Hello Eric., I find it interesting concerning the Arctic Islands and kimberlite occurances., yes I think the Wyoming rock groups., and lamphroites are similiar to the Zimbabwee occurances as well., a nice
source of information on rock types comparisions., of early rock groups are documented in some research on the internet. What I
was wondering concerning the Arctic Isle kimberlites., is a very basic
question., specifically towards the Victoria Island geology. Aber has
a very large land base spanning the island., Northern areas. which
are Proterozoic Sedementary rocks., with Proterozoic Mafic Volcanics., a map I am looking at shows what appears to be a major
tectonic fault transversing the property., and assuming this was staked by Aber sometime ago based on the nickel prospects.
As I understand it., and may be wrong., which you could clarify.,
as land masses are closer to the polar regions., more seismic activity
faulting occurrs., looking at the area on this map., I see a major fault
transversing the property. We have Mackenzie Dyke swarms eminating as well., the inference is being made that Debeers pipes
(4 diamond bearing) and Major Generals pipes., run along this Mackenzie dyke swarm. to the east of Major Generals property there
is Archean rock outcrops., as well as to the far North., on the S.E
corner of Abers block. the word I have heard is that the Archean basement rocks outcropped in 3 locations. Unfortunately.,
I have been unable to confirm this in any published data. It is as well
stated that these outcrops have been age dated.,2.6bil years.,
I see there is no oil drilling in the past to substantiate the age of these
rocks., a conversation with Glen S of Major General has led me to
believe that DeBeers has age dated these occurances. My next question., is who debunked the potential of VI in 94., i.e. the
"industry experts." My personal view is that the pipes probably did
sample the archean basement rocks., the chromite counts of 63.4%
look to support that theory., the nickel thermal window is encouraging., and the dyke swarms transecting the property as well
encourages me to believe a major diamond bearing province is unfolding before my very eyes. The archean rock outcrops appear
on the literature around 30 miles east of Majors east corner of the
property., as I understand it., a 5km area surrounding the property remains in the JV agreement., and the additional 160,000 acre parcel
adjoins the property towards the Archean outcropped area.
Seeing petrological samples havent been reported as yet., and knowing the secrecy of DeBeers in publishing geologic information until they see fit., I was wondering what your thoughts are concerning
the potential of VI to host both significant diamond and nickel deposits.? The area outcropped I am told is the Washhburn lake area. Is this information available from the GSC. literature.?
Also how does the carbonate platform and shaler rock groups affect
the ease of discovery vs., heavy overburden and em responses.
Would polar influences be a detriment or an asset in discerning slight
EM responses., or should the bulleyes signatures be very prevelant
in this type of rock group and carbonate platform.?
Sincerely
George J. Tromp
DCHRReport
Miner450@aol.com
Is this the reason the "industry experts" debunked the potential of
Victoria Island to host major kimberlite fields., because they couldnt
document the Archean basement rocks.????
Secular Evolution of Sub-Continental Mantle: Geophysical Effects
W L Griffin (GEMOC, Macquarie Univ., Sydney 2109, and CSIRO-EM, Box 136, NSW 2113, Australia)
S Y O'Reilly, O Gaul, D Ionov (all at GEMOC, Earth Sciences, Macquarie Univ., Sydney 2109, Australia) and C G Ryan (CSIRO-EM, P.O. Box 136, NSW 2113, Australia)
Lithosphere mapping using garnet concentrates from kimberlites and other volcanic rocks shows consistent differences between Archean and younger lithosphere. Mantle sections beneath Archean terranes contain 10-60% garnet harzburgites, typically concentrated between 140 to 180 km depth and interspersed with depleted lherzolites. In Proterozoic and Phanerozoic sections, harzburgitic rocks are rare, and the dominant lherzolitic garnets are less depleted in LIL and HFSE elements. Lherzolitic garnets from Archean sections have high mean Zr/Y (³5) and low mean Y/Ga (<3), those from Phanerozoic areas have low mean Zr/Y (²1) and high mean Y/Ga (³4), and garnets from Proterozoic sections have intermediate values. Xenolith data and numerical modelling based on partition coefficients indicate that these differences reflect an increase in the average Cpx/Gnt ratio and the average modal (Cpx+Gnt) content of lithospheric mantle from Archean to Phanerozoic time.
The compositional evolution outlined here will result in differences in seismic signature between areas with mantle of different tectonothermal age. Typical Archean and Phanerozoic lherzolites have Vp of 8.1 and 7.8 km/sec at 600°C. At 1000°C the difference in Vp decreases to 7.8 and 7.6 respectively. If the harzburgitic component is considered, the average velocities beneath Archean cratons will be lowered further. The keels with high Vs and Vp, extending to depths of 250-450 km beneath the older (>1.7 Ga) parts of many cratons, commonly are interpreted as cooler than the mantle beneath younger cratons and Phanerozoic mobile belts, which have no significant Vs anomalies. However, at least part of the difference in seismic signature may be related to compositional differences. The harzburgites and highly depleted lherzolites of Archean mantle will contribute to the Vs and Vp anomaly beneath the >2.5 Ga cratons, but the roots of Early Proterozoic cratons do not contain such rocks; this suggests that moderately depleted lherzolites also can provide a seismic anomaly. In areas where Archean lithospheric mantle has been replaced by Phanerozoic material, dramatic changes in the seismic and gravity signatures and topography can occur, reflecting changes in both the density and the thermal state of the lithospheric mantle. An example is the eastern part of the Sino-Korean Craton (Griffin et al. 1996), |
