The metamorphic alteration caused extensive geochemical mobility, as indicated by wide scat-
tering of Na, K, Rb, Cs, Sr, Ba, Eu, Ca, Cu, Zn, and S data on MgO variation diagrams Larson,
1996. Such mobility is common Lahaye et al., 1995; Lahaye and Arndt, 1996 and these data are
not considered further. All other elements exhibit regular trends on MgO variation plots and are
therefore considered immobile. The REE are mo- bile during carbonate alteration Lahaye et al.,
1995, but the REE trends described below do not appear to have been affected and these samples
contain only minor to trace amounts of carbonate minerals.
3. Analytical methods
Concentrations of major, minor and trace ele- ments were determined by XRF using a Philips
PW1450 spectrometer at the University of West- ern Ontario. Precision and accuracy errors are
within 1 for the major elements and 5 for the minor and trace element values \ 15 ppm and
30 for values B 5 ppm Larson, 1996. Probe polished thin sections were prepared and olivine
and amphibole analysed at the University of Ala- bama using a JEOL JXA-86003 electron probe
equipped with five wavelength-dispersion X-ray spectrometers and a TN-5400 energy-dispersion
X-ray analysis spectrometer.
The REE were analysed by ICP-MS in the Ultratrace lab at the University of Montreal util-
ising the analytical strategies of Cheatham et al. 1993 and Lahaye and Arndt 1996. Whole-rock
samples, 100 mg in size, were dissolved in high- purity HF and HClO
4
under clean-room condi- tions. The resulting fluoride and perchlorate salts
were converted to high-purity nitrates and diluted to 200 ml in 2 HNO
3
. All samples were analysed using a VGFisons ICP-MS PQII + with : 10
ppt detection limits. Precision and accuracy er-
Fig. 1. Map showing the location of the study area outlined in black, and distribution of the main rock types in the Shaw Dome area, Abitibi greenstone belt, Ontario modified from Pyke, 1982; Jensen, 1985. Field work focused on the komatiitic rocks.
rors, as determined from replicate analyses of internal and international rock standards, are
within 5.
4. Komatiitic rock types
A wide variety of komatiitic rock types with diverse textures, geochemical compositions, grain
sizes, and rock units are recognised in the LKH and UKH. They are described in detail below.
4
.
1
. Lower komatiitic horizon and footwall dykes The LKH rock types are dunite, ortho- to
mesocumulate wehrlite, amphibole clinopyroxen- ite, clinopyroxenite and cumulate and noncumu-
late amphibole gabbro Table 1. These rock types comprise a variety of undifferentiated and differ-
entiated sills and dykes Table 2 interlayered with iron-formation and calc-alkalic volcanic rocks. In-
trusive contacts were observed in some outcrop areas, whereas others were covered.
The LKH consists of massive dunite sills that are inferred at map scale to pass laterally to
massive wehrlite
and differentiated
wehrlite base-clinopyroxenite-amphibole
gabbro top
sills Pyke, 1982; Tables 1 and 2. The amphibole gabbro zone in a single differentiated sill appears
to cut the surrounding rocks and is interpreted in part to be a dyke Fig. 2A. Wehrlite dykes have
been recognised in a single area stratigraphically downsection of the LKH, which appear to cut the
footwall rocks Fyon, 1980; Fig. 1, 2B and 3A.
The dunite sills are fine to coarse grained and locally appear to embay the underlying calc-alka-
lic volcanic rocks Fig. 3B. Olivine is preserved in only a single LKH dunite sample Table 3;
Fo
92.4
. The massive wehrlite sills show mesocu- mulate to orthocumulate textures and appear to
be stratigraphically conformable. The differenti- ated wehrlite – amphibole gabbro units are mainly
sills up to 1 km thick and, from stratigraphic bottom to top, consist of: wehrlite, clinopyroxen-
ite, amphibole clinopyroxenite, and amphibole gabbro zones. These rock zones are described
below. The wehrlite zones in the differentiated units
are 5 – 20 m thick and are indistinguishable from those of the massive wehrlite sills Tables 2 and
3, except for the presence of igneous amphibole. The clinopyroxenite and amphibole clinopyroxen-
ite zones are B 3 m thick each, consisted of mesocumulus clinopyroxene and rim amphibole,
and appear to grade on a scale of centimetres to tens of centimetres to amphibole gabbro Pyke,
1982; this study. The amphibole gabbro zones are up to 50 m thick, medium-grained, leuco-
cratic, and contain coarse-grained to pegmatitic patches near the base Table 2; Fig. 3C and D.
