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ABRASION OF KIMBERLITE PEBBLES DURING A TUMBLING MILL EXPERIMENT: IMPLICATIONS FOR DIAMOND EXPLORATION

by

Don I. Cummings

Deliverable 10 of 12 Submitted to the Geological Survey of Canada

in partial fulfillment of contract 08-AMI026711W

Ottawa, Ontario

March 10, 2010

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EXECUTIVE SUMMARY A tumbling mill experiment was performed to quantify the rate at which pebble-

sized kimberlite cubes abrade (lose mass) during transport relative to basalt, gabbro, tonalite, and Dubawnt sandstone clasts from the Keewatin sector of the Precambrian Shield (Fig 1). The kimberlite cubes lost mass 3 to 3500 times faster than the Shield bedrock cubes. One tuffisitic kimberlite cube disaggregated completely into sand- and mud-sized particles after only several hours of soaking before the experiments started (Fig. 2). These results suggest that

1) some kimberlite facies will break down “immediately” into sand- and mud-sized particles upon entrainment, and

2) kimberlite pebbles that do not break apart “immediately” may abrade up to an order of magnitude faster than common Shield clasts as they are dispersed across the landscape.

Figure 1. Abrasion experiment results. The cube-shaped pebbles were initially ~ 2 cm in diameter (see Appendix 1). Note that kimberlite samples (Samples 1 to 6) lost mass faster than “common” bedrock types from the Precambrian Shield (Samples 7 to 10). 1 – Tuffisitic kimberlite from diatreme zone of Fox mine, Ekati, NWT; 2 – Tuffisitic kimberlite from diatreme zone of Premier-Cullinan mine, South Africa; 3 – Pyroclastic kimberlite from crater zone of 175 body, Fort à la Corne, SK; 4 – Olivine crystal tuff from crater zone of Star body, Fort à la Corne, SK; 5 –Hypabyssal kimberlite from root zone of Peddie body, New Liskeard, ON; 6 – Hypabyssal kimberlite from root zone of Mark body, Ekati, NWT; 7 – Tonalite. Slave Province, Archean; 8 – Gabbro. East Arm of Great Slave Lake, Mesoproterozoic; 9 – Massive flow basalt. East Arm, Et Then Fm, Paleoproterozoic; 10 – Coarse reddish-pink Dubawnt sandstone, Keewatin.

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Figure 2. Photograph of rock cubes after 8 hours of soaking. Note that all cubes are intact except Sample 1 (tuffisitic kimberlite from the Fox mine, Ekati), which has completely disaggregated.

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ACKNOWLEDGEMENTS Mike Burns (GSC) cut fantastic-looking rock cubes; Rob Rainbird (GSC) provided the Dubawnt sandstone sample; Tomasz Kalkowski (University of Ottawa) ran the experiments; and Bill Arnott (University of Ottawa) let us use his lab.

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APPENDIX 1: MATERIALS The following materials were used in the experiment (see Appendix 4 for details):

Lortone QT6 rotary polishing tumbler (Fig. 3) Ten rock cubes, each ~ 2 cm in diameter and ~ 20 g in weight (see below) Silicon carbide abrasive #1 (90.0 g – about 4 tablespoons) (Fig. 4) Tap water at 20˚C (338.51 g of water – just enough to cover cubes) Digital camera Calipers to measure initial cube dimensions High-precision scale to measure cube weight

Rock cubes

Sample Description Sample location Sample

provided by… Initial cube

dimensions (mm)

Initial weight of cube before

experiments started (g)

