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Nickel-Mineralogy and Chemical Composition ofSome Nickel-Bearing Laterites in Southern Oregonand Northern CaliforniaBy Michael P. Foose
Abstract
The mineralogy and chemistry of 109 samples from11 nickel-bearing laterites located in southern Oregon andnorthern California were determined. The laterites areprimarily composed of serpentine, chlorite, goethite, andmaghemite. Some contain additional minor amounts ofsmectite, quartz, talc, hornblende, orthopyroxene, andtremolite. Smectite (possibly nontronite) occurs only inlaterites located on hillslopes and appears to be restrictedto areas where ground water may have been enriched inSiO2 and MgO from downslope flow across bedrock.Nickel content of the laterites averages 0.64 weight per-cent but varies between 0.45 and 1.4 weight percent;cobalt averages 0.06 weight percent and ranges between0.03 and 0.15 weight percent. Neither nickel nor cobalt haspredictable distributions. In contrast, patterns made bymajor elements follow trends defined by relatively simplechemical models. Calculated net changes in laterite chem-istry indicate that the mobility of components is, frommost depleted to least, MgO, SiO2 , nickel, MnO, Fe2 03 ,and cobalt. These calculations also show that only a few ofthe laterites have significant amounts of net enrichment ineither nickel or cobalt.
INTRODUCTION
The United States is import-dependent for a numberof important commodities, among which are nickel andcobalt. Several potentially important domestic depositscontaining these elements have been identified. Of these,the most important are the magmatic sulfides in the Still-water Complex (Montana) and the Duluth Complex (Min-nesota), the sediment-hosted and strata-bound Cu-rich sul-fides and arsenides of the Blackbird deposit (Idaho),Mississippi Valley-type lead deposits (southeast Missouri),and the nickel-bearing laterites in Oregon and northernCalifornia (Foose, 1991). Although one of these, a nickellaterite located near Riddle, Oreg., was recently mined (fig.1), none of these deposits are currently in production.Othernickel-bearing laterites occur in southern Oregon and north-
ern California, and several of these have recently beenexamined as potential additional sources of nickel andbyproduct cobalt. This study looks at some of the mineral-ogical and chemical features associated with several ofthese occurrences.
GENERAL SETTING
The nickel laterite deposits in Oregon and northernCalifornia occur over ophiolites that are part of severaldifferent accreted terranes. As a result of the accretionaryprocesses by which these terranes were affixed to thewestern margin of the United States, these ophiolitic rocksnow form subparallel belts that range in age from Paleozoic(easternmost) to upper Jurassic (westernmost) (Irwin,1977). Subsequent to emplacement, many of these ophi-olitic bodies were exposed to extensive weathering thatresulted in formation of laterites. There is some uncertaintyas to the exact age of weathering. Most probably occurredduring the Miocene formation of the Klamath peneplain(Diller, 1902). Some weathering, however, was muchyounger, as shown by the occurrence of laterite on Pleis-tocene terraces (Hotz, 1964; Moring, oral commun., 1986).Subsequently, most laterites have been uplifted and dis-sected so that many now occur on plateaus or as cappings onridges and saddles and as transported debris on sides of hillsand in valleys.
Nickel laterites similar to these are a common productof tropical weathering of ultramafic rocks. They, in fact,constitute the world's largest land-based resource of nickel(Chamberlain, 1986). The features associated with thesedeposits have been reviewed by a number of authors, mostnotably Trescases (1975), Evans and others (1979), andGolightly (1981). Features typical of laterite profiles fromthis area are reported as follows: Upper parts of lateriteprofiles consist of an extensively leached iron-rich zone(limonitic zone) that is dark reddish brown in color; ironoxide pellets locally occur near the profile top. This reddishzone grades downward into a yellow-brown zone (saprolitic
Nickel-Mineralogy and Chemical Composition of Some Nickel-Bearing Laterites El
122030" 1240
42'30"1
42'15" -.
X Mount25Emily
N ~~~~~~~~~OREGON
-~~ ~ CALIFORNIA
K) ~~~233 199'4 ~~Gas'ut '
I '\ Mount fV232 231
Earl I ~ ~~0 5 10 MILES
0 5 10 KILOMETERS
*11pCrescent City
Figure 1. A, Approximate area of the northern California-southern Oregonlaterite district (dashed boundary). B, Sample sites (solid diamonds). Shadedarea represents approximate boundary of the Kalmiopsis Wilderness area.
E2 Contributions to Commodity Geology Research
zone) in which there commonly are pieces of partlyweathered peridotite and in which the degree ofpreservation of relict bedrock structures increases withdepth. The saprolite zone grades into greenish-brownweathered peridotite and then into fresh peridotite orserpentine (Hotz, 1964; Ramp, 1978).
In some laterites, nickel occurs in the lower saproliticzone as a solid solution replacement of magnesium in avariety of secondary magnesium silicates (mostly serpen-tine, talc, and chlorite). These nickel-magnesium silicatesare referred to as the "garnierite group" (Faust, 1966) andform what are commonly known as either saprolite orsilicate ores. Nickel content of these ores typically isbetween 2 and 3 percent. In contrast, nickel in the overlyinglimonitic zone occurs mostly in goethite and rarely exceeds2 percent. Significant amounts of cobalt also occur in manylaterites and are associated mostly with manganese oxides(asbolite) that are concentrated in the lower part of thelimonitic soil zone.
In Oregon and northern California, laterites having anextensively developed nickel-bearing silicate zone areknown to occur only near Riddle, Oreg. Saprolite is presentin other deposits but generally does not contain significantamounts of gamierite-type mineralization. The reason forthe apparent restriction of higher grade nickel ores to theRiddle area is not clear, but Hotz (1964) speculates thatrocks associated with this deposit may have had a longerweathering history. As a result of its higher nickel grades,the deposit near Riddle was the first to be developed.
In addition to its relatively greater nickel content, theores at Riddle also contain relatively high amounts of silicaand magnesium. As a result of this composition, refiningmust be done by pyrometallurgical processes (Canterford,1975). The product was ferronickel containing about 49percent nickel; cobalt was not recovered separately. Incontrast, the lower SiO2 and MgO contents of limonitic orescommonly allow them to be refined by a variety ofhydrometallurgical techniques, many of which enablerecovery of both nickel and cobalt. Specific processesdesigned to extract both nickel and cobalt from therelatively low grade laterites in northern California andOregon have been developed and tested (Siemens andothers, 1975; Duyvesteyn and others, 1979; Kukura andothers, 1979), and, for this reason, several of these depositshave been evaluated as possible domestic sources of bothnickel and cobalt.
SAMPLE DESCRIPTION AND TREATMENT
Samples from several laterite deposits were collectedas part of a program to evaluate the mineral resources of theKalmiopsis Wilderness (Page and others, 1982; fig. 1).Sample sites were both within or near the wilderness areaand from an adjacent area, near Gasquet Mountain, Calif.
This latter area contains several laterite deposits that may becommercially usable. Samples from the Gasquet Mountainarea were collected from prospect pits in which profiles asthick as 7 m were exposed. In contrast, other samples werecollected with a hand auger and, because of the limitationsof this device, seldom penetrated more than 2 to 3 m oflaterite. In eight cases, this amount of penetration wassufficient to sample profiles that exhibited all the featuresfound in the more completely exposed pits as well as toshow the same features that have been described for otherlaterites in this region (Hotz, 1964; Ramp, 1978). Samplescollected from these eight locations as well as those takenfrom the exploration pits provide the material discussed inthis report.
One hundred laterite samples and nine rock sampleswere analyzed for nickel, cobalt, copper, and 10 majoroxides. Results are given in table 1. In addition, themineralogy of samples was determined by X-ray diffrac-tion. Samples were ground to less than 325 mesh and thenpressed into circular wafers. Wafers were made by placingthe ground material on a layer of boric acid and methylcellulose, a compound added to provide strength. Thismixture was compressed in a hydraulic press for at least 30seconds at a pressure of 10,000 pounds per square inch.Wafers were then exposed to CuK., radiation by using a1.00 beam slit, a 0.10 detection slit, a crystal monochrom-eter, and a proportional counter detector. The samples werescanned between 20 and 600 20 at a rate of 1/20 20/minute.
In order to resolve some ambiguous mineralogicalidentifications, several samples received further treatment.Splits from these were suspended in water and then allowedto settle onto porcelain tiles, a procedure which oriented theclay-size fraction. Four X-ray diffraction patterns, between2° and 18° 20, were made of the clay fraction; first, after thesamples had been air dried; second, after the samples weretreated with ethylene glycol (EG) for at least 1 hour; third,after the samples had been heated to 350 0C for at least 1hour; and fourth, after heating the samples to 550 0C for atleast one hour.
This procedure enables the distinction of smectitefrom chlorite and vermiculite and the distinction of serpen-tine from kaolinite. Mineral identification is based on thefollowing responses (Grim, 1968; Hathaway, unpublishedreport):
Upon treatment with EG, the 14-A peak of smectiteexpands to 17 A, while the 14-A peaks of chlorite and (or)vermiculite are essentially unchanged.
Upon heating to 350 °C, the 14-A peak of smectitecollapses to 10 A, while the chlorite and (or) vermiculite14-A peak is unchanged.
Upon heating to 550 °C, the 14-A peak of chloritemay increase in intensity, the 14-A peak of vermiculitecollapses to 10 A, and the 7-A peak of serpentine remainsstable, while the 7-A peak of kaolinite is usually destroyed.
Nickel-Mineralogy and Chemical Composition of Some Nickel-Bearing Laterites E3
Table 1. Analyses from 11 laterites[Locations of profile sample numbers are shown in figure 1; depth is in meters below surface. Nickel, cobalt, and copper are given in parts per million(J.S. Wahlberg, J. Baker, and J. Taggart, analysts). Mineralogy was determined by X-ray diffraction; numbers represent qualitative estimates of relative
Site/Sampe SampleSample type Chlorite Serpentine Goethite Maghemite Quartz Smectite Talc Oto TremoliteHonnumber depth (in) pyroxene blencde
211-1 ..... 0.23 .211-2 ..... 3
211-3 .... 6
211-4 ..... 9
211-5 ..... 1.22 .
211-6.....1.53 .211-7.....1.83 .
211-8.....2.14 .
211-9 ..........
213-1 ..... 213-2 .... 3
213-3 ..... 6
213-4 ..... 9
213-5.....1.22 .
213-6 ..... 1.53 .
213-7.....1.88 .
213-8 ..........
214-1 ..... 214-2 ..... 3
214-3 ..... 6
214-4 ..... 9
214-5 ..... 1.22 .
214-6 ..... 1.37 .
214-7 ..........
215-1 .... 1
215-2 ..... 3
215-3 .... 6
215-4 ..... 9
215-5 ..... 1.22 .
215-6 ..........
216-1 .... 1
216-2 ..... 3
216-3 .... 6
216-4 ..... 9
216-5.....1.22 .
216-6 ..........
