Electronic Appendix-Analytical methods

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1 Electronic Appendix-Analytical methods A1. U-Pb Geochronology: Analytical Techniques and Data Interpretation All sample preparation, geochemical separations and mass spectrometry were done at the Pacific Centre for Isotopic and Geochemical Research in the Department of Earth and Ocean Sciences, University of British Columbia. Zircon was separated from samples using conventional crushing, grinding, and Wilfley table techniques, followed by final concentration using heavy liquids and magnetic separations. Mineral fractions for analysis were selected on the basis of grain quality, size, magnetic susceptibility and morphology. All zircon was pretreated (chemical abrasion) employing the technique outlined in Scoates and Friedman (2008). Single zircon grains were then dissolved in subboiled 48% HF and 14 M HNO 3 (ratio of ~10:1, respectively, ~75 ml total) in the presence of a mixed U- 205 Pb tracer; zircons for 40 hours at 240 C in 300 ml PFA or PTFE teflon microcapsules contained in high pressure vessels (Parr acid digestion vessels with 125 ml PTFE liners). Sample solutions were then dried to salts at ~130 C. Zircon residues were re-dissolved in ~50 ml of sub-boiled 6.2 M HCl for 12 hours at 210 C in high pressure vessels. These solutions were transferred to 7 ml PFA beakers, dried to a small droplet after addition of 2 ml of 0.5 N H 3 PO 4. Samples were then loaded on single, degassed zone refined Re filaments in 5 ml of a silicic acid - phosphoric acid emitter (Gerstenberger and Haase, 1997). Isotopic ratios were measured using a modified single collector VG-54R thermal ionization mass spectrometer equipped with an analogue Daly photomultiplier. Measurements were done in peak-switching mode on the Daly detector. Analytical blanks during the course of this study were 0.2 pg for U and for Pb up to 5 pg. U fractionation was determined directly on individual runs using the U tracer, and Pb isotopic ratios were corrected for fractionation of 0.23%/amu, based on replicate analyses of the NBS-982 Pb standard and the values recommended by Thirlwall (2000). Reported precisions for Pb/U and Pb/Pb dates were determined by numerically propagating all analytical uncertainties through the entire age calculation using the technique of Roddick (1987). Standard concordia diagrams were constructed (see Figures below) and regression intercepts calculated with Isoplot 3.00

2 (Ludwig, 2003). Unless otherwise noted, all errors are quoted at the 2σ level. The samples and the rationale for the calculated ages are shown in the Table below.

3 Table. U-Th-Pb isotopic data used for age calculations. Wt. U Th Pb 206 Pb* mol % Pb* Pb c 206 Pb 208 Pb 207 Pb 207 Pb 206 Pb corr. 207 Pb 207 Pb 206 Pb Sample mg ppm U ppm x10-13 mol 206 Pb* Pb c (pg) 204 Pb 206 Pb 206 Pb % err 235 U % err 238 U % err coef. 206 Pb ± 235 U ± 238 U ± % disc (a) (b) (c) (d) (c) (e) (e) (e) (e) (f) (g) (g) (h) (g) (h) (g) (h) (i) (h) (i) (h) (i) (h) 15-2 (09WB-15-2 on plots) Compositional Parameters Radiogenic Isotope Ratios B % C % D % E % F % (09WB13 on plots) B % C % D % E % (09WB4 on plots) A % B % C % E % (09WB29 on plots) A % B % C % D % (09WB229 on plots) A % B % C % D % E % (a) A, B etc. are labels for fractions composed of single zircon grains or fragments; all fractions annealed and chemically abraded after Mattinson (2005). (b) Nominal fraction weights estimated from photomicrographic grain dimensions, adjusted for partial dissolution during chemical abrasion. (c) Nominal U and total Pb concentrations subject to uncertainty in photomicrographic estimation of weight and partial dissolution during chemical abrasion. (d) Model Th/U ratio calculated from radiogenic 208Pb/206Pb ratio and 207Pb/235U age. (e) Pb* and Pbc represent radiogenic and common Pb, respectively; mol % 206 Pb* with respect to radiogenic, blank and initial common Pb. (f) Measured ratio corrected for spike and fractionation only. Daly analyses, based on analysis of NBS-982. (g) Corrected for fractionation, spike, and common Pb; up to 2 pg of common Pb was assumed to be procedural blank: 206Pb/204Pb = ± 1.0%; 207Pb/204Pb = ± 1.0%; 208Pb/204Pb = ± 1.0% (all uncertainties 1-sigma). Excess over blank was assigned to initial common Pb. (h) Errors are 2-sigma, propagated using the algorithms of Schmitz and Schoene (2007) and Crowley et al. (2007). (i) Calculations are based on the decay constants of Jaffey et al. (1971). 206Pb/238U and 207Pb/206Pb ages corrected for initial disequilibrium in 230Th/238U using Th/U [magma] = 3. (j) Corrected for fractionation, spike, and blank Pb only. Isotopic Ages

