Distribution of gold, arsenic, antimony and tungsten around the Dest-Or Orebody, Noranda district, Abitibi, Quebec

Journal of Geochemical Exploration, 28 (1987) 41-70 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

41

Lithogeochemical studies

Distribution of Gold, Arsenic, Antimony and Tungsten around the Dest-Or Orebody, Noranda District, Abitibi, Quebec A. B E A U D O I N

~,G. P E R R A U L T

I and M. B O U C H A R D

2

iDdpartement de gdnie mindral, IEcolePolytechnique, Montrdal, Que. H 3 C 3A 7, Canada 2Ressources Aiguebelle, 170 ave. Principale, Rouyn, Que. J9X 4P7, Canada (Received M a y 14, 1986)

ABSTRACT Beaudoin, A., Perrault, G. and Bouchard, M., 1987. Distribution of gold, arsenic, antimony and tungsten around the Dest-Or orebody, Noranda District,Abitibi,Quebec. In: R.G. Garrett (Editor),Geochemical Exploration 1985. J. Geochem. Explor., 28: 41-70. The Dest-Or epigenetic Au deposit occurs in a breccia zone within gabbro, basalt and andesite of the Archean Upper Deguisier Formation. It is located approximately 30 k m N E of Noranda, Quebec and 2.5 k m N of the Porcupine-Destor Fault,an important verticalshear zone that extends east-west for more than 100 kin. The known orebody contains 2.44 M t of ore at 4.29 g/t Au. Host rocks of the Upper Deguisier Formation typicallycontain 3.6 ppb Au, 0.8 p p m Sb and 4.5 p p m As. The Au values are comparable to those of tholeiiticmafic rocks elsewhere in the world, but Sb and As values are a littlehigher. Gold values on approximately 30% of the area of the Dest-Or and Bassignac properties define a log-normal distribution with a median at 9.4 ppb Au (P~6 at 3.1 and Ps4 at 27). These are referred to as ore zone halos: they envelop orebody halos which in turn envelop orebodies. An orebody ha/o can best be defined by close sampling in the immediate vicinity of a known orebody. Around the Dest-Or orebody, this halo isapproximately 100 m wide (60 m on the hanging wall and 40 m on the footwall), and it has a median value at 37 ppb Au (Pie at 17 and P ~ at 74). Gold enrichment in the orebody is 1900 times background value. There are also lesserbut significant Sb and As enrichments (20 × each). High W values occur in the ore ( > 30 p p m W), but background values were too low ( < 5 ppm) to be established with confidence. Gold analyses in the 0.2-100 ppb range can be gainfully used in the search for blind gold ore deposits; As, Sb and W can also be used, but anomalies are less extensive and enrichment is also lesspronounced.

INTRODUCTION T h e work of Roslyakov and Roslyakova (1975) in the U.S.S.R. has revealed anomalous Au c o n c e n t r a t i o n s (ppb level) in Au mining districts, in certain 0375-6742/87/$03.50

© 1987 Elsevier Science Publishers B.V.

42

geological formations and in rocks immediately adjacent to hydrothermal gold ore deposits. Similar geochemical studies in the Archean Abitibi greenstone belt of Canada (Daigneault, 1983; Perrault et al., 1984, Perrault, 1985) have established that such Au deposits are frequently enclosed by positive Au anomalies. Gold distributions, be they in the mining camp, in the ore zone or immediately adjacent to an ore deposit, are also likely to tell something about the Au mineralizing process; as such, they deserve attention. Roslyakov and Roslyakova (1975), in their study of U.S.S.R. gold fields have identified three distinct types of Au distributions: (1) The ore field distribution, defined by the Au content of rocks in areas of hundreds of square kilometers. Perrault et al. (1985) and Perrault (1985) have suggested that regional Au distribution in Archean greenstone belts may be essentially stratigraphic with some formations containing more Au than others. ( 2 ) The ore zone distribution, defined by the Au content of rocks in an area containing many orebodies. Gold content is generally higher by one order of magnitude in ore zones compared to ore fields. (3) The orebody halo is defined by the Au content of rocks surrounding an orebody. Gold contents in orebody halos may be an order of magnitude higher than those in ore zones. Finally, the Au content of an orebody would define a fourth and ultimate distribution; such Au contents are a further one or two orders of magnitude higher and extremely restricted in areal extent. In a study undertaken at Dest-Or mine (Qudbec) in 1984 (i.e., approximately one year after the start of production), we have identified these various Au distributions around the Dest-Or orebody. We have simultaneously studied As, Sb, and W distributions around this deposit. REGIONAL GEOLOGY

The Dest-Or mine is located 30 km NE of Rouyn-Noranda in the Destor Township, Qudbec, in the Abitibi greenstone belt, Superior Province (Fig. 1 ). The Abitibi greenstone belt is Archean (ca. 2.5-2.8 Ga) in age and approximately 200 km wide by 700 km long, being the largest greenstone belt in the Superior Province. The Abitibi greenstone belt is made up of lensoid volcano-sedimentary domains. Both tholeiitic and calc-alkaline volcanic rocks are present; basalt predominates in many volcanic sequences, but all show variable proportions of more felsic volcanics. Pyroclastic rocks are common. The associated sedimentary sequences are principally graywacke. These volcanic and sedimentary assemblages are intruded by large syn-tectonic and post-tectonic granodioritic masses (Goodwin and Ridler, 1970; Goodwin, 1979, 1984).