217-1 ..... 217-2 ..... 3
217-3 .... 6
217-4 .... 9217-5.....1.22 .217-6.....1.53 .217-7 ..........
red-brown
gray-yellow
gray-yellow
gray-yellow
gray-yellow
gray-yellow
gray-green
gray-green
rock
red-brown
red-brown
green-gray
blackblackyellow-green
green-black
rock
red-brown
red-brown
yellow-green
yellow-green-black
green-black
green-black
rock
red-brown
red-brown
dark-red-brown
yellow-green
yellow-green
rock
red-brown
red-brown
yellow-brown
yellow-brown
yellow-brown
rock
dark-red-brown
red-brown
green-gray
green-gray
green-gray
green-gray
rock
red-yellow
yellow-brown
red-brown
red-brownred-brown
red-brown
red-brown
red-brown
yellow-brown
yellow-brown
yellow-brown
yellow-brown
yellow-brown
11 0.0
13 8.0
13 17
15 16
9.5 42
6.5 62
7.0 46
7.5 54
12 2.0
10 1.58.0 2.0
8.0 8.0
7.0 8.0
6.0 10
6.0 8.5
5.0 9.0
0.0
.0
3.0
3.0
3.5
5.0
2.5
5.0
15 4.0 11.5 1.0 11 .0 2.0 4.0 3.0
15 4.0 12.5 1.0 13 1.5 2.5 3.5 3.511 4.0 12.5 5.0 8.5 3.5 2.5 3.0 2.56.5 2.5 12.5 8.0 3 5.0 2.0 1.5 .0
6.5 2.5 11.5 7.5 3 4.0 .0 1.5 .06.0 3.5 8.0 14 2 7.5 .0 .0 .05.0 8.0 6.0 13 4 7.5 .0 .0 .0
10 .0
11 10
6.0 465.0 75
6.5 657.5 72
14 7.0 5 .0 4.0
10 11 4 .0 4.511 8 3 4.0 .0
3.5 10 2 5.0 .0
4.5 7.0 1 2.5 .0
4.0 7.0 1 2.0 .0
1 1
10
4.0.0
4.5
3.0
16 1.5 10 2.5 23 4.0 6.0
15 2.5 10 2.5 22.5 5.0 6.0
19 .0 10 2.5 23 5.0 7.5
11 3.0 11 .0 15 6.0 9.5
12 .0 14 .0 10.5 8.0 8.0
2.5
2.0
4.5
5.5
7.0
40 7.5 14 3.0 7.5 .0 70
44 5.0 14 6.0 4.0 .0 75
55 2.5 16 6.0 3.5 5.5 82
43 3.5 10 3.5 4.5 5.0 57
47 4.0 12 1.5 5.0 5.0 65
7.5
9
10
7
11
231-1 ....231-2 ....231-3 ....
231-4 ....23 1-5.....
231-6.....
23 1-7.....
231-8.....
23 1-9.....
231-10....
231-11....
231-12....
231-13 .. ..
.46 ....
.87 ....1.20 ....
1.55 ....2.01 ....2.32 ....2.62 ....2.93 ....3.23 ....3.54 ....3.84 ....4.15 ....4.45 ....
5.0 4.0
7.0 4.5
6.5 42
9.5 59
5.5 58
6.0 100
9.0 43
43 4.0
12 20
8.5 10
8.5 11
7.5 20
8.5 3.0
7.0 81
8.0 86
8.0 6.0
6.0 5.0
6.5 8.0
.0 4.0
12 6.0
12 6.0
12 13
6.0 1 1
5.0 12
6.0 13
2.5
4.5
3.5
5.0
2.0
2.0
9.0 2.0 10
12 .0 3.0
11 3.0 11
10 .0 1312 .0 16
10 .0 1612 1.0 13
10 3.5 11
9.5 3.5 12
10 .0 1212 2.0 1012 2.5 109.5 2.5 7.5
E4 Contributions to Commodity Geology Research
and were determined by flame atomic absorption (M. Doughten, analyst). Major oxides are in weight percent and were determined by X-ray spectroscopy
mineral abundance and are proportional to X-ray peak height as discussed in the text. LOI, loss on ignition; <, less than; IS, insufficient sample]
Sio 2 A1203 Fe203 MgO CaO Na2 O K2O Tio 2 P205 MnO LOINi (ppm) Co (ppm) Cu (ppm) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %)
6800
8300
8800
8300
8000
8600
8800
9700
2500
4900
4900
5200
5700
6200
6000
7500
3800
4800
5200
6800
6300
5400
5000
4700
1100
1 100
1100
1200
1300
260
5700
5600
5900
6400
6500
3000
8400
7000
6900
7000
6400
5900
6800
3700
4500
4600
4000
3500
3400
3700
3400
3200
3800
4000
4400
4200
1000
1600
1300
1100
940
830
800
660
130
130 15.1
95 20.8
77 27.1
80 25.5
82 27.2
80 27.9
72 26.6
52 29.2
28 40.4
700 130 14.7
700 110 18.6
640 130 14.4
1100 120 15.3
1100 120 18.4
760 110 24.0
570 75 27.8
140 10 40.3
440 40 16.6
540 37 17.8
390 23 26.8
360 23 28.8
370 25 26.3
340 23 28.3
160 10 38.7
14.2 41.0
9.0 37.6
8.1 30.8
9.3 33.2
6.9 29.9
4.9 30.5
5.0 33.0
4.4 29.7
2.1 8.4
12.6 48.3
12.8 43.9
10.0 54.1
7.9 53.7
6.6 51.6
7.2 43.9
4.5 37.8
.8 8.6
8.7 51.7
6.7 51.7
4.5 36.0
3.9 31.6
5.3 35.8
4.9 32.5
.4 8.8
190 120 21.2 23.0 33.2
180 120 22.4 22.8 33.0
180 120 24.1 23.1 31.6
140 100 25.0 22.5 29.7
160 90 22.3 21.6 33.2
56 10 42.4 16.3 9.1
530 110 27.1 5.4 34.9
620 120 25.0 5.0 38.2
540 120 30.5 5.0 33.6
530 80 32.2 3.7 31.1
440 100 34.2 4.4 29.1
140 44 38.9 1.2 9.8
10.1 0.16 <0.2
12.9 .55 <.2
15.3 .37 <.2
12.3 3.17 <.2
17.3 1.13 <.2
18.4 .70 <.2
17.2 .55 <.2
18.5 .65 <.2
37.1 2.08 <.2
4.8 .28 <.2
5.0 .37 <.2
3.2 .27 <.2
5.0 .40 <.2
3.0 .31 <.2
4.3 1.01 <.2
9.2 .83 <.2
37.7 .43 <.2
4.8 1.11 <.2
6.3 .90 <.2
15.8 .59 <.2
17.9 .54 <.2
14.7 .86 <.2
16.5 .81 <.2
36.8 .07 <.2
2.2 .26 <.2
1.8 .19 <.2
2.4 .35 <.2
2.8 .37 <.2
3.2 .61 <.2
8.5 16.50 .4
11.8 1.23 .3
11.9 1.27 .3
12.4 1.15 .4
14.5 .90 <.2
14.7 1.50 .3
36.9 .59 <.2
3.4 .74 <.2
3.1 1.97 <.2
19.2 1.10 <.2
24.0 2.00 <.2
27.6 1.15 <.2
29.7 .57 <.2
35.6 .12 <.2
4.5 .08 <.2
2.6 <.02 <.2
1.9 <.02 <.2
1.9 .03 <.2
3.8 <.02 <.2
1.8 <.02 <.2
1.5 <.02 <.2
4.2 <.02 <.2
4.3 <.02 <.2
1.8 <.02 <.2
2.1 <.02 <.2
1.7 <.02 <.2
1.6 <.02 <.2
<0.02
<.02
<.02
<.02
<.02
<.02
<.02
<.02.
<.02
.11
.15
.13
.07
.05
.05
.03
<.02
.09
.06
.05
.04
.06
.07
<.02
.26
.27
.31
.18
.15
.03
.07
.06
.07
.04
.05
<.02
.03
.03
<.02
<.02
<.02
<.02
<.02
.13
.15
.17
.20
.09
.20
.19
.17
.16
.15
.12
.13
.11
0.28 <0.1
.11 <.1
.06 <.I
.22 <.1
.11 <.1
.08 <.1
.09 <.1
.08 <.1
.03 <.I
.48 <.1
.64 <.1
.32 <.1
.21 <.1
.14 <.1
.20 <.1
.09 <.1
<.02 <.1
.40 .1
.29 <.1
.19 <.1
.16 <.1
.24 <.1
.23 <.1
<.02 <. 1
.90 1
1.01 .1
1.02 .1
.89 <.1
.79 <.1
.88 <.1
.25 <.1
.23 <.1
.20 <.1
.14 <.1
.26 <.1
<.02 <.1
.11 <.1
.10 <.1
.04 <.1
<.02 <.1
<.02 <.1
<.02 <.1
<.02 <.1
.66 .1
.51 <.1
.65 1
.69 1
.52 <.1
.68 .1
.67 .1
.62 <.1
.60 <.1
.61 .1
.57 .1
.53 <.I
.49 <. I
0.42 13.76
.58 13.61
.33 14.11
.38 12.72
.35 13.88
.37 13.82
.43 13.38
.37 13.99
.17 9.19
.60 11.40
.64 12.28
.44 12.15
.10 11.94
1.07 14.29
.90 14.99
.92 15.02
.16 10.86
.35 13.69
.41 12.88
.42 13.36
.41 15.20
.44 14.10
.41 14.21
.20 13.62
.28 16.52
.28 15.71
.24 14.84
.01 15.14
.11 15.46
.16 4.64
.51 11.30
.43 8.32
.39 10.59
.38 11.46
.33 10.84
.14 11.02
1.42 15.08
.64 13.76
.44 13.22
.29 12.30
.27 12.39
.23 12.41
.14 13.92
.56 13.20
.37 10 99
.36 11.20
.37 10.75
.42 13.49
.39 11.18
.35 11.51
.37 11.41
.38 11.10
.37 10.34
.36 11.68
.33 11.60
.35 10.79
710 100 8.6
630 85 16.8
460 60 30.0
330 60 34.7
330 60 34.7
320 230 35.3
120 12 38.9
6.5 58.0
5.9 52.9
3.1 30.5
2.0 21.9
1.8 20.1
1.7 18.6
.6 8.5
450 75 17.1 12.7 47.1
600 92 14.7 13.0 52.6
450 82 16.2 14.2 50.5
450 85 17.2 14.5 49.4
380 87 15.5 13.6 47.9
310 82 16.0 15.2 50.1
300 85 15.6 15.1 50.4
350 60 17.5 13.8 47.9
460 62 16.9 13.3 48.4
300 82 13.8 13.9 53.4
290 75 12.9 13.9 53.3
260 75 13.0 13.8 53.1
260 72 11.8 12.9 56.1
Nickel-Mineralogy and Chemical Composition of Some Nickel-Bearing Laterites E5
Table 1. Analysis from 11 laterites-Continued
Site/Sample Sample Ortho- Horn-number depth (in) Sample type Chlorite Serpentine Goethite Maghemite Quartz Smectite Talc prxn Tremoliteblne
231-14 ....231-15 ....231-16 ....231-17 ...
231-18 ....231-19 ....231-20 ....
4.76 ....
5.06 ....5.37 ....5.67 ....
5.98 ....6.28 ....6.59 ....
232-1 ..... 3
232-2 ..... 6
232-3.....1.22 .
232-4.....1.53 .
232-5 ..... 1.83 .
232-6.....2.14 .
232-7.....2.44 .
232-8 ..... 2.75 .
232-9 ..... 3.05 .
232-10 .... 3.36 .
232-it....3.66 .
232-12 .... 3.97 .
232-13 .... 4.27 .
232-14 .... 4.58 .
233-1 .... 3
233-2 ..... 6233-3.....1.22 .
233-4.....1.53 .
233-5.....1.83 .
233-6.....2.t4 .
233-7.....2.44 .
233-8 ..... 2.75 .
233-9 ..... 3.05 .
233-t0.....3.36 .
233-ti .... 3.66 .
233-12 .... 3.97 .
233-13..........
259-1 .....
259-2 .... 3
259-3 .... 6
259-4 .... 9
259-5 ..... 1.22 .
259-6 ..... 1.53 .
259-7.....1.83 .
259-8.....2.14 .
259-9 . . . . . . . . .
261-1 ..... 261-2 .... 3
261-3 ..... 6
261-4 .... 9
261-5 ..... 1.22 .
261-6 ..... 1.53 .
261-7 ..... 1.83 .
261-8 ..... 2.14 .
261-9 ..... 2.44 .
