Nickel-Mineralogy and Chemical Composition of

Some Nickel-Bearing Laterites in Southern Oregon

and Northern California
By Michael P. Foose

Abstract ern California, and several of these have recently been

examined as potential additional sources of nickel and
The mineralogy and chemistry of 109 samples from
11 nickel-bearing laterites located in southern Oregon and byproduct cobalt. This study looks at some of the mineral-
northern California were determined. The laterites are ogical and chemical features associated with several of
primarily composed of serpentine, chlorite, goethite, and these occurrences.
maghemite. Some contain additional minor amounts of
smectite, quartz, talc, hornblende, orthopyroxene, and
tremolite. Smectite (possibly nontronite) occurs only in GENERAL SETTING
laterites located on hillslopes and appears to be restricted
to areas where ground water may have been enriched in The nickel laterite deposits in Oregon and northern
SiO 2 and MgO from downslope flow across bedrock. California occur over ophiolites that are part of several
Nickel content of the laterites averages 0.64 weight per- different accreted terranes. As a result of the accretionary
cent but varies between 0.45 and 1.4 weight percent; processes by which these terranes were affixed to the
cobalt averages 0.06 weight percent and ranges between western margin of the United States, these ophiolitic rocks
0.03 and 0.15 weight percent. Neither nickel nor cobalt has
now form subparallel belts that range in age from Paleozoic
predictable distributions. In contrast, patterns made by
(easternmost) to upper Jurassic (westernmost) (Irwin,
major elements follow trends defined by relatively simple
chemical models. Calculated net changes in laterite chem- 1977). Subsequent to emplacement, many of these ophi-
istry indicate that the mobility of components is, from olitic bodies were exposed to extensive weathering that
most depleted to least, MgO, SiO2 , nickel, MnO, Fe2 03 , resulted in formation of laterites. There is some uncertainty
and cobalt. These calculations also show that only a few of as to the exact age of weathering. Most probably occurred
the laterites have significant amounts of net enrichment in during the Miocene formation of the Klamath peneplain
either nickel or cobalt. (Diller, 1902). Some weathering, however, was much
younger, as shown by the occurrence of laterite on Pleis-
tocene terraces (Hotz, 1964; Moring, oral commun., 1986).
INTRODUCTION Subsequently, most laterites have been uplifted and dis-
sected so that many now occur on plateaus or as cappings on
The United States is import-dependent for a number ridges and saddles and as transported debris on sides of hills
of important commodities, among which are nickel and and in valleys.
cobalt. Several potentially important domestic deposits Nickel laterites similar to these are a common product
containing these elements have been identified. Of these, of tropical weathering of ultramafic rocks. They, in fact,
the most important are the magmatic sulfides in the Still- constitute the world's largest land-based resource of nickel
water Complex (Montana) and the Duluth Complex (Min- (Chamberlain, 1986). The features associated with these
nesota), the sediment-hosted and strata-bound Cu-rich sul- deposits have been reviewed by a number of authors, most
fides and arsenides of the Blackbird deposit (Idaho), notably Trescases (1975), Evans and others (1979), and
Mississippi Valley-type lead deposits (southeast Missouri), Golightly (1981). Features typical of laterite profiles from
and the nickel-bearing laterites in Oregon and northern this area are reported as follows: Upper parts of laterite
California (Foose, 1991). Although one of these, a nickel profiles consist of an extensively leached iron-rich zone
laterite located near Riddle, Oreg., was recently mined (fig. (limonitic zone) that is dark reddish brown in color; iron
1), none of these deposits are currently in production.Other oxide pellets locally occur near the profile top. This reddish
nickel-bearing laterites occur in southern Oregon and north- zone 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 Mount25
Emily

N ~~~~~~~~~OREGON
-~~ ~ CALIFORNIA

K) ~~~233 199
'4 ~~Gas'ut '

I '\ Mount fV
232 231

I
Earl ~ ~~0 5 10MILES

0 5 10 KILOMETERS

*11pCrescent City

Figure 1. A, Approximate area of the northern California-southern Oregon

laterite district (dashed boundary). B, Sample sites (solid diamonds). Shaded
area represents approximate boundary of the Kalmiopsis Wilderness area.

E2 Contributions to Commodity Geology Research

zone) in which there commonly are pieces of partly This latter area contains several laterite deposits that may be
weathered peridotite and in which the degree of commercially usable. Samples from the Gasquet Mountain
preservation of relict bedrock structures increases with area were collected from prospect pits in which profiles as
depth. The saprolite zone grades into greenish-brown thick as 7 m were exposed. In contrast, other samples were
weathered peridotite and then into fresh peridotite or collected with a hand auger and, because of the limitations
serpentine (Hotz, 1964; Ramp, 1978). of this device, seldom penetrated more than 2 to 3 m of
In some laterites, nickel occurs in the lower saprolitic laterite. In eight cases, this amount of penetration was
zone as a solid solution replacement of magnesium in a sufficient to sample profiles that exhibited all the features
variety of secondary magnesium silicates (mostly serpen- found in the more completely exposed pits as well as to
tine, talc, and chlorite). These nickel-magnesium silicates show the same features that have been described for other
are referred to as the "garnierite group" (Faust, 1966) and laterites in this region (Hotz, 1964; Ramp, 1978). Samples
form what are commonly known as either saprolite or collected from these eight locations as well as those taken
silicate ores. Nickel content of these ores typically is from the exploration pits provide the material discussed in
between 2 and 3 percent. In contrast, nickel in the overlying
this report.
limonitic zone occurs mostly in goethite and rarely exceeds
One hundred laterite samples and nine rock samples
2 percent. Significant amounts of cobalt also occur in many
were analyzed for nickel, cobalt, copper, and 10 major
laterites and are associated mostly with manganese oxides
oxides. Results are given in table 1. In addition, the
(asbolite) that are concentrated in the lower part of the
mineralogy of samples was determined by X-ray diffrac-
limonitic soil zone.
In Oregon and northern California, laterites having an tion. Samples were ground to less than 325 mesh and then
extensively developed nickel-bearing silicate zone are pressed into circular wafers. Wafers were made by placing
known to occur only near Riddle, Oreg. Saprolite is present the ground material on a layer of boric acid and methyl
in other deposits but generally does not contain significant cellulose, a compound added to provide strength. This
amounts of gamierite-type mineralization. The reason for mixture was compressed in a hydraulic press for at least 30
the apparent restriction of higher grade nickel ores to the seconds at a pressure of 10,000 pounds per square inch.
Riddle area is not clear, but Hotz (1964) speculates that Wafers were then exposed to CuK., radiation by using a
rocks associated with this deposit may have had a longer 1.00 beam slit, a 0.10 detection slit, a crystal monochrom-
weathering history. As a result of its higher nickel grades, eter, and a proportional counter detector. The samples were
the deposit near Riddle was the first to be developed. scanned between 20 and 600 20 at a rate of 1/20 20/minute.
In addition to its relatively greater nickel content, the In order to resolve some ambiguous mineralogical
ores at Riddle also contain relatively high amounts of silica identifications, several samples received further treatment.
and magnesium. As a result of this composition, refining Splits from these were suspended in water and then allowed
must be done by pyrometallurgical processes (Canterford, to settle onto porcelain tiles, a procedure which oriented the
1975). The product was ferronickel containing about 49 clay-size fraction. Four X-ray diffraction patterns, between
percent nickel; cobalt was not recovered separately. In 2° and 18° 20, were made of the clay fraction; first, after the
contrast, the lower SiO 2 and MgO contents of limonitic ores samples had been air dried; second, after the samples were
commonly allow them to be refined by a variety of treated with ethylene glycol (EG) for at least 1 hour; third,
hydrometallurgical techniques, many of which enable after the samples had been heated to 350 0C for at least 1
recovery of both nickel and cobalt. Specific processes hour; and fourth, after heating the samples to 550 0C for at
designed to extract both nickel and cobalt from the least one hour.
relatively low grade laterites in northern California and This procedure enables the distinction of smectite
Oregon have been developed and tested (Siemens and from chlorite and vermiculite and the distinction of serpen-
others, 1975; Duyvesteyn and others, 1979; Kukura and tine from kaolinite. Mineral identification is based on the
others, 1979), and, for this reason, several of these deposits following responses (Grim, 1968; Hathaway, unpublished
have been evaluated as possible domestic sources of both report):
nickel and cobalt. Upon treatment with EG, the 14-A peak of smectite
expands to 17 A, while the 14-A peaks of chlorite and (or)
vermiculite are essentially unchanged.
SAMPLE DESCRIPTION AND TREATMENT Upon heating to 350 °C, the 14-A peak of smectite
collapses to 10 A, while the chlorite and (or) vermiculite
Samples from several laterite deposits were collected 14-A peak is unchanged.
as part of a program to evaluate the mineral resources of the Upon heating to 550 °C, the 14-A peak of chlorite
Kalmiopsis Wilderness (Page and others, 1982; fig. 1). may increase in intensity, the 14-A peak of vermiculite
Sample sites were both within or near the wilderness area collapses to 10 A, and the 7-A peak of serpentine remains
and from an adjacent area, near Gasquet Mountain, Calif. stable, 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 TremoliteHon
blencde
number depth (in) pyroxene

211-1 ..... 0.23 . red-brown 11 0.0 12 2.0 0.0

211-2 ..... 3 gray-yellow 13 8.0 10 1.5 .0
211-3 .... 6 gray-yellow 13 17 8.0 2.0 3.0
211-4 ..... 9 gray-yellow 15 16 8.0 8.0 3.0
211-5 ..... 1.22 . gray-yellow 9.5 42 7.0 8.0 3.5
211-6.....1.53 . gray-yellow 6.5 62 6.0 10 5.0
211-7.....1.83 . gray-green 7.0 46 6.0 8.5 2.5
211-8.....2.14 . gray-green 7.5 54 5.0 9.0 5.0
211-9 .......... rock

213-1 ..... red-brown 15 4.0 11.5 1.0 11 .0 2.0 4.0 3.0

213-2 .... 3 red-brown 15 4.0 12.5 1.0 13 1.5 2.5 3.5 3.5
213-3 ..... 6 green-gray 11 4.0 12.5 5.0 8.5 3.5 2.5 3.0 2.5
213-4 ..... 9 black 6.5 2.5 12.5 8.0 3 5.0 2.0 1.5 .0
213-5.....1.22 . black 6.5 2.5 11.5 7.5 3 4.0 .0 1.5 .0
213-6 ..... 1.53 . yellow-green 6.0 3.5 8.0 14 2 7.5 .0 .0 .0
213-7.....1.88 . green-black 5.0 8.0 6.0 13 4 7.5 .0 .0 .0
213-8 .......... rock

214-1 ..... red-brown 10 .0 14 7.0 5 .0 4.0 11

214-2 ..... 3 red-brown 11 10 10 11 4 .0 4.5 10
214-3 ..... 6 yellow-green 6.0 46 11 8 3 4.0 .0 4.0
214-4 ..... 9 yellow-green-black 5.0 75 3.5 10 2 5.0 .0 .0
214-5 ..... 1.22 . green-black 6.5 65 4.5 7.0 1 2.5 .0 4.5
214-6 ..... 1.37 . green-black 7.5 72 4.0 7.0 1 2.0 .0 3.0
214-7 .......... rock