43

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Fig. 1. Locationof the studyarea in the Abitibigreenstonebelt. AfterGoodwinand Ridler (1970). REGIONALGEOLOGYNEAR THE STUDYAREA The geology within 25 km of the Dest-Or mine is shown in Fig. 2. The main structural feature in this area is the Porcupine-Destor fault that passes 2.5 km south of the Dest-Or mine shaft. It strikes at 100 °, dips approximately vertically and divides the area in two. Hubert et al. (1984) have suggested that there may have been major horizontal transposition along this fault; it is clear that rock formations on each side of the fault belong to different rock groups. The Porcupine-Destor fault is the locus of many small intrusive masses; it is also an area of intense carbonatization, chloritization and silicification (Boivin, 1974; Trudel, 1975; Dimroth et al., 1983; Hubert et al., 1984). South of the Porcupine-Destor fault, the Blake River Group comprises at its base, a variolitic horizon and tholeiitic basalt, andesite and gabbro; its midpart is essentially calc-alkaline (basalt, andesite, rhyolite, and pyroclastic rocks) and its upper part is tholeiitic (basalt and rhyolite). The Kewagama Group comprises essentially conglomerate, graywacke, and argillite. The Malartic Group contains basalt and ultramafic rocks. North of the Porcupine-Destor fault, the two principal rock groups are the Kinojevis Group and Duparquet Formation; the latter is sedimentary (conglomerate, arkose, graywacke) and rests discordantly on the former. The Kinojevis Group is host to the Dest-Or Au deposit. Knowledge of the stratigraphy and structure of this group is derived from the work of Buffam (1925), Bannerman (1940), Graham (1954), Baragar (1968), Boivin (1974), Trudel (1975), Dimroth (1976), Gdlinas et al. (1977), Hocq (1977, 1979),

44

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Fig. 2. Geology of the Northern Noranda area. 1 =Palmarolle granite; 2=Other granites; 3=Duparquet group (conglomerates arkoses, greywackes); 4=Blake River volcanics; 5 = Kewagama group (greywackes,argillites ); 6 = Destor complex/ultramafites, basalts; 7 = Upper Deguisier Formation (gabbro, basalts, andesites); 8 - Lower Deguisier Formation (basalts) ; 9=Huntermine Formation {rhyolites, tufts, iron formation) (6 to 9 are part of the Kinoj~vis Group); 10= Malartic Group. After Hocq {1979), Dimroth et al. {1982), Goldie (1982), Gdlinas et al. {1984). D i m r o t h et al. (1982, 1983 ), Goldie (1982) a n d H u b e r t et al. (1984). Principal lithologic c o m p o n e n t s for these groups are given in Fig. 2. Rock f o r m a t i o n s n o r t h of the fault have been folded along e a s t - w e s t axes (Abitibi anticline, Abijevis syncline ). MINEAREAGEOLOGY Figure 3 shows the geology of the Dest-Or p r o p e r t y a n d p a r t of the surrounding Bassignac property; the latter e x t e n d s considerably b e y o n d the limits of

45 Fig. 3 in all directions. The principal (65%) rock type observed is gabbro. It may represent the central part of thick flows but some of it is known to be intrusive (quasi-concordant sills). Basalt and andesite are the next most abundant rocks (30%). Locally, some rhyolite has been observed (e.g., 500 m southeast of Dest-Or Mine) ; tuff is rare but locally present (e.g., 1 km south of Dest-Or Mine). This sequence is essentially comagmatic and tholeiitic and belongs to the Upper Deguisier Formation. The Dest-Or gold deposit contains 2.44 Mt of ore at 4.29 g/t Au. The orebody is essentially a breccia zone striking N15 °W and dipping 50 ° W. Host rocks have been intensely silicified, carbonatized and hematitized; quartz, carbonates, illite, and pyrite are the gangue minerals. The only known ore mineral belongs to the gold-electrum series; microprobe analyses of individual particles give from 83% Au-17% Ag to 72% Au-28% Ag. The Au particles are very finegrained (median at 5/lm) ; they occur as inclusions and fracture fillings in a very fine-grained (10-20/~m) pyrite and as disseminations in the host rocks. Hydrothermal alteration of wall rocks is extensive but mostly cryptic; it can be identified microscopically for 10-15 m into the host rocks. This alteration comprises silicification, carbonatization and hematitization. Potassium addition has caused the development of illite. Ferromagnesian minerals (augite, actinolite, epidote, chlorite), albite and ilmeno-magnetite have been destroyed. SAMPLING AND ANALYTICALMETHODS Two sets of samples were collected: (1) A property set of 139 samples, to represent the 14 km 2 of the Dest-Or and Bassignac properties (Fig. 3). All rock types are represented. Sheared, fractured or visibly altered areas of outcrop, were not sampled; sampling was based on a regular grid when possible (ca. 100-200 m ) , as shown in Figs. 9, 11 and 13 (Table 1). ( 2 ) A mine set comprising 34 samples (Table 2). This set was made up from drill cores on mine section 165 N (Figs. 10, 12, 14 and 15). All samples were analyzed for Au, As, Sb, and W by neutron activation analysis using the Slowpoke reactor at ]~cole Polytechnique (1012 n/cm2/s). The analytical procedure is essentially adapted from Crocket et al. (1968), Rowe and Simon (1968), Gottfried et al. (1972) and Hoffman et al. (1979). Our recent experience has shown that valid measurements at a = 3 ppb Au can be obtained on specimens containing more than 15 ppb Au by INAA (instrumental neutron activation analysis, i.e., irradiation in the reactor and counting on y-spectrometers after a suitable decay period); for specimens containing less than 15 ppb Au, it is necessary to use RNAA (radiochemical neutron activation analysis, i.e., concentration of Au from the activated sample by chemical separation on a suitable resin followed by counting on 7-spectrometers). Analytical details on accuracy and precision data are given in Perrault et al.

46

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47 TABLE 1 Au, As, and Sb; property data set.Dest-Or and Bassignac properties Sample No.