261-10..........
yellow-brown
yellow-brown
yellow-brown
yellow-brown
yellow-brown
yellow-brown
yellow-brown
red-brown
red-brown
red-brown
red-brown
red-yellow
red-yellow
red-yellow
red-yellow
red-yellowred-yellow
red-yellow
red-yellow
red-yellow
red-yellow
red-brown
red-brown
red-brown
yellow-brown
yellow-brown
yellow-brown
yellow-brown
yellow-brown
yellow-brown
yellow-brown
yellow-brown
yellow-brown
rock
red-brown
red-brown
yellow-red
yellow-red
yellow-brown
yellow-brown
yellow-brown
yellow-brown
rock
red-brown
red-brown
red-brown
gray-brown
gray-brown
yellow-brown
yellow-brown
yellow-brown
yellow-brown
rock
4.5 0.0 10 4.5 8.5
7.5 .0 11 5.0 9.0
9.0 .0 11 4.0 8.5
4.5 .0 12 7.0 8.0
1.5 .0 13 8.5 2.0
6.5 .0 14 8.0 4.0
5.5 .0 13 7.5 2.5
6.0 .0
6.5 1.5
5.0 .5
7.0 1.5
4.5 .0
2.0 .0
2.5 .5
5.0 .0
3.5 .0
2.5 .0
2.5 0
5.5 .0
7.5 1.5
4.0 .0
.0 .0
.0 .0
5.0 .0
7.0 7.0
12 30
16 40
9.0 50
5.0 33
4.5 20
4.0 15
7.5 20
2.5 10
25 .0
16 8.512 47.5
9.0 100
10.5 100
8.0 100
6.0 100
6.0 100
12 3.0
11 4.0
12 2.0
11 2.5
13 .018 .08.0 4.5
13 1.5
15 3.514 18
12 7.0
12 2.5
1 1 3.0
12 1.5
22 3.0
20 2.0
18 2.0
16 2.0
15 2.0
14 4.0
13 8.5
16 4.0
13 3.0
13 5.5
9.5 10.5
14 6.5
1615
1618
13
10
10
12
5.0
2.0
4.0
15
14
11
7.0
6.0
7.5
3.0
8.0
5.5
5.55.0
3.5
.0
3.5
6.5
6.0
5.5
.0 4.5
.0 9.5
.0 13
.0 12
.0 13
.0 13
2.0 3.5
.0 5.5
.0 3.5
.0 1.5
.0 1.5
.0 3.0
2.0
3.0
4.0
1.5
3.0
1.5
2.5
1.5
1.5
.0
2.0
4.0
1.5
2.0
.0
.0
.0
.0
2.5
3.0
3.0
2.0
3.0
1.52.5
2.5
.0
.0
.0
.0
11.0
.0
.0
2.0
1.04.0
9.5
I11 7.0 8.0
16 3.0 5.0
13 5.0 4.0
10 6.0 4.5
10 7.0 2.0
9 7.0 2.0
8 7.0 2.0
8 9.0 1.0
5.5
5.5
5.0
5.55.0
1 1
15
6.5
10
2.0
5.0
4.0
5.0
1.0
4.0
6.0
.0 .0
.0 .0
3.5 .0
2.0 .0
3.0 .0
8.0 25
6.5 20
3.0 18
2.0 100
13 9.0
14 9.0
13 1113 11
13 9.5
13 1 1
12 9.0
14 13
11 14
.0
.0
.0
.0
5.5
1.53.0
3.0
2.5
.0
.0
.0
.0
.0
.0
2.0
1.0
2.0
E6 Contributions to Commodity Geology Research
SiO2 A1203 Fe203 MgO CaO Na20 K~O TiO2 P205 MnO LOINi (ppm) Co (ppm) Cu (ppm) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %)
5200
50005400
6300
6100
5700
5700
5300
5200
5800
3900
5700
5500
6100
6100
7900
6200
6400
58005800
7000
7300
7200
7000
9200
13000
13000
11000
14000
14000
5500
16000
15000
6200
4300
5900
5400
4800
5000
4300
4400
5000
2100
8100
8800
8100
10000
13000
14000
12000
11000
10000
2700
340
480
470
660
860
2000
1500
720
700
720
510
910
600
1000
570
630
480
660
760
720
1000
630
760
1200
1300
700
1000
1000
880
920
440
1100
840
110
55 13.7 10.5 58.8 1.8
57 15.3 11.6 56.6 1.7
60 15.1 10.8 57.6 1.8
62 10.7 8.9 63.6 1.8
67 6.5 7.8 69.4 1.8
77 11.6 9.7 62.5 2.4
97 14.1 10.9 56.1 3.5
70 23.2 11.2 41.4 4.7
70 24.0 11.4 41.0 4.5
70 23.5 10.5 42.6 4.7
87 28.1 13.2 35.7 4.7
80 22.1 10.0 44.3 4.8
63 10.4 7.0 60.2 2.6
70 20.3 11.3 46.4 3.3
63 21.6 11.1 45.5 3.4
85 9.9 10.2 58.3 1.5
110 2.5 5.2 77.6 .7
80 8.4 6.7 68.0 1.9
67 23.0 11.1 43.1 4.1
65 22.9 10.9 43.4 4.5
72 16.1 9.8 51.9 3.7
70 5.1
70 4.0
57 7.4
57 10.0
63 21.0
53 17.4
71 11.4
43 21.3
68 24.2
97 Is
98 Is
63 19.2
14 41.2
5.9 66.1 1.7
5.3 67.8 1.4
5.2 65.3 2.9
4.5 63.1 4.0
3.2 48.2 10.2
3.4 52.9 8.6
3.0 66.6 5.2
2.9 48.5 10.9
3.4 44.8 12.4
Is IS IS
is Is Is
3.0 50.3 9.9
.6 9.3 39.1
14.2 32.7 10.2
13.8 42.1 6.8
12.0 40.3 9.1
9.9 32.8 14.7
8.6 28.6 18.2
6.8 23.1 21.7
5.4 20.3 24.7
4.1 18.6 26.1
1.8 8.4 36.5
<0.02 <0.02 0.15
<.02 <.2 .22
<.02 <.2 .19
<.02 <.2 .12
<.02 <.2 .05
<.02 <.2 .11
<.02 <.2 .11
.46 <.2 .21
.47 <.2 .23
.55 <.2 .21
.44 <.2 .30
.55 <.2 .15
.19 <.2 .05
.32 <.2 .15
.31 <.2 .25
.06 <.2 .15
<.02 <.2 <.02
.13 <.2 .08
.44 <.2 .20
.46 <.2 .18
.27 <.2 .16
<.02 <.2 .03
<.02 <.2 <.02
.12 <.2 .03
.25 <.2 <.02
1.07 <.2 <.02
.66 <.2 <.02
.38 <.2 <.02
.88 <.2 <.02
.99 <.2 <.02
is Is is
Is IS IS
.72 <.2 <.02
.54 <.2 <.02
1.67 <.2 .19
.59 <.2 .12
.83 <.2 .09
.56 <.2 .08
1.20 <.2 .06
.76 <.2 .04
.77 <.2 <.02
.64 <.2 <.02
.98 <.2 <.02
.08 <.2 .06
.04 <.2 .05
<.02 <.2 .04
.03 <.2 <.02
.05 <.2 <.02
.27 <.2 <.02
.72 <.2 <.02
.57 <.2 <.02
.17 <.2 <.02
.71 <.2 <.02
0.38 <0. 1 0.39 8.22
.43 <.1 .44 9.01
.43 <.1 .48 8.84
.28 <.1 .51 8.09
.14 <.1 .56 7.72
.24 <.1 .78 7.92
.25 <.1 .83 9.45
.52 .1 .70 11.85
.55 .1 .70 12.30
.50 .1 .65 11.51
.69 .1 .73 11.32
.43 .1 .76 11.68
.17 <.1 .36 13.65
.53 .1 .85 11.15
.50 .1 .45 11.10
.28 .1 .28 13.54
.06 <.1 .18 8.36
.18 <.1 .37 9.01
.53 .1 .63 11.16
.51 .1 .61 10.85
.37 .1 .57 11.95
.11 <.1 .39 15.59
.07 <.1 .37 15.49
.07 <.1 .49 13.20
.04 <.1 .65 13.05
.03 <.1 .57 11.68
<.02 <.1 .87 11.62
<.02 <.1 1.09 8.60
<.02 <.1 .97 10.60
<.02 <.1 .78 9.00
IS IS IS IS
is Is IS IS
<.02 <.1 .90 11.04
<.02 <.1 .13 8.15
.45 <.1 .57 12.46
.34 <.1 .39 13.84
.29 <.1 .50 13.05
.26 <.1 .64 12.69
.22 <.1 .40 11.96
.16 <.1 .39 12.02
.11 <.1 .34 11.64
.08 <.1 .34 10.89
<.02 <.1 .14 11.28
.13 <.1 .76 13.91
.13 <.1 .66 13.61
.11 <.1 .78 11.38
.08 <.1 1.44 10.65
.07 <.1 1.20 10.41
.06 <.1 1.17 12.76
.06 <.1 .94 12.28
.05 <.1 1.05 11.30
<.04 <.1 .92 10.22
<.02 <.1 .21 6.48
400 72 23.9
410 120 17.8
430 95 19.4
430 72 24.6
300 60 27.6
260 45 31.6
250 35 33.6
250 20 35.8
100 10 39.4
1200
950
1200
2700
2000
1800
1200
1200
950
170
120 3.9 7.7 66.4 1.1
110 3.7 8.3 67.4 .8
100 3.2 8.0 70.8 .9
65 3.2 5.0 74.1 .9
45 4.1 4.2 73.0 1.2
55 5.7 4.7 68.2 2.0
95 7.7 6.4 63.6 2.7
100 7.7 6.5 65.9 2.8
70 12.1 5.6 58.9 8.2
10 40.3 .8 9.2 41.5
Nickel-Mineralogy and Chemical Composition of Some Nickel-Bearing Laterites E7
Table 2. Mineralogical and chemical summary
Relative change in mineral abundance with increasing sample depthW
Site Serpentine Chlorite Goethite Maghemite Smectite Quartz Talc Horn- Ortho- Tremoliteblendle pyroxene
211 ........ Inc Dec Dec Inc Inc213 ........ Inc Dec Dec Inc Inc Dec Dec Dec Dec214 ........ Inc Dec Dec Inc Inc Dec Dec Dec215 ........ NC Dec NC Dec Inc Dec Dec Inc216 ........ NC NC NC NC Inc NC Dec Inc217 ........ Inc NC Dec Inc NC231 ........ Dec Dec NC Inc Dec232 ........ Inc NC NC NC Dec NC NC233 ........ Inc Inc Dec Inc Dec Inc Inc259 ........ Inc Dec Dec Inc Dec Inc NC261 ........ Inc Inc Dec Inc Inc Inc
Bedrock mineralogy2
Site Serpentine Chlorite Olivine Ortho- Clino- Maghemite Goethite Talc Horn- Magnetite Tremolitepyroxene pyroxene blende
211 ......... x x x x x213 ........ x x x x214 ......... x x215 x x x x216 ......... x x x x x x x217 ......... x x x233 ......... x x x x259 ......... x x x x x261 ......... x x x
Trends in laterite chemistry with increasing depth'
Site MgO Sio 2 Fe2O3 A1203 TiO2 CaO Ni Co MnO Cu
211 ........ Inc Inc Dec Dec Dec Inc Inc Dec NC Dec213 ........ Inc Inc Dec Dec Dec Inc Inc Inc Inc Dec214 ........ Inc Inc Dec Dec Dec NC NC Dec Inc Dec215 ........ Inc NC NC NC NC Inc Inc Dec Dec Dec216 ........ Inc Inc Dec Dec Dec NC Inc Dec Dec Dec217 ........ Inc Inc Dec Dec Dec NC Dec Dec Dec Dec231 ........ NC NC Inc Dec Dec NC Inc Inc Inc NC232 ........ NC NC NC NC NC NC Inc NC NC NC233 ........ Inc Inc Dec Dec Dec Inc Inc NC Inc NC259 ........ Inc Inc Dec Dec Dec NC NC Dec Dec Dec261 ........ Inc Inc Dec Dec Dec Inc Inc NC Inc Dec
'Inc, increase; Dec, decrease; NC, no change.2x indicates presence of mineral.