215-1 .... 1 red-brown 16 1.5 10 2.5 23 4.0 6.0 2.5

215-2..... 3 red-brown 15 2.5 10 2.5 22.5 5.0 6.0 2.0
215-3 .... 6 dark-red-brown 19 .0 10 2.5 23 5.0 7.5 4.5
215-4..... 9 yellow-green 11 3.0 11 .0 15 6.0 9.5 5.5
215-5..... 1.22 . yellow-green 12 .0 14 .0 10.5 8.0 8.0 7.0
215-6 .......... rock

216-1 .... 1 red-brown 40 7.5 14 3.0 7.5 .0 70 7.5

216-2..... 3 red-brown 44 5.0 14 6.0 4.0 .0 75 9
216-3 .... 6 yellow-brown 55 2.5 16 6.0 3.5 5.5 82 10
216-4..... 9 yellow-brown 43 3.5 10 3.5 4.5 5.0 57 7
216-5.....1.22 . yellow-brown 47 4.0 12 1.5 5.0 5.0 65 11
216-6 .......... rock

217-1 ..... dark-red-brown 5.0 4.0 12 6.0 2.5

217-2..... 3 red-brown 7.0 4.5 12 6.0 4.5
217-3 .... 6 green-gray 6.5 42 12 13 3.5
217-4 .... 9 green-gray 9.5 59 6.0 11 5.0
217-5.....1.22 . green-gray 5.5 58 5.0 12 2.0
217-6.....1.53 . green-gray 6.0 100 6.0 13 2.0
217-7 .......... rock

231-1 .... .46 .... red-yellow 9.0 43 9.0 2.0 10

231-2 .... .87.... yellow-brown 43 4.0 12 .0 3.0
231-3 .... 1.20 .... red-brown 12 20 11 3.0 11
231-4 .... 1.55 .... red-brown 8.5 10 10 .0 13
23 1-5..... 2.01.... red-brown 8.5 11 12 .0 16
231-6..... 2.32 .... red-brown 7.5 20 10 .0 16
23 1-7..... 2.62 .... red-brown 8.5 3.0 12 1.0 13
231-8..... 2.93 .... red-brown 7.0 81 10 3.5 11
23 1-9..... 3.23 .... yellow-brown 8.0 86 9.5 3.5 12
231-10.... 3.54 .... yellow-brown 8.0 6.0 10 .0 12
231-11.... 3.84 .... yellow-brown 6.0 5.0 12 2.0 10
231-12.... 4.15 .... yellow-brown 6.5 8.0 12 2.5 10
231-13 .. .. 4.45 .... yellow-brown .0 4.0 9.5 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 A1 03 Fe 03 MgO CaO Na O KO Tio P 05 MnO LOI

Ni (ppm) Co (ppm) Cu (ppm) (wt. 2%) (wt.2 %) (wt.2 %) (wt. %) (wt. %) (wt.2 %) (wt.2 %) (wt. 2%) (wt.2 %) (wt. %) (wt. %)

6800 1000 130 15.1 14.2 41.0 10.1 0.16 <0.2 <0.02 0.28 <0.1 0.42 13.76

1600 95 20.8 9.0 37.6 12.9 .55 <.2 <.02 .11 <.1 .58 13.61
8300
1300 77 27.1 8.1 30.8 15.3 .37 <.2 <.02 .06 <.I .33 14.11
8800
1100 80 25.5 9.3 33.2 12.3 3.17 <.2 <.02 .22 <.1 .38 12.72
8300
940 82 27.2 6.9 29.9 17.3 1.13 <.2 <.02 .11 <.1 .35 13.88
8000
830 80 27.9 4.9 30.5 18.4 .70 <.2 <.02 .08 <.1 .37 13.82
8600
800 72 26.6 5.0 33.0 17.2 .55 <.2 <.02 .09 <.1 .43 13.38
8800
9700 660 52 29.2 4.4 29.7 18.5 .65 <.2 <.02. .08 <.1 .37 13.99
130 28 40.4 2.1 8.4 37.1 2.08 <.2 <.02 .03 <.I .17 9.19
2500

700 130 14.7 12.6 48.3 4.8 .28 <.2 .11 .48 <.1 .60 11.40
4900
700 110 18.6 12.8 43.9 5.0 .37 <.2 .15 .64 <.1 .64 12.28
4900
640 130 14.4 10.0 54.1 3.2 .27 <.2 .13 .32 <.1 .44 12.15
5200
1100 120 15.3 7.9 53.7 5.0 .40 <.2 .07 .21 <.1 .10 11.94
5700
1100 120 18.4 6.6 51.6 3.0 .31 <.2 .05 .14 <.1 1.07 14.29
6200
760 110 24.0 7.2 43.9 4.3 1.01 <.2 .05 .20 <.1 .90 14.99
6000
570 75 27.8 4.5 37.8 9.2 .83 <.2 .03 .09 <.1 .92 15.02
7500
140 10 40.3 .8 8.6 37.7 .43 <.2 <.02 <.02 <.1 .16 10.86
3800

440 40 16.6 8.7 51.7 4.8 1.11 <.2 .09 .40 .1 .35 13.69
4800
540 37 17.8 6.7 51.7 6.3 .90 <.2 .06 .29 <.1 .41 12.88
5200
390 23 26.8 4.5 36.0 15.8 .59 <.2 .05 .19 <.1 .42 13.36
6800
360 23 28.8 3.9 31.6 17.9 .54 <.2 .04 .16 <.1 .41 15.20
6300
370 25 26.3 5.3 35.8 14.7 .86 <.2 .06 .24 <.1 .44 14.10
5400
340 23 28.3 4.9 32.5 16.5 .81 <.2 .07 .23 <.1 .41 14.21
5000
160 10 38.7 .4 8.8 36.8 .07 <.2 <.02 <.02 <. 1 .20 13.62
4700

190 120 21.2 23.0 33.2 2.2 .26 <.2 .26 .90 1 .28 16.52
1100
180 120 22.4 22.8 33.0 1.8 .19 <.2 .27 1.01 .1 .28 15.71
1100
180 120 24.1 23.1 31.6 2.4 .35 <.2 .31 1.02 .1 .24 14.84
1100
140 100 25.0 22.5 29.7 2.8 .37 <.2 .18 .89 <.1 .01 15.14
1200
160 90 22.3 21.6 33.2 3.2 .61 <.2 .15 .79 <.1 .11 15.46
1300
260 56 10 42.4 16.3 9.1 8.5 16.50 .4 .03 .88 <.1 .16 4.64

530 110 27.1 5.4 34.9 11.8 1.23 .3 .07 .25 <.1 .51 11.30
5700
620 120 25.0 5.0 38.2 11.9 1.27 .3 .06 .23 <.1 .43 8.32
5600
540 120 30.5 5.0 33.6 12.4 1.15 .4 .07 .20 <.1 .39 10.59
5900
530 80 32.2 3.7 31.1 14.5 .90 <.2 .04 .14 <.1 .38 11.46
6400
6500 440 100 34.2 4.4 29.1 14.7 1.50 .3 .05 .26 <.1 .33 10.84
140 44 38.9 1.2 9.8 36.9 .59 <.2 <.02 <.02 <.1 .14 11.02
3000

710 100 8.6 6.5 58.0 3.4 .74 <.2 .03 .11 <.1 1.42 15.08
8400
630 85 16.8 5.9 52.9 3.1 1.97 <.2 .03 .10 <.1 .64 13.76
7000
460 60 30.0 3.1 30.5 19.2 1.10 <.2 <.02 .04 <.1 .44 13.22
6900
330 60 34.7 2.0 21.9 24.0 2.00 <.2 <.02 <.02 <.1 .29 12.30
7000
330 60 34.7 1.8 20.1 27.6 1.15 <.2 <.02 <.02 <.1 .27 12.39
6400
320 230 35.3 1.7 18.6 29.7 .57 <.2 <.02 <.02 <.1 .23 12.41
5900
120 12 38.9 .6 8.5 35.6 .12 <.2 <.02 <.02 <.1 .14 13.92
6800

450 75 17.1 12.7 47.1 4.5 .08 <.2 .13 .66 .1 .56 13.20
3700
4500 600 92 14.7 13.0 52.6 2.6 <.02 <.2 .15 .51 <.1 .37 10 99
4600 450 82 16.2 14.2 50.5 1.9 <.02 <.2 .17 .65 1 .36 11.20
450 85 17.2 14.5 49.4 1.9 .03 <.2 .20 .69 1 .37 10.75
4000
380 87 15.5 13.6 47.9 3.8 <.02 <.2 .09 .52 <.1 .42 13.49
3500
310 82 16.0 15.2 50.1 1.8 <.02 <.2 .20 .68 .1 .39 11.18
3400
300 85 15.6 15.1 50.4 1.5 <.02 <.2 .19 .67 .1 .35 11.51
3700
3400 350 60 17.5 13.8 47.9 4.2 <.02 <.2 .17 .62 <.1 .37 11.41
460 62 16.9 13.3 48.4 4.3 <.02 <.2 .16 .60 <.1 .38 11.10
3200
300 82 13.8 13.9 53.4 1.8 <.02 <.2 .15 .61 .1 .37 10.34
3800
290 75 12.9 13.9 53.3 2.1 <.02 <.2 .12 .57 .1 .36 11.68
4000
260 75 13.0 13.8 53.1 1.7 <.02 <.2 .13 .53 <.I .33 11.60
4400
4200 260 72 11.8 12.9 56.1 1.6 <.02 <.2 .11 .49 <. I .35 10.79

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 .... 4.76 .... yellow-brown 4.5 0.0 10 4.5 8.5

231-15 .... 5.06 .... yellow-brown 7.5 .0 11 5.0 9.0
231-16.... 5.37 .... yellow-brown 9.0 .0 11 4.0 8.5
231-17 ... 5.67 .... yellow-brown 4.5 .0 12 7.0 8.0
231-18 .... 5.98 .... yellow-brown 1.5 .0 13 8.5 2.0
231-19.... 6.28 .... yellow-brown 6.5 .0 14 8.0 4.0
231-20.... 6.59 .... yellow-brown 5.5 .0 13 7.5 2.5

