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Diamonds: Historical Longest Dimension based Micro Diamond Data


(From the archives - originally published in 2002)

Historical Longest Dimension based Micro Diamond Data

Definition: micro diamonds recovered from samples up to 1,000 kg through caustic or acid dissolution or fusion processes are divided into 2 groups called "micros" and "macros". The bottom cutoff is achieved through a sieve that usually has a 0.1 mm square mesh, but sometimes goes as low as 0.074 mm or as high as 0.15 mm. Companies do not always report the bottom cutoff, though they should because the frequency of micro diamonds often soars as size gets smaller. A "macro" is a micro diamond which is greater than 0.5 mm in its longest axis, or "dimension" as it is more commonly called. This measurement is made visually using a microscope. It does not distinguish between intact crystals and fragments, nor does it distinguish between flat crystals such as macles and heavier dodecahedra that have the same longest dimension measurement. The term "macro" in the context of small sample derived micro diamonds conflicts with the traditional definition of a "macro" as a diamond exceeding the minimum size recovered by a commercial mining operation. The minimum "commercial macro" size ranges from a 1.0 mm screen to 1.65 mm. When a grade (ie carats per tonne) is quoted for a kimberlite, it is understood to include only commercially recoverable diamonds. Sometimes companies report the total weight of their micro diamonds, which encourages people to calculate a diamond grade they extrapolate to the entire body. This extrapolation is inappropriate because the typical micro diamond sample is too small to be representative. However, a bigger mistake is to confuse total diamond grade with commercial macro grade. Unlike metals such as gold where particle size does not matter and all the recovered metal gets melted into a homogenous form whose value is defined purely by weight, diamonds must retain their original crystal form, whose clarity, colour, shape and size defines the value of each stone. Micro diamonds have no economic value, so their weight is irrelevant. Furthermore, it may surprise people to learn that the total diamond grade for a kimberlite that includes the weight of micro diamonds can be substantially higher than the "commercial macro" grade. In fact, simply switching from a 1.0 mm recovery screen to a 1.5 mm screen can result in significant variations in commercial grade. The paradox of micro diamond analysis is that micro diamonds are never mined; they provide only an oblique peek at the macro grade potential.

Analytical usage of longest dimension macro-micro data: the classification of micro diamonds into "macros" and "micros" based on a 0.5 mm measurement of the longest dimension does not contain any information that allows grade calculation. Analytical evaluation of longest dimension micro-macro data has thus been done on a comparative basis where the ratio of macros to micros or macros per weight unit (ie 10 kg) for new discoveries are compared to the micro diamond ratios of pipes for which a commercial macro grade has been established by bulk sampling. This evaluation approach is deeply flawed because 1) it ignores the fundamental nature of a diamond population as a continuum with a lognormal particle size frequency distribution, 2) the empirical record of longest dimension based micro diamond results published by Canadian companies since 1991 shows no correlation between commercial macro grade and longest dimension macro based ratios, and 3) it is blind to emplacement related physical factors such as resorption and aerial distribution that may negatively affect the smaller micro diamonds more than the larger ones.

Many public companies involved in diamond exploration publish tables which compare the longest dimension micro-macro count ratios with those of selected kimberlites with known commercially viable grades. The following tables include the longest dimension micro-macro results for kimberlites where bulk sampling has established uneconomic macro grades.