The abundance of a mineral in these samples is, inpart, reflected by the intensity of its X-ray diffraction peaks.Peak intensity is, however, also dependent on other factors,such as degree of crystallinity, orientation, and interfer-ences. As a result, obtaining quantitative mineral modesfrom diffraction data is an extremely difficult task (Grim,1968) and was not done for these samples. An attempt wasmade, however, to qualitatively estimate mineral abun-dances within each of the 11 laterite profiles. Theseestimates were made by measuring the height above back-ground of each mineral's most intense reflection. Mineralabundance estimates derived from X-ray diffraction datamost often are made by measuring the area under peaks.Although less accurate, measurement of peak height hasalso been shown to be closely related to mineral abundance(Gibbs, 1965).
The mineralogical and chemical data for the 11profiles are presented in table 1 and are partly summarizedin tables 2 and 3. The X-ray traces and plots of mineralog-ical and chemical data from two profiles (sites 216 and 233)are given in figures 2 and 3 as further illustration of theapproach used in this study.
LATERITE MINERALOGY
The mineralogy of these laterite profiles is relativelysimple (table 2). All contain serpentine, chlorite, goethite,and maghemite. Additional phases that are present in somesamples, but not all, are smectite, quartz, talc, and horn-blende. No attempt was made to further identify thesmectite, but on the basis of the iron-rich composition of
E8 Contributions to Commodity Geology Research
Table 3. Range of laterite compositions
[Mean values are computed on untransformed data (arithmetic (Ar.) means) and on log-transformed data (geometric (Gm.) means). Sd., standard
deviations. Numbers in parentheses indicate number of samples analyzed]
Site Ni (ppm) Co (ppm) SiO2 (percent) MgO (percent) Fe203 (percent) Al 203 (percent) MnO (percent)
211 Min. 6,800 660 15.1 10.1 29.7 4.4 0.33
(8) Max. 9,700 1,600 29.2 18.5 41.0 14.2 .58
Ar. mean 8,413 1,029 24.9 15.3 33.2 7.7 .40
Sd. 827 303 4.7 3.1 4.1 3.2 .08
Gm. mean 8,375 993 24.5 14.9 33.0 7.2 .40
Sd. 1.1074 1.327 1.25 1.25 1.12 1.49 1.19
213 Min. 4,900 570 14.4 3.0 37.8 4.5 .10
(7) Max. 7,500 1,100 27.8 9.2 54.1 12.8 1.07
Ar. mean 5,771 796 19.0 4.9 47.6 8.8 .67
Sd. 920 216 5.1 2.0 6 3.1 .33
Gm. mean 5,712 773 18.5 4.6 47.3 8.3 .55
Sd. 1.1644 1.294 1.29 1.44 1.14 1.46 2.25
214 Min. 4,800 340 16.6 4.8 31.6 3.9 .35
(6) Max. 6,800 540 28.8 17.9 51.7 8.7 .44
Ar. mean 5,583 407 24.1 12.7 39.9 5.7 .41
Sd. 791 74 5.4 5.6 9.3 1.8 .03
Gm. mean 5,539 402 23.5 11.3 39.0 5.5 .41
Sd. 1.1471 1.184 1.28 1.77 1.25 1.34 1.08
215 Min. 1,100 140 21.2 1.8 29.7 21.6 .01
(5) Max. 1,300 190 25.0 3.2 33.2 23.1 .28
Ar. mean 1,160 170 23.0 2.5 32.1 22.6 .18
Sd. 89 20 1.5 .5 1.5 .6 .12
Gm. mean 1,157 169 23.0 2.4 32.1 22.6 .12
Sd. 1.0780 1.130 1.07 1.25 1.05 1.03 4.15
216 Min. 5,600 440 25.0 11.8 29.1 3.7 .33
(5) Max. 6,500 620 34.2 14.7 38.2 5.4 .51
Ar. mean 6,020 532 29.8 13.1 33.4 4.7 .41
Sd. 409 64 3.7 1.4 3.5 .7 .07
Gm. mean 6,009 529 29.6 13.0 33.2 4.7 .40
Sd. 1.0698 1.130 1.14 1.11 1.11 1.16 1.18
217 Min. 5,900 320 8.6 3.1 18.6 1.7 .23
(6) Max. 8,400 710 35.3 29.7 58.0 6.5 1.42
Ar. mean 6,933 463 26.7 17.8 33.7 3.5 .55
Sd. 838 170 11.3 11.8 17.4 2.2 .45
Gm. mean 6,893 439 23.8 12.6 30.2 3.0 .44
Sd. 1.1249 1.425 1.78 2.89 1.65 1.83 1.98
231 Min. 3,200 260 6.5 1.5 47.1 7.8 .33
(20) Max. 6,300 2,000 17.5 4.5 69.4 15.2 .83
Ar. mean 4,490 559 14.3 2.4 54.2 12.5 .45
Sd. 966 441 2.7 1 5.9 2.1 .14
Gm. mean 4,394 467 14.0 2.3 54.0 12.3 .43
Sd. 1.2351 1.732 1.25 1.45 1.11 1.20 1.30
232 Min. 3,900 480 2.5 .7 35.7 5.2 .18
(14) Max. 7,900 1,000 28.1 4.8 77.6 13.2 .85
Ar. mean 5,907 713 18.3 3.5 50.0 10.0 .56
Sd. 908 163 7.5 1.3 11.9 2.2 .20
Gm. mean 5,840 696 15.9 3.1 48.8 9.7 .52
Sd. 1.1727 1.252 1.92 1.74 1.25 1.30 1.56
233 Min. 5,500 440 4.0 1.4 44.8 2.9 .37
(10)* Max. 16,000 1,300 24.2 12.4 67.8 5.9 1.09
Ar. mean 11,017 898 11.7 6.7 57.4 4.0 .71
Sd. 3626 245 7.4 4.1 9.2 1.1 .25
Gm. mean 10,414 864 12.0 5.3 56.7 3.8 .66
Sd. 1.4355 1.351 1.9 2.23 1.18 1.31 1.47
259 Min. 4,300 250 17.8 6.8 18.6 4.1 .34
(8) Max. 5,900 430 35.8 26.1 42.1 14.2 .64
Nickel-Mineralogy and Chemical Composition of Some Nickel-Bearing Laterites E9
Table 3. Range of laterite compositions-Continued[Mean values are computed on untransformed data (arithmetric (Ar.) means) and on log-transformed data (geometric (Gm.) means). Sd., standarddeviations. Numbers in parentheses indicate number of samples analyzed]
Site Ni (ppm) Co (ppm) SiO2 (percent) MgO (percent) Fe203 (percent) A12 03 (percent) MnO (percent)
Ar. mean 4,888 341 26.8 16.4 29.8 9.3 .45Sd. 567 84 6.5 7.4 8.8 3.8 .11Gm. mean 4,860 332 26.1 14.8 28.6 8.6 .44Sd. 1.1202 1.286 1.29 1.65 1.36 1.57 1.27
261 Min. 8,100 950 3.2 .8 58.9 4.2 .66(9) Max. 14,000 2,700 12.1 8.2 74.1 8.3 1.44
Ar. mean 10,556 1,467 5.7 2.3 67.6 6.2 .99Sd. 2118 585 3 2.4 4.7 1.5 .25Gm. mean 10,371 1,380 5.1 1.7 67.4 6.1 .96Sd. 1.2204 1.428 1.6 2.15 1.07 1.28 1.28
All Min. 1,100 140 2.5 .7 18.6 1.7 .01profiles Max. 16,000 2,700 35.8 29.7 77.6 23.1 1.44(98)** Ar. mean 6,575 704 18.5 7.3 45.7 8.8 .53
Sd. 3032 439 8.6 7.1 14.2 4.9 .27Gm. mean 5,864 593 16.3 4.8 44.3 7.7 .47Sd. 1.6800 1.813 1.84 2.61 1.40 1.78 1.86
All Min. 3,200 250 2.5 .7 18.6 -1.7 .10profiles Max. 16,000 2,700 35.8 29.7 77.6 15.2 1.44
except 215 Ar. mean 6,860 732 18.3 7.6 46.4 8.0 .55(93)*** Sd. 2835 433 8.7 7.1 14.2 3.8 .27
Gm. mean 6,387 633 16.0 5.0 45.1 7.2 .51Sd. 1.4454 1.704 1.86 2.64 1.40 1.70 1.58
* Data for Ni and Co based on 12 samples; all other data are from 10 samples.** Data for Ni and Co based on 100 samples; all other data are from 98 samples.
*** Data for Ni and Co based on 95 samples; all other data are from 93 samples.
these laterites and the yellow-green color of some clay-richsamples, it is reasonable to assume that they are nontronitic.Only two profiles contain orthopyroxene, and only one hassmall amounts of tremolite.
The bedrock mineralogy is also simple and consistspredominantly of serpentine, with lesser amounts of chlo-rite, olivine, and maghemite. Additionally, clino- andorthopyroxene, talc, goethite, hornblende, tremolite, andmagnetite occur in some samples. The bedrock at site 215,however, differs markedly in composition from the otherrock samples as it is composed predominantly of horn-blende, chlorite, talc, and goethite and contains little or noserpentine.
There are three mineralogical associations that areworth noting. First, all soil profiles that contain hornblendealso have talc. Although talc typically is derived from theweathering of pyroxenes (Boeglin and others, 1983), theassociation noted here may indicate that in these samplessome talc results from the alteration of homblende. Second,tremolite occurs only in one of the two samples containingorthopyroxene, perhaps indicating that it is an alteration oforthopyroxene. Third, samples having smectite occur onlyin the northern part of the area sampled, within theboundaries of the Kalmiopsis Wilderness (fig. 1). A possi-ble explanation for this distribution is presented later.
Within most profiles, mineralogy changes systemat-ically. In general, serpentine, maghemite, smectite, andhomblende increase with depth. Conversely, goethite, chlo-rite, talc, and quartz are usually most abundant toward thesurface. Notable exceptions to these trends occur in samplesfrom sites 215, 216, 231, and 232 (table 2).
As previously mentioned, the profile at site 215formed over a hornblende-rich bedrock that is composition-ally distinct from the serpentine-rich rocks associated withthe base of the other profiles. As a result, little serpentine ispresent in the profile from site 215, and evidently most ofthe other mineralogical trends present in the other profilesalso did not develop. The samples from site 215 are alsomarkedly lower in nickel than those which formed overultramafic bedrock (1,100-1,300 ppm vs. 3,200-16,000ppm).
The profiles from sites 216, 231, and 232, which alsodo not show the systematic mineralogical trends of the otherprofiles, have been slumped and mixed. Sites 216 and 232both are in landslide masses and have evidently been socompletely homogenized that any initial vertical change inmineralogy has been eliminated. The profile for site 231 isalso from a landslide but has apparently retained somecomponent of its original profile. Increases in serpentineand maghemite and decreases in goethite and chlorite areobserved to a depth of about 3.2 m, but below this depth
E10 Contributions to Commodity Geology Research
A
U,z
z
T
T ICI+T
CI ~~~~CI+Sm
SlS
G Ch G Hb 216-1
216-2
216-3 Cl
216-4
216-5
S I
CI CI CI
S+Mh Il
T 1216-
oici1 01 s bedrock
30 20 10 0 2 THETAI
C
T
S
-I
ifI__)P
5500C
3500C
EG
A
5500C
350°C
EG
A
216-1
J UJ216-3
5500C
3500C
EG
A
I
216-5
5500C
216-bedrock
I J
A
I1 1 I I l 1 1 1l . . . .l
60 50 4Cr . . . . . . .16 14 12 10 8 6 4 2
2 THETA
I
Figure 2. X-ray mineralogy and chemistry for profile fromsite 216. A, Hand-smoothed X-ray diffraction patterns.(Abbreviations: Cl, chlorite; S, serpentine; G, goethite;Mh, maghemite; Q, quartz; Sm, smectite; T, talc; 01,olivine; Hb, hornblende.) B, Diffraction patterns of sam-ples settled from water onto porcelain tiles and then dried
in air (A), treated with ethylene glycol (EG), heated to 350°C, and heated to 550 'C. C, Qualitative vertical variationsin mineral abundances. D, Vertical variations in profilechemistry. E, Net change in Ni, Co, SiO2 , Fe2 03 , MgO,and MnO calculated assuming A12 03 is constant. Methodof calculation discussed in text.
