GEOLOGICAL SURVEY OF CANADA OPEN FILE 5876
Petrology of kimberlite debris from the GSC showing, Amaruk Kimberlite Field (NTS 57A/03), Kitikmeot region, Nunavut, Canada
H.A. Sandeman and J.J. Ryan
2008
Natural Resources Canada
Ressources naturelles Canada
GEOLOGICAL SURVEY OF CANADA OPEN FILE 5876
Petrology of kimberlite debris from the GSC showing, Amaruk Kimberlite Field (NTS 57A/03), Kitikmeot region, Nunavut, Canada
H.A. Sandeman and J.J. Ryan
2008
©Her Majesty the Queen in the Right of Canada 2008 Available from Geological Survey of Canada 625 Robson St. Vancouver, British Columbia, V6B 5J3
Sandeman, H.A. and Ryan, J.J., 2008: Petrology of kimberlite debris from the GSC showing, Amaruk Kimberlite Field (NTS 57A/03), Kitikmeot region, Nunavut, Canada, Open File 5876, 20 p.
Open files are products that have not gone through the GSC formal publication process.
Hamish A.I. Sandeman: Northwest Territories Geoscience Office, P.O. Box 1500, 4601-B 52nd Avenue Yellowknife, NT, X1A 2R3;
[email protected] James J. Ryan: Geological Survey of Canada, 625 Robson St., Vancouver, British Columbia, V6B 5J3;
[email protected]
Table of Contents Abstract ..................................................................................................................................... 1 Introduction............................................................................................................................... 1 Analytical methods ................................................................................................................... 4 SGS Lakefield methodology................................................................................................. 4 University of Alberta methods.............................................................................................. 4 Petrography ............................................................................................................................... 4 Mineral Chemistry .................................................................................................................... 7 Garnet chemistry................................................................................................................... 7 Chrome spinel chemistry ...................................................................................................... 7 Ilmenite chemistry ................................................................................................................ 8 Conclusions............................................................................................................................. 13 Acknowledgements................................................................................................................. 13 References............................................................................................................................... 14
List of Figures Figure 1: Simplified geological map of the western Churchill Province Figure 2: Photographs a & b Figure 3: Diamond indicator mineral extraction flowsheet Figure 4: Photomicrographs a-d Figure 5: Ca/(Ca+Mg) versus Mg/(Mg+Fe) plot Figure 6: Garnets plotted in the Cr2O3 versus CaO (wt. %) diagram Figure 7: Plot of Cr/(Cr+Al) versus Fe2+/(Fe2++Mg2+) for spinel Figure 8: Cr2O3 versus MgO (wt. %) for chrome spinel Figure 9: Cr2O3 versus MgO (wt. %) for ilmenite Figure 10: Plot of TiO2 versus MgO (wt. %) for ilmenites Figure 11: Ternary plot of ilmenites in ilmenite-geikielite-hematite space
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List of Appendices Appendix 1: Kimberlite indicator mineral picking results Appendix 2: Electron microprobe data for reference materials Appendix 3: Electron microprobe data for GSC kimberlite debris
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Abstract Kimberlite debris was discovered on a regional geological traverse in 2005 by geologists of the Geological Survey of Canada’s Boothia Integrated Geoscience Project. Petrographic and mineral chemical data indicate that the debris comprises an ‘archetypal’, Group I, segregation textured serpentine-calcite kimberlite. Heavy mineral separates and petrographic studies indicate that the kimberlite contains common ilmenite nacrocrysts, and peridotite paragenesis garnets of both lherzolitic G9 and sheared high-TiO2 G11 types. Chrome spinels are not common and have MgO and Cr2O3 contents less than those from other known diamond intergrowths and diamond inclusions. Ilmenites form rounded macrocrysts and anhedral groundmass grains and exhibit complex compositional variations. Ilmenite macrocryst compositions mimic those of Mitchell (1986) although trending to slightly higher Fe2O3. Ilmenite mantles on the macrocrysts are MgO-rich and Cr2O3poor, whereas groundmass ilmenites are MgO and Cr2O3 rich. These observations suggest a three phase evolution for the kimberlite: 1) entrapment and disaggregation of ilmenite macro/megacrystic-bearing lherzolitic lithospheric mantle in a kimberlitic magma; 2) reequilibration of these mantle xenocrysts during magmatic ascent through the lithosphere and; 3) crystallization of small groundmass ilmenite during final emplacement and cooling of the kimberlite.