Igneous amphiboles are preserved as kaersutite and titanian pargasite to hastingsite oikocrysts
Table 3. Upsection, the proportion of igneous amphibole gradually decreases relative to plagio-
clase, and that of igneous quartz increases. The absence of cumulate textures and the high abun-
dance of Si, alkalis, and incompatible trace ele- ments
Table 4
suggest the
quartz-bearing amphibole gabbros are noncumulate rocks, and
could represent near-liquid compositions. The contact of amphibole gabbro with the overlying
calc-alkalic volcanic rock is exposed only in a single location and is sharp.
At a single locality, the lower portion of the amphibole gabbro zone, in what appears in part
to be a dyke rather than a sill Fig. 2A, contains subrounded patches of amphibole clinopyroxen-
ite. The amphibole clinopyroxenite patches may represent xenoliths of partially melted roof-rock
fragments. Alternatively, these patches could have been derived from the adjacent amphibole gab-
bro. Evidence in support of a xenolith origin for the amphibole clinopyroxenite patches is not
apparent.
Two massive wehrlite dykes intrude calc-alkalic volcanic rocks and sulphide iron-formations,
which stratigraphically underlie the LKH and contain xenoliths of those rocks Fyon, 1980; Fig.
1, 2B and 3A. These dykes are talc-carbonate altered and the degree of alteration precludes
identification of igneous textures. However, the geochemistry of the dykes suggests that cumulate
olivine 9 clinopyroxene were originally present cf. Section 5. Sulfide minerals occur at dyke –
xenolith contacts, but are absent internally within the dyke.
Table 1 Rock types and petrographic characteristics of the Shaw Dome komatiitic rocks
Wehrlite Clinopyroxenite
Dunite Amphibole clinopy-
Rock type Amphibole gabbro
roxenite Unit type
a
UCS, UCD, DCS, UCS
DCS, DCD DCS, DCD
DCS, DCD DCD
5 2 km apparent
10–100 m Rock type thick-
5 1.5 m
5 1.5 m
10–40 m ness
Amp 9 Srp 9 Ab Amp 9 Carb 9 Chl
Observed min- SrpOl 9 Carb
Ab 9 Amp 9 Qtz Srp 9 Carb 9 Tlc
eral assem- 9
Carb 9 Chl 9
Tlc 9 Mag 9 Chl 9
Carb 9 Fe-Ti ox- 9
Ttn 9
Mag 9 Amp blage
ide 9 Ttn 9 Chl 9
Chl 9 Chr 9
Mag 9 Chr 9
Chr 9
Zo Ol \90
Ol 40–90 Cpx 60–100
Cumulus miner- Chr B0.5
Pl 35–65 als
Chr B0.5 Chr ?
Chr B0.5 Medium-coarse
Fine-medium Medium
Medium-coarse Fine-pegmatitic
Cumulate grain size
Orthocumulate- Orthocumulate-
Adcumulate Cumulate texture
Mesocumulate ? Mesocumulate
mesocumulate mesocumulate
9 crescumulate
Glass B10 Intercumulus
Glass B15 Glass B15
Cpx 60–100 Amp 10–20
phases Cpx B10
Chr ? Amp B25
Chr B0.5 Cpx B10
Amp B10 Glass ?