C D0
0.2
0
0.2
0.4
uz
1--
Lu
Z> 0.6
w3l
0
0.8
0.4
(I)
uj 0.6
z
l'-CLw0
0.8
1.0 1.0
1.21.2
10 20 30 40 50 60 70 80
QUALITATIVE MINERAL ABUNDANCEEXPLANATION
Chlorite + Serpentine 0 GoethSmectite 7 Quartz X TalcMaghemite e Hornblende
90 2 4 6 8 10 12 14 16
AMOUNT OF ELEMENT/OXIDE
DUA
ite D Nix10(WT%)
X Fe2A3/10 (WT%)e TiO2x 10 (WT%)
EXPLANATION+ Co x 100 (WT%)V MgO (WT%)
(O Cu/10 (ppm)
A SiO2/10 (WT%)* Al 3(WT%)
0 MnOxlO(WT%), CaO x 10 (WT%)Figure 2. Continued.
Figure 2. Continued.
E12 Contributions to Commodity Geology Research
E CHEMICAL VARIATIONS0.1
0.3
0.5
LI-wCC
LU
z 0.7
I-I-00~
0.9
Data for SiO2, Fe2 03 , and A1203 most closelyapproximate normal distributions and, therefore, may bestbe characterized by arithmetic means. Data for Ni, Co,MgO, and MnO, however, approximate lognormal distri-butions, and for these elements the geometric mean (aver-age value of the log-transformed data) provides a bettermeasure of the central tendency of these data. Table 3 givesthe arithmetic and geometric means, the maximum andminimum values, and standard deviations of these ele-ments.
With the exception of samples from site 215, geo-metric means of Ni and Co are 6,387 ppm and 633 ppm(range of means are 4,394 to 10,414 ppm for Ni and 332 to1,380 ppm for Co). Abundance of Si0 2 (arithmetic mean of18.3; range of 5.7 to 29.8 percent) and MgO (geometricmean of 5.0; range of 1.7 to 14.9 percent) is directlyrelated to mineralogy, the greatest amounts occurring inprofiles that have the largest relative amounts of serpentine(or talc, in the case of profile 216). Similarly, abundance ofFe2O3 (arithmetic mean 46.4, range of 29.8 to 67.6 percent)increases as the amount of goethite increases.
The range in composition of these laterites agreeswith those reported in a survey of laterites occurring in thisarea (Ramp, 1978) and also in specific studies of the RedFlats (Libbey and others, 1947; Hundhausen and others,1954), Pine Flat, and Diamond Flat (Benson, 1963) depos-its. These compositions also fit the category defined byChandra and Ruud (1976) as transitional between high-ironnickeliferous limonite deposits and high-silica serpentinousores. Some of these profiles are similar to compositions thathave been used to test the recovery of nickel and cobalt bya variety of hydrometallurgical processes (Siemens andothers, 1975; Duyvesteyn and others, 1979; Kukura andothers, 1979).
Those profiles that have changes in mineralogy alsoshow systematic changes in chemistry (table 2). Amongprofiles that are largely undisturbed, there are consistentdepth-related increases in MgO and SiO2 content and
decreases with depth in Fe2O3 , A1203 , and TiO2 content.Changes associated with CaO, MnO, and nickel, whichgenerally increase with depth, and copper, which generallydecreases with depth, are less consistent. Cobalt, in con-trast, exhibits neither a predictable increase nor decreasewith depth. Most of these chemical trends are also presentin the disturbed profile at site 216. However, these trendsare not found in the other disturbed profiles (231 and 232)and appear not to be developed at site 215.
As expected, many of these oxides show reasonablyconsistent correlations (table 4). Particularly good positivecorrelations are noted between MgO and SiO2 , which couldbe expected as both oxides are associated with serpentineand increase downward from the leached upper part of thelaterite profile to the higher concentrations found in the
1.1
1.3 _-100 -50
PERCENT CHANGE
0
EXPLANATION
D Ni + Co
X Fe203 V MgOA
SiO2
MnO
Figure 2. Continued.
there is little discernible change in relativet mineral abun-dances. The abrupt change at 3.2 m occurs where two
profiles have been juxtaposed; the upper part has themineral zonation typical of most of the other profiles andhas apparently moved over a material that either had beenpreviously homogenized or over a material in which therewas relatively little mineralogical variation.
Nickel-Mineralogy and Chemical Composition of Some Nickel-Bearing Laterites E13
I
A
/
IlB
233-1
233-2
233-3
233-4
/233-5
233-6
233-7
233-8
2233-9
1233-10
233-111
233-12
233- I)edrock
O1
5500C3500C
IEG 231A
550°C350°C 233-4EGA
5500C3500C 233-5EGA
550°C3500C 233-8EGA
5500C350°C 233-1CEGA
550°C
3500C 233-12EGA
5500C
233-bed roc
A
U,z
z
I
;k
r . , . .. .. .. .. . . . . . . . ..I . . .I . I . . . . I . . . . I . . . . I I .
60 50 40 30 20 1 0I I I I I I I 1
16 14 12 10 8 6 4 2 0
2 THETA2 THETA
Figure 3. X-ray mineralogy and chemistry for profile fromsite 233. A, Hand-smoothed X-ray diffraction patterns.(Abbreviations: Cl, chlorite; S, serpentine; G, goethite;Mh, Maghemite; T, talc; 01, olivine; Opx, orthopyrox-ene.) B, Diffraction patterns of samples settled from wateronto porcelain tiles and then dried in air (A), treated
with ethylene glycol (EG), heated to 350 °C, and heated to550 'C. C, Qualitative vertical variations in mineralabundances. D, Vertical variations in profile chemistry. E,Net change in Ni, Co, SiO2, Fe203, MgO, and MnOcalculated assuming A1203 is constant. Method ofcalculation discussed in the text.
C D0
UnLU
LU
z
a-
LU0
2
3
U)
W
LU
LU
zI-l-LU
0
A0 10 20 30 40 50
QUALITATIVE MINERAL ABUNDANCE(RELATED TO X-RAY PEAK HEIGHT)
EXPLANATION
D Chlorite + Serpentine 0 Goett
A Maghemite X Orthopyroxene V Talc
@ Hornblende
60 0 2 4 6 8 10 12 14 16 18 20
titeEl Ni x 10 (WT0,
X FeA/10 (WT
* TiO2 x 10 (W
AMOUNT OF ELEMENT/OXIDEEXPLANATION
'.) + Cox 100(WT%) 0 MnO,
%) V MgO (WT%) 0 Al203 (
r%) A Cu/10 (ppm) A SiO2/1
( 10 (WT%)
WT%)
0 (WT%)
1 0 (WT%)* CaO x
Figure 3. Continued. Figure 3. Continued.
Nickel-Mineralogy and Chemical Composition of Some Nickel-Bearing Laterites E15
E DISCUSSION0
The distribution of major oxides appears to followtrends predicted by relatively simple models. Golightly(1981) shows that the depth-related change in the concen-tration of an element (x) that is leached during lateriticweathering may be modeled by
Cx=C, * (1-e Ax d) (1)
1-
un
i-
4 2
I-'
0
3-
4-100
where:Cx is the concentration of element x in the laterite,
Cx is the initial concentration of element x,Ax is a constant related to the solubility of the element,
andd is the depth.
Similarly, the relationship between two oxides (x and y)may be expressed as:
l/Ay' ln[1-(CyICy,)1=l/Ax- ln[l-(Cx/Cx,)] (2)or
y= Cy -y *, l[(A /Ax) In(1 -(CX/Cx))] (3)
-50 0PERCENT CHANGE
EXPLANATIONNi + Co AFeO., V MgO 0
The solid curve in figure 4 represents the solution toequation 3 for bedrock concentrations of SiO2 and MgO,respectively, of 39 and 37 weight percent. A value of 2 wasassigned for the constant AY/Ax and was chosen to producea curve which fit the data. Actual solubility values for A.and Ay are not known and in fact will change with differentweathering conditions. The ratio used here, however, isconsistent with the observed greater mobility of MgOrelative to SiC 2 and also approximates the extreme ends ofthe relative mobility scale given by Trescases (1975) inwhich the mobility of magnesium is given as 1.0, while thatof silicon ranges between 0.5 and 1.0.
Similar complexities are observed in the relationbetween MgO and Fe2 03 (fig. 5). Samples from profiles213, 215, 231, and 232 again do not lie on the exponentialcurve made by samples from the other profiles. The fittingof a theoretically derived curve to the pattern made by thesedata is, however, not as straightforward as in the previouscase. Both MgO and Si0 2 are removed during weathering,and equation 3 is designed to accommodate the leaching ofsuch oxides. Iron, on the other hand, is residually enrichedin the laterite, and its behavior is, therefore, not directlypredicted by the leaching model (eq. 3).
By making certain assumptions, however, the abovemodel may be simplified and redesigned to approximatevariations in Fe2O3 . First, Fe2O3 and A12 03 are consideredto be the only two major oxides not leached from the lateriteand, therefore, are residually enriched in the upper part ofthe profile. This assumption is supported by the trendsshown in table 2. Second, because all other oxides areremoved during weathering, they may be lumped togetherand treated as the "leached component" and modeled byequation 1 as:
x ISiO2
MnO
Figure 3. Continued.
parent rock. However, the correlations for several of theprofiles are not as high as expected, and a plot of these datareveals at least two different trends (fig. 4). The first ofthese is defined by samples from profiles 213, 215, 231,and 232 (dashed line; fig. 4), while samples from theremaining profiles define a second curve. Cic=Ci= c -Cic * e - (4)
E16 Contributions to Commodity Geology Research
Table 4. Correlation of abundance of elements, oxides, and minerals
[Numbers with asterisk give correlation at the 1-percent confidence level; numbers without asterisk give correlation at the 5-percent confidence level; blanksare not significantly correlated at the 5-percent confidence level. Correlations were made by using data that either fit a normal distribution or that were
transformed to be normally distributed. Values for SiO2 , Fe2O3 , A1203, goethite, and serpentine are normally distributed; data for MgO, MnO, TiO2 , Ni,and Co are lognormally distributed and were transformed]
51C0 Lo Log Log Log Goe- LogSite VS.02 Mgogg Sv5o2 FeC, Fe2, 21 Cog Log Log Ni vs. Ni vs. Log Log Co Co vs. Log Co thite MgO
Site log VS. VS. vs. log vs. log Co vs. Ni vs. Ni vs. log lg Co VS. VS. log vs.I log VS SlogA log , MO i, o N io e.,Sio 2 Fe,03 MnO srpn
MggO eVS* A1203 TiO2 Ni 5;° 2 MgO MnO MgO Fe,23 tine
211 ..... 0.89* -0.88* -0.91* 0.84* 0.79 0.86* -0.76 0.77 0.91* 0.95*
213 ...... -.77 .99* 8 .8 .88*
214 ....... 99* -.98* -. 94 .91* .98* -.68 -0.87 0.9* -0.83 .78 .96*
215 0.96*
216 ...... .9 -. 9 .95* -.95* .99* .91
217 ....... 96* -.98* -. 99* .99* 0.95* .99* -. 83 .St -.79 0.91* -. 97* .98* -0.96* .96* .87 .94*
231 ...... -.45 .72* -. 89* .49 .92* .64* -. 68* .88* .6* .52 .9* .53 .74*
232 ...... . 93* -.93* .91* -.94* -. 89* .95* -.6 .53 .62
233 ...... .97* -. 91* .92* .96* .94* -. 88* .95* .81* .72*
259 ...... . 97* -.97* -.93* .91* .97* -.92* .92* -. 88* .81 .94* .83*
261 ...... .99* - .83* .65 .67 .77 .86* .99*
All ....... .84* -. 81* .37* .82* .75* -.2 .33* .6* -. 44* -. 52* .63* .56* .71*
50 80
70
60
40
PzLUU
uJ
0Cl)
30
20
PzLLI
DC-LU
U-0Ov
50
40
10
0
30
20
10
0
0 10 20 30 40 0 10 20 30 40
MgO (PERCENT)
Figure 4. Plot of MgO vs. SiO2 contents. Rectangles, Alllaterites except those from sites 213, 215, 231, and 232.Solid curve, Curve calculated to fit data represented byrectangles. Dashed line, Curve calculated to fit data fromsites 213, 215, 231, and 232. See text for discussion.