11 10 9 82 8 33 53 54 52 51 50 49

12 122 123 30 121 31 83 84 7 81 80 32 14 112 113 115 116 46 117 48

Au ppb

3.0 8.7 11.8 12 5.7 5.4 2.2 4.0 8.4 4.6 4.5 4.4

4.3 10 1.7 3.5 3.2 10.6 2.6 12 27.5 12 10 12.2 4.3 28 12 10 1.1 3.6 2.0 7.6

As ppm

2.2 5.3 2.6 4.0 2.2 1 1.7 1 5.8 1 12.4 1

5.0 2.3 10.7 1.7 10.6 2.1 4.9 2.1 1.0 8.9 1.7 1 1.87 11.5 0.7 5.4 13.6 1 1.7 1

Sb ppm

4.83 0.24 1.29 0.44 0.89 0.59 0.19 0.07 1.38 0.07 0.14 0.07

0.74 3.28 0.89 1.50 1.46 0.24 0.18 0.29 0.07 2.61 7.15 0.71 1.72 7.71 1.36 0.11 1.58 0.1 0.53 0.1

Lithology

UTM N

E

5372500 to 5372000

Increasing

5 372 135 115 145 205 045 085 125 170 075 245 215 170

651 075 285 580 870 2 175 450 -3 155 180 790 4 155 420 5 000

5372000 to 5371500

Increasing

5 371 615 945 695 645 855 565 905 615 635 930 785 775 515 980 720 655 905 615 575 965

650 835 0 955 1 070 1 230 1 270 1 350 1 485 1 650 1 940 1 960 2 215 2 505 2 560 2 660 2 985 3 260 3 360 3 560 3 760 5 020

R G BA G BA BA BA G BA BA T BA

BA G BA BA BA T G G G G BA BA BA BA G BA BA G BA G

48 TABLE 1 (continued) Sample No.

129 127 128 29 124 125 126 28 131 130 132 87 86 85 150 13 149 151 110 111 6 152 114 47 118

107 108 27 106 98 97 15 146 145 109 147 79 55

Au ppb

5.4 10 2.3 38 2.9 5.1 25 213 4.8 5.4 10 3.3 16 16 4.3 55 3.7 1 17 1.6 2.9 12 7.7 81 7.8

3.6 2.0 36 2.0 3.8 1.1 2.8 0.8 1 5.9 6.7 10 3.8

As ppm

0.9 1 2.6 9.8 0.6 3.6 7.0 1 8.4 7.8 2.0 2.6 3.2 2.9 10.0 1.6 2.8 3.0 1 4.2 1 1.5 ] 1 1

10.4 2.7 1 4.5 1.3 1.7 1.8 1 6.3 3.1 1.4 3.5 4.7

Sb ppm

0.30 0.1 1.35 0.69 0.31 1.02 0.71 0.70 4.49 0.99 2.82 0.62 1.90 2.06 0.28 2.15 0.10 1.05 2.07 3.53 0.98 0.28 0.85 1.05 0.78

2.17 0.79 0.17 1.69 0.43 0.1 1.00 0.1 0.85 0.12 1.91 0.1 0.73

Lithology

UTM N

E

5371500 to 5371000

Increasing

5 371 145 100 100 235 385 165 020 255 355 175 445 015 345 480 275 165 245 475 050 045 135 335 440 415 105

650 840 845 845 1 030 1 070 1 070 1 080 1 180 ! 200 1 240 1 385 1 550 1 560 1 760 l 870 I 970 2 030 2 235 2 250 2 260 2 515 2 515 2 900 4 380 4 495

5371000 to 5370500

Increasing

5 370 625 725 625 630 725 625 775 595 530 840 685 965 535

651 060 1 100 1 110 1 190 1 460 1 660 1 940 2 120 2 280 2 315 652 460 2 485 2 565

T R BA BA BA G G G G BA G BA BA G G G BA R G R G G BA BA

BA BA BA BA G G BA G BA G R G BA

49 T A B L E 1 (continued)

Sample No.

78 148 77 45 44 43 120 140 139 41 138 119 40 39

104 26 103 105 101 102 16B 16A 17 94 96 95 18 88 74 69 75 73 22 71 70 76

Au ppb

4.4 1.7 2.3 3.8 4.9 6.3 1.3 2.4 1.1 248 1.3 15 3.4 8.6

0.3 15 40 2.5 1.9 2.6 22 6.9 4.4 3.4 5.2 1.6 3.0 0.9 1.4 3.6 15.4 17 43 15 4.1 18

As ppm

1 1 15.8 1 1 1 3.7 8.1 1.5 1 6.3 2.0 1 2.0

11.5 1 4.4 5.9 22.6 1.5 20.3 1 5.1 21.1 3.4 4.9 3.3 2.2 1 3.6 2.3 3.1 1 14.3 1.5 2.0

Sb

Lithology

UTM

ppm

2.47 0.97 0.89 0.1 0.13 0.1 0.76 0.76 0.53 0.11 1.95 0.30 0.22 0.12

1.52 0.22 0.83 1.90 1.04 0.46 3.99 0.1 1.60 1.19 1.57 2.47 1.04 0.47 0.14 0.90 0.30 0.79 0.1 1.94 1.02 1.29

N

E

5371000 to 5370500

Increasing

5 370 775 960 605 805 930 625 945 685 635 685 585 945 815 505

2 570 2 735 2 760 3 010 3 560 3 785 3 845 3 995 4 070 4 085 4 230 4 635 4 860 5 060

5370500 to 5370000

Increasing

5 370 410 125 235 415 070 260 460 495 145 015 385 275 015 375 075 180 345 075 055 005 055 410

650 940 0 980 1 110 1 200 1 280 1 330 1 415 1 460 1 520 1 660 1 680 1 740 1 930 2 060 2 160 652 310 2 360 2 430 2 525 2 630 2 680 2 725