1 Tuffisitic kimberlite from diatreme zone Fox mine, Ekati, NWT

B. Kjarsgaard (GSC)

21.5 x 21.0 x 20.0 18.4*

2

Tuffisitic kimberlite from diatreme zone

Premier–Cullinan mine, South Africa

B. Kjarsgaard (GSC)

21.5 x 20.0 x 19.5 19.59*

3 Pyroclastic kimberlite from crater zone

175 body, Fort à la Corne, SK

B. Kjarsgaard (GSC)

22.5 x 21.5 x 20.0 23.97**

4 Olivine crystal tuff from crater zone

Star body, Fort à la Corne, SK

B. Kjarsgaard (GSC)

21.5 x 20.5 x 19.5 20.48**

5 Hypabyssal kimberlite from root zone

Peddie body, New Liskeard, ON

B. Kjarsgaard (GSC)

21.0 x 20.0 x 19.5 22.51**

6 Hypabyssal kimberlite from root

Mark body, Ekati, NWT

B. Kjarsgaard (GSC)

23.0 x 21.0 x 19.5 27.41**

7 Tonalite, Archean Slave Province B. Kjarsgaard (GSC)

21.0 x 20.5 x 19.5 21.65**

8 Gabbro, Mesoproterozoic

East Arm of Great Slave Lake

B. Kjarsgaard (GSC)

21.0 x 20.0 x 18.1 22.68**

9 Massive flow basalt, Et Then Fm, Paleoproterozoic

East Arm of Great Slave Lake

B. Kjarsgaard (GSC)

21.0 x 20.5 x 20.5 23.94**

10 Reddish-pink coarse Dubawnt sandstone

Keewatin R. Rainbird (GSC)

22.0 x 22.0 x 20.0 21.84**

*dry (Samples 1 and 2 would have spalled apart during pre-soak) **after 4 days soaking (to saturate pores prior to experiment)

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Figure 3. The Lortone QT6 polishing tumbler used in the experiments.

Figure 4. The silicon carbide abrasive used in the experiments.

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APPENDIX 2: METHODS 1. The ten rock cubes1, water, and abrasive were added together to the tumbling mill. 2. The tumbling mill was turned on and allowed to run for a designated amount of

time (usually ~ 24 hours; initially less). 3. The mill was stopped and opened. The rock cubes were removed, cleaned of grit,

dipped in clean water, dried with a paper towel, and weighed immediately (see Appendix 3).

4. The cubes were allowed to dry for ~ 5 minutes, just enough so that their surfaces became dry. They were then photographed (see Appendix 4).

5. The cubes were then dipped in clean water to re-wet their surfaces and reintroduced into the tumbler. Steps 2 to 5 were repeated over and over. With the exception of minor water lost permanently to evaporation, and the temporary extraction of the rock cubes, no material was introduced or extracted from the tumbling mill during the experiments.

1 All rock cubes were soaked for 4 days prior to the experiment to ensure they were completely saturated prior to starting the experiment (see Appendix 5, page 1). This ensured that no mass would be gained from infiltration of pore space with water at the start of the experiments. Exceptions to this are Samples 1 and 2. These tuffisitic kimberlite samples proved too delicate to pre-soak: they either disaggregated completely (Sample 1) or spalled apart slightly (Sample 2) during the pre-soak. As such, these two samples were added dry to the tumbler. As the results show (see Fig. 1), any mass they gained by water infiltration during the experiments was minuscule compared to the mass loss they experienced.

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APPENDIX 3: MASS-LOSS DATA

Weight (in grams) SAMPLE 00h00 00h05 00h10 00h15 00h20 00h25 00h30 01h00 02h00 03h00 04h00 1 18.4 12.5 8.08 4.96 0.84 --- --- --- --- --- --- 2 19.59 19.53 19.35 19.12 18.96 18.75 16.77 15.56 13.63 11.19 9.94 3 23.97 23.96 23.94 23.94 23.93 23.92 23.92 23.89 23.8 23.73 23.68 4 20.48 20.44 20.41 20.39 20.35 20.36 20.3 20.16 19.88 19.63 19.35 5 22.51 22.48 22.46 22.44 22.41 22.4 22.38 22.3 22.15 22 21.82 6 27.41 27.38 27.38 27.37 27.35 27.35 27.35 27.29 27.2 27.13 27.07 7 21.65 21.64 21.65 21.64 21.63 21.62 21.63 21.6 21.58 21.57 21.53 8 22.68 22.68 22.66 22.65 22.65 22.65 22.64 22.64 22.6 22.58 22.54 9 23.94 23.94 23.93 23.93 23.94 23.91 23.92 23.9 23.88 23.84 23.83 10 21.84 21.85 21.83 21.83 21.83 21.83 21.82 21.8 21.79 21.76 21.76 Date 21-Feb-