MgO (PERCENT)
Figure 5. Plot of Fe203 vs. MgO contents. Rectangles, Alllaterites except those from sites 213, 215, 231, and 232.Solid curve, Curve calculated to fit data represented byrectangles. Dashed line, Curve calculated to fit data fromsites 213, 215, 231, and 232.
Nickel-Mineralogy and Chemical Composition of Some Nickel-Bearing Laterites E17
[
where Cl. and C1, denote original and subsequentconcentrations of the "leached component." Since theconcentration of the residual component (rs) is
Crs= 100 C1 c,
equation 4 may be rewritten as
C=C.+(l00-Cr) . ec d(5)
When combined with equation 3, the variation of theresidual components (rs0 denotes original residualcomponent) with MgO may be stated as
Cr =C,, +(100-Crs.) * e(Alc/AMgo)* (In(' - (CMgO/cMgoo))) .(6)
Finally, the concentration of Fe203 may be modeled byassuming that the Fe2 03 /(Fe2 0 3 +A1 203 ) ratio is 0.79, avalue consistent with the data in table 1. The concentrationof Fe2O3 (CFe) is then given by
CFe=0.7 9 * [Crs.+(10 CrO)
e(Ajc/AMgo) (-fn(l(CMgo/CMgo.)))] (7)
The curve derived from this relation is plotted in figure 5(solid line) and provides a reasonable fit to the curveddistribution of points, especially considering theassumptions that have been made.
The models given above, however, apparently fail toreproduce the relations found in profiles for sites 213, 215,231, and 232. The fact that profiles for sites 231 and 232have evidently been mechanically mixed does little toexplain their different patterns; the chemical patterns inanother disturbed profile, those at site 216, for example, aremodeled quite well. Also, the above equations depend onlyon the local chemical equilibrium between components andnot on the ordering of the samples. Thus these patternsshould not be affected by mechanical mixing.
The most striking feature shared by all four of theseprofiles is a relatively large abundance of quartz (table 1).This abundance of quartz is also indicated by the verticaldistribution of SiO2 (table 2). In other profiles, Si0 2 clearlyincreases with depth. However, in these four profiles,quartz is most abundant at the top of the profile and resultsin high SiO2 values that tend to offset the downwardincrease in SiC2 due to increases in abundance of othersilicate minerals. As a result, Si0 2 in profiles for sites 215,231, and 232 shows no vertical change, while only a minorincrease in SiO2 occurs at site 213.
Golightly (1981) showed that the solubility of mostmagnesium silicate minerals found in laterites decreaseswith increasing pH. In contrast, the solubility of quartz isrelatively independent of pH, while goethite has a solubilityminimum at a pH of approximately 8. These relationsindicate that in ground waters with relatively high pH, SiO2will mostly be used up in the formation of the relativelyinsoluble secondary magnesium-bearing silicates.However, as ground-water pH decreases and the solubilityof these magnesium-bearing phases increases, SiO2 is more
likely to precipitate as quartz. The presence of quartz maythus be a useful pH indicator in some laterites (Golightly,1981). The large amounts of quartz in profiles from sites213, 215, 231, and 232, therefore, most likely indicatemore acidic ground water at these four locations than at theother sample sites.
In terms of equation 3, the increase in solubility ofmagnesium-silicates with respect to quartz as pH decreaseswill be expressed by increases in values of Asi/AMg. Thedashed line in figure 4 was calculated by using a largervalue for this constant than was used in calculating the solidcurve (6 vs. 2). The result is a reasonable fit to theMgO-SiO2 data for the quartz-rich samples. Similarreasoning indicates that decreases in ground-water pHshould also be accompanied by increases in the termAlc/AMgo given in equation 7. Figure 5 shows the result ofincreasing this constant from 2 (solid curve) to 5 (dashedline).
Since the MgO-SiO2 and MgO-Fe2 O3 data from thesefour profiles lie mostly on the nearly linear portion of thesetwo dashed curves, it is not clear how accurately theseequations fit the data, but it is clear that the observed dataare consistent with behavior predicted by equations 3 and 7.It also should be noted that the curves in figures 4 and 5 arebased on an ultramafic parent rock composition, while, tobe treated accurately, the data for profile 215 should befitted to curves defined by their different parent rockchemistry.
As previously discussed, smectite is found only in thenorthernmost sample sites (fig. 1). Although the precisecompositions of these minerals are not known, inferencebased on comparison with other laterites suggests that theyshould be nontronitic. The stability of some magnesium-bearing silicates common in laterites as well as that ofmagnesium-bearing nontronite from laterites in New Cale-donia (Trescases, 1975) is plotted in figure 6. This plot isderived from the dissolution reaction for these minerals,which, in the case of serpentine, may be written as
Mg3 Si205(OH)4 + 6H+ = 3Mg+ + + 2H4 SiO4 + H2 0, (8)
which has an equilibrium constant (Kd) of
Kd= 29.5 = 31og[Mg+ +] +21og[H4 SiO4 ] + 6pH. (9)
Reorganization of equation 9 as
3(log[Mg+ +] +2pH)=29.5-2log[H 4 SiO4] (10)
enables direct construction of figure 6.This plot shows that waters having a concentration of
Mg++ and SiO2 represented by point A will not precipitatetalc or Mg-bearing nontronite. However, an increase inconcentration of Mg++ and (or) Si0 2 may result in first theformation of talc (B) and then talc and nontronite (C). Inmost instances, smectite occurs only in poorly drainedprofiles where ground waters may be enriched in cations
E18 Contributions to Commodity Geology Research
0.CL
+
++04
0)
2o
20 -
19 _
18 -
17 - -
16
15 -
14
13 -
12 -
11 _
10
9
8-.-5.4
1.1
1.0
0.9
0.8
zCI 0.7-J
A: 0.6fLC,,
_ 0.5
.i02 mgL {L
l o0 0.4-2.6
lI I I I I I I I I l
-5 -4.6 -4.2 -3.8 -3.4 -3
Log(H 4SiO 4)
Figure 6. Stability of some minerals found in lateritesplotted as log (Mg"+) + 2pH vs. log (H4 SiO4 ). A, B, and Crepresent three possible ground-water compositions.Methods of calculation are discussed in text. Data arefrom Trescases (1975), Golightly (1981), and Boeglin andothers (1983).
0.3
0.2
0.1
Al203 (PERCENT)
through prolonged interactions with the bedrock (Golightly,1981).
In these laterite profiles, however, the smectite-bearing profiles all occur on slopes in the topographicallyrugged Kalmiopsis Wilderness. Laterite profiles withoutsmectite are situated on relatively level terraces or plateaus.Both environments are extremely well drained and,therefore, would normally not be expected to have smectite.However, study of laterites in New Caledonia (Trescases,1975) shows that ground waters on hillslopes are enrichedin Si0 2 and Mg++ as a result of their movement downthrough laterite and across the bedrock that makes thehilltops. As a result, laterites on hillslopes typically containsmectite, while those from flatter, well-drained areas donot. The distribution of smectite in these laterite profiles isin accord with these observations.
Three main conclusions may be drawn from theabove discussion. First, the distribution of major oxides inthese laterites follows patterns predicted by relativelysimple mathematical models. Second, laterite mineralogysuggests that the pH of ground waters in four of theseprofiles was significantly more acidic than in others. Thisconclusion is consistent with the different patterns thatMgO, SiO2 , and Fe2O3 make in these profiles. Third,ground waters moving down hillslopes apparently becameenriched in Mg++ and SiO2 and, as a result, precipitatedsmectite.
Relations between many of the other oxides in theselaterites appear to be somewhat less complex. Good inter-
Figure 7. Plot of Al 2 03 vs. TiO 2 contents. Labeled trianglesshow values for bedrock at sites 211 and 215. X (valuesnear origin) shows A1203 values for samples in which TiO2was below the detection limit of 0.02 weight percent. Solidline represents best fit to all data shown by rectangles;dashed line shows best fit for data from site 211.
element correlations are observed between A12 03 and TiO2(table 4) and define a nearly linear trend (fig. 7). Both theseoxides are among the least mobile, and their nearly linearrelation suggests that they are being residually enriched inabout the same relative proportions as in the bedrock. Mostbedrock values of TiO2 are below limits of analyticaldetection (table 1). However, TiO2 in bedrock from site 211was detected, and its ratio with A1203 is similar to thoseratios in the overlying laterites (fig. 7). The best-fit linethrough the TiO2 -A12 03 data (with values from profiles 213and 215 excepted) indicates a TiO2/Al20 3 ratio of 0.05.This value is near the middle of the range commonlyobserved in ultramafic rocks from ophiolite complexes(Coleman, 1977).
Correlation between Fe2 03 and A12 03 varies fromstrongly positive to highly negative (table 4; fig. 8). Manystudies have shown that aluminum substitutes for ironwithin goethite, and it is therefore reasonable to assume thatthis substitution has occurred in cases where highly positivecorrelations of these elements are found. Not surprisingly,the profiles having the highest positive correlations (214,
Nickel-Mineralogy and Chemical Composition of Some Nickel-Bearing Laterites E19
I'
80
70
60
50
Pz
C-0
30
cc
I I I I I I I I
E)
~XXx
N A
0 100X x 0 1
V~~~~ El El
- )1- O'J
7 215
40 F-
30 H-
20 h
10
0 10 +l l l l l l l t
i 4 8 12 16
Al 203 (PERCENT)
I I I number of different minerals. In general, nickel increases
<PLANATION with depth in these laterites, a relation consistent with thatSITE observed in many other laterites and attributable to the
; 211 dissolution of nickel in the upper parts of the profile and* 213@ 214 reprecipitation in the lower parts where ground-water pHA 215 increases, Cobalt, in contrast, shows no consistent trend* 216 and, in fact, highest values commonly occur in middle parts
®217El 231 of profiles. With the exception of a relatively small
+ 232 correlation in profile 231, significant correlation of cobalt0 233A 259 and nickel does not occur within individual profiles (tableX 261 4), thus confirming the independent behavior of nickel andV bedrock cobalt. Interestingly, analyses of the data from all profiles
result in a significant correlation of cobalt and nickel. A plotof cobalt and nickel (fig. 9) clearly shows that this
A ,kk correlation results from superimposing data fromA independent populations.
The correlation data (table 4), however, does showthat nickel occurs in two distinct associations. In the first(profiles 211, 213, 216, and 233), it is directly related toSiO2. Most of these also show a positive correlation withMgO and a negative relation with Fe20 3; in the second(profiles 217, 231, and 232), nickel correlates with Fe20 3.Because Fe20 3 and MgO generally have high positivecorrelations, respectively, with abundances of goethite andserpentine (table 4), the nickel in profiles 211, 213, 216,
20 24 and 233 probably occurs mostly as a substitution inserpentine, while nickel in 217, 231, and 232 is in goethite.