R R G G G G G G BA BA BA G G G

G T G G G G G G BA G BA BA G BA G G G G G BA G BA

50 TABLE 1 (continued) Sample No.

142 34 141 42 135 137 37 38

100 25 24 99 89 90 23 93 92 91 19 144 143 65 66 20 21 72 67 68 35 133 134 36 136

Au ppb

6.1 5.1 2.6 7.9 29 2.3 11.2 20.1

15 9.9 7.7 6.5 46 2.4 30 4.8 0.8 0.6 6.8 2.2 6.7 3.1 17 32 120 2.4 12 1.3 10.0 2.0 4.3 5.7 20

As ppm

8.6 1.6 5.5 1 3.4 5.8 4.4 5.5

26.8 6.2 16.8 0.8 4.5 25.9 8.2 31.9 3.2 47.8 29.7 5.8 3.8 41.6 28.6 9.8 38.5 4.1 14.0 1 5.2 6.4 1 5.2 2.6

Sb

Lithology

UTM

ppm

0.90 0.23 0.74 0.21 2.31 0.58 1.06 0.40

0.15 3.36 2.98 0.70 3.30 6.65 1.23 0.34 2.17 1.68 1.38 2.77 2.38 2.41 3.13 1.08 6.71 1.20 2.93 0.25 0.12 0.21 0.36 0.96 1.90

N

E

5370500 to 5370000

Increasing

5 370 025 060 385 225 050 405 015 005

2 3 3 3 4 4 4 4

920 095 860 970 260 370 650 970

5370000 to 5369400

Increasing

5 369 950 600 685 845 605 690 655 825 600 660 575 815 835 655 515 515 510 975 450 455 555 885 685 805 825

651 080 1 090 1 200 1 220 1 450 1 475 1 530 1 560 1 580 1 610 1 910 2 000 2 005 2 080 2 320 2 360 2 400 2 450 2 630 2 810 653 250 3 450 3 610 3 960 4 410

Lithology: G = gabbro; BA-- basalt and andesite; R = rhyolite; T = tuff; P = porphyry.

G BA BA T G G BA G

G G BA BA G BA T BA T BA BA T BA G BA P BA BA BA G G G G G G

61 TABLE 2

Au, As, Sb and W, mine data set,section 165N, Dest-Or Mine Sample No.

Au ppb

As ppm

Sb ppm

W ppm

Elevation m (1)

0.84 1.55 2.67 2.30 4.16 2.87 8.31 9.15 11.2 9.09 22.8 11.9 13.0 12.6 6.34 4.51 3.92 3.34

5 9 5 5 5 5 32 16 76 41 60 32 24 37 9 11 7 6

1492.7 1473.0 1443.0 1432.9 1430.0 1428.0 1426.1 1424.0 1420.9 1418.0 1413.0 1408.9 1408.0 1406.0 1393.2 1383.9 1374.9 1369.1

1.73 3.16 3.71 13.3 11.7 20.8 17.1 12.5 6.81 2.94

5 5 6 30 25 31 61 31 5 5

1503.0 1489.0 1477.0 1448.0 1447.2 1446.0 1435.0 1421.8 1403.0 1378.7

5.55 13.2 12.9 17.0 12.6 11.0

5 30 67 16 29 36

1514.5 1476.5 1473.4 1465.1 1436.5 1429.5

Drill hole 81-39; UTM 5 271 565N, 652 070E 249 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267

29 39 22 28 22 8.5 6360 4660 1560 60 72 34 50 79 10.2 44 54 27

1.3 3.3 4.3 2.2 8.5 3.3 179.8 49.1 19.1 4.0 7.0 3.1 3.2 10.0 3.0 3.8 2.8 1.8

Drill hole 81-31; UTM 5 371 580N, 652 095E 238 239 240 242 243 244 245 246 247 248

124 39 45 73 952 4950 24700 13600 16.2 18.9

1.4 2.6 7.9 12.9 13.9 139.8 42.3 67.3 3.3 2.3

D r i l l h o ~ 8 2 - 8 ~ U T M 5 371 600N, 652 123 268 269 270 271 273 274

29 44 28 3170 57 144

11.0 22.7 9.5 12.7 7.8 17.0

(1) Arbitrary mine reference datum. For a and minimum detection limit,see text.

52

(1984) who quote the following measured precisions and minimum detection limits:

Au> 15ppb < 15ppb As Sb W

a

M i n . detection limit

Technique

3 ppb 0.2 ppb 0.7 ppm 0.1 ppm 5 ppm

0.2ppb 0.7 ppm 0.1 ppm 5 ppm

INAA RNAA INAA INAA INAA

Our value

Recommended

1.06±0.4

1.5±0.3

Accuracy:

BHVO- 1 (basalt, Hawaii)

DATAINTERPRETATION

The distributions of Au, As, Sb, and W are log-normal best presented on log probability diagrams. There is abundant evidence in Figs. 4-7 to show this for gold. The As, Sb, and W probability plots are similar; they are not presented. Analyses of populations were reported using median, P16 and P84 values. Discrimination between populations was done graphically using the techniques of Lepeltier (1969) and Sinclair (1976). Kolmogorov-Smirnov tests (Miller and Kahn, 1962 ) were used to verify that populations had been correctly distinguished. Confidence limits were set using the diagram in Lepeltier (1969, fig. 3, p. 542 ) ; they are essentially a function of the number of samples in each population and define a 0.05 probability envelope. Gabbro, basalt~nd andesite of the Upper Deguisier Formation on the DestOr and Bassignac properties are co-magmatic. There is no significant difference in Au content between them; as shown in Figs. 4-6 and by KolmogorovSmirnov tests. Similar conclusions are derived from As, Sb, and W data (not illustrated). GOLD DISTRIBUTIONS

The distributions of Au in Dest-Or mine rocks are shown in Figs. 4-7. A summary of these data is presented in Table 3. There are three distinct distributions.

