PEREGRINEDIAMONDS LTD.
MINERAL SERVICES
An MS Group BusinessM.C. BaumgartnerM. Harder C.M. Hetman J. Pell
REFERENCESSweet, A.R., Stasiuk, L.D., Nassichuk, W.W., Catuneanu, O., McIntyre, D.J., 1998. Paleontology and diamonds: geological environments associated with kimberlite emplacement, Lac deGras, Northwest Territories, Canada. In: ExtendedAbstracts of the VIIIth International Kimberlite Conference, Victoria.Abstract FLA_0086.
Doyle, B.J., Kivi, K., Scott Smith, B.H., 1999. The Tli Kwi Cho (DO27 and DO18) Diamondiferous Kimberlite Complex, Northwest Territories, Canada. In: Proceedings of the VIIthInternational Kimberlite Conference, Cape Town. Vol 1, 194-204.
Harder, M., Hetman, C.M., Scott Smith, B.H., Pell, J., Baumgartner, M.C., This Volume. The evolution of geological models for the DO-27 kimberlite, NWT, Canada: implications forevaluation.
ACKNOWLEDGEMENTSThe authors would like to thank Meilani Smith and Deanna Hanchar for their draftingassistance in preparing this contribution.
PIPE FORMATION AND DEPOSITIONALPROCESSES
Legend
Mud Cover Sediments
Mud-rich Kimberlite
Water
Glacier
Eruption ColumnGranitoid
Pyroclastic Kimberlite
Coherent Kimberlite Fractured granite
7
�Continental glaciers cover the area,removing the Cretacous/Paleocenemudstones and likely the uppermostportion of the pipe.
6
�
�
Following cessation of the eruption,the crater rim erodes by sedimentaryprocessesA crater lake forms, and minorsedimentation into the crater lakeoccurs.
5
�
�
The crater rim continues to grow andto erode into the crater.Zones dominated by resedimentedkimberlite become more commonand larger. These zones areconcentrated near the pipe walls.
4
�
�
As the crater rim grows, this material,including juvenile and mud-richkimberlite and surface mud, locallyfalls into the crater by mass wasting.The pipe is progressively infilled bypyroclastic kimberlite, likely bycolumn collapse events into the pipe.
3
�
�
A crater rim starts to develop aroundthe vent. Pyroclastic fall and flowsare likely the dominant volcanicdeposition mechanisms.Zones of fractured/pulverizedcountry-rock locally fall into the pipe,increasing the pipe diameter.
2
�
�
The kimberlite breaches surfacecreat ing a pyroclast ic cloudcomprising kimberlitic ash, granitefragments, and mud.The marginal country-rock continuesto fracture as the pipe develops.
1
�
�
Pre-pipe fracturing of country-rockgranite; intrusive coherent kimberliteis present to the south of the pipe.The surface at the time of eruptionwas terrestrial with a thin veneer ofCretaceous mudstones.
DISCUSSION�
�
�
�
Although DO-18 is similar to most Lac de Gras kimberlites in pipe morphology and thepresence of mud-rich resedimented kimberlite, DO-18 is atypical in the high proportion ofaccessory granite and locally developed country-rock breccias. DO-18 is furthercharacterised by common unbroken olivine grains and locally common kimberlitic ash.
The energy of volcanic explosions producing and infilling the DO-18 pipe was insufficient toeffectively break all olivine grains. The eruption column was likely not high enough orsustained for long enough to allow for dispersal of the country-rock granitic material andkimberlitic ash to significant distances from the vent.
The marginal breccias likely represent the remnant products of pipe formation andexcavation processes that did not efficiently ream out the pipe prior to infilling.
DO-18 is interpreted to have been excavated and infilled by a relatively low-energy, shortlived volcanic eruption dominated by one kimberlite phase (pulse of magma from themantle).
Mineral Abundances
653
55
664
468
141
0
522
00
200
400
600
800
1000
Garnet Chromite Ilmenite Cr Diopside
Mineral Type
Pyroclastic Kimberlite Resedimented Kimberlite
30
0-4
25
um
gra
ins
pe
rkg
All Garnet
CaO (wt%)
0 2 4 6 8 10 120
2
4
6
8
10
12
14
16Pyroclastic KimberliteResedimented Kimberlite
G10D
G10 / G10D
G12G9 / G11
G3 / G4
Cr
O(w
t%)
23
�
�
Mantle indicator mineral chemistryindicates that the pyroclastic andresedimented kimberlite sampled thesame mantle material.