232-1 ..... 3 red-brown 6.0 .0 12 3.0 16 7.0 2.0

232-2..... 6 red-brown 6.5 1.5 11 4.0 15 6.0 3.0
232-3.....1.22 . red-brown 5.0 .5 12 2.0 16 7.5 4.0
232-4.....1.53 . red-brown 7.0 1.5 11 2.5 18 3.0 1.5
232-5 ..... 1.83 . red-yellow 4.5 .0 13 .0 13 8.0 3.0
232-6.....2.14 . red-yellow 2.0 .0 18 .0 10 5.5 1.5
232-7.....2.44 . red-yellow 2.5 .5 8.0 4.5 10 5.5 2.5
232-8 ..... 2.75 . red-yellow 5.0 .0 13 1.5 12 5.0 1.5
232-9 ..... 3.05 . red-yellow 3.5 .0 15 3.5 5.0 3.5 1.5
232-10 .... 3.36 . red-yellow 2.5 .0 14 18 2.0 .0 .0
232-it....3.66 . red-yellow 2.5 0 12 7.0 4.0 3.5 2.0
232-12 .... 3.97 . red-yellow 5.5 .0 12 2.5 15 6.5 4.0
232-13 .... 4.27 . red-yellow 7.5 1.5 11 3.0 14 6.0 1.5
232-14 .... 4.58 . red-yellow 4.0 .0 12 1.5 11 5.5 2.0

233-1 .... 3 red-brown .0 .0 22 3.0 .0 4.5 .0 .0

233-2 ..... 6 red-brown .0 .0 20 2.0 .0 9.5 .0 .0
233-3.....1.22 . red-brown 5.0 .0 18 2.0 .0 13 .0 .0
233-4.....1.53 . yellow-brown 7.0 7.0 16 2.0 .0 12 .0 .0
233-5.....1.83 . yellow-brown 12 30 15 2.0 .0 13 11 2.5
233-6.....2.t4 . yellow-brown 16 40 14 4.0 .0 13 .0 3.0
233-7.....2.44 . yellow-brown 9.0 50 13 8.5 2.0 3.5 .0 3.0
233-8 ..... 2.75 . yellow-brown 5.0 33 16 4.0 .0 5.5 .0 2.0
233-9 ..... 3.05 . yellow-brown 4.5 20 13 3.0 .0 3.5 2.0 3.0
233-t0.....3.36 . yellow-brown 4.0 15 13 5.5 .0 1.5 1.0 1.5
233-ti .... 3.66 . yellow-brown 7.5 20 9.5 10.5 .0 1.5 4.0 2.5
233-12 .... 3.97 . yellow-brown 2.5 10 14 6.5 .0 3.0 9.5 2.5
233-13.......... rock

259-1 ..... red-brown 25 .0 I11 7.0 8.0 5.5 10

259-2 .... 3 red-brown 16 8.5 16 3.0 5.0 5.5 2.0
259-3 .... 6 yellow-red 12 47.5 13 5.0 4.0 5.0 5.0
259-4 .... 9 yellow-red 9.0 100 10 6.0 4.5 5.5 4.0
259-5 ..... 1.22 . yellow-brown 10.5 100 10 7.0 2.0 5.0 5.0
259-6 ..... 1.53 . yellow-brown 8.0 100 9 7.0 2.0 11 1.0
259-7.....1.83 . yellow-brown 6.0 100 8 7.0 2.0 15 4.0
259-8.....2.14 . yellow-brown 6.0 100 8 9.0 1.0 6.5 6.0
259-9 . . . . . . . . . rock

261-1 ..... red-brown .0 .0 13 9.0 .0 .0

261-2 .... 3 red-brown .0 .0 14 9.0 .0 .0
261-3 ..... 6 red-brown 3.5 .0 13 11 .0 .0
261-4 .... 9 gray-brown 2.0 .0 13 11 .0 .0
261-5 ..... 1.22 . gray-brown 3.0 .0 13 9.5 5.5 .0
261-6 ..... 1.53 . yellow-brown 8.0 25 13 11 1.5 .0
261-7 ..... 1.83 . yellow-brown 6.5 20 12 9.0 3.0 2.0
261-8 ..... 2.14 . yellow-brown 3.0 18 14 13 3.0 1.0
261-9 ..... 2.44 . yellow-brown 2.0 100 11 14 2.5 2.0
261-10.......... rock

E6 Contributions to Commodity Geology Research

 SiO2 A1203 Fe203 MgO CaO Na2 0 K~O TiO2 P205 MnO LOI
Ni(ppm) Co (ppm) Cu (ppm) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %)

5200 340 55 13.7 10.5 58.8 1.8 <0.02 <0.02 0.15 0.38 <0. 1 0.39 8.22
5000 480 57 15.3 11.6 56.6 1.7 <.02 <.2 .22 .43 <.1 .44 9.01
5400 470 60 15.1 10.8 57.6 1.8 <.02 <.2 .19 .43 <.1 .48 8.84
6300 660 62 10.7 8.9 63.6 1.8 <.02 <.2 .12 .28 <.1 .51 8.09
6100 860 67 6.5 7.8 69.4 1.8 <.02 <.2 .05 .14 <.1 .56 7.72
5700 2000 77 11.6 9.7 62.5 2.4 <.02 <.2 .11 .24 <.1 .78 7.92
5700 1500 97 14.1 10.9 56.1 3.5 <.02 <.2 .11 .25 <.1 .83 9.45

5300 720 70 23.2 11.2 41.4 4.7 .46 <.2 .21 .52 .1 .70 11.85
5200 700 70 24.0 11.4 41.0 4.5 .47 <.2 .23 .55 .1 .70 12.30
5800 720 70 23.5 10.5 42.6 4.7 .55 <.2 .21 .50 .1 .65 11.51
3900 510 87 28.1 13.2 35.7 4.7 .44 <.2 .30 .69 .1 .73 11.32
5700 910 80 22.1 10.0 44.3 4.8 .55 <.2 .15 .43 .1 .76 11.68
5500 600 63 10.4 7.0 60.2 2.6 .19 <.2 .05 .17 <.1 .36 13.65
6100 1000 70 20.3 11.3 46.4 3.3 .32 <.2 .15 .53 .1 .85 11.15
6100 570 63 21.6 11.1 45.5 3.4 .31 <.2 .25 .50 .1 .45 11.10
7900 630 85 9.9 10.2 58.3 1.5 .06 <.2 .15 .28 .1 .28 13.54
6200 480 110 2.5 5.2 77.6 .7 <.02 <.2 <.02 .06 <.1 .18 8.36
6400 660 80 8.4 6.7 68.0 1.9 .13 <.2 .08 .18 <.1 .37 9.01
5800 760 67 23.0 11.1 43.1 4.1 .44 <.2 .20 .53 .1 .63 11.16
5800 720 65 22.9 10.9 43.4 4.5 .46 <.2 .18 .51 .1 .61 10.85
7000 1000 72 16.1 9.8 51.9 3.7 .27 <.2 .16 .37 .1 .57 11.95

7300 630 70 5.1 5.9 66.1 1.7 <.02 <.2 .03 .11 <.1 .39 15.59
7200 760 70 4.0 5.3 67.8 1.4 <.02 <.2 <.02 .07 <.1 .37 15.49
7000 1200 57 7.4 5.2 65.3 2.9 .12 <.2 .03 .07 <.1 .49 13.20
9200 1300 57 10.0 4.5 63.1 4.0 .25 <.2 <.02 .04 <.1 .65 13.05
13000 700 63 21.0 3.2 48.2 10.2 1.07 <.2 <.02 .03 <.1 .57 11.68
13000 1000 53 17.4 3.4 52.9 8.6 .66 <.2 <.02 <.02 <.1 .87 11.62
11000 1000 71 11.4 3.0 66.6 5.2 .38 <.2 <.02 <.02 <.1 1.09 8.60
14000 880 43 21.3 2.9 48.5 10.9 .88 <.2 <.02 <.02 <.1 .97 10.60
14000 920 68 24.2 3.4 44.8 12.4 .99 <.2 <.02 <.02 <.1 .78 9.00
5500 440 97 Is Is IS IS is Is is IS IS IS IS
16000 1100 98 Is is Is Is Is IS IS is Is IS IS
15000 840 63 19.2 3.0 50.3 9.9 .72 <.2 <.02 <.02 <.1 .90 11.04
6200 110 14 41.2 .6 9.3 39.1 .54 <.2 <.02 <.02 <.1 .13 8.15

4300 400 72 23.9 14.2 32.7 10.2 1.67 <.2 .19 .45 <.1 .57 12.46
5900 410 120 17.8 13.8 42.1 6.8 .59 <.2 .12 .34 <.1 .39 13.84
5400 430 95 19.4 12.0 40.3 9.1 .83 <.2 .09 .29 <.1 .50 13.05
4800 430 72 24.6 9.9 32.8 14.7 .56 <.2 .08 .26 <.1 .64 12.69
5000 300 60 27.6 8.6 28.6 18.2 1.20 <.2 .06 .22 <.1 .40 11.96
4300 260 45 31.6 6.8 23.1 21.7 .76 <.2 .04 .16 <.1 .39 12.02
4400 250 35 33.6 5.4 20.3 24.7 .77 <.2 <.02 .11 <.1 .34 11.64
5000 250 20 35.8 4.1 18.6 26.1 .64 <.2 <.02 .08 <.1 .34 10.89
2100 100 10 39.4 1.8 8.4 36.5 .98 <.2 <.02 <.02 <.1 .14 11.28

8100 1200 120 3.9 7.7 66.4 1.1 .08 <.2 .06 .13 <.1 .76 13.91
8800 950 110 3.7 8.3 67.4 .8 .04 <.2 .05 .13 <.1 .66 13.61
8100 1200 100 3.2 8.0 70.8 .9 <.02 <.2 .04 .11 <.1 .78 11.38
10000 2700 65 3.2 5.0 74.1 .9 .03 <.2 <.02 .08 <.1 1.44 10.65
13000 2000 45 4.1 4.2 73.0 1.2 .05 <.2 <.02 .07 <.1 1.20 10.41
14000 1800 55 5.7 4.7 68.2 2.0 .27 <.2 <.02 .06 <.1 1.17 12.76
12000 1200 95 7.7 6.4 63.6 2.7 .72 <.2 <.02 .06 <.1 .94 12.28
11000 1200 100 7.7 6.5 65.9 2.8 .57 <.2 <.02 .05 <.1 1.05 11.30
10000 950 70 12.1 5.6 58.9 8.2 .17 <.2 <.02 <.04 <.1 .92 10.22
2700 170 10 40.3 .8 9.2 41.5 .71 <.2 <.02 <.02 <.1 .21 6.48