Longest Dimension Based Reporting for Micro Diamond Results
Sorted by macros per 10 kg
Pipe Sample kg <0.5 mm >0.5 mm Macro/Micro Macro/10 kg Grade ct/t
DMM - Misery - 61 kg - 4.26 ct/t 61 259 155 0.6 25.6 4.260
Ashton K14C w/frag - 0.12 ct/t 89 422 94 0.2 10.6 0.120
MPV 5034 - 6027 kg - 1.64 ct/t 6027 11064 5458 0.5 9.1 1.640
Snap Lake - 214 kg - 1.78 ct/t 214 325 169 0.5 7.9 1.780
Tahera-JD/0D1 - 2415 kg - 0.84 ct/t 2415 2589 1764 0.7 7.3 0.840
Bandore-Area E - 250 kg - 0.05 ct/t 250 9094 141 0.0 5.6 0.050
DMM 97/C - 57 kg 57 45 32 0.7 5.6
Aber - A154S - 1352 kg - 4.8 ct/t 1352 1406 728 0.5 5.4 4.800
Aber A418 - 3.7 ct/t 997 994 503 0.5 5.0 3.700
DMM 92/I - 122 kg 122 132 55 0.4 4.5
Aber - A154N - 1067 kg - 2.4 ct/t 1067 1023 424 0.4 4.0 2.400
DMM-Phoenix - 240 kg - 1.41 ct/t 240 158 95 0.6 4.0 1.410
ACA - Artemisia - 332 kg - 0.11 ct/t 332 1121 120 0.1 3.6 0.110
DMM 92/F - 177 kg 177 198 64 0.3 3.6
Twin Torngat 1 - 322 kg - 0.04 ct/t 322 214 112 0.5 3.5 0.040
DMM 93/L - 123 kg 123 143 40 0.3 3.3
DMM 92/D - 71 kg 71 155 23 0.1 3.2
DMM 92/B - 72 kg 72 117 23 0.2 3.2
DMM Wildebeest - 35 kg 35 41 11 0.3 3.1
DHK - DO27 Pyro - 314 kg - 0.36 ct/t 314 299 96 0.3 3.1 0.360
DMM 97/A - 67 kg 376 166 106 0.6 2.8
DMM-Bear Tooth - 376 kg - 1.2 ct/t 376 166 106 0.6 2.8 1.200
DMM Point Lake - 59 kg - 0.63 ct/t 59 65 16 0.2 2.7 0.630
Tanqueray-Torrie - 198 kg - 0.026 ct/t 198 181 53 0.3 2.7 0.026
DMM 97/B - 407 kg 407 167 102 0.6 2.5
Tanqueray - Sue - 71 kg 71 52 17 0.3 2.4
DMM 93/A - 86 kg 86 60 19 0.3 2.2
Aber - A21 - 1385 kg - 3.0 ct/t 1385 789 300 0.4 2.2 3.000
DMM Pegasus - 295 kg 295 291 62 0.2 2.1
DMM 97/D - 232 kg 232 78 47 0.6 2.0
DMM 92/A - 108 kg 108 95 21 0.2 1.9
DMM-Koala North - 268 kg - 0.63 ct/t 268 38 51 1.3 1.9 0.630
DMM 99/A - 235 kg 235 266 39 0.1 1.7
DMM 92/E - 70 kg 70 36 11 0.3 1.6
DMM 98/B - 73 kg 73 12 11 0.9 1.5
DMM 93/M - 111 kg 111 73 13 0.2 1.2
Ashton Renard 3 - 156 kg 156 21 17 0.8 1.1
ACA Potentilla - 208 kg 208 230 22 0.1 1.1
Ashton K91 - 117 kg - 0.14 ct/t 117 180 12 0.1 1.0 0.140
DHK - DO27 Diat - 160 kg - 0.013 ct/t 160 14 13 0.9 0.8 0.013
Ashton K252 - 0.55 ct/t 107 135 8 0.1 0.7 0.550
Ashton K14 - 153 kg - 0.12 ct/t 153 139 11 0.1 0.7 0.120
DMM 92/G - 122 kg 122 45 8 0.2 0.7
DMM 92/C - 161 kg 161 28 10 0.4 0.6
DMM Kodiak - 301 kg 301 74 17 0.2 0.6
Shore-Star - 2,245 kg - 0.065 ct/t 2245 403 120 0.3 0.5 0.065
Candle Lake #29 - 65 kg - 0.04 ct/t 65 14 3 0.2 0.5 0.037
Ashton K14C no frag - 0.12 ct/t 89 152 4 0.0 0.4 0.120
DMM 98/A - 195 kg 195 11 8 0.7 0.4
Twin Freightrain 1026 kg - 0.2 ct/t 1026 385 40 0.1 0.4 0.200
Tahera Ranch Lake - 208 kg - 0.22 ct/t 208 38 6 0.2 0.3 0.220
Winspear CL25 - 350 kg 350 212 9 0.0 0.3
Ashton K6 - 117 kg - 0.072 ct/t 154 33 3 0.1 0.2 0.072
SUD 92-2 - 1104 kg 1104 35 21 0.6 0.2
DMM 92/H - 60 kg 60 7 1 0.1 0.2