06 21-Feb-06 21-Feb-06 21-Feb-06 21-Feb-06 21-Feb-06 21-Feb-06 21-Feb-06 21-Feb-06 21-Feb-06 21-Feb-06

Weight (in mass %) SAMPLE 00h00 00h05 00h10 00h15 00h20 00h25 00h30 01h00 02h00 03h00 04h00 1 1 0.679348 0.43913 0.269565 0.045652 0 0 0 0 0 0 2 1 0.996937 0.987749 0.976008 0.967841 0.957121 0.856049 0.794283 0.695763 0.57121 0.507402 3 1 0.999583 0.998748 0.998748 0.998331 0.997914 0.997914 0.996662 0.992908 0.989987 0.987902 4 1 0.998047 0.996582 0.995605 0.993652 0.994141 0.991211 0.984375 0.970703 0.958496 0.944824 5 1 0.998667 0.997779 0.99689 0.995558 0.995113 0.994225 0.990671 0.984007 0.977343 0.969347 6 1 0.998906 0.998906 0.998541 0.997811 0.997811 0.997811 0.995622 0.992339 0.989785 0.987596 7 1 0.999538 1 0.999538 0.999076 0.998614 0.999076 0.997691 0.996767 0.996305 0.994457 8 1 1 0.999118 0.998677 0.998677 0.998677 0.998236 0.998236 0.996473 0.995591 0.993827 9 1 1 0.999582 0.999582 1 0.998747 0.999165 0.998329 0.997494 0.995823 0.995405 10 1 1.000458 0.999542 0.999542 0.999542 0.999542 0.999084 0.998168 0.997711 0.996337 0.996337

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Weight (in grams) SAMPLE 05h00 13h00 25h30 34h00 39h00 60h30 84h00 107:30 131h00 154:30 178h00

1 --- --- --- --- --- --- --- --- --- --- --- 2 3.68 0.34 --- --- --- --- --- --- --- --- --- 3 23.61 23.04 21.87 21.12 20.56 18.59 16.75 15.15 13.75 12.5 11.39 4 19.1 17.1 13.28 11 9.75 5.34 2.53 1.47 1.05 0.84 0.72 5 21.66 20.58 18.23 16.66 15.79 12.44 9.7 7.61 5.92 4.61 3.69 6 26.99 26.47 25.3 24.49 24.02 22.14 20.33 18.79 17.43 16.24 15.18 7 21.51 21.33 20.93 20.72 20.45 19.75 19.09 18.49 17.95 17.42 16.97 8 22.51 22.32 21.86 21.55 21.32 20.52 19.76 19.03 18.4 17.81 17.29 9 23.8 23.62 23.24 22.97 22.75 22.08 21.42 20.82 20.27 19.76 19.31

10 21.66 21.53 21.26 21.1 20.92 20.36 19.88 19.43 19.01 18.62 18.26

21-Feb-06 22-Feb-06 22-Feb-06 23-Feb-06 23-Feb-06 24-Feb-06 25-Feb-06 26-Feb-06 27-Feb-06 28-Feb-06 01-Mar-06

Weight (in mass %) SAMPLE 05h00 13h00 25h30 34h00 39h00 60h30 84h00 107:30 131h00 154:30 178h00