Background This is population A of Figs. 4-6. It is sufficient to recall the statistical parameters of the gabro-basalt-andesite population: median at 3.6 ppb Au, P~6

53 TABLE 3 Gold distribution, Dest-Or Mine, Quebec; in ppb Background (confidence limits ) Gabbro Median Pls Ps4 n

3.1 (2.5- 3.9) 1.7 (1.3- 2.0) 6.0 (4.7- 7.6) 42

Basalt and andesite Median Pls Ps4 n

3.2 (2.4- 4.3) 1.5 (1.2- 1.9) 7.0 (5.1- 9.5) 42

Gabbro, basalt and andesite Median P~6 Ps4 n

3.6 (2.5- 5.1) 1.5 (1.1- 2.1) 8.8 (6.0-13) 88

Felsic tuff Geometric mean n

5.4 12

Ore zone halo

Orebody halo

9.4 ( 7.0-12 ) 3.1 ( 2.3- 3.9) 27 (20 -34 ) 34

37 (25- 56) 17 (10- 25) 74 (55-140) 26

at 1.5, Ps4 at 8.8, and population size 88. The median value is very close to mean values for basalt and gabbro elsewhere in the world: 2.3 ppb Au for Hawaii and 3.3 ppb Au for circum-Pacific tholeiites (Gottfried et al., 1972), 3.2 ppb Au for basalts (Jones, 1969 ), 3.2 ppb Au for mafic rocks generally (Rose et al., 1979 ) and 5.2 ppb Au for gabbros ( Jones, 1969). We think that this Au content is primary (magmatic) and represents background in the Upper Deguisier Formation. Background Au values are indicated for 65% of the area sampled. Ore zone halo

Statistical parameters for this population are: median at 9.4 ppb Au, P16 at 3.1, Ps4 at 27 and the population size 34 in the property data set (population B, Figs. 4-6). In Fig. 9, the limits of ore zone halos have been set at 7 ppb Au for the threshold (i.e., approximately the mean point between Ps4 of background at 8.8 and Pls of ore zone halos at 3.4) and 20 ppb Au for the upper limit (i.e., approximately the mean point between Ps4 of ore zone halos at 27 and P16 orebody halos at 17) ; slight differences between these values and exact mean points are considered small compared to errors in defining statistical

54

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37 n:24 ; 36% OREZONEHALO

Au

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95

PROBABILITY Fig. 4. Gold content of gabbro. Property data set.

parameters and confidence limits indicated by Lepeltier tests (Figs. 4-6). On the Dest-Or and Bassignac properties, 30% of the area is estimated to be within ore zone halos. Roslyakov and Roslyakova {1975 ) suggest that ore zone halos envelop many orebodies in an ore field; it is not clear in their text whether ore zone halos are the result of dispersion of Au from orebodies (and mineralizing fluid channels) to the country rock, or whether they represent an area where some weak but identifiable preconcentration of Au preceded the actual formation of the orebodies. Petrographic and other geochemical investigations during this study have not shed any light on this subject but it is presumed that ore zone halos result from the dispersion of Au from the orebodies via the orebody halos.

Orebody halo One such halo is observed around the one orebody actually known on the property. It is defined from the mine data set (Fig. 7): median at 37 ppb Au, Pm at 17, P ~ at 74, and population size 26. The extent of this halo is shown in

55 2

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n = 14 ; 25% OREZONE

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84

95

Fig. 5. Gold content of basalt and andesite. Property data set.

Fig. 10, which suggests that it is conformable with the orebody and is somewhat more extensive on the hanging-wall side (ca. 60 m ) than on the footwall side (ca. 40 m ). Note that the extent of the orebody suggested here is derived from section 165 N ( Fig. 8); at the surface, the halo is recognized in only two surface samples. Observed alteration (silicification, carbonatization, pyritization, illitization) in orebody halo rocks suggests dispersion from the orebody to the orebody halo; in rocks of the orebody halo containing more than 40 ppb Au, microshears are also visible under the microscope in about 50% of the samples. To represent these various Au populations in Figs. 9 and 10, slight differ: ences between contents indicated by Pie and Ps4 of adjacent populations have been smoothed; thus, the principal contour line at 7 ppb Au marks the difference between background values with P ~ at 8.8 ppb Au and ore zone halo values with P]s at 3.1 ppb Au (see Fig. 9). The contour line at 20 ppb Au separates areas with ore zone halo values (P84 at 27 ppb Au) from areas with orebody halo values (P]s at 17 ppb Au). Sb, As AND W DISTRIBUTIONS

These three elements are sometimes used by explorationists as possible indicators of Au mineralization. In the course of neutron activation analysis for

56 iOO

Au

Log

Population B

B

ppb

Median

9.4 ppb Au

Pie

3. t

ps4

27

n

=

ppb --

Au

/

34 ~ 2 7 %

O R E Z O N E HALO Confidence Limits

/' I

/ Population A

/

/ / / /

~

/

Median

/

3.6 ppb Au

pie

1.5

p84

8.8

n : 88 ; 73% BACKGROUND

5

16

50 PROBABILITY

84

95

Fig. 6. Gold contents of gabbro, basalt and andesite. Property data set.

Au, they can be measured at little extra cost. We feel that, once their distributions in and around Au deposits and in enclosing rock formations are better known, we may also gain some further insight into Au mineralizing processes.