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- Tremolite
blendle pyroxene
211 ........ Inc Dec Dec Inc Inc
213 ........ Inc Dec Dec Inc Inc Dec Dec Dec Dec
214 ........ Inc Dec Dec Inc Inc Dec Dec Dec
215 ........ NC Dec NC Dec Inc Dec Dec Inc
216 ........ NC NC NC NC Inc NC Dec Inc
217 ........ Inc NC Dec Inc NC
231 ........ Dec Dec NC Inc Dec
232 ........ Inc NC NC NC Dec NC NC
233 ........ Inc Inc Dec Inc Dec Inc Inc
259 ........ Inc Dec Dec Inc Dec Inc NC
261 ........ Inc Inc Dec Inc Inc Inc
Bedrock mineralogy 2
Site Serpentine Chlorite Olivine Ortho- Clino- Maghemite Goethite Talc Horn- Magnetite Tremolite
pyroxene pyroxene blende
211 ......... x x x x x
213 ........ x x x x
214 ......... x x
215 x x x x
216 ......... x x x x x x x
217 ......... x x x
233 ......... x x x x
259 ......... x x x x x
261 ......... x x x
Trends in laterite chemistry with increasing depth'
Site MgO Sio 2 Fe 2O3 A1203 TiO 2 CaO Ni Co MnO Cu
211 ........ Inc Inc Dec Dec Dec Inc Inc Dec NC Dec
213 ........ Inc Inc Dec Dec Dec Inc Inc Inc Inc Dec
214 ........ Inc Inc Dec Dec Dec NC NC Dec Inc Dec
215 ........ Inc NC NC NC NC Inc Inc Dec Dec Dec
216 ........ Inc Inc Dec Dec Dec NC Inc Dec Dec Dec
217 ........ Inc Inc Dec Dec Dec NC Dec Dec Dec Dec
231 ........ NC NC Inc Dec Dec NC Inc Inc Inc NC
232 ........ NC NC NC NC NC NC Inc NC NC NC
233 ........ Inc Inc Dec Dec Dec Inc Inc NC Inc NC
259 ........ Inc Inc Dec Dec Dec NC NC Dec Dec Dec
261 ........ 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, in The mineralogical and chemical data for the 11
part, reflected by the intensity of its X-ray diffraction peaks. profiles are presented in table 1 and are partly summarized
Peak intensity is, however, also dependent on other factors, in tables 2 and 3. The X-ray traces and plots of mineralog-
such as degree of crystallinity, orientation, and interfer- ical and chemical data from two profiles (sites 216 and 233)
ences. As a result, obtaining quantitative mineral modes are given in figures 2 and 3 as further illustration of the
from diffraction data is an extremely difficult task (Grim, approach used in this study.
1968) and was not done for these samples. An attempt was
made, however, to qualitatively estimate mineral abun-
dances within each of the 11 laterite profiles. These LATERITE MINERALOGY
estimates were made by measuring the height above back-
ground of each mineral's most intense reflection. Mineral The mineralogy of these laterite profiles is relatively
abundance estimates derived from X-ray diffraction data simple (table 2). All contain serpentine, chlorite, goethite,
most often are made by measuring the area under peaks. and maghemite. Additional phases that are present in some
Although less accurate, measurement of peak height has samples, but not all, are smectite, quartz, talc, and horn-
also been shown to be closely related to mineral abundance blende. No attempt was made to further identify the
(Gibbs, 1965). smectite, but on the basis of the iron-rich composition of

E8 Contributions to Commodity Geology Research

Table 3. Range of laterite compositions
(geometric (Gm.) means). Sd., standard
[Mean values are computed on untransformed data (arithmetic (Ar.) means) and on log-transformed data
deviations. Numbers in parentheses indicate number of samples analyzed]

Co (ppm) SiO 2 (percent) MgO (percent) Fe203 (percent) Al 203 (percent) MnO (percent)
Site Ni (ppm)
660 15.1 10.1 29.7 4.4 0.33
211 Min. 6,800
1,600 29.2 18.5 41.0 14.2 .58
(8) Max. 9,700
1,029 24.9 15.3 33.2 7.7 .40
Ar. mean 8,413
303 4.7 3.1 4.1 3.2 .08
Sd. 827
993 24.5 14.9 33.0 7.2 .40
Gm. mean 8,375
1.327 1.25 1.25 1.12 1.49 1.19
Sd. 1.1074
570 14.4 3.0 37.8 4.5 .10
213 Min. 4,900
1,100 27.8 9.2 54.1 12.8 1.07
(7) Max. 7,500
796 19.0 4.9 47.6 8.8 .67
Ar. mean 5,771
216 5.1 2.0 6 3.1 .33
Sd. 920
773 18.5 4.6 47.3 8.3 .55
Gm. mean 5,712
1.294 1.29 1.44 1.14 1.46 2.25
Sd. 1.1644
340 16.6 4.8 31.6 3.9 .35
214 Min. 4,800
540 28.8 17.9 51.7 8.7 .44
(6) Max. 6,800
407 24.1 12.7 39.9 5.7 .41
Ar. mean 5,583
74 5.4 5.6 9.3 1.8 .03
Sd. 791
402 23.5 11.3 39.0 5.5 .41
Gm. mean 5,539
1.184 1.28 1.77 1.25 1.34 1.08
Sd. 1.1471
140 21.2 1.8 29.7 21.6 .01
215 Min. 1,100
190 25.0 3.2 33.2 23.1 .28
(5) Max. 1,300
170 23.0 2.5 32.1 22.6 .18
Ar. mean 1,160
20 1.5 .5 1.5 .6 .12
Sd. 89
169 23.0 2.4 32.1 22.6 .12
Gm. mean 1,157
1.130 1.07 1.25 1.05 1.03 4.15
Sd. 1.0780
440 25.0 11.8 29.1 3.7 .33
216 Min. 5,600
620 34.2 14.7 38.2 5.4 .51
(5) Max. 6,500
532 29.8 13.1 33.4 4.7 .41
Ar. mean 6,020
64 3.7 1.4 3.5 .7 .07
Sd. 409
529 29.6 13.0 33.2 4.7 .40
Gm. mean 6,009
1.130 1.14 1.11 1.11 1.16 1.18
Sd. 1.0698
5,900 320 8.6 3.1 18.6 1.7 .23
217 Min.
710 35.3 29.7 58.0 6.5 1.42
(6) Max. 8,400
463 26.7 17.8 33.7 3.5 .55
Ar. mean 6,933
170 11.3 11.8 17.4 2.2 .45
Sd. 838
439 23.8 12.6 30.2 3.0 .44
Gm. mean 6,893
1.425 1.78 2.89 1.65 1.83 1.98
Sd. 1.1249
3,200 260 6.5 1.5 47.1 7.8 .33
231 Min.
2,000 17.5 4.5 69.4 15.2 .83
(20) Max. 6,300
559 14.3 2.4 54.2 12.5 .45
Ar. mean 4,490
966 441 2.7 1 5.9 2.1 .14
Sd.
467 14.0 2.3 54.0 12.3 .43
Gm. mean 4,394
1.2351 1.732 1.25 1.45 1.11 1.20 1.30
Sd.
480 2.5 .7 35.7 5.2 .18
232 Min. 3,900
1,000 28.1 4.8 77.6 13.2 .85
(14) Max. 7,900
5,907 713 18.3 3.5 50.0 10.0 .56
Ar. mean
163 7.5 1.3 11.9 2.2 .20
Sd. 908
696 15.9 3.1 48.8 9.7 .52
Gm. mean 5,840
1.1727 1.252 1.92 1.74 1.25 1.30 1.56
Sd.
440 4.0 1.4 44.8 2.9 .37
233 Min. 5,500
1,300 24.2 12.4 67.8 5.9 1.09
(10)* Max. 16,000
898 11.7 6.7 57.4 4.0 .71
Ar. mean 11,017
3626 245 7.4 4.1 9.2 1.1 .25
Sd.
864 12.0 5.3 56.7 3.8 .66
Gm. mean 10,414
1.4355 1.351 1.9 2.23 1.18 1.31 1.47
Sd.
250 17.8 6.8 18.6 4.1 .34
259 Min. 4,300
5,900 430 35.8 26.1 42.1 14.2 .64
(8) Max.

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., standard
deviations. 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 .45
Sd. 567 84 6.5 7.4 8.8 3.8 .11
Gm. mean 4,860 332 26.1 14.8 28.6 8.6 .44
Sd. 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 .99
Sd. 2118 585 3 2.4 4.7 1.5 .25
Gm. mean 10,371 1,380 5.1 1.7 67.4 6.1 .96
Sd. 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 .01
profiles 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 .27
Gm. mean 5,864 593 16.3 4.8 44.3 7.7 .47
Sd. 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 .10
profiles 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 .51
Sd. 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-rich Within most profiles, mineralogy changes systemat-
samples, it is reasonable to assume that they are nontronitic. ically. In general, serpentine, maghemite, smectite, and
Only two profiles contain orthopyroxene, and only one has homblende increase with depth. Conversely, goethite, chlo-
small amounts of tremolite. rite, talc, and quartz are usually most abundant toward the
The bedrock mineralogy is also simple and consists surface. Notable exceptions to these trends occur in samples
predominantly of serpentine, with lesser amounts of chlo- from sites 215, 216, 231, and 232 (table 2).
rite, olivine, and maghemite. Additionally, clino- and As previously mentioned, the profile at site 215
orthopyroxene, talc, goethite, hornblende, tremolite, and formed over a hornblende-rich bedrock that is composition-
magnetite occur in some samples. The bedrock at site 215, ally distinct from the serpentine-rich rocks associated with
however, differs markedly in composition from the other the base of the other profiles. As a result, little serpentine is
rock samples as it is composed predominantly of horn- present in the profile from site 215, and evidently most of
blende, chlorite, talc, and goethite and contains little or no the other mineralogical trends present in the other profiles
serpentine. also did not develop. The samples from site 215 are also
There are three mineralogical associations that are markedly lower in nickel than those which formed over
worth noting. First, all soil profiles that contain hornblende ultramafic bedrock (1,100-1,300 ppm vs. 3,200-16,000
also have talc. Although talc typically is derived from the ppm).
The profiles from sites 216, 231, and 232, which also
weathering of pyroxenes (Boeglin and others, 1983), the
do not show the systematic mineralogical trends of the other
association noted here may indicate that in these samples
profiles, have been slumped and mixed. Sites 216 and 232
some talc results from the alteration of homblende. Second,
both are in landslide masses and have evidently been so
tremolite occurs only in one of the two samples containing
completely homogenized that any initial vertical change in
orthopyroxene, perhaps indicating that it is an alteration of mineralogy has been eliminated. The profile for site 231 is
orthopyroxene. Third, samples having smectite occur only also from a landslide but has apparently retained some
in the northern part of the area sampled, within the component of its original profile. Increases in serpentine
boundaries of the Kalmiopsis Wilderness (fig. 1). A possi- and maghemite and decreases in goethite and chlorite are
ble explanation for this distribution is presented later. observed to a depth of about 3.2 m, but below this depth

E10 Contributions to Commodity Geology Research

 CI
A 5500C
T
T
3500C
S
T I EG
216-1
-I
CI+T
CI ~~~~CI+Sm if
I A

G Ch G
SlS

Hb 216-1
__)P
5500C

350°C
216-3

216-2
J
J
U
EG

U, Cl
216-3 5500C
z
z 3500C
216-5
EG

A
216-4

216-5
5500C

216-
S I bedrock

CI CI CI
S+Mh Il A

T1216-
oici1 01 s bedrock I J

I1 1I I l 1 1 1l . . . .l

20 10 0 r 14. 12. 10. 8. 6. 4. 2. I

60 50 4C 30 16
2 THETAI 2 THETA

Figure 2. X-ray mineralogy and chemistry for profile from in air (A), treated with ethylene glycol (EG), heated to 350
site 216. A, Hand-smoothed X-ray diffraction patterns. °C, and heated to 550 'C. C, Qualitative vertical variations
(Abbreviations: Cl, chlorite; S, serpentine; G, goethite; in mineral abundances. D, Vertical variations in profile
Mh, maghemite; Q, quartz; Sm, smectite; T, talc; 01, chemistry. E, Net change in Ni, Co, SiO2 , Fe2 03 , MgO,
olivine; Hb, hornblende.) B, Diffraction patterns of sam- and MnO calculated assuming A12 03 is constant. Method
ples settled from water onto porcelain tiles and then dried of calculation discussed in text.
 C D
0 0

0.2 0.2

0.4 0.4

uz (I)
Lu

Z> 0.6 uj 0.6

1--
z
w
3l

l'-
CL
0 w
0

0.8 0.8

1.0 1.0

1.2 1.2

10 20 30 40 50 60 70 80 2 4 6 8 10 12 14 16
90
QUALITATIVE MINERAL ABUNDANCE AMOUNT OF ELEMENT/OXIDE
EXPLANATION EXPLANATION
D Chlorite + Serpentine 0 Goeth ite D Nix10(WT%) + Co x 100 (WT%) A SiO /10 (WT%)
2
U Smectite 7 Quartz X Talc X FeA
2 3/10 (WT%)
V MgO (WT%) * Al 3(WT%)
A Maghemite e
Hornblende e TiO2 x 10 (WT%) (O Cu/10 (ppm) 0 MnOxlO(WT%)
Figure 2. Continued.
,
CaO x 10 (WT%)

Figure 2. Continued.