4 Table. Results of U-Pb dating of diamondiferous rocks in Wawa area. Sample Material used for zircon extraction Type of dated rock and location Age Basis for the age estimate Comments 15-2 Matrix of lamprophyric breccia 13 Granite clast in conglomerate Lamprophyric breccia at pt 15-2 Conglomerate outcrop at pt 13, on highway ± 1.8 Ma ± 1.5 Ma based on one concordant grain that gives the youngest age result upper intercept of 3-point regression, with one of the grains concordant at the interpreted age The maximum age for the rock as we cannot be certain that the dated zircon is not a concordant xenocryst rather than a primary magmatic grain. 4 Felsic dyke crosscutting conglomerate 29 Granite clast in conglomerate 229 Gabbro clasts in conglomerate Conglomerate outcrop at pt 4 Conglomerate outcrop at pt 29, on the east side of the Mildred Lake fault Conglomerate outcrop at pt 229 Sample numbers correspond to points on the map of Fig ± 1.8 Ma ± 1.1 Ma ± 1.2 Ma upper intercept of 3 point regression all grains concordant and overlapping with age based on 4 point weighted average of 207 Pb/ 206 Pb dates. all grains concordant and overlapping with age based on 5 point weighted average of 207 Pb/ 206 Pb dates One of four grains does not lie along otherwise linear trend, suggesting that it underwent a distinct Pb loss history.

5 206 Pb/ 238 U WB4 3 point regression excluding grain B that is off trend B 2670 data-point error ellipses are A E 0.49 C Intercepts at 223 ± 110 & ± 1.8 [±7.3] Ma MSWD = Pb/ 235 U WB ± 1.8 Ma, based on 207 Pb/206 Pb date for concordant F data-point error ellipses are D Pb/ 238 U F C 2680 E B Pb/ 235 U 0.53 data-point error ellipses are 2 09WB E 206 Pb/ 238 U D 0.49 B Intercepts at 302 ± 79 & ± 1.5 [±7.4] Ma MSWD = 1.3 Electronic Supplementary Fig Pb/ 235 U

6 WB /- 1.0 Ma data-point error ellipses are data-point error symbols are Pb/ 238 U Pb/ 206 Pb Age (Ma) Mean = ± 1.0 [0.037%] 2 Wtd by data-pt errs only, 0 of 4 rej. MSWD = 0.86, probability = 0.46 (error bars are 2 ) Pb/ 235 U WB /-!"#$%%"& 1.2 Ma!"#$%#&'&$%!&()& data-point error ellipses are data-point error symbols are Pb/ 238 U Pb/ 235 U 207 Pb/ 206 Pb Age (Ma) Mean = ± 1.2 [0.046%] 2 Wtd by data-pt errs only, 0 of 5 rej. MSWD = 0.39, probability = 0.81 (error bars are 2 ) Electronic Supplementary Fig. 2