FeTi oxide B5 Chr B0.5
Qtz B5 Komatiitic basalt
Komatiite DCF; 25 cm–50 m
UCF; 10s–100s m UNF; 12–15 m
UNF; B40 cm Flow unit
b
and DCF; 7–12 m
? thickness
SrpOl 9 Amp 9 Mag 9 Carb 9 Chl 9 Tlc 9 Chr Amp 9 Carb 9 Chl 9 Tlc 9 Chr
Observed min- eral assem-
blage Ol 40–90, Chr
Cumulus miner- Ol 40–90, Chr
Cpx ?, Ol ?, Chr none
Cpx ?, Ol ?, Chr B0.5
B0.5 als
B0.5 B0.5
Intercumulus Glass, Cpx
Glass na
Glass Glass
phases Orthocumulate-
Cumulate texture Orthocumulate; fine-
Aphyric; very fine Aphyric; very fine
and grain size mesocumulate; fine-
medium medium
10 cm–50m 10s–100s m ? en-
Cumulate zone na
thickness tire unit
Ol: coarse oriented na
na na
Cpx: coarse ori- Spinifex mineral
and texture platy and fine ran-
ented acicular and dom
fine random Spinifex zone
30 cm–2m na
na 3–3.5m
na thickness
a
Unit type: UCS, undifferentiated cumulate sill, UCD, undifferentiated cumulate dyke, DCS, differentiated cumulate sill, DCD, differentiated cumulate dyke. Mineral abbreviations after Kretz 1983.
b
Flow unit: DCF, differentiated cumulate flow, UCF, undifferentiated cumulate flow, UNF, undifferentiated noncumulate flow. Mineral abbreviations after Kretz 1983.
M .S
. Stone
, W
.E .
Stone Precambrian
Research
102 2000
21 –
46
Table 2 Summary of vsubvolcanicvolcanic features of the Shaw Dome komatiitic units
a
Undifferentiated Differentiated
Horizon UKH
LKH LKH
UKH Sill
Dyke Flow
Unit type Sill
Dyke Flow
Wehrlite Aphyric ko-
Wehrlite, Cumulate or
Dunite or Cumulate ko-
Cumulate ko- Rock type
Wehrlite, matiitic basalt
wehrlite matiite, Ol
clinopyroxenite, aphyric komati-
clinopyroxenite, matiitic basalt,
amphibole amphibole
spinifex-textured ite
Cpx spinifex-tex- tured komatiitic
clinopyroxenite komatiite,
clinopyroxenite aphyric komati-
basalt ite
Massive cumu- Massive cumu-
Massive cumu- Rock texture
Lower massive Brecciated non-
Lower massive Massive cumu- Massive cumu-
late or brec- late
cumulate late
late and noncu- cumulate zone
late and noncu- cumulate zone
mulate zones ciated 9 massive
mulate zones with upper
with upper of different
noncumulate spinifex-textured spinifex-textured
of different rock types
zone zone
rock types 9
brecciated noncumulate
zone Ol mesocumu-
Ol orthocumu- Ol mesocumu-
Grain packing Ol orthocumu-
Ol adcumulate Ol mesocumu-
Cpx orthocumu- late?
or Ol mesocu- late-orthocumu-
late-mesocumu- late-orthocumu-
late-mesocumu- late-mesocumu-
late mulate-orthocu-
late; gabbroic late?
late late; gabbroic
cumulate-non- cumulate-non-
mulate cumulate
cumulate High
Low Low
Low Moderate
Low Magmalava
High Moderate
flux Lobe
Sheet Dyke
Dyke Sheet
Channel Sheet
Channel Subvolcanicvol-
dunite or sheet canic facies
wehrlite Central
Channel, lobe Lobe
Mid-distal Central
Mid-distal Distal
Location Proximal
North, east, North, west
East, south, West
North, east, North, east, west
East Dome flank
North, south west
south, west south
a
Mineral abbreviations after Kretz 1983. Locations are relative; distances vary with discharge rate, flow rate, lava volume, eruption distance, and time.
Whole-rock geochemical analyses indicate that the dunites are characterised by high Mg 44 – 51
MgO, Mg c \ 92 and Ni 2800 – 4300 ppm Ni, and low Fe 6 – 10 FeO
t
, Al B 1.1 Al
2
O
3
,, Ti B 0.1 TiO
2
, and REE REE=1.1 ppm, con- sistent with accumulation of forsteritic olivine
Pyke, 1982; Tables 3 and 4. In comparison, wehrlites have lower Mg \ 29 MgO, Mg c
82 – 91 and Ni \ 600 ppm Ni, and higher Fe B 15 FeO
t
, Al B 6 Al
2
O
3
, Ti B 0.5 TiO
2
, and REE REE B4.0 ppm, consistent with accumulation of olivine and entrapment of
residual liquid. Pyroxenites and gabbros have the lowest Mg 4 MgO, Mg c 60 and Ni 50 ppm
Ni, and highest Fe 13 FeO
t
, Al 18 Al
2
O
3
, Ti 1.3 TiO
2
, and REE 84.0 ppm, consistent with accumulation of clinopyroxene 9 plagioclase
or entrapment of residual liquids Table 4. The lack of spinifex textures and breccia and
inferred presence of altered glass Table 1 are considered evidence for emplacement of the ko-
matiitic dykes and the LKH as subvolcanic bodies Table 2. The komatiitic cumulate rocks formed
mainly by fractional accumulation of olivine e.g.