Antimony Antimony contents of gabbro differ slightly from those of basalt and andesite: medians are 0.48 and 1.20 ppm respectively (Table 4). The combined median value for gabbro, basalt and andesite ( 0.80 ppm Sb, Table 4) is higher than known abundances for these rock types: 0.17 ppm Sb for tholeiitic basalt and andesite of the lower Malartic Group (Lacroix and Perrault, 1984), 0.11 ppm Sb for calc-alkaline intermediate to felsic volcaniclastic rocks of the upper part of the Blake River Group, Doyon Mine, 0.43 ppm Sb for calc-alkaline intermediate to felsic volcanics of the Val d'Or Formation (Perrault, 1985), 0.1-0.2 ppm Sb as a tentative world average for basalt and gabbro (Onishi,

1967). Antimony distributions (Table 4) can also be interpreted to define orebody and ore zone halos; the limits 2 and 10 ppm Sb were used to define both halos,

57 I0,000

/. Log

Au ppb

I

:

+

ppb Au

1,000

78%

Confidence Limits

-_ ,J

I00

//

1

--

Populat on 'A

-

M e d i a n 3 7 ppb AU - I0

Ple

17

pe4

74

-

-

n = 2 6 ; 78% OREBODY HALO

I 50

84

95

PROBABILITY

Fig. 7. Gold distribution in orebody halo. Mine data set. All rock types.

both being approximate limits between P84 and P16 of adjacent populations. The spatial distribution of Sb is shown in Figs. 11 and 12; it is clear that both Sb ore zone halos and orebody halos are less extensive than comparable Au halos. Antimony is not much more enriched in the ore itself: the mean Sb content for the six ore samples ( A u > 3000 ppb, Table 2) is 14.1 ppm. Enrichment factors calculated with background values as reference give 4 X for ore zone halos, 15X for orebody halos and approximately 20X for the orebody. Comparable factors for Au are 3 X, 10 X and 1900 X respectively.

58 S-60°W

~1-40

N-60°E

81-39

1525

81-31

82-86

,=

80-18

Bedrock

1500

1475

t450

1425

1400 1 - 3 DPm Au > 3 Ore body 1375 Shear zone

Elevation (m) Hematitiaed rock

Fig. 8. Section 165, Dest-Or orebody. Extent of shear zone and hematitization. From mine data.

Arsenic

The average background for As as determined from the property set of data is 4.5 ppm (Table 4 ). It is high compared to known values for these types of rocks: 1.1 ppm for tholeiitic basalt and andesite of the lower Malartic Group (Lacroix and Perrault, 1984), 1.4 ppm for calc-alkaline intermediate to felsic volcaniclastic rocks of the Upper Blake River Group, Doyon Mine, QuSbec, 1.9 ppm for calc-alkaline intermediate to felsic volcanics of the Val d'Or Forma-

59

o

T

o

I

o

I

I

r

\ ID []~ DO •

• "~~

~

~

~ ~

g ®

o

E

O

60

S-60°W

,N-6OOE =,,=

1525

1500

--

1475

--

1450

--

~

/

~REBODY

1425

1400

~(b0 ~1~ / / 2~ // /

•

AuinhostroCks Au(Dpb) • Sample

1375 Elevation

(m)

~r

Fig. 10. Gold around the Dest-Or orebody. The 20 ppb Au contour line defines the orebodyhalo and the 100 ppb line practicallycoincideswith the orebodylimits. tion ( Perrault, 1985) and 1.5 ppm as a tentative world average for basalt and gabbro ( Onishi, 1969). The mine data set suggests a zone of As enrichment (orebody halo) t h a t is about 15 m wide on each side of the orebody as defined by the 7 ppm contour line (Fig. 14); it is also the Pls value for this distribution (Table 4). The property data set does not allow the definition of an ore zone halo. Furthermore, As values define a large anomalous (?) area in the SW quarter of the map area (Fig. 13). There are also some high Au and Sb values in this area

61 TABLE 4 Sb, As and W distributions,Dest-Or Mine, Quebec; in ppm

Sb Background

As Ore zone halo

Orebody halo

Background

W Orebody halo

Background

Orebody halo

<5

37 29 48

Gabbro

Median Pie

Ps4 n

0.48 0.13 1.80 51

4.2 1.7 12 51

1.20 0.52 2.40 47

3.6 1.0 13 47

Basalt and andesite

Median P16 Ps4 n

Gabbro, basalt and andesite

Median Pie Ps4 n

0.80 0.30 2.10 98

3.4 1.9 5.8 16

12.5 11 15

4.5 1.4 14

13.7 7.3 27

16

98

13

15

Felsic tuff

Geometric mean n

0.6 13

but they seem much more restricted in areal extent. Two alternative explanations should be considered: the As distribution is stratigraphic, or it may be related to the Porcupine-Destor Fault (roughly at the southern limit of the map area, not shown in Fig. 13 ). Arsenic is enriched approximately 4 × in the orebody halo and 20)< in the orebody. Tungsten

In our INAA analyses, conditions were set to obtain the best Au values: 7spectrometry measurements were made after a decay time of approximately 7 days, which is optimal for measuring Au. It is unfortunately a little too long for W measurements. Tungsten-187 has a half life of 24 h and 7-spectrometry after two days would have been preferable. Difficulties are further compounded by the fact t h a t after one or two days, rock samples are still too active (mainly because of contained Na) to yield any meaningful 7-spectrometry measure-

62

8

o --,,~

~

•

E

~

o

~

~

^

~

V

1180

"A " \./ . ~,1,...,,

E

8

,,,,)

o O

.

\

O

O

8 o

63 N - 6 0 ° E ~.~

S-60°W

t525

--

1500 - -

1475

1450

--

1425

140C

\\

•

Sample

\

1375 Elevation(m) 3

~'ig.12. Antimony around the Dest-Or orebody. The I0 p p m contour lineenvelops the orebody. Normal content is 0.3-2.1 ppm.

ments for W. Hence .the W data are less reliable at concentrations below 10 ppm. Notwithstanding this, high W concentrations were observed in the orebody samples and in adjacent rocks (up to 10 m from it); 17 of the 34 values in the mine data are centered on 31 ppm W (P18 at 24 and Ps4 at 60) (Fig. 15). Krauskopf (1970) proposes 0.5-1.0 ppm W as a general average for mafic rocks. Thus it is clear that W is enriched in the orebody and in the rocks immediately adjacent to it.