7 A2. Infrared spectroscopy Thirty diamonds were analyzed for nitrogen content and aggregation state studies using a Nicolet 710 Fourier Transform Infrared (FTIR) spectrometer with a Nic-Plan IR microscope attachment and a liquid nitrogen reservoir, at the EOS Department (UBC). Absorption spectra were measured in the range of 4, cm -1 at a resolution of 8 cm -1 and at a signal of 256 scans. Forty nine diamonds were analyzed at the FTIR miscroscope fitted with a Thermo Nicolet Nexus 470 FTIR spectrometer and a liquid nitrogen reservoir (Department of Earth and Atmospheric Sciences, the University of Alberta). Duplicate samples were used to ensure compatibility of analyses from both labs. The spectra were measured in the same wavelength range at a signal of 200 scans. All diamonds were mounted on the edge of a glass slide and spectra were recorded at the point of maximum light transmission through the sample. A Type II diamond of known thickness was used as a reference to correct for varying diamond thicknesses in the mounted samples. Baseline spectra corrections were performed using Omnic version 6.0a software and de-convoluted using least square techniques into spectra of single N, paired N, tetrahedral N and platelets as described in De Stefano et al. (2006). Based on the concentration of nitrogen and its aggregation state, diamonds are divided into type I (stones with >20 ppm N) or II (stones with no measurable N). Type I diamonds were further subdivided into type Ib (stones with single N atoms) and type Ia (stones with aggregated N). The latter are in turn classified into Type IaA (stones containing mainly pairs of N), type IaB (stones containing mainly N tetrahedra), as well as into the transitional group IaAB. A3. Extraction of heavy minerals Samples collected from outcropping metaconglomerates were processed for recovery of heavy minerals (olivine, pyroxenes, ilmenite, garnet, corundum, magnetite, rutile, sapphirine, chromite with occasional quartz, plagioclase and amphibole). The recovery was done in 3 commercial laboratories. Small conglomerate samples were processed at CF Minerals Ltd (Kelowna, Canada) by attrition milling. Mill design precludes contamination as heavy minerals are continuously removed during attrition. Among five samples from pits# 4; 5; 6; 7; and 13 weighing 24.58kg; 23.04kg; kg; kg

8 and 25.38kg, indicator minerals were recovered from only the samples from pits # 6 and #7 (see map with pit locations in Verley 2009). A total of 644 chromite, 20 olivine, 3 garnet, 1 ilmenite and 1 clinopyroxene grains were recovered. Larger samples from pits # 1; 4 and 8 weighing 710.5, and kgs respectively were processed at SGS Mineral Services (Lakefield, Canada) by a standard diamond recovery method (Dense Media Separation plant). The indicator minerals (178) were picked from the concentrates generated by DMS operations. The plant was specifically assembled for the exclusive use of conglomerate testing to exclude a possibility of sample cross-contamination. A total of 91 chromite, 18 olivine, 51 garnet, 5 ilmenite grains were recovered. The conglomerate was also sampled by105 pit sites, and the samples weighing on average 5 tonnes were processed to recover diamonds and heavy minerals through DMS plant (SGS Mineral Services). A total of 349 tonnes was processed, yielding 3603 diamonds weighing 82.7 carats. All heavy minerals extracted from these samples are probed and the analyses are reported in Electronic Supplementary Table 2. The largest metaconglomerate samples (70 to 80 tones) were collected in original test pits and processed by DMS at Kennecott Exploration Canada Inc Facility (Thunder Bay, Canada). The 298 ton sample of this material yielded 3265 diamonds weighing in total 89.4 carats, with the largest recovered diamonds 1.5 and 1.0 carats. Additional information about the processes of diamond and indicator recovery can be found in Verley (2009). Comparison of heavy mineral counts between duplicate samples processed at different laboratories (see Table below) shows a significant heterogeneity in the heavy minerals distribution. The similar processing for indicator minerals was performed on samples of overlying metasandstones. They are found to be barren for diamonds, but contain few occasional grains of heavy minerals of the same type and compositions as those found in metaconglomerates.