E12 Contributions to Commodity Geology Research

 E CHEMICAL VARIATIONS
0.1
Data for SiO 2, Fe 2 03 , and A1 203 most closely
approximate normal distributions and, therefore, may best
be characterized by arithmetic means. Data for Ni, Co,
MgO, and MnO, however, approximate lognormal distri-
butions, and for these elements the geometric mean (aver-
0.3 age value of the log-transformed data) provides a better
measure of the central tendency of these data. Table 3 gives
the arithmetic and geometric means, the maximum and
minimum values, and standard deviations of these ele-
ments.
With the exception of samples from site 215, geo-
0.5 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 to
1,380 ppm for Co). Abundance of Si0 2 (arithmetic mean of
CC 18.3; range of 5.7 to 29.8 percent) and MgO (geometric
LI-
w
LU
mean of 5.0; range of 1.7 to 14.9 percent) is directly
related to mineralogy, the greatest amounts occurring in
z 0.7 profiles that have the largest relative amounts of serpentine
(or talc, in the case of profile 216). Similarly, abundance of
I-
I-0 Fe 2O3 (arithmetic mean 46.4, range of 29.8 to 67.6 percent)
0~ increases as the amount of goethite increases.
The range in composition of these laterites agrees
with those reported in a survey of laterites occurring in this
0.9 area (Ramp, 1978) and also in specific studies of the Red
Flats (Libbey and others, 1947; Hundhausen and others,
1954), Pine Flat, and Diamond Flat (Benson, 1963) depos-
its. These compositions also fit the category defined by
Chandra and Ruud (1976) as transitional between high-iron
nickeliferous limonite deposits and high-silica serpentinous
1.1
ores. Some of these profiles are similar to compositions that
have been used to test the recovery of nickel and cobalt by
a variety of hydrometallurgical processes (Siemens and
others, 1975; Duyvesteyn and others, 1979; Kukura and
others, 1979).
Those profiles that have changes in mineralogy also
show systematic changes in chemistry (table 2). Among
1.3 _
-100 -50 0 profiles that are largely undisturbed, there are consistent
depth-related increases in MgO and SiO2 content and
PERCENT CHANGE decreases with depth in Fe 2O3 , A1203 , and TiO 2 content.
EXPLANATION Changes associated with CaO, MnO, and nickel, which
D Ni + Co SiO generally increase with depth, and copper, which generally
A MnO2 decreases with depth, are less consistent. Cobalt, in con-
X Fe203 V MgO
trast, exhibits neither a predictable increase nor decrease
Figure 2. Continued. with depth. Most of these chemical trends are also present
in the disturbed profile at site 216. However, these trends
are not found in the other disturbed profiles (231 and 232)
there is little discernible change in relativet mineral abun- and appear not to be developed at site 215.
dances. The abrupt change at 3.2 m occurs where two As expected, many of these oxides show reasonably
profiles have been juxtaposed; the upper part has the consistent correlations (table 4). Particularly good positive
mineral zonation typical of most of the other profiles and correlations are noted between MgO and SiO2 , which could
has apparently moved over a material that either had been be expected as both oxides are associated with serpentine
previously homogenized or over a material in which there and increase downward from the leached upper part of the
was relatively little mineralogical variation. laterite profile to the higher concentrations found in the

Nickel-Mineralogy and Chemical Composition of Some Nickel-Bearing Laterites E13

 I

A IlB 5500C
3500C
IEG 231
A

233-1
550°C
350°C 233-4
EG
233-2 A

233-3
5500C
/
3500C 233-5
EG
233-4 A

/233-5
550°C
3500C 233-8
EG
A
233-6

233-7 5500C
350°C 233-1C
EG
A
233-8
U,
z
z 2233-9 550°C
3500C 233-12 I
EG
A
1233-10

233-111
5500C

233-
bed roc;k

233-12
A

233- I
)edrock

.. .. .. .. . . . ..
r . , I . . . .I ... I ... . ... . .. I . . I . . I . I I I I I I I I 1
60 50 40 30 20 10 O1 16 14 12 10 8 6 4 2 0
2 THETA 2 THETA
Figure 3. X-ray mineralogy and chemistry for profile from with ethylene glycol (EG), heated to 350 °C, and heated to
site 233. A, Hand-smoothed X-ray diffraction patterns. 550 'C. C, Qualitative vertical variations in mineral
(Abbreviations: Cl, chlorite; S, serpentine; G, goethite; abundances. D, Vertical variations in profile chemistry. E,
Mh, Maghemite; T, talc; 01, olivine; Opx, orthopyrox- Net change in Ni, Co, SiO2 , Fe2 03, MgO, and MnO
ene.) B, Diffraction patterns of samples settled from water calculated assuming A1203 is constant. Method of
onto porcelain tiles and then dried in air (A), treated calculation discussed in the text.
 C D
0

Un U)
LU LU

LU LU
W

z 2 z
a- I-
l-LU
LU
0 0

A
10 20 30 40 50 60 0 2 4 6 8 10 12 14 16 18 20
0

QUALITATIVE MINERAL ABUNDANCE AMOUNT OF ELEMENT/OXIDE

(RELATED TO X-RAY PEAK HEIGHT) EXPLANATION
0
EXPLANATION El Ni x 10 (WT,'.) + Cox 100(WT%) 0 MnO, ( 10 (WT%)
D Chlorite + Serpentine 0 Goett tite X FeA/10 (WT%) V MgO (WT%) 0 Al203 (WT%)
A Maghemite X Orthopyroxene V Talc * TiO2 x 10 (Wr%) A Cu/10 (ppm) A SiO2/10 (WT%)
@ Hornblende * CaO x 10 (WT%)

Figure 3. Continued. Figure 3. Continued.

Nickel-Mineralogy and Chemical Composition of Some Nickel-Bearing Laterites E15

 E DISCUSSION
0
The distribution of major oxides appears to follow
trends 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 lateritic
weathering may be modeled by

Cx=C, * (1-e Ax d) (1)

where:
1- 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,
and
d is the depth.
un 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 *, /Ax) In(1
l[(A -(CX/Cx))]
i- (3)
I-'
The solid curve in figure 4 represents the solution to
0 equation 3 for bedrock concentrations of SiO 2 and MgO,
respectively, of 39 and 37 weight percent. A value of 2 was
assigned for the constant AY/Ax and was chosen to produce
a curve which fit the data. Actual solubility values for A.
and Ay are not known and in fact will change with different
43-
2
weathering conditions. The ratio used here, however, is
consistent with the observed greater mobility of MgO
relative to SiC 2 and also approximates the extreme ends of
the relative mobility scale given by Trescases (1975) in
which the mobility of magnesium is given as 1.0, while that
of silicon ranges between 0.5 and 1.0.
Similar complexities are observed in the relation
between MgO and Fe 2 03 (fig. 5). Samples from profiles
213, 215, 231, and 232 again do not lie on the exponential
curve made by samples from the other profiles. The fitting
4
-100 -50 0 of a theoretically derived curve to the pattern made by these
PERCENT CHANGE
data is, however, not as straightforward as in the previous
case. Both MgO and Si0 2 are removed during weathering,
EXPLANATION
and equation 3 is designed to accommodate the leaching of
Ni + Co A SiO2
such oxides. Iron, on the other hand, is residually enriched
x IFeO., V MgO 0 MnO
in the laterite, and its behavior is, therefore, not directly
predicted by the leaching model (eq. 3).
Figure 3. Continued.
By making certain assumptions, however, the above
model may be simplified and redesigned to approximate
variations in Fe2O3 . First, Fe 2O3 and A12 03 are considered
to be the only two major oxides not leached from the laterite
and, therefore, are residually enriched in the upper part of
parent rock. However, the correlations for several of the the profile. This assumption is supported by the trends
profiles are not as high as expected, and a plot of these data shown in table 2. Second, because all other oxides are
reveals at least two different trends (fig. 4). The first of removed during weathering, they may be lumped together
these is defined by samples from profiles 213, 215, 231, and treated as the "leached component" and modeled by
and 232 (dashed line; fig. 4), while samples from the equation 1 as:
remaining 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; blanks
are 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 , Fe 2O3 , A12 03, 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- Log

Site
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.Ilog VS S
logA , MO i, o N io e.,Sio log 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

40
60

50
P 30 P
z
z LLI
LU
U DC-
LU
uJ 40
U-
0Ov
0
Cl)
20
30

20

10

10

0 0
0 10 20 30 40 0 10 20 30 40

MgO (PERCENT) MgO (PERCENT)

Figure 4. Plot of MgO vs. SiO2 contents. Rectangles, All Figure 5. Plot of Fe2 03 vs. MgO contents. Rectangles, All
laterites except those from sites 213, 215, 231, and 232. laterites except those from sites 213, 215, 231, and 232.
Solid curve, Curve calculated to fit data represented by Solid curve, Curve calculated to fit data represented by
rectangles. Dashed line, Curve calculated to fit data from rectangles. Dashed line, Curve calculated to fit data from
sites 213, 215, 231, and 232. See text for discussion. sites 213, 215, 231, and 232.