Any differences in the indicator mineral,and therefore diamond, distributionbetween these two rock types is thereforelikely dependent on the volcanicprocesses involved in deposition of thekimberlite rock types.
Pyroclastic KimberliteRelative Abundance
9%
86%
2%
3%
<1%
G10D Peridotite Megacryst Low-Cr Low-Cr D
Garnet Paragenesis
Resedimented KimberliteRelative Abundance
7%
89%
2%
2%
<1%
MINERAL CHEMISTRY
300 m
0 m
VOLCANICLASTICKIMBERLITE
NorthSouth
200 m
Lower Confidence SolidBelow 200 m
?
?
?
?
0 50 100 m
A A’
PYROCLASTICKIMBERLITE
RESEDIMENTEDVOLCANICLASTIC
KIMBERLITE
0 50 100 m
B B’
RESEDIMENTEDVOLCANICLASTIC
KIMBERLITE
PYROCLASTICKIMBERLITE
GEOLOGICAL MODEL
�
�
The DO-18 kimberlite is oval in plan view with inward-tapering, steep-sided pipe walls.
Pyroclastic kimberlite is the volumetrically dominant rock type, with lenses of resedimentedvolcaniclastic kimberlite.
4 hectareDO-18 pipe
outline
Drill Trace
Drill Collar
TILL
GRANITE
TILL
GRANITE
1.7 mm
C)
olivine
granitexenocrysts
mud
1 cm
A)
PK
RVK
1.7 mm
B)
olivine
granitexenocryst
mud
1.7 mm
E) olivine
granitexenocrysts
juvenilemagmaclast
mud
1 cm
C)
mud
granite
1.7 mm
F)
olivine
granitexenocryst
mud
mud
1.7 mm
D) olivine
granitexenocrysts
juvenilemagmaclast
1 cm
B)
1 cm
A)
mud
granite
OTHER RESEDIMENTED KIMBERLITE
�Highly variable, very mud-rich kimberlite is present as lenseswithin the PK and as late-stage crater infill.
Figure 3: A) Drill core photograph showing mud-rich RVK; softsediment mixing of different types of mud is common;B) Photomicrograph comprising common brown mud clasts and freshgranitic xenocrysts.
1.7 mm
B)
olivine
granitexenocrysts
mud
mud
1 cm
A)
mud
RVK
very mud-rich RVK
granite
RESEDIMENTED VOLCANICLASTIC KIMBERLITE
�
�
Resedimented volcaniclastic kimberlite (RVK) containing ahigh proportion of unbroken olivines and kimberlitic ash.
This domain is variable and comprises coarser-grained beds aswell as quartz, mud, or kimberlitic ash-rich beds.
Figure 2: A) Drill core photographcomparing PK (top two core slabs)with mud-rich RVK (bottom two coreslabs); B) Photomicrograph showingcommon unbroken olivines; C)Photomicrograph showing commonfresh granitic xenocrysts.
PYROCLASTIC KIMBERLITE
�
�
Dominant rock type infilling the DO-18 pipe, characterised by ahigh proportion of accessory granite (<25%, locally >75%).
Olivine-rich, juvenile magmaclast-bearing, generally massivepyroclastic kimberlite (PK).
Figure 1: A, B, C) Drill core photographs showing common accessorygranite and mud clasts; D, E, F) Photomicrographs comprising olivine,magmaclasts, granitic xenocrysts, and mud clasts.
�
�
�
DO-18 was emplaced intoArchean granitoids and an overlyingveneer of now eroded mudstones.
Palynology dating of these mudstones indicates DO-18 to beLate Cretaceous to Paleocene in age.
DO-18 is atypical of other Lac de Gras kimberlites due to thehigh abundance of accessory country-rock granite xenolithsand locally preserved marginal country-rock breccias.
INTRODUCTION
The Preliminary Geology of the DO-18 Kimberlite,Lac de Gras Kimberlite Province, Canada
The Preliminary Geology of the DO-18 Kimberlite,Lac de Gras Kimberlite Province, Canada
M. Harder , C.M. Hetman , M.C. Baumgartner , J. Pell1 1 1 2
1 2Mineral Services Canada Inc., North Vancouver, BC; Peregrine Diamonds Ltd., Vancouver, BC, Canada
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