There is, in contrast, no evidence of cobalt being
Best-fit lines associated with silicate minerals. Instead, cobalt is mostly217, 214, and positively correlated with either Fe2 O3 (profiles 214, 216,d not include 217, 231, 259, and 261) or MnO (215, 217, 231, 232, 259,i, which was and 261). Fe2 O3 and MnO generally vary together (profiles'the generalhlered to be 217, 231, 259, and 261), and therefore it is not usually
possible to determine if cobalt is mostly in goethite or inmanganese oxides. That cobalt may occur within bothphases is shown where significant correlation occurs with
pear to have only Fe2 O3 or MnO. For example, in profiles 214 and 216,er aluminum- cobalt is significantly positively correlated with Fe20 3 anda from these not with MnO. In these profiles it is, therefore, likely thatvary between cobalt is hosted by goethite. Conversely, in profile 215 andp to 33 mole 232, cobalt is significantly correlated with MnO and notresponding to with Fe203, indicating that cobalt probably is in manganesethe exception oxides.le of natural The preceding discussion of laterite chemistryeach of these provides no information as to the net gain or loss ofaries between chemical constituents during laterite formation. One way tosingle profile. estimate absolute changes in laterite chemistry is to
correlations compare element abundances with those of a constituentr) homblende that is assumed to be unchanged. For the purposes of this
study, A1203 has been used not only because it is known toto explain the be quite immobile (Golightly, 1981) but also because it ises. To a large sufficiently abundant to be measured relatively accurately.listribution of The percentage net change in concentration of an elemento reside in a (C.) relative to A12 03 is calculated as
Figure 8. Plot of A12 03 vs. Fe20 3 contents.and slopes are given for data from sites 233,259. (Note: Best-fit calculations for site 259 didata from circled open triangle. This daturrfrom the first sample in the profile, fell offtrend of the other points and was consiianomalous.)
217, 233, and 259) are also those that approportionately the smallest amounts of othtbearing phases. Best-fit lines through dataprofiles indicate that the Fe20 3 /Al 203 ratios2.9 to 11.7. Natural goethite may contain u]percent aluminum (Schwertmann, 1983), conan Fe2O3/A1 2 O3 ratio of 3.1 or greater. Withof site 259, these data are within the rantgoethites. The linear distribution of data fromsites suggests that the Al content of goethite v;sites but remains relatively constant within a sConversely, poor or negative A1203 -Fe2 O3
occur mostly in profiles where chlorite and (oaare relatively abundant.
Simple models, however, do not appeardistribution of nickel and cobalt in these profil,extent, the absence of simple controls on the dthese trace elements is due to their ability t
E20 Contributions to Commodity Geology Research
3000
2800
2600
2400
2200
2000
0-J
C-,
1800
1600
I I I I I I I I I I I I I I
EXPLANATIONSITE
[ 211+ 2130 214L 215X 216v 217* 231*232* 233A 259® 261V bedrock
n
-+ X I
* On7
* c~x +
V VI 1 7 V V v
1400
1200
1 000 1
800 I
600
400 F
200
u0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000
Ni (PARTS PER MILLION)
Figure 9. Plot of nickel vs. cobalt contents.
C = [(X /Xp) * (Al203)p/(AI203)J)-1] * 100 (11)
where X, and (A120 3), are the values of component x andA12 03 in laterite, and XP and (Al203)p are those values inthe parent rock. Percentage net changes in six constituentsbased on this equation are given in table 5; variations inprofiles 216 and 233 are plotted in figures 2 and 3.
The trends in net compositional change are similar inmost profiles. With the exception of the mineralogically andchemically distinct profile 215, most profile averages showan ordering from most depleted component to least of MgO,SiO2 , Ni, MnO, Fe2 03, and Co. Exceptions occur in profile211, where the average MnO value is more depleted thanthe nickel value, and in profiles 214, 231, and 259, wherethe average cobalt values are just slightly more depletedthan the averages for Fe2 03 . These profiles almost all showan overall loss of all their major components, with enrich-ments only evident in profiles 211 (Co, Ni, Fe2 03), 233(Co), and 261 (Co, Fe20 3). In contrast to these profiles,values from sample site 215 differ significantly. Significant
enrichments occur in average values of nickel, Fe2O3 , andcobalt, with nickel showing the largest amounts of enrich-ment.
The most surprising feature of these patterns is theabsence of consistent and significant increases in nickel.Hotz (1964) conducted a similar study using data from theRiddle laterite deposit and from laterite on Eight DollarMountain (located 15 km east of Pearsoll Peak; fig. 1). Inboth profiles, nickel was found to be the most enrichedcomponent, with net gains commonly exceeding 120 per-cent. Cobalt and iron also typically showed net increases.The general order of enrichment determined by Hotz was,from most depleted to most enriched, MgO, SiO2 , Mn, Fe,Co, and Ni. With the exception of nickel, this sequence issimilar to the one found in these laterites.
CONCLUSIONS
Ten of the eleven laterites studied formed overserpentinized peridotite and, in general, are mineralogicallyand chemically similar. All contain serpentine, chlorite,goethite, and maghemite. Profiles located on hillslopes alsohave smectite. Quartz, talc, hormblende, orthopyroxene,and tremolite are additional components of some laterites.Within profiles that have not been physically disrupted, theleast soluble minerals (mostly goethite) are most abundantat tops of profiles, and the more soluble phases generallyincrease with depth.
Mean values of major chemical constituents in these10 profiles are nickel, 0.64 weight percent; cobalt, 0.063weight percent; SiO2 , 18.3 weight percent; MgO, 5.0weight percent; Fe2O3 , 46.4 weight percent; A12 03 , 8.0weight percent; and MnO, 0.51 weight percent. Amounts ofMgO and Fe2O3 generally directly reflect abundance,respectively, of serpentine and goethite. These composi-tions are similar to those of other laterites described fromthis area.
The profile at site 215 differs from the others inhaving formed over a homblende-rich parent rock. Theselaterites are also distinguished by having relatively largeamounts of quartz, chlorite, and talc and by low values ofMgO and nickel (having mean values of 2.4 and 0.11weight percent, respectively).
The restriction of smectite to laterites located onhillslopes results from local variations in ground-waterchemistry. Precipitation of smectite is favored by highconcentrations of SiO2 and MgO in ground water, but theexcellent drainage present in these laterites tends to preventenrichment in these components. As a result of downslopeflow over serpentine, however, waters on hillsides locallyhave dissolved enough SiO2 and MgO to precipitate smec-tite.
The distribution of MgO, SiO2 , and Fe2 03 in theselaterites appears to follow trends predicted by the relativelysimple equation:
Nickel-Mineralogy and Chemical Composition of Some Nickel-Bearing Laterites E21
I'
Table 5. Net change in laterite composition[Calculations made assuming no change in A1203, as discussed in text; whole-rock values from site 233 were used to calculate values for profiles 231 and232. IS, insufficient sample]
Site Sample Percent changesample depthnumber (in) Ni Co Si0 2 Fe2O3 MgO MnO
211-1 .. 0.23 -59.8 13.8 -94.5 -27.6 -96.0 -63.5
211-2 ... 38 -22.4 187.8 -88.0 5.1 -91.9 -20.2
211-3 ... 64 -8.6 159.6 -82.6 -4.5 -89.3 -49.6
211-4 ... 92 -25.0 91.1 -85.7 -10.4 -92.5 -49.5
211-5 ... 1.22 -2.5 120.4 -79.5 8.9 -85.8 -37.2
211-6 .. 1.53 47.4 173.6 -70.4 56.2 -78.7 -6.7
211-7 .. 1.83 47.0 156.9 -72.5 64.6 -80.6 5.6
211-8 .. 2.14 85.2 142.3 -65.5 69.4 -76.2 3.9
213-1 ... 15 -91.9 -68.7 -97.7 -64.7 -99.2 -76.5
213-2 ... 31 -92.0 -69.1 -97.2 -68.4 -99.2 -75.3
213-3 ... 61 -89.1 -63.7 -97.2 49.9 -99.3 -78.2
213-4 ... 92 -85.0 -21.4 -96.2 -37.3 -98.7 -93.8
213-5 ... 1.22 -80.4 -5.8 -94.5 -27.8 -99.0 -19.8213-6 ... 1.53 -82.7 -40.4 -93.5 -43.7 -98.7 -38.2
213-7 ... 1.88 -65.4 -28.5 -87.9 -22.6 -95.7 .9
214-1 . . 15 -95.3 -87.3 -98.0 -72.9 -99.4 -91.9
214-2 .... 31 -93.4 -79.9 -97.3 -65.0 -99.0 -87.8
214-3 ... 61 -87.1 -78.3 -93.8 -63.6 -96.2 -81.3
214-4 ... 92 -86.3 -76.9 -92.4 -63.2 -95.0 -79.0
214-5 ... 1.22 -91.2 -82.4 -94.8 -69.0 -97.0 -83.2
214-6 ... 1.37 -91.3 -82.7 -94.0 -69.9 -96.3 -83.3
215-1 ... 15 199.8 140.5 -64.6 158.3 -81.7 24.0
215-2 ... 31 202.5 129.8 -62.2 159.0 -84.9 25.1
215-3 ... 61 198.5 126.8 -59.9 144.8 -80.1 5.8
215-4 .... 92 234.4 81.1 -57.3 136.2 -76.2 -95.5
215-5 ... 1.22 277.3 115.6 -60.3 175.0 -71.6 -48.1
216-1 ... 15 -57.5 -15.2 -84.4 -20.5 -92.8 -18.4216-2 ... 31 -55.2 6.3 -84.6 -6.7 -92.3 -26.3
216-3 ... 61 -53.2 -8.2 -81.3 -18.6 -92.0 -33.7216-4 ... 92 -30.8 22.8 -73.2 2.6 -87.3 -12.0
216-5 . .. 1.22 -40.9 -14.3 -76.0 -19.3 -89.1 -35.7
217-1 ... 15 -88.3 -43.7 -97.9 -34.8 -99.1 -3.5
217-2 ... 31 -89.2 -44.9 -95.5 -34.4 -99.1 -52.0217-3 ... 61 -79.7 -23.3 -84.6 -27.9 -89.2 -37.1
217-4 ... 92 -68.1 -14.8 -72.3 -19.8 -79.1 -35.8
217-5 .. 1.22 -67.6 -5.3 -69.3 -18.2 -73.3 -33.6
217-6 .. 1.53 -68.4 -2.7 -66.9 -19.8 -69.6 -40.1
231-1 ... 46 -97.4 -82.0 -98.2 -77.6 -99.5 -81.0
231-2 ... 87 -96.9 -76.5 -98.5 -75.6 -99.7 -87.7
231-3 .. 1.20 -97.1 -83.9 -98.4 -78.5 -99.8 -89.1
231-4 ... 1.55 -97.5 -84.2 -98.4 -79.4 -99.8 -89.0
231-5 .. 2.01 -97.7 -85.8 -98.5 -78.7 -99.6 -86.7
231-6 ... 2.32 -98.0 -89.6 -98.6 -80.1 -99.8 -88.9
231-7 .. 2.62 -97.8 -89.9 -98.6 -79.9 -99.9 -90.0
231-8 ... 2.93 -97.8 -87.1 -98.3 -79.1 -99.6 -88.5