Nickel-Mineralogy and Chemical Composition of Some Nickel-Bearing Laterites E17

where Cl. and C1, denote original and subsequent likely to precipitate as quartz. The presence of quartz may
concentrations of the "leached component." Since the thus be a useful pH indicator in some laterites (Golightly,
concentration of the residual component (rs) is 1981). The large amounts of quartz in profiles from sites
Crs= 100 C1 c, 213, 215, 231, and 232, therefore, most likely indicate
equation 4 may be rewritten as more acidic ground water at these four locations than at the
other sample sites.
C=C.+(l00-Cr) . ec d(5)
In terms of equation 3, the increase in solubility of
When combined with equation 3, the variation of the magnesium-silicates with respect to quartz as pH decreases
residual components (rs0 denotes original residual will be expressed by increases in values of Asi/AMg. The
component) with MgO may be stated as dashed line in figure 4 was calculated by using a larger
value for this constant than was used in calculating the solid
Cr =C,, +(100-Crs.) * e(Alc/AMgo)* (In(' - (CMgO/cMgoo))) .(6) curve (6 vs. 2). The result is a reasonable fit to the
Finally, the concentration of Fe 20 3 may be modeled by MgO-SiO 2 data for the quartz-rich samples. Similar
assuming that the Fe2 03 /(Fe2 0 3 +A1 20 3 ) ratio is 0.79, a reasoning indicates that decreases in ground-water pH
value consistent with the data in table 1. The concentration should also be accompanied by increases in the term
of Fe 2O3 (CFe) is then given by Alc/AMgo given in equation 7. Figure 5 shows the result of
increasing this constant from 2 (solid curve) to 5 (dashed
CFe=0. 7 9 * [Crs.+(10 CrO) line).
e(Ajc/AMgo) (-fn(l(CMgo/CMgo.)))] (7) Since the MgO-SiO2 and MgO-Fe2 O3 data from these
four profiles lie mostly on the nearly linear portion of these
The curve derived from this relation is plotted in figure 5 two dashed curves, it is not clear how accurately these
(solid line) and provides a reasonable fit to the curved equations fit the data, but it is clear that the observed data
distribution of points, especially considering the are consistent with behavior predicted by equations 3 and 7.
assumptions that have been made. It also should be noted that the curves in figures 4 and 5 are
The models given above, however, apparently fail to based on an ultramafic parent rock composition, while, to
reproduce the relations found in profiles for sites 213, 215, be treated accurately, the data for profile 215 should be
231, and 232. The fact that profiles for sites 231 and 232 fitted to curves defined by their different parent rock
have evidently been mechanically mixed does little to chemistry.
explain their different patterns; the chemical patterns in As previously discussed, smectite is found only in the
another disturbed profile, those at site 216, for example, are northernmost sample sites (fig. 1). Although the precise
modeled quite well. Also, the above equations depend only compositions of these minerals are not known, inference
on the local chemical equilibrium between components and based on comparison with other laterites suggests that they
not on the ordering of the samples. Thus these patterns should be nontronitic. The stability of some magnesium-
should not be affected by mechanical mixing. bearing silicates common in laterites as well as that of
The most striking feature shared by all four of these magnesium-bearing nontronite from laterites in New Cale-
profiles is a relatively large abundance of quartz (table 1). donia (Trescases, 1975) is plotted in figure 6. This plot is
This abundance of quartz is also indicated by the vertical derived from the dissolution reaction for these minerals,
distribution of SiO 2 (table 2). In other profiles, Si0 2 clearly which, in the case of serpentine, may be written as
increases with depth. However, in these four profiles,
quartz is most abundant at the top of the profile and results Mg3 Si 20 5 (OH)4 + 6H+ = 3Mg+ + + 2H 4 SiO4 + H2 0, (8)
in high SiO2 values that tend to offset the downward which has an equilibrium constant (Kd) of
increase in SiC 2 due to increases in abundance of other
silicate minerals. As a result, Si0 2 in profiles for sites 215, Kd= 29.5 = 31og[Mg+ +] +21og[H 4 SiO4 ] + 6pH. (9)
231, and 232 shows no vertical change, while only a minor
increase in SiO2 occurs at site 213. Reorganization of equation 9 as
Golightly (1981) showed that the solubility of most 3(log[Mg+ +] +2pH)=29.5-2log[H 4 SiO4] (10)
magnesium silicate minerals found in laterites decreases
with increasing pH. In contrast, the solubility of quartz is enables direct construction of figure 6.
relatively independent of pH, while goethite has a solubility This plot shows that waters having a concentration of
minimum at a pH of approximately 8. These relations Mg++ and SiO2 represented by point A will not precipitate
indicate that in ground waters with relatively high pH, SiO2 talc or Mg-bearing nontronite. However, an increase in
will mostly be used up in the formation of the relatively concentration of Mg++ and (or) Si0 2 may result in first the
insoluble secondary magnesium-bearing silicates. formation of talc (B) and then talc and nontronite (C). In
However, as ground-water pH decreases and the solubility most instances, smectite occurs only in poorly drained
of these magnesium-bearing phases increases, SiO2 is more profiles where ground waters may be enriched in cations

E18 Contributions to Commodity Geology Research

 20 - 1.1

19 _
1.0
18 -

17 - -
0.9
0. 16
CL

+ 15 - 0.8
+ 14
04
+ z
C
0) 13 - I 0.7
2o -J
12 -

11 _
A: 0.6
fL
C,,
10
_ 0.5
9
.i02 mgL {L
8-. lI I I I I I I I l I l o0 0.4
-5.4 -5 -4.6 -4.2 -3.8 -3.4 -3 -2.6

Log(H 4SiO 4) 0.3

Figure 6. Stability of some minerals found in laterites 0.2

plotted as log (Mg"+) + 2pH vs. log (H4 SiO4 ). A, B, and C
represent three possible ground-water compositions.
0.1
Methods of calculation are discussed in text. Data are
from Trescases (1975), Golightly (1981), and Boeglin and
others (1983).

Al 203 (PERCENT)

through prolonged interactions with the bedrock (Golightly, Figure 7. Plot of Al 2 03 vs. TiO 2 contents. Labeled triangles
1981). show values for bedrock at sites 211 and 215. X (values
In these laterite profiles, however, the smectite- near origin) shows A1203 values for samples in which TiO2
bearing profiles all occur on slopes in the topographically was below the detection limit of 0.02 weight percent. Solid
rugged Kalmiopsis Wilderness. Laterite profiles without line represents best fit to all data shown by rectangles;
dashed line shows best fit for data from site 211.
smectite 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, element correlations are observed between A1 2 03 and TiO 2
1975) shows that ground waters on hillslopes are enriched (table 4) and define a nearly linear trend (fig. 7). Both these
in Si0 2 and Mg++ as a result of their movement down oxides are among the least mobile, and their nearly linear
through laterite and across the bedrock that makes the relation suggests that they are being residually enriched in
hilltops. As a result, laterites on hillslopes typically contain about the same relative proportions as in the bedrock. Most
smectite, while those from flatter, well-drained areas do bedrock values of TiO 2 are below limits of analytical
not. The distribution of smectite in these laterite profiles is detection (table 1). However, TiO2 in bedrock from site 211
in accord with these observations. was detected, and its ratio with A1203 is similar to those
Three main conclusions may be drawn from the ratios in the overlying laterites (fig. 7). The best-fit line
above discussion. First, the distribution of major oxides in through the TiO2 -A12 03 data (with values from profiles 213
these laterites follows patterns predicted by relatively and 215 excepted) indicates a TiO 2/Al20 3 ratio of 0.05.
simple mathematical models. Second, laterite mineralogy This value is near the middle of the range commonly
suggests that the pH of ground waters in four of these observed in ultramafic rocks from ophiolite complexes
profiles was significantly more acidic than in others. This (Coleman, 1977).
conclusion is consistent with the different patterns that Correlation between Fe2 03 and A12 03 varies from
MgO, SiO2 , and Fe2O3 make in these profiles. Third, strongly positive to highly negative (table 4; fig. 8). Many
ground waters moving down hillslopes apparently became studies have shown that aluminum substitutes for iron
enriched in Mg++ and SiO2 and, as a result, precipitated within goethite, and it is therefore reasonable to assume that
smectite. this substitution has occurred in cases where highly positive
Relations between many of the other oxides in these correlations of these elements are found. Not surprisingly,
laterites appear to be somewhat less complex. Good inter- the profiles having the highest positive correlations (214,

Nickel-Mineralogy and Chemical Composition of Some Nickel-Bearing Laterites E19

I
 80 I I I I I I I I I I number of different minerals. In general, nickel increases
E)<PLANATION with depth in these laterites, a relation consistent with that
SITE observed in many other laterites and attributable to the
70 ~XX ; 211 dissolution of nickel in the upper parts of the profile and
x * 213
@ 214 reprecipitation in the lower parts where ground-water pH
0100X x 0 1 A 215 increases, Cobalt, in contrast, shows no consistent trend
El El
* 216 and, in fact, highest values commonly occur in middle parts
60 V~~~~ ®217
El 231 of profiles. With the exception of a relatively small
N A + 232 correlation in profile 231, significant correlation of cobalt
0 233
50 A 259 and nickel does not occur within individual profiles (table
P X 261 4), thus confirming the independent behavior of nickel and
z V bedrock cobalt. Interestingly, analyses of the data from all profiles

C-
0 40 F-
result in a significant correlation of cobalt and nickel. A plot
cc
- )1- O'J of cobalt and nickel (fig. 9) clearly shows that this
A ,kk correlation results from superimposing data from
30 A independent populations.
30 H-
The correlation data (table 4), however, does show
that nickel occurs in two distinct associations. In the first
(profiles 211, 213, 216, and 233), it is directly related to
20 h
SiO. 2 Most of these also show a positive correlation with
MgO and a negative relation with Fe02 3; in the second
(profiles 217, 231, and 232), nickel correlates with Fe02 .3
10 7 215 Because Fe02 3 and MgO generally have high positive
correlations, respectively, with abundances of goethite and
serpentine (table 4), the nickel in profiles 211, 213, 216,
0 10+
and 233 probably occurs mostly as a substitution in
l l l l l l l t

i 4 8 12 16 20 24
serpentine, while nickel in 217, 231, and 232 is in goethite.
Al 203 (PERCENT)
There is, in contrast, no evidence of cobalt being
Figure 8. Plot of A12 03 vs. Fe02 3 contents. Best-fit lines associated with silicate minerals. Instead, cobalt is mostly
and slopes are given for data from sites 233, 217, 214, and positively correlated with either Fe 2 O3 (profiles 214, 216,
259. (Note: Best-fit calculations for site 259di dnotinclude 217, 231, 259, and 261) or MnO (215, 217, 231, 232, 259,
data from circled open triangle. This daturri, which was and 261). Fe 2 O3 and MnO generally vary together (profiles
from the first sample in the profile, fell off 'the general
trend of the other points and was consii hlered to be 217, 231, 259, and 261), and therefore it is not usually
anomalous.) possible to determine if cobalt is mostly in goethite or in
manganese oxides. That cobalt may occur within both
phases is shown where significant correlation occurs with
217, 233, and 259) are also those that ap pear to have only Fe 2 O3 or MnO. For example, in profiles 214 and 216,
proportionately the smallest amounts of otht er aluminum- cobalt is significantly positively correlated with Fe20 3 and
bearing phases. Best-fit lines through data a from these not with MnO. In these profiles it is, therefore, likely that
profiles indicate that the Fe20 3 /Al 203 ratios vary between cobalt is hosted by goethite. Conversely, in profile 215 and
2.9 to 11.7. Natural goethite may contain u]p to 33 mole 232, cobalt is significantly correlated with MnO and not
percent aluminum (Schwertmann, 1983), con responding to with Fe20 3, indicating that cobalt probably is in manganese
an Fe2O3/A1 2 O3 ratio of 3.1 or greater. With the exception oxides.
of site 259, these data are within the rant le of natural The preceding discussion of laterite chemistry
goethites. The linear distribution of data from each of these provides no information as to the net gain or loss of
sites suggests that the Al content of goethite v;aries between chemical constituents during laterite formation. One way to
sites but remains relatively constant within a ssingle profile. estimate absolute changes in laterite chemistry is to
Conversely, poor or negative A1203 -Fe2 O3 correlations compare element abundances with those of a constituent
occur mostly in profiles where chlorite and (oar) homblende that is assumed to be unchanged. For the purposes of this
are relatively abundant. study, A1 203 has been used not only because it is known to
Simple models, however, do not appear to explain the be quite immobile (Golightly, 1981) but also because it is
distribution of nickel and cobalt in these profil,es. To a large sufficiently abundant to be measured relatively accurately.
extent, the absence of simple controls on the dlistribution of The percentage net change in concentration of an element
these trace elements is due to their ability to reside in a (C.) relative to A12 03 is calculated as