Introduction The Boothia Integrated Geoscience Project (BIGP) is a multi-year, collaborative mapping project in the Boothia mainland area (Fig. 1), Kitikmeot Region, Nunavut, jointly funded by Geological Survey of Canada’s (GSC) Northern Resources Development Program, the CanadaNunavut Geoscience Office (CNGO), the Polar Continental Shelf Project, and university partners. The main focus of the project entails 1:250,000 scale bedrock mapping (see Ryan et al., 2008a, 2008b) of the region covering parts of NTS map sheets Pelly Bay (57A), Rae Strait (57B), Spence Bay (57C) and Harrison Island (57D), to elucidate the gold and base metal potential of this generally underexplored region. In concert with the bedrock mapping, detailed local surficial mapping and regional ice-flow studies supported a regional update of the Quaternary geology of Boothia mainland area, wherein a complex, four stage ice-flow history was resolved (Tremblay et al., 2007). As Diamond Geologist for the Northwest Territories and Nunavut, the first author’s role in the project is to help investigate and document the diamond potential of this portion of the northwest Rae domain of the western Churchill Province, a region that saw a diamond exploration staking rush in 2004. Prior to that time, the Churchill Province had received little diamond exploration attention because of a widely held perception that its subcontinental lithosphere was probably extensively reworked in the Paleoproterozoic, potentially lessoning or even destroying its ability to produce diamondiferous kimberlites. Recent discoveries of diamondiferous kimberlites in the northwestern Churchill Province (e.g., Diamonds North Resources’ Amaruk property (http://www.diamondsnorthresources.com/s/Amaruk.asp) and Stornoway Diamond Corporation’s Aviat property (http://www.stornowaydiamonds.com/advanced/aviat/) has, however, greatly changed this perception. Kimberlite debris was discovered on a regional (12 km long) traverse by two field assistants (Jamie Kraft and Jenrene Martel) in NTS 57A/03 on July 8th, 2005 at field station 05RAYJM-011 (located at 68.09330 N, 90.51179 W; Fig. 1); an exciting and historically uncommon find for a regional geological survey crew. Senior geologists from the project revisited the site on July 17th, 1
Figure 1: Simplified geological map of the region showing the location of the GSC kimberlite debris in comparison to the location of other kimberlite fields in the region. Also shown are the major lithotectonic features of the western Churchill Province. Key: star – GSC kimberlite; dots – known kimberlite clusters; BB – Barclay Belt; CB – Committee Bay Belt; WB – Woodburn Belt; MB – MacQuoid Belt; RB – Rankin Inlet Belt; KB – Kaminak Belt; YB – Yathkyed Belt; STZ – Snowbird Tectonic Zone; WBsz – Wager Bay shear zone; AMsz – Amer shear zone.
2005 and carefully prospected a ca. 500 m2 area around these coordinates. The second visit located numerous, subangular, 5 to 20 cm-scale fragments of olive green kimberlite intermixed with more abundant granitoid detritus (Fig. 2a) that blankets the glacial till. The kimberlite float was concentrated in a series of small, rocky frost boils on the south-southwest side of an elongate, narrow, east-southeast-trending valley, and along the base of the northern slope of a rocky ridge also trending east-southeast (Fig. 2b). A ca. 3 kg sample of the kimberlite was collected at station 05RAYHS-068 (68.09333 N latitude, 90.51197 W longitude) for petrographic examination, as well as for crushing and extraction of kimberlite indicator minerals (KIMs). A till sample was also collected from this site for KIM analysis, the results of which will be published in a later open file report as part of a regional reconnaissance survey (Tremblay et al., in prep.).
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Figure 2: a) Photograph of a number of fist-sized kimberlite fragments (K) at location 05RAYHS-068 along with more typical foliated granitoid clasts (G). Geological pick for scale. b) Photograph outlining the local topography and outcrop extent around the kimberlite debris locality. View is to the west-northwest.
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Analytical methods SGS Lakefield methodology The ca. 3 Kg sample was sent to SGS Lakefield Research (http://www.met.sgs.com/) for sample processing, picking of kimberlite indicator minerals and, microprobe analysis of the selected KIM grains. For the extraction of KIMs, the sample was crushed and wet screened using a maximum sieve size of 1.68 mm and a minimum sieve size of 0.25 mm. All of the >1.68 mm and 500 g of the 1.1-2 * Mg(Mg/Fe) (Fig. 5). They are all of peridotitic paragenesis having Cr2O3 > 1 wt. % in conjunction with TiO2 ≤ 0.5 wt. %. More specifically, because they also exhibit CaO< 5.9+0.27*Cr2O3 (wt. %), the garnets are of lherzolitic paragenesis. According to the classification scheme of Grutter et al. (2004), the majority of garnets (78%) are lherzolitic, G9 garnets having Cr2O3>10.70