231-9 .. 3.23 -97.8 -82.4 -98.3 -78.0 -99.5 -87.7
231-10 . 3.54 -97.5 -89.0 -98.7 -76.8 -99.8 -88.5
231-11 . 3.84 -97.4 -89.4 -98.7 -76.9 -99.8 -88.8
231-12 . 4.15 -97.1 -90.4 -98.7 -76.8 -99.8 -89.7231-13 . 4.45 -97.1 -89.7 -98.8 -73.8 -99.8 -88.3
Site Sample Percent changesample depthnumber (Mn) Ni Co Si0 2 Fe,0 3 MgO MnO
231-14 . . 4.76 -95.5 -83.5 -98.2 -66.2 -99.8 -84.0
231-15 . . 5.06 -96.1 -78.9 -98.2 -70.6 -99.8 -83.7
231-16 . . 5.37 -95.5 -77.8 -98.1 -67.8 -99.8 -80.9
231-17 . . 5.67 -93.6 -62.4 -98.4 -57.0 -99.7 -75.4
231-18 . . 5.98 -92.9 43.5 -98.9 -46.0 -99.7 -68.9
231-19 . . 6.28 -94.7 4.5 -98.4 -61.3 -99.6 -65.5
231-20 . . 6.59 -95.3 -29.9 -98.2 -68.9, -99.5 -67.2
232-1 ... 31 -95.7 -67.3 -97.2 -77.7 -99.4 -73.1
232-2 ... 61 -95.9 -68.7 -97.1 -78.3 -99.4 -73.5232-3 ... 1.22 -95.0 -65.1 -97.0 -75.5 -99.4 -73.3
232-4 ... 1.53 -97.3 -80.3 -97.1 -83.7 -99.5 -76.2
232-5 .. 1.83 -94.8 -53.5 -97.0 -73.2 -99.3 -67.1
232-6 .. 2.14 -92.9 -56.0 -98.0 47.7 -99.5 -77.7
232-7 ... 2.44 -95.1 -54.9 -97.6 -75 2 -99.6 -67.6
232-8 .. 2.75 -95.0 -73.9 -97.4 -75.3 -99.6 -82.5232-9 .. 3.05 -93.0 -68.6 -98.7 -65.5 -99.8 -88.2
232-10 .. 3.36 -89.1 -52.6 -99.3 -9.1 -99.8 -84.9
232-11 .. 3.66 -91.3 49.5 -98.3 -38.3 -99.6 -76.0
232-12 .. 3.97 -95.3 -65.1 -97.2 -76.6 -99.5 -75.6232-13 .. 4.27 -95.2 -66.4 -97.1 -76.0 -99.4 -75.9
232-14 .. 4.58 -93.6 -48.1 -97.8 -68.1 -99.5 -75.0
233-1 ... 31 -88.9 45.9 -98.8 -32.7 -99.6 -71.7
233-2 ... 61 -87.8 -27.4 -99.0 -23.2 -99.6 -70.1
233-3 .. 1.22 -87.8 18.2 -98.0 -23.8 -99.2 -59.2
233-4 .. 1.53 -81.5 47.1 -97.0 -15.4 -98.7 -37.8
233-5 .. 1.83 -63.3 11.4 -91.1 -9.1 -95.4 -23.3233-6 ... 2.14 -65.5 49 7 -93.0 -6.1 -96.4 10.2
233-7 .. 2.44 -66.9 69.7 -94.8 34.0 -97.5 56.5
233-8 ... 2.75 -56.4 54.5 -90.0 .9 -94.6 44.1
233-9 .. 3.05 -62.8 37.8 -90.3 -20.5 -94.8 -1.2
233-10 .. 3.36 is is is is is is
233-11 .. 3.66 is is is is is is233-12 .. 3.97 -54.8 42.5 -91.3 1.2 -95.3 29.2
259-1 ... 15 -74.0 -49.3 -92.3 -50.8 -96.5 -48.4259-2 ... 31 -63.4 -46.5 -94.1 -34.9 -97.6 -63.7
259-3 ... 61 -61.4 -35.5 -92.6 -28.3 -96.3 -46.4
259-4 ... 92 -58.3 -21.5 -88.6 -29.0 -92.6 -16.5
259-5 .. 1.22 -50.0 -37.0 -85.3 -28.7 -89.5 -40.0
259-6 .. 1.53 -45.9 -31.3 -78.8 -27.6 -84.3 -26.4
259-7 .. 1.83 -29.5 -15.9 -71.3 -19.0 -77.2 -18.3
259-8 .. 2.14 4.5 9.8 -60.1 -3.1 -68.6 6.6
261-1 ... 15 -68.3 -25.5 -99.0 -23.8 -99.7 -61.8
261-2 ... 31 -68.1 45.3 -99.1 -28.3 -99.8 -69.3
261-3 ... 61 -69.4 -28.1 -99.2 -21.6 -99.8 -62.2
261-4 ... 92 -40.0 157.3 -98.7 30.5 -99.7 11.1
261-5 ... 1.22 -7.1 126.9 -98.0 53.0 -99.4 10.2
261-6 ... 1.53 -10.6 82.5 -97.6 27.8 -99.2 -4.0
261-7 ... 1.83 43.5 -10.2 -97.6 -12.1 -99.2 43.1
261-8 . .. 2.14 -48.8 -11.4 -97.6 -10.0 -99.2 -37.2
261-9 ... 2.44 -46.0 -18.6 -95.6 -6.7 -97.1 -36.2
E22 Contributions to Commodity Geology Research
CY=C, -Cy .-e [(A,/A) ln(1-(CIC ))] (12)
where:C, and Cy are the concentration of components x and y in
the laterite,Cx, and Cy are the initial concentration of x and y, and
Ax and Ay are constants related to the solubility of x and
Y.Trends fitted by this equation and its derivatives for
profiles 213, 215, 231, and 232 differ from those in the
other laterites. These four profiles contain relatively large
amounts of quartz, which commonly is a mineralogical
indicator of relatively acidic ground waters. The shift in themajor element trends in these four profiles from those in the
other laterites is consistent with the presence of ground
water having a lower pH.The distribution of other oxides reveals a variety of
relations. Good positive correlation exists betweenabundance of A1203 and TiO2. Both are relatively immobile
and appear to be residually enriched in about the same
proportions as occur in the parent rock. A1203 and Fe2 03, incontrast, are strongly positively correlated in goethite-richlaterites, but not in laterites having large amounts of
aluminum-bearing minerals. It is probable that, where
positively correlated, most of the aluminum occurs as a
substitution for iron in goethite. Fairly constantAl203/Fe2 03 ratios occur in the goethite-rich profiles andindicate a uniformity of goethite compositions within
individual laterites. Nickel in some profiles is positively
correlated with Fe2 03, indicating that it occurs in goethite;in other laterites, nickel is mostly present in serpentine as
shown by its good correlation with MgO. Cobalt, on the
other hand, apparently occurs primarily in either goethite or
in manganese oxides, but in most profiles its host phasecould not actually be determined.
Calculations of net changes in laterite chemistry show
that loss of chemical components during weathering
generally occurs in a well-defined order. This sequence is,from most depleted to most enriched, MgO, SiO2 , Ni,
MnO, Fe2 03 , and Co. The observed net chemical changes
in these deposits differ from those observed in the adjacent
laterite on Eight Dollar Mountain and the deposit at Riddle,
Oreg., in two ways. First, nickel is the most enrichedcomponent in those deposits. Second, the large amounts of
net enrichment in nickel and cobalt observed at Eight Dollar
Mountain and at Riddle were not found in the lateritesstudied here.
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Boeglin, J.L., Melfi, A.J., Nahon, D., Paquet, H., and Tardy,
Y., 1983, Early formed mineral paragenesis in the deep zones
of supergene ores in lateritic weathering, in Melfi, A.J., and
Carvalho, A., eds., Lateritisation processes-Proceedings ofthe 2nd International Lateritisation Seminar on LateritisationProcesses: Sao Paulo, Brazil, p. 71-88.
Canterford, J.H., 1975, The treatment of nickeliferous laterites:Minerals Science and Engineering, v. 7, p. 3-17.
Chamberlain, P.G., 1986, Nickel, in U.S. Bureau of Mines,Mineral Commodity Summaries 1986: Washington, D.C., p.
108-109.Chandra, D., and Ruud, C.O., 1976, Characterization study of
domestic nickeliferous laterites by electron optical and X-ray
techniques: U.S. Bureau of Mines Open File Report 95-76,
58 p.Coleman, R.G., 1977, Ophiolites: New York, Springer-Verlag,
229 p.Diller, J.S., 1902, Topographic development of the Klamath
Mountains: U.S. Geological Survey Bulletin 196, 69 p.
Duyvesteyn, W.P., Wicker, G.R., and Doane, R.E., 1979, Anomnivorous process for laterite deposits, in Evans, D.J.I.,Shoemaker, R.S., and Veltman, H., eds., International
laterite symposium: New York, Society of Mining Engineersof the American Institute of Mining, Metallurgical and
Petroleum Engineers, p. 553-570.Evans, D.J.I., Shoemaker, R.S., and Veltman, H. , eds., 1979,
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Mining Engineers of the American Institute of Mining,Metallurgical and Petroleum Engineers, 688 p.
Faust, G.T., 1966, The hydrous nickel-magnesium silicates-Thegarnierite group: American Mineralogist, v. 51, p. 279-298.
Foose, M.P., 1991, Deposits containing nickel, cobalt, chro-mium, and platinum-group elements in the United States, in
The geology of North America-Economic geology:
Geological Society of America, v. P-2, p. 87-102.Gibbs, R.J., 1965, Error due to segregation in quantitative clay
mineral X-ray diffraction mounting techniques: AmericanMineralogist, v. 50, p. 741-751.
Grim, R.E., 1968, Clay mineralogy: New York, McGraw-HillBook Co., 596 p.
Golightly, J.P., 1981, Nickeliferous laterite deposits, in Skinner,B.J., ed., Economic Geology 75th Anniversary Volume: p.
710-735.Hotz, P.E., 1964, Nickeliferous laterites in southwestern Oregon
and northwestern California: Economic Geology, v. 59, no.
3, p. 355-396.Hundhausen R.J., McWilliams, J.R., and Banning, L.H., 1954,
Preliminary investigation of the Red Flats nickel deposit,Curry County, Oregon: U.S. Bureau of Mines Report ofInvestigations 5072, 19 p.
Irwin, W.P., 1977 , Ophiolitic terranes of California, Oregon, andNevada, in Coleman, R.G. and Irwin, W.P., eds., North
American ophiolites: Oregon Department of Geology and
Mineral Industries Bulletin 95, p. 75-92.Kukura, M.E., Stevens, L.G., and Auck, Y.T., 1979, Develop-
ment of the UOP process for oxide silicate ores of nickel and
cobalt, in Evans, D.J.I., Shoemaker, R.S., and Veltman, H.,
eds., International laterite symposium: New York, Society ofMining Engineers of the American Institute of Mining,
Metallurgical and Petroleum Engineers, p. 527-552.Libbey, F.W., Lowry, W.D., and Mason, R.S., 1947, Nickel-
bearing laterite, Red Flats, Curry County, Oregon: Ore Bin,
v. 9, no. 3, p. 19-27.
Nickel-Mineralogy and Chemical Composition of Some Nickel-Bearing Laterites E23
Page, N.J, Miller, M.S., Grimes, D.J., Leinz, R.W., Blakely,R.W., Lipin, B.R., Foose, M.P., and Gray, F., 1982,Mineral resource potential map of the Kalmiopsis Wilder-ness, southwestern Oregon: U.S. Geological Survey Miscel-laneous Field Studies Map MF-1240-E, scale 1:62,500.
Ramp, L., 1978, Investigations of nickel in Oregon: OregonDepartment of Geology and Mineral Industries MiscellaneousPaper 20, 68 p.
Schwertmann, U., 1983, The role of aluminium in iron oxidesystems, in Melfi, A.J., and Carvalho, A., eds., Lateritisa-
tion processes-Proceedings of the II International Seminaron Lateritisation Processes: University of Sao Paulo, Brazil,p. 65-68.
Siemens, R.E., Good, P.C., and Stickney, W.A., 1975, Recoveryof nickel and cobalt from low-grade domestic laterites: U.S.Bureau of Mines Report of Investigations 8027, 14 p.
Trescases, Jean-Jacques, 1975, L'evolution geochimique super-gene des roches ultrabasiques en zone tropicale-Formationdes gisements nickeliferes de Nouvelle-Caledonia: MemoiresO.R.S.T.O.M., no. 78, 259 p.
E24 Contributions to Commodity Geology Research