E20 Contributions to Commodity Geology Research

 3000 I I I I I I I I I I I I I I
enrichments occur in average values of nickel, Fe 2O3 , and
cobalt, with nickel showing the largest amounts of enrich-
EXPLANATION
2800
SITE ment.
[ 211 The most surprising feature of these patterns is the
2600 + 213 absence of consistent and significant increases in nickel.
0 214
L 215
Hotz (1964) conducted a similar study using data from the
2400
X 216 Riddle laterite deposit and from laterite on Eight Dollar
2200
v 217 Mountain (located 15 km east of Pearsoll Peak; fig. 1). In
* 231
*232
both profiles, nickel was found to be the most enriched
2000 * 233 component, with net gains commonly exceeding 120 per-
0 A 259 cent. Cobalt and iron also typically showed net increases.
-J 1800 ® 261
The general order of enrichment determined by Hotz was,
V bedrock
1600 n from most depleted to most enriched, MgO, SiO2 , Mn, Fe,
Co, and Ni. With the exception of nickel, this sequence is
1400 similar to the one found in these laterites.
C-,
1200
-+ X I CONCLUSIONS
1000 1
Ten of the eleven laterites studied formed over
800 I serpentinized peridotite and, in general, are mineralogically
* On7 and chemically similar. All contain serpentine, chlorite,
600
goethite, and maghemite. Profiles located on hillslopes also
* c~x +
have smectite. Quartz, talc, hormblende, orthopyroxene,
400 F
and tremolite are additional components of some laterites.
200 Within profiles that have not been physically disrupted, the
17 I VV VV
v
least soluble minerals (mostly goethite) are most abundant
u
0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000
at tops of profiles, and the more soluble phases generally
increase with depth.
Ni (PARTS PER MILLION)
Mean values of major chemical constituents in these
Figure 9. Plot of nickel vs. cobalt contents. 10 profiles are nickel, 0.64 weight percent; cobalt, 0.063
weight percent; SiO 2 , 18.3 weight percent; MgO, 5.0
weight percent; Fe2O3 , 46.4 weight percent; A12 03 , 8.0
weight percent; and MnO, 0.51 weight percent. Amounts of
MgO and Fe2O3 generally directly reflect abundance,
respectively, of serpentine and goethite. These composi-
C = [(X /Xp) *(Al203)p/(AI203)J)-1] * 100 (11)
tions are similar to those of other laterites described from
where X, and (A120 3), are the values of component x and this area.
A12 03 in laterite, and XP and (Al2 03 )p are those values in The profile at site 215 differs from the others in
the parent rock. Percentage net changes in six constituents having formed over a homblende-rich parent rock. These
based on this equation are given in table 5; variations in laterites are also distinguished by having relatively large
amounts of quartz, chlorite, and talc and by low values of
profiles 216 and 233 are plotted in figures 2 and 3.
MgO and nickel (having mean values of 2.4 and 0.11
The trends in net compositional change are similar in
weight percent, respectively).
most profiles. With the exception of the mineralogically and
The restriction of smectite to laterites located on
chemically distinct profile 215, most profile averages show
hillslopes results from local variations in ground-water
an ordering from most depleted component to least of MgO,
chemistry. Precipitation of smectite is favored by high
SiO2 , Ni, MnO, Fe2 0 3, and Co. Exceptions occur in profile concentrations of SiO 2 and MgO in ground water, but the
211, where the average MnO value is more depleted than excellent drainage present in these laterites tends to prevent
the nickel value, and in profiles 214, 231, and 259, where enrichment in these components. As a result of downslope
the average cobalt values are just slightly more depleted flow over serpentine, however, waters on hillsides locally
than the averages for Fe2 03 . These profiles almost all show have dissolved enough SiO 2 and MgO to precipitate smec-
an overall loss of all their major components, with enrich- tite.
ments only evident in profiles 211 (Co, Ni, Fe 2 0 3), 233 The distribution of MgO, SiO2 , and Fe2 03 in these
(Co), and 261 (Co, Fe20 3). In contrast to these profiles, laterites appears to follow trends predicted by the relatively
values from sample site 215 differ significantly. Significant simple equation:

Nickel-Mineralogy and Chemical Composition of Some Nickel-Bearing Laterites E21

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 and
232. IS, insufficient sample]

Site Sample Percent change Site Sample Percent change

sample depth sample depth
number (in) Ni Co Si0 2 Fe2O3 MgO MnO number (Mn) Ni Co Si0 2 Fe,0 3 MgO MnO
211-1 .. 0.23 -59.8 13.8 -94.5 -27.6 -96.0 -63.5 231-14 .. 4.76 -95.5 -83.5 -98.2 -66.2 -99.8 -84.0
211-2 ... 38 -22.4 187.8 -88.0 5.1 -91.9 -20.2 231-15 .. 5.06 -96.1 -78.9 -98.2 -70.6 -99.8 -83.7
211-3 ... 64 -8.6 159.6 -82.6 -4.5 -89.3 -49.6 231-16 .. 5.37 -95.5 -77.8 -98.1 -67.8 -99.8 -80.9
211-4 ... 92 -25.0 91.1 -85.7 -10.4 -92.5 -49.5 231-17 .. 5.67 -93.6 -62.4 -98.4 -57.0 -99.7 -75.4
211-5 ... 1.22 -2.5 120.4 -79.5 8.9 -85.8 -37.2 231-18 .. 5.98 -92.9 43.5 -98.9 -46.0 -99.7 -68.9
211-6 .. 1.53 47.4 173.6 -70.4 56.2 -78.7 -6.7 231-19 .. 6.28 -94.7 4.5 -98.4 -61.3 -99.6 -65.5
211-7 .. 1.83 47.0 156.9 -72.5 64.6 -80.6 5.6 231-20 .. 6.59 -95.3 -29.9 -98.2 -68.9, -99.5 -67.2
211-8 .. 2.14 85.2 142.3 -65.5 69.4 -76.2 3.9
232-1 ... 31 -95.7 -67.3 -97.2 -77.7 -99.4 -73.1
213-1 ... 15 -91.9 -68.7 -97.7 -64.7 -99.2 -76.5 232-2 ... 61 -95.9 -68.7 -97.1 -78.3 -99.4 -73.5
213-2 ... 31 -92.0 -69.1 -97.2 -68.4 -99.2 -75.3 232-3 ... 1.22 -95.0 -65.1 -97.0 -75.5 -99.4 -73.3
213-3 ... 61 -89.1 -63.7 -97.2 49.9 -99.3 -78.2 232-4 ... 1.53 -97.3 -80.3 -97.1 -83.7 -99.5 -76.2
213-4 ... 92 -85.0 -21.4 -96.2 -37.3 -98.7 -93.8 232-5 .. 1.83 -94.8 -53.5 -97.0 -73.2 -99.3 -67.1
213-5 ... 1.22 -80.4 -5.8 -94.5 -27.8 -99.0 -19.8 232-6 .. 2.14 -92.9 -56.0 -98.0 47.7 -99.5 -77.7
213-6 ... 1.53 -82.7 -40.4 -93.5 -43.7 -98.7 -38.2 232-7 ... 2.44 -95.1 -54.9 -97.6 -75 2 -99.6 -67.6
213-7 ... 1.88 -65.4 -28.5 -87.9 -22.6 -95.7 .9 232-8 .. 2.75 -95.0 -73.9 -97.4 -75.3 -99.6 -82.5
232-9 .. 3.05 -93.0 -68.6 -98.7 -65.5 -99.8 -88.2
214-1 . . 15 -95.3 -87.3 -98.0 -72.9 -99.4 -91.9
232-10 .. 3.36 -89.1 -52.6 -99.3 -9.1 -99.8 -84.9
214-2 .... 31 -93.4 -79.9 -97.3 -65.0 -99.0 -87.8
232-11 .. 3.66 -91.3 49.5 -98.3 -38.3 -99.6 -76.0
214-3 ... 61 -87.1 -78.3 -93.8 -63.6 -96.2 -81.3
232-12 .. 3.97 -95.3 -65.1 -97.2 -76.6 -99.5 -75.6
214-4 ... 92 -86.3 -76.9 -92.4 -63.2 -95.0 -79.0
232-13 .. 4.27 -95.2 -66.4 -97.1 -76.0 -99.4 -75.9
214-5 ... 1.22 -91.2 -82.4 -94.8 -69.0 -97.0 -83.2
232-14 .. 4.58 -93.6 -48.1 -97.8 -68.1 -99.5 -75.0
214-6 ... 1.37 -91.3 -82.7 -94.0 -69.9 -96.3 -83.3
233-1 ... 31 -88.9 45.9 -98.8 -32.7 -99.6 -71.7
215-1 ... 15 199.8 140.5 -64.6 158.3 -81.7 24.0
233-2 ... 61 -87.8 -27.4 -99.0 -23.2 -99.6 -70.1
215-2 ... 31 202.5 129.8 -62.2 159.0 -84.9 25.1
233-3 .. 1.22 -87.8 18.2 -98.0 -23.8 -99.2 -59.2
215-3 ... 61 198.5 126.8 -59.9 144.8 -80.1 5.8
233-4 .. 1.53 -81.5 47.1 -97.0 -15.4 -98.7 -37.8
215-4 .... 92 234.4 81.1 -57.3 136.2 -76.2 -95.5
233-5 .. 1.83 -63.3 11.4 -91.1 -9.1 -95.4 -23.3
215-5 ... 1.22 277.3 115.6 -60.3 175.0 -71.6 -48.1
233-6 ... 2.14 -65.5 49 7 -93.0 -6.1 -96.4 10.2
216-1 ... 15 -57.5 -15.2 -84.4 -20.5 -92.8 -18.4 233-7 .. 2.44 -66.9 69.7 -94.8 34.0 -97.5 56.5
216-2 ... 31 -55.2 6.3 -84.6 -6.7 -92.3 -26.3 233-8 ... 2.75 -56.4 54.5 -90.0 .9 -94.6 44.1
216-3 ... 61 -53.2 -8.2 -81.3 -18.6 -92.0 -33.7 233-9 .. 3.05 -62.8 37.8 -90.3 -20.5 -94.8 -1.2
216-4 ... 92 -30.8 22.8 -73.2 2.6 -87.3 -12.0 233-10 .. 3.36 is is is is is is
216-5 . .. 1.22 -40.9 -14.3 -76.0 -19.3 -89.1 -35.7 233-11 .. 3.66 is is is is is is
233-12 .. 3.97 -54.8 42.5 -91.3 1.2 -95.3 29.2
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 -52.0 259-1 ... 15 -74.0 -49.3 -92.3 -50.8 -96.5 -48.4
217-3 ... 61 -79.7 -23.3 -84.6 -27.9 -89.2 -37.1 259-2 ... 31 -63.4 -46.5 -94.1 -34.9 -97.6 -63.7
217-4 ... 92 -68.1 -14.8 -72.3 -19.8 -79.1 -35.8 259-3 ... 61 -61.4 -35.5 -92.6 -28.3 -96.3 -46.4
217-5 .. 1.22 -67.6 -5.3 -69.3 -18.2 -73.3 -33.6 259-4 ... 92 -58.3 -21.5 -88.6 -29.0 -92.6 -16.5
217-6 .. 1.53 -68.4 -2.7 -66.9 -19.8 -69.6 -40.1 259-5 .. 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
231-1 ... 46 -97.4 -82.0 -98.2 -77.6 -99.5 -81.0
259-7 .. 1.83 -29.5 -15.9 -71.3 -19.0 -77.2 -18.3
231-2 ... 87 -96.9 -76.5 -98.5 -75.6 -99.7 -87.7
259-8 .. 2.14 4.5 9.8 -60.1 -3.1 -68.6 6.6
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 -89.0 261-1 ... 15 -68.3 -25.5 -99.0 -23.8 -99.7 -61.8
231-5 .. 2.01 -97.7 -85.8 -98.5 -78.7 -99.6 -86.7 261-2 ... 31 -68.1 45.3 -99.1 -28.3 -99.8 -69.3
231-6 ... 2.32 -98.0 -89.6 -98.6 -80.1 -99.8 -88.9 261-3 ... 61 -69.4 -28.1 -99.2 -21.6 -99.8 -62.2
231-7 .. 2.62 -97.8 -89.9 -98.6 -79.9 -99.9 -90.0 261-4 ... 92 -40.0 157.3 -98.7 30.5 -99.7 11.1
231-8 ... 2.93 -97.8 -87.1 -98.3 -79.1 -99.6 -88.5 261-5 ... 1.22 -7.1 126.9 -98.0 53.0 -99.4 10.2
231-9 .. 3.23 -97.8 -82.4 -98.3 -78.0 -99.5 -87.7 261-6 ... 1.53 -10.6 82.5 -97.6 27.8 -99.2 -4.0
231-10 . 3.54 -97.5 -89.0 -98.7 -76.8 -99.8 -88.5 261-7 ... 1.83 43.5 -10.2 -97.6 -12.1 -99.2 43.1
231-11 . 3.84 -97.4 -89.4 -98.7 -76.9 -99.8 -88.8 261-8 . .. 2.14 -48.8 -11.4 -97.6 -10.0 -99.2 -37.2
231-12 . 4.15 -97.1 -90.4 -98.7 -76.8 -99.8 -89.7 261-9 ... 2.44 -46.0 -18.6 -95.6 -6.7 -97.1 -36.2
231-13 . 4.45 -97.1 -89.7 -98.8 -73.8 -99.8 -88.3