9 Table. Recovery of heavy minerals for identical or proximal samples Locations Sample Recovery method Grains found weight Pit kg Attrition milling at CFM Lab 149 Chr, 10 Ol Pit tn Attrition milling, then DMS at SGS Lab 2 Pyr, 1 Rut Pit kg Attrition milling at CFM Lab 125 Chr, 1 Alm, 1 Cpx, 1 Ilm, 10 Ol, 2 Pyr 25 m away from Pit 7 - MBP tn Attrition milling, then DMS at SGS Lab 1 Pyr Pit kg DMS at SGS Lab 200+ Chr, 40 Pyr 5 m from Pit 4 - MBP tn DMS at SGS Lab 1 Cpx, 2 Qz 5 m from Pit 4 - MBP tn DMS at SGS Lab 1 Ol, 2 Ilm Pit kg DMS at SGS Lab 200+ Chr, 1 Pyr, 3 Ilm 10 m from Pit 8 - MBP tn DMS at SGS Lab 1 Qz, 4 cpx, 2 Ol, 9 Pyr, 2 Ilm MBP tn Kennecott DMS 16 Chr, 80 Cpx,32 Pyr, 4 Ol, 8 Sap, 7 Rub, 10 Ilm MBP401 ~ 6 tn DMS at SGS Lab No indicators MBP301 ~ 6 tn DMS at SGS Lab 1 Ilm, 2 Cd, 1 Pyr, 1Alm, 11 Cpx, 4 Ol, 2 Qz, 5 Mt MBP tn DMS at SGS Lab 5 Chr, 3 Pyr, 10 Cpx, 6 Ol, 1 Ruby MBP tn DMS at SGS Lab No indicators Abbreviations for minerals are Chr (chromite), Ol (olivine), Alm (almandine), Cpx (clinopyroxene), Ilm ( ilmenite), Pyr (pyrope), Qz (quartz), Sap (sapphire), Rub (ruby), Mt (magnetite), Cd (corund)

10 A4. Electron microprobe analysis Heavy minerals with grain sizes mm from bulk samples processed in commercial labs were analyzed for major and minor element contents by electron microprobe (JEOL 733 Superprobe) under standard operating conditions (15 KeV, 20 na operating current, 500 micron beam size, 20 seconds counting time) in the C.F. Mineral Research Ltd Laboratory. The minimum detection limits for these conditions are wt% SiO 2, wt% TiO 2, wt% Al 2 O 3, wt% Cr 2 O 3, 0.05 wt% FeO, wt% MnO, wt% CaO, wt% Na 2 O, wt% K 2 O, NiO, 0.08 ZnO. Quality of the analysis was ascertained by repeat analyses of standards, i.e. diopside, pyrope, chromite, Ni spinel, magnetite and rutile. Analysis of almandine from panned concentrates were carried out on the JXA 8100 X-ray microprobe (The Sobolev Institute of Geology and Mineralogy, Siberian Branch, Russian Academy of Sciences) under standard operating conditions (15 KeV, 20 na operating current, 3 micron beam size, 20 seconds counting time) using natural minerals as standards. References: Gerstenberger, H., Haase, G., A highly effective emitter substance for mass spectrometric Pb isotope ratio determinations. Chem. Geol. 136, 3-4, Ludwig, K.R., Isoplot 3.00, A Geochronological Toolkit for Microsoft Excel. University of California at Berkely Scoates, J.S. Friedman, R.M., Precise age of the platiniferous Merensky Reef, Bushveld Complex, South Africa by the U-Pb zircon chemical abrasion ID-TIMS techique, Econ. Geol., 103, Roddick, J.C., Generalized numerical error analysis with application to geochronology and thermodynamics. Geoch. Cosmoch. Acta, 51, Thirlwall, M.F., Inter-laboratory and other errors in Pb isotope analyses investigated using a 207 Pb 204 Pb double spike. Chem. Geol.,163,