
"Between 14% and 68% of the chromite compositions plot within the compositional field of world-wide chromite inclusions in diamond, with an average of 46%."
"Between 9% and 56% (avg 28%) of the garnets are classified as sub calcic, G10 Cr-pyrope and between 0% and 12% (avg. 5%) as high pressure eclogitic garnet, both of which are similar to compositions of garnet inclusions in diamond worldwide."
"The data compares very favourably with kimberlite pipes under development elsewhere in Canada. Diavik's A154S pipe grades approx. 4.5 c/t and contains about 28% chromite and 23.5% G10's. A154N (2.2c/t), A21 (2.7 c/t) and A418 (4 c/t) grade 23.6%, 15.9% and 10.2% G10's respectively."
"In the RSA concentrates from Finsch (.9c/t), Premier (.3 c/t) and Newlands (.65 c/t) contain 42.2%, 18.9% and 23.8% G10's respectively."
I presume nobody is going to question the motives or voracity of Lakefield Research...
In that respect, I also find it interesting that according the Aug 27th NM article, LR actually brought the JI claims (Freighttrain) to the attention of TWG's oft maligned President. This suggests to me that LR must have been fairly intrigued by the sample data submitted by the bush pilot who originally staked it and must have had some reason for choosing Mr. Derbuch rather than some more obvious candidates. In my mind that speaks well of HD.
I'll pass along a few more links on another post Will.
Bottom line: I like the numbers...
Regards
Vaughn |