E22 Contributions to Commodity Geology Research

 CY=C, -Cy . -e [(A,/A) ln(1-(CIC ))] (12) of supergene ores in lateritic weathering, in Melfi, A.J., and
Carvalho, A., eds., Lateritisation processes-Proceedings of
where: the 2nd International Lateritisation Seminar on Lateritisation
Processes: Sao Paulo, Brazil, p. 71-88.
C, and Cy are the concentration of components x and y in
Canterford, J.H., 1975, The treatment of nickeliferous laterites:
the laterite, Minerals Science and Engineering, v. 7, p. 3-17.
Cx, and Cy are the initial concentration of x and y, and Chamberlain, P.G., 1986, Nickel, in U.S. Bureau of Mines,
Ax and Ay are constants related to the solubility of x and Mineral Commodity Summaries 1986: Washington, D.C., p.
Y. 108-109.
Trends fitted by this equation and its derivatives for Chandra, D., and Ruud, C.O., 1976, Characterization study of
domestic nickeliferous laterites by electron optical and X-ray
profiles 213, 215, 231, and 232 differ from those in the
techniques: U.S. Bureau of Mines Open File Report 95-76,
other laterites. These four profiles contain relatively large
58 p.
amounts of quartz, which commonly is a mineralogical Coleman, R.G., 1977, Ophiolites: New York, Springer-Verlag,
indicator of relatively acidic ground waters. The shift in the 229 p.
major element trends in these four profiles from those in the Diller, J.S., 1902, Topographic development of the Klamath
other laterites is consistent with the presence of ground Mountains: U.S. Geological Survey Bulletin 196, 69 p.
water having a lower pH. Duyvesteyn, W.P., Wicker, G.R., and Doane, R.E., 1979, An
The distribution of other oxides reveals a variety of omnivorous process for laterite deposits, in Evans, D.J.I.,
relations. Good positive correlation exists between Shoemaker, R.S., and Veltman, H., eds., International
abundance of A1203 and TiO 2. Both are relatively immobile laterite symposium: New York, Society of Mining Engineers
and appear to be residually enriched in about the same of the American Institute of Mining, Metallurgical and
Petroleum Engineers, p. 553-570.
proportions as occur in the parent rock. A1203 and Fe2 0 3, in
Evans, D.J.I., Shoemaker, R.S., and Veltman, H. , eds., 1979,
contrast, are strongly positively correlated in goethite-rich International laterite symposium: New York, Society of
laterites, but not in laterites having large amounts of Mining Engineers of the American Institute of Mining,
aluminum-bearing minerals. It is probable that, where Metallurgical and Petroleum Engineers, 688 p.
positively correlated, most of the aluminum occurs as a Faust, G.T., 1966, The hydrous nickel-magnesium silicates-The
substitution for iron in goethite. Fairly constant garnierite group: American Mineralogist, v. 51, p. 279-298.
Al 20 3/Fe 2 03 ratios occur in the goethite-rich profiles and Foose, M.P., 1991, Deposits containing nickel, cobalt, chro-
indicate a uniformity of goethite compositions within mium, and platinum-group elements in the United States, in
individual laterites. Nickel in some profiles is positively The geology of North America-Economic geology:
correlated with Fe2 0 3, indicating that it occurs in goethite; Geological Society of America, v. P-2, p. 87-102.
in other laterites, nickel is mostly present in serpentine as Gibbs, R.J., 1965, Error due to segregation in quantitative clay
mineral X-ray diffraction mounting techniques: American
shown by its good correlation with MgO. Cobalt, on the
Mineralogist, v. 50, p. 741-751.
other hand, apparently occurs primarily in either goethite or Grim, R.E., 1968, Clay mineralogy: New York, McGraw-Hill
in manganese oxides, but in most profiles its host phase Book Co., 596 p.
could not actually be determined. Golightly, J.P., 1981, Nickeliferous laterite deposits, in Skinner,
Calculations of net changes in laterite chemistry show B.J., ed., Economic Geology 75th Anniversary Volume: p.
that loss of chemical components during weathering 710-735.
generally occurs in a well-defined order. This sequence is, Hotz, P.E., 1964, Nickeliferous laterites in southwestern Oregon
from most depleted to most enriched, MgO, SiO2 , Ni, and northwestern California: Economic Geology, v. 59, no.
MnO, Fe2 0 3 , and Co. The observed net chemical changes 3, p. 355-396.
in these deposits differ from those observed in the adjacent Hundhausen R.J., McWilliams, J.R., and Banning, L.H., 1954,
laterite on Eight Dollar Mountain and the deposit at Riddle, Preliminary investigation of the Red Flats nickel deposit,
Curry County, Oregon: U.S. Bureau of Mines Report of
Oreg., in two ways. First, nickel is the most enriched
Investigations 5072, 19 p.
component in those deposits. Second, the large amounts of
Irwin, W.P., 1977 , Ophiolitic terranes of California, Oregon, and
net enrichment in nickel and cobalt observed at Eight Dollar Nevada, in Coleman, R.G. and Irwin, W.P., eds., North
Mountain and at Riddle were not found in the laterites American ophiolites: Oregon Department of Geology and
studied here. 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
REFERENCES cobalt, in Evans, D.J.I., Shoemaker, R.S., and Veltman, H.,
eds., International laterite symposium: New York, Society of
Benson, W.T., 1963, Pine Flat and Diamond Flat nickel-bearing Mining Engineers of the American Institute of Mining,
laterite deposits, Del Norte County, Calif.: U.S. Bureau of Metallurgical and Petroleum Engineers, p. 527-552.
Mines Report of Investigations 6206, 19 p. Libbey, F.W., Lowry, W.D., and Mason, R.S., 1947, Nickel-
Boeglin, J.L., Melfi, A.J., Nahon, D., Paquet, H., and Tardy, bearing laterite, Red Flats, Curry County, Oregon: Ore Bin,
Y., 1983, Early formed mineral paragenesis in the deep zones 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, tion processes-Proceedings of the II International Seminar
R.W., Lipin, B.R., Foose, M.P., and Gray, F., 1982, on Lateritisation Processes: University of Sao Paulo, Brazil,
Mineral resource potential map of the Kalmiopsis Wilder- p. 65-68.
ness, southwestern Oregon: U.S. Geological Survey Miscel- Siemens, R.E., Good, P.C., and Stickney, W.A., 1975, Recovery
laneous Field Studies Map MF-1240-E, scale 1:62,500. of nickel and cobalt from low-grade domestic laterites: U.S.
Ramp, L., 1978, Investigations of nickel in Oregon: Oregon Bureau of Mines Report of Investigations 8027, 14 p.
Department of Geology and Mineral Industries Miscellaneous Trescases, Jean-Jacques, 1975, L'evolution geochimique super-
Paper 20, 68 p. gene des roches ultrabasiques en zone tropicale-Formation
Schwertmann, U., 1983, The role of aluminium in iron oxide des gisements nickeliferes de Nouvelle-Caledonia: Memoires
systems, in Melfi, A.J., and Carvalho, A., eds., Lateritisa- O.R.S.T.O.M., no. 78, 259 p.

E24 Contributions to Commodity Geology Research