1 0 0 0 0 0 0 0 0 0 0 0 2 0.187851 0.017356 0 0 0 0 0 0 0 0 0 3 0.984981 0.961202 0.91239 0.881101 0.857739 0.775553 0.69879 0.63204 0.573634 0.521485 0.475177 4 0.932617 0.834961 0.648438 0.537109 0.476074 0.260742 0.123535 0.071777 0.05127 0.041016 0.035156 5 0.962239 0.91426 0.809862 0.740116 0.701466 0.552643 0.43092 0.338072 0.262994 0.204798 0.163927 6 0.984677 0.965706 0.923021 0.89347 0.876323 0.807734 0.7417 0.685516 0.635899 0.592484 0.553812 7 0.993533 0.985219 0.966744 0.957044 0.944573 0.91224 0.881755 0.854042 0.829099 0.804619 0.783834 8 0.992504 0.984127 0.963845 0.950176 0.940035 0.904762 0.871252 0.839065 0.811287 0.785273 0.762346 9 0.994152 0.986633 0.97076 0.959482 0.950292 0.922306 0.894737 0.869674 0.8467 0.825397 0.8066

10 0.991758 0.985806 0.973443 0.966117 0.957875 0.932234 0.910256 0.889652 0.870421 0.852564 0.836081

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Weight (in grams) SAMPLE 203h25 228:00 251h30 275h00 298h30 332h30 355h30 381h00 404h15

1 --- --- --- --- --- --- --- --- --- 2 --- --- --- --- --- --- --- --- --- 3 10.32 9.42 8.57 7.79 7.05 6.4 5.83 5.3 4.88 4 0.62 0.59 0.54 0.51 0.49 0.46 0.43 0.42 0.4 5 3 2.57 2.24 2 1.82 1.68 1.56 1.46 1.4 6 14.16 13.32 12.52 11.82 11.16 10.55 9.99 9.42 8.96 7 16.51 16.11 15.73 15.39 15.04 14.72 14.43 14.11 13.84 8 16.76 16.33 15.92 15.55 15.19 14.88 14.57 14.27 14.03 9 18.85 18.49 18.13 17.82 17.49 17.19 16.91 16.64 16.44

10 17.88 17.63 17.33 17.08 16.83 16.59 16.36 16.14 15.95

Date 02-Mar-06

03-Mar-06

05-Mar-10

06-Mar-10

07-Mar-10

08-Mar-10

09-Mar-10

10-Mar-10

11-Mar-10

Weight (in mass %) SAMPLE 203h25 228:00 251h30 275h00 298h30 332h30 355h30 381h00 404h15

1 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0 0 3 0.430538 0.392991 0.35753 0.32499 0.294118 0.267 0.243221 0.22111 0.203588 4 0.030273 0.028809 0.026367 0.024902 0.023926 0.022461 0.020996 0.020508 0.019531 5 0.133274 0.114171 0.099511 0.088849 0.080853 0.074633 0.069303 0.06486 0.062195 6 0.5166 0.485954 0.456768 0.431229 0.407151 0.384896 0.364466 0.34367 0.326888 7 0.762587 0.744111 0.726559 0.710855 0.694688 0.679908 0.666513 0.651732 0.639261 8 0.738977 0.720018 0.70194 0.685626 0.669753 0.656085 0.642416 0.629189 0.618607 9 0.787385 0.772348 0.75731 0.744361 0.730576 0.718045 0.706349 0.695071 0.686717

10 0.818681 0.807234 0.793498 0.782051 0.770604 0.759615 0.749084 0.739011 0.730311

APPENDIX 4: PHOTOS

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Photo of the mud-rich fluid in the tumbling mill after 381 hours of tumbling. The mud is entirely the product of abrasion (initially the fluid was clear tap water). The gradual increase in mud concentration is suspected to have played a part in the gradual reduction of abrasion rates with time (Fig. 1). Note that the reduction in abrasion rates is most pronounced for the smallest, roundest, most spherical grains (Samples 4 and 5 in Figure 1). The elevated viscosity may have kept these smaller grains in suspension, thus reducing the number of times they impacted the larger clasts travelling as “bedload”. At the same time, their roundness and sphericity means that they had less surface area, and fewer “protrusions”, to abrade than the square-shaped clasts. (The added buoyancy should have affected all clasts about equally, irrespective of clast size.)

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APPENDIX 5: LAB NOTES

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