Fig. 2. A Field map showing the distribution of LKH rock types in the area of the interpreted wehrlite – amphibole gabbro dyke. B Field map showing wehrlite dykes cutting felsic volcano-sedimentary and iron-formation stratigraphy down section of the LKH.
The northernmost dyke hosts a large iron-formation xenolith see Fig. 3A.
Fig. 3. A Photograph of a wehrlite dyke enclosing a large xenolith of sulphide iron-formation IF. Person for scale is 1.8 m tall. This dyke outcrops stratigraphically below the LKH on the east flank of the Shaw Dome. B Photograph of very coarse-grained
serpentinised dunite. Coin for scale is 1 cm in diameter. C Photograph of amphibole gabbro. Coin for scale is 1 cm in diameter. D Photomicrograph of amphibole gabbro in doubly polarised light. Igneous amphibole Amp occurs in the interstices between
anhedral quartz grains Qtz and altered subhedral plagioclase Pl. Field of view is 6 mm.
dunites 9 clinopyroxene e.g. wehrlites; Tables 1 and 2. By analogy to Hill et al. 1995, the
presence of dunite implies olivine accumulation under dynamic flow conditions, under which the
cumulate pile is drained of magma in a proximal flow-through environment. The presence of ig-
neous
hydroxy-amphibole suggests
that the
magma from which the differentiated wehrlite – clinopyroxenite – amphibole gabbro units formed
was hydrous e.g. Stone et al., 1997. The vertical variation from dykes to sills and the lateral varia-
tions from dunite to wehrlite – gabbro bodies are interpreted to represent the transition from hotter,
more dynamic and channelised proximal to cooler, more static and sheet flow distal facies
variations. Komatiitic intrusions and intrusive fa- cies models are not well documented in the scien-
tific literature.
4
.
2
. Upper komatiitic horizon The rock types of the UKH are cumulate,
spinifex textured, and aphyric komatiitic rocks Table 1. They occur in a variety of undifferenti-
ated and differentiated, noncumulate and cumu- late komatiite and komatiitic basalt flow units
Table 2 interlayered with and overlain by tholei- itic basalt flows.
The UKH consists of up to 50 m thick, mainly massive komatiite flows which appear at map
scale to pass laterally and vertically to a series of thinner [K1] 5 10 m, massive to brecciated or
spinifex textured komatiite flows Fig. 4A. These flows at map scale are inferred to pass laterally and
vertically to massive or spinifex textured ko-mati- itic basalt flows Fig. 4B. Locally, the 50-m thick
massive flows host minor nickel sulphide minerali- sation Green and Naldrett, 1981.
The undifferentiated UKH flows are massive and or brecciated Fig. 4B. The differentiated flows
exhibit significant geochemical and textural differ- entiation, and comprise at least two different zones
Fig. 4A: an upper spinifex textured zone and a lower olivine cumulate zone Fig. 4C and D,
typical of komatiites e.g. Pyke et al., 1973; Arndt et al., 1979. These zones exhibit fine-scale phase
and textural zonation. Preserved olivine cores range from Fo
91.7-93.1
Fig. 4C; Table 3. The komatiite flows are geochemically character-
ised by high Mg 18 – 45 MgO, Mg c 80 – 91 and Ni up to 2700 ppm Ni, and low Fe 7 – 13
FeO
t
, Al 3 – 12 Al
2
O
3
, Ti B 0.5 TiO
2
, and REE 4.2–23.6 ppm, consistent with accumula-
tion of forsteritic olivine Table 4. The komatiitic basalts are characterised by lower Mg down to 5
MgO, Mg c 70 – 80 and Ni B 1000 ppm Ni, and higher Fe up to 13 FeO
t
, Al 8 – 14 Al
2
O
3
, Ti up to 0.6 TiO
2
, REE 7.0–19.5 ppm, and other olivine incompatible elements Table 4.