64 g o

g o

oo

g

o

o_ ~t i

\\ \ \\ \

g

BO

~

g

o

®

o

Q

c~

o

c~ E

g

o

o

C~ o

0

oo

o

,.~

~

65 N-60=E

S-60°W

1525

1500

u

1475

1450

m

1425

1400

--

1375l

As (pc.m) •

•

Sample

f

E l e v a t i o n (m)

Fig. 14. Arsenic around the Dest-Or orebody.The 15 ppm contour lineenvelopsthe orebody. Normal contentis 1-15 ppm HALOS A N D G O L D PROSPECTING It is clear from this study that gold orebody halos are m u c h more extensive than gold orebodies (ca. 100 m for the former and 5 m for the latter). The larger orebody halo targets should certainly be easier to find. Only experience will determine whether this type of search will yield very m a n y targets with very few new orebodies. The Dest-Or data show possible indications of other orebody halos in addition to the one enveloping the k n o w n orebody: some of

66 S-60°W

1525

--

t500

--

1475

--

1450

--

1425

--

N-6OOE

/

30 20 10

1400

--

q~

~

W in host r o c k s

~0 •

1375

--

0

W (ppm) •

Sample

0 Elevation (m)

Fig. 15. Tungsten around the Dest-Or orebody. The 30 ppm contour line envelops the orebody. Normal content is below 5 ppm and is not defined beyond this.

these have been insufficiently sampled and it is not certain whether they are orebody halos or isolated erratic Au values. None have yet been sufficiently investigated to establish that there is no contained orebody (frequently an impossible task! ). Ore zone halos promise to be valuable tools in the selection of favorable areas. They are very extensive: 30% of the Dest-Or and Bassignac properties are above the 7 ppb Au threshold value. In another case history, Perrault (1985) studied Au distribution around the Doyon orebody; an orebody halo approxi-

67 mately 400 m wide was defined at the 50 ppb Au contour line. They did not identify an orezone halo in this latter area, but it was recognized that the surrounding Blake River Group intermediate and felsic pyroclastic rocks have an unusually high Au content (median at 28 ppb Au, P16 at 19, and Ps4 at 39). Perrault (1985) has similarly determined that the Au content of the Val d'Or Formation (intermediate and felsic volcanics hosting gold mines in the Val d'Or area) is also high in Au (median at 13 ppb Au, P16 at 5 and P ~ at 30). Work in progress at Ecole Polytechnique on the Kiena, Sigma, and New Pascalis deposits at Val d'Or gives further indication of important orebody halos and high Au content in host rocks. Gold determinations are critical in applying these techniques. Gold can be measured in concentrations between 15 and 1000 ppb by INAA (instrumental neutron activation analysis) at reasonable cost (ca. 10-15S/sample); however, in the 0.2-15 ppb range, to obtain reliable data it is necessary to proceed to the separation of Au after activation and before going on to ~-spectrometry (RNAA). This multiplies the cost by a factor of approximately 5 at present. It is clear from the Dest-Or data that 80% of the samples must be analyzed by RNAA. This is the principal drawback to the application of the technique. Caution should be exercised while using Au distribution maps of the Fig. 9 type: orebody halos indicated by single samples should be questioned and certainly resampled if possible. It is well known that it is very difficult to adequately represent Au content by a single specimen. Similarly, the authors would recommend the use of large specimens (ca. 2-3 kg) in this type of mapping. In the area of Fig. 9, beyond the orebody halo around the Dest-Or mine, five other halos are indicated by two samples each and a few others are indicated by single samples. It is appropriate to close this discussion on Au distribution with a citation from Roslyakov and Roslyakova (1975): "Only this approach [determination of gold] permits a correct assessment of the potential of an area and the discovery within it of blind deposits at least cost" (p. 198 in the translation). We share these views. Arsenic, Sb, and W are also commonly used in defining orebody halos. The Dest-Or data certainly indicate that these elements give useful halos. CONCLUSIONS (1) The Upper Deguisier Formation, host to the Dest-Or gold deposit, is essentially composed of comagmatic gabbro (65%) and basalt (30%). Gold, Sb, As and W are log-normally distributed within this formation. Median Au content for normal mafic rocks of this group is 3.6 ppb Au (P16 at 1.5 and P ~ at 8.8). For Sb, the median is 0.80 ppm (PI~ at 0.30 and Ps4 at 2.10); for As, the median is 4.5 ppm (P16 at 1.4 and Ps4 at 14). Tungsten values are too low to permit a reliable definition of the background. The Au content is compara-