Longest Dimension Based Reporting for Micro Diamond Results
Sorted by macros per micros kg
Pipe Sample kg <0.5 mm >0.5 mm Macro/Micro Macro/10 kg Grade ct/t
DMM-Koala North - 268 kg - 0.63 ct/t 268 38 51 1.3 1.9 0.630
DHK - DO27 Diat - 160 kg - 0.013 ct/t 160 14 13 0.9 0.8 0.013
DMM 98/B - 73 kg 73 12 11 0.9 1.5
Ashton Renard 3 - 156 kg 156 21 17 0.8 1.1
DMM 98/A - 195 kg 195 11 8 0.7 0.4
DMM 97/C - 57 kg 57 45 32 0.7 5.6
Tahera-JD/0D1 - 2415 kg - 0.84 ct/t 2415 2589 1764 0.7 7.3 0.840
DMM 97/A - 67 kg 376 166 106 0.6 2.8
DMM-Bear Tooth - 376 kg - 1.2 ct/t 376 166 106 0.6 2.8 1.200
DMM 97/B - 407 kg 407 167 102 0.6 2.5
DMM 97/D - 232 kg 232 78 47 0.6 2.0
DMM-Phoenix - 240 kg - 1.41 ct/t 240 158 95 0.6 4.0 1.410
SUD 92-2 - 1104 kg 1104 35 21 0.6 0.2
DMM - Misery - 61 kg - 4.26 ct/t 61 259 155 0.6 25.6 4.260
Twin Torngat 1 - 322 kg - 0.04 ct/t 322 214 112 0.5 3.5 0.040
Snap Lake - 214 kg - 1.78 ct/t 214 325 169 0.5 7.9 1.780
Aber - A154S - 1352 kg - 4.8 ct/t 1352 1406 728 0.5 5.4 4.800
Aber A418 - 3.7 ct/t 997 994 503 0.5 5.0 3.700
MPV 5034 - 6027 kg - 1.64 ct/t 6027 11064 5458 0.5 9.1 1.640
DMM 92/I - 122 kg 122 132 55 0.4 4.5
Aber - A154N - 1067 kg - 2.4 ct/t 1067 1023 424 0.4 4.0 2.400
Aber - A21 - 1385 kg - 3.0 ct/t 1385 789 300 0.4 2.2 3.000
DMM 92/C - 161 kg 161 28 10 0.4 0.6
Tanqueray - Sue - 71 kg 71 52 17 0.3 2.4
DMM 92/F - 177 kg 177 198 64 0.3 3.6
DHK - DO27 Pyro - 314 kg - 0.36 ct/t 314 299 96 0.3 3.1 0.360
DMM 93/A - 86 kg 86 60 19 0.3 2.2
DMM 92/E - 70 kg 70 36 11 0.3 1.6
Shore-Star - 2,245 kg - 0.065 ct/t 2245 403 120 0.3 0.5 0.065
Tanqueray-Torrie - 198 kg - 0.026 ct/t 198 181 53 0.3 2.7 0.026
DMM 93/L - 123 kg 123 143 40 0.3 3.3
DMM Wildebeest - 35 kg 35 41 11 0.3 3.1
DMM Point Lake - 59 kg - 0.63 ct/t 59 65 16 0.2 2.7 0.630
DMM Kodiak - 301 kg 301 74 17 0.2 0.6
Ashton K14C w/frag - 0.12 ct/t 89 422 94 0.2 10.6 0.120
DMM 92/A - 108 kg 108 95 21 0.2 1.9
Candle Lake #29 - 65 kg - 0.04 ct/t 65 14 3 0.2 0.5 0.037
DMM Pegasus - 295 kg 295 291 62 0.2 2.1
DMM 92/B - 72 kg 72 117 23 0.2 3.2
DMM 93/M - 111 kg 111 73 13 0.2 1.2
DMM 92/G - 122 kg 122 45 8 0.2 0.7
Tahera Ranch Lake - 208 kg - 0.22 ct/t 208 38 6 0.2 0.3 0.220
DMM 92/D - 71 kg 71 155 23 0.1 3.2
DMM 99/A - 235 kg 235 266 39 0.1 1.7
DMM 92/H - 60 kg 60 7 1 0.1 0.2
ACA - Artemisia - 332 kg - 0.11 ct/t 332 1121 120 0.1 3.6 0.110
Twin Freightrain 1026 kg - 0.2 ct/t 1026 385 40 0.1 0.4 0.200
ACA Potentilla - 208 kg 208 230 22 0.1 1.1
Ashton K6 - 117 kg - 0.072 ct/t 154 33 3 0.1 0.2 0.072
Ashton K14 - 153 kg - 0.12 ct/t 153 139 11 0.1 0.7 0.120
Ashton K91 - 117 kg - 0.14 ct/t 117 180 12 0.1 1.0 0.140
Ashton K252 - 0.55 ct/t 107 135 8 0.1 0.7 0.550
Winspear CL25 - 350 kg 350 212 9 0.0 0.3
Ashton K14C no frag - 0.12 ct/t 89 152 4 0.0 0.4 0.120
Bandore-Area E - 250 kg - 0.05 ct/t 250 9094 141 0.0 5.6 0.050

 
 

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