The asymmetric development of spinifex textures and volcanic breccia together with the presence of
major amounts of inferred altered glass and altered skeletal olivine grains in the UKH are considered
evidence for extrusion and rapid solidification Arndt, 1977; Auvray et al., 1982; Stone et al., 1995.
The komatiitic cumulate rocks formed by accumu- lation of olivine 9 clinopyroxene Tables 1 and 2.
The vertical and lateral variations in flow unit thickness thick to thin, texture massive to differ-
entiated, and mineralogy olivine to clinopyrox- ene are interpreted to represent the transition from
hotter, dynamic proximal to cooler, more static distal facies variations. This interpreted channel
to sheet flow facies transition is similar to facies models for the Kambalda komatiites e.g. Cowden
and Roberts, 1990; Lesher and Arndt, 1995.
Table 3 Representative average 1 S.D. electron microprobe analyses of relict igneous olivines and amphiboles from the lower and UKHs
in the Shaw Dome Phase
Olivine Olivine
Olivine Olivine
Amphibole Amphibole
amp gabbro Wehrlite
oc komatiite oc komatiite
Rock type
a
oc komatiite Dunite
9 5
8 n
4 1
1 42.5
42.5 0.45
41.6 0.43
40.8 0.15
41.8 SiO
2
wt 0.41
41.4 4.75
3.80 TiO
2
0.00 B
0.02 B
0.02 0.00
B 0.02
0.01 B
0.02 0.00
11.6 12.1
Al
2
O
3
0.01 0.07
0.09 0.01
0.08 0.02
0.10 0.04
0.07 0.36
0.04 0.21
0.01 0.17
Cr
2
O
3
0.02 0.15
0.02 0.07
6.98 11.8
0.29 6.79
0.27 6.64
0.21 8.09
FeO
t
0.21 6.96
0.21 0.30
0.12 0.01
0.09 MnO
0.01 0.12
0.01 16.0
13.8 MgO
0.10 0.11
0.29 50.2
0.32 50.5
0.35 51.0
0.13 50.7
B 0.02
0.02 0.32
0.01 0.35
0.10 0.02
0.34 0.02
0.35 NiO
CaO 11.3
0.16 0.02
0.22 0.01
0.23 0.03
0.26 0.03
11.6 2.84
1.62 n.d.
Na
2
O n.d.
n.d. n.d.
n.d. n.d.
n.d. K
2
O n.d.
0.55 0.27
n.d. n.d.
n.d. F
n.d. B
0.01 B
0.01 n.d.
n.d. n.d.
Cl n.d.
0.09 0.06
Total
b
98.9 0.60
100.4 0.95
99.9 97.3
0.37 101.1
97.5 0.40
92.4 93.1
Fo
c
93.1 91.7
na na
67.6 80.3
na na
na na
Mg c 82.2
82.4 82.5
Mg c liq
d
81.2 na
na
a
Rock type: oc, orthocumulate; amp, amphibole; FeO
t
, total iron as FeO; n.d., not determined.
b
Total, analytical total.
c
Fo, forsterite content calculated by MgMg+Fe atomic ratio.
d
Mg c liq, equilibrium liquid composition calculated assuming K
D
value for FeOMgO olivinemelt partitioning = 0.3.
M .S
. Stone
, W
.E .