68 ble to that of mafic rocks elsewhere in the world but the Sb and As values are significantly higher. ( 2 ) Gold distribution on the Dest-Or and Bassignac properties shows inflections on log Au-probability plots that are interpreted as defining ore zone and orebody halos. The ore zone halo is statistically defined by its median (9.4 ppb Au), and its P16 (3.1 ppb Au) and Pss (27 ppb Au) values. The orebody halo is characterized by a median at 37 ppb Au (P16 at 17 and P84 at 74). (3) Approximately 30% of the Dest-Or/Bassignac property is above the 7 ppb Au threshold set for ore zone halos. (4) The orebody halo ( threshold at 20 ppb Au ) around the Dest-Or orebody is approximately 100 m wide (60 m on the hanging wall and 40 m on the footwall). (5) There are As, Sb and W halos around the Dest-Or orebody; but they are somewhat less extensive than the Au halo. (6) Gold analyses in the 0.2 to 100 ppb range and the definition of their distributions can be gainfully used in the search for blind gold ore deposits. ACKNOWLEDGEMENTS We wish to express our sincere appreciation to Ressources Aiguebelle Inc., the owners of the Dest-Or Au deposit, for their financial and technical assistance and for providing access and material; to MERQ (Minist~re de l']~nergie et des Ressources du Quebec) for financial support (research agreement on Metallogeny of Gold in Quebec ); to NSERC (National Science and Engineering Research Council, Canada) for financial support (scholarship to Alain Beaudoin and grant A-1180 to Guy Perrault for some of the analytic expenses) ; to FCAC (Formation de Chercheurs et Action Concert~e, Minist~re de l'Education du QuSbec) for financial support; to IGN ( Institut de Gdnie Nucldaire, t~cole Polytechnique) for the reactor work; to our geochemical staff at t~cole Polytechnique, and more particularly, Jean-Luc Bastien, for the neutron activation analyses; to Andrd Lacombe for the drafting and to Sylvia Morneau for typing of the manuscript. Numerous colleagues have variously contributed via informal discussions (R. Darling, P. Trudel, M.F. Taner, P. Sauvd and others). Nevertheless, the authors must be charged for any final shortcomings in the data sets, their interpretation and the manuscript derived from them.

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69

Boivin, P., 1974. Pdtrographie, stratigraphie et structure de la ceinture de "schistes verts" de Noranda, dans les cantons de Hebecourt, de Duparquet et de Destor, Quebec, Canada. Th~se de doctorat de sp&ialit~, Universitd de Clermont, France, 157 p. Buffam, B.S.W., 1925. Destor area, Abitibi County. Geol. Surv. Can., Sumrn~Rep., Part C: 82-104. Crocket, J.H., Keays, R.R. and Hsieh, S., 1968. Determination of some precious metals by neutron activation analysis. J. Radioanal. Chem., 1: 487-507. Daigneault, R., 1983. Gdologie et g~ochimie du gisement d'or de la Mine Lamaque, Val d'Or, Quebec. M.A.Sc. thesis, F~colePolytechnique, 174 p. Dimroth, E., 1976. Physical volcanology and sedimentology of the Abitibi Greenstone Belt, Quebec. Geol. Surv. Can., Pap., 76-18: 107-111. Dimroth, E., Imreh, L., Rocheleau, M. and Goulet, N., 1982. Evolution of the south-central part of the Archean Abitibi Belt, Quebec. Part I: Stratigraphy and paleogeographic model. Can. J. Earth Sci., 19: 1729-1758. Dimroth, E., Imreh, L., Goulet, N. and Rocheleau, M., 1983. Evolution of the south-central segment of the Archean Abitibi Belt, Quebec. Part II: Tectonic evolution and geomechanicalmodel. Can. J. Earth Sci., 20: 1355-1373. G~linas, L., Brooks, C., Perrault, G., Carignan, J., Trudel, P. and Grasso, F., 1977. Chemostratigraphic divisions within the Abitibi volcanic belt, Rouyn-Noranda District, Quebec. Geol. Assoc. Can., Spec. Pap., 16: 265-295. G~linas, L., Trudel, P. and Hubert, C., 1984. Chemostratigraphic division of the Blake River Group, Rouyn-Noranda area, Abitibi, Quebec. Can. J. Earth Sci., 21: 220-231. Goldie, R., 1982. Lithostratigraphy and the distribution of gold in the south-central Abitibi belt of Quebec. In: Geology of Canadian Gold Deposits. Can. Inst. Min. Metall., Spec. Vol., 24: 15-26. Goodwin, A.M., 1979. Archean volcanic studies in the Timmins-Kirkland Lake-Noranda region of Ontario and Quebec. Geol. Surv. Can., Bull. 278, 51 p. Goodwin, A.M., 1984. Archean greenstone belts and gold mineralization, Superior Province, Canada. In: R.P. Foster (Editor), Gold 82: The Geology,Geochemistry and Genesis of Gold Deposits. A.A. Balkema, Rotterdam, pp. 71-97. Goodwin, A.M and Ridler, R.I:I., 1970. The Abitibi Orogenic Belt. In: A.J. Baer (Editor), Symposium on Basins and Geosynclines of the Canadian Shield. Geol. Surv. Can., Pap., 70-40: 1-30. Gottfried, D., Rowe, J.J. and Tilling, R.I., 1972. Distribution of gold in igneous rocks. U.S. Geol. Surv., Prof. Pap. 727, 42 p. Graham, R.B., 1954. Parts of Hebecourt, Duparquet and Destor Townships. Geological Report 61, Ministate des Richesses Naturelles du Quebec, 63 p. Hocq, M., 1977. Demie-Sud du Canton d'Aiguebelle. Minist~re des Richesses Naturelles du Quebec, DPV-544, 23 p. Hocq, M., 1979. Demie-Nord et quart sud-ouest du Canton d'Aiguebelle. Minist~re des Richesses NatureUes du Quebec, DPV-644, 37 p. Hoffman, E.L., Brooker, E.J. and White, M.V., 1979. The determination of gold by neutron activation analyses. In: Proceedings of the Gold Workshop, Yellowknife, N.W.T., December 1979, pp. 79-99. Hubert, C., Trudel, P. and G~linas, L., 1984. Archean wrench fault tectonics and structural evolution of the Blake River Group, Abitibi Belt, Quebec. Can. J. Earth Sci., 21: 1024-1032. Jones, R.S., 1969. Gold in igneous, sedimentary and metamorphic rocks. U.S. Geol. Surv., Circ. 610, 26 p. Krauskopf, K.B., 1979. Tungsten. Parts B to 0 in Wedepohl (1978). Lacroix, R. and Perrault,G., 1984. Distributionde l'ordans les roches hStes, propri~t~ N e w Pascalis,Val d'Or, Quebec. Private reportto S O Q U E M , 23 pp., 8 mai 1984.

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