Stone Precambrian
Research
102 2000
21 –
46
Table 4 Representative whole-rock geochemical analyses of Shaw Dome komatiitic rocks volatile-free
27586 27597
22161 22145
22469 27584
22138 22122
Sample 22466
22401 22140
22338 22388
22390 27589
LKH Dike
LKH LKH
LKH LKH
LKH LKH
LKH Horizon
LKH LKH
LKH LKH
LKH LKH
Rx type
a
amp gb dunite
wehrlite dunite
dunite wehrlite
wehrlite wehrlite
cpx amp cpx
amp gb wehrlite
wehrlite amp gb
wehrlite oc
ac ac
oc mc
oc ac
mc Texture
oc 41.2
42.8 53.1
44.6 42.1
41.6 44.9
44.6 42.5
53.4 50.5
54.4 43.2
43.4 SiO
2
wt 50.2
0.125 0.023
0.282 0.275
B 0.010
0.013 0.189
0.09 0.083
0.189 0.203
1.08 0.093
0.113 1.17
TiO
2
12.86 5.28
0.09 0.88
3.91 2.1
1.88 2.06
4.11 2.90
4.53 18.0
17.02 Al
2
O
3
0.3 1.87
0.634 0.164
0.192 0.462
0.19 0.182
0.316 0.56
0.2 0.492
0.514 0.022
0.486 0.426
0.001 Cr
2
O
3
6.76 11.9
6.60 6.64
10.2 11.4
10.4 FeO
t
8.97 7.79
10.2 7.46
8.63 10.9
12.47 11.9
0.15 0.15
0.10 0.09
0.14 0.15
0.18 0.16
0.18 0.11
0.17 0.12
MnO 0.14
0.15 0.14
40.8 49.7
12.6 30.3
50.4 50.0
38.9 40.4
38.4 26.1
25.3 6.48
45.1 41.5
4.70 MgO
0.022 0.287
0.439 0.479
0.295 0.32
0.39 0.039
NiO 0.158
0.426 0.002
0.433 0.319
0.006 0.321
1.40 6.77
0.02 0.09
1.11 0.37
5.94 1.17
6.36 8.73
8.31 7.39
CaO 0.26
0.04 0.36
1.41 B
0.01 0.04
B 0.01
B 0.01
0.03 0.01
Na
2
O 0.08
0.03 0.02
4.38 B
0.01 B
0.01 3.81
0.05 1.16
B 0.01
B 0.01
B 0.01
B 0.01
B 0.01
B 0.01
B 0.01
0.02 K
2
O B
0.01 0.50
1.47 0.01
B 0.01
B 0.01
B 0.01
B 0.01
0.05 B
0.01 B
0.01 B
0.01 0.01
B 0.01
0.01 0.05
0.02 0.11
B 0.01
B 0.01
0.25 P
2
O
5
B 0.01
0.016 B
0.01 0.008
0.182 0.088
0.075 0.184
0.14 B
0.005 0.087
B 0.01
S 1.12
0.118 0.056
11.8 12.9
1.00 27.4
18.7 20.3
10.3 10.7
9.9 5.1
5.8 2.8
14.2 11.2
1.3 L.O.I.
99.78 99.88
100.14 100.11
99.9 100.06
100.23 100.00
99.71 100.46
99.49 99.05
99.97 99.89
101.18 Total
b
78.7 83.5
93.8 93.7
88.3 87.5
81.8 85.2
87.2 83.1
88.3 63.3
91.2 43.0
Mg c 92.7
B 2
B 2
38 4
B 2
B 2
B 2
B 2
B 2
B 2
B 2
11 B
2 B
2 Rb ppm
63 197
B 5
B 5
B 5
B 5
B 5
B 5
Ba B
5 B
5 B
5 190
B 5
B 5
120 B
5 95
133 B
2 B
2 B
2 B
2 107
15 7
2 26
566 Sr
311 B
2 B
2 129
108 42
119 106
122 107
121 125
69 88
32 152
124 35
Co 177
2181 3455
3775 2331
2521 3076
306 Ni
1239 3356
173 3412
2511 47
2526 7
B 5
B 5
B 5
7 B
5 B
5 B
5 12
Cu 6
B 5
67 B
5 16
B 5
42 83
26 30
35 40
77 Zn
44 32
53 81
69 41
69 42
135 147
12 15
78 48
34 56
89 V
115 165
256 61
25 14
4461 1158
1354 3506
1338 1282
2235 3958
1413 3484
3602 154
3429 2998
7 Cr
9 7
B 2
B 2
3 B
5 5
2 4
B 2
7 20
Ga 19
2 2
B 1
B 1
11 6
B 1
B 1
2 B
1 11
6 6
4 1
2 30
Y 16
3 34
24 2
24 18
15 19
25 18
62 8
10 137
Zr B
0.5 B
0.5 B
0.5 2
2 B
0.5 2
1 B
0.5 B
0.5 3
4 1
7 Nb
2 0.125
0.533 3.05
0.376 0.292
La ppm 12.04
6.94 Ce
0.325 0.716
0.69 29.11
1.01 0.948
0.136 0.047
Pr 3.96
0.113 0.083
0.607 0.196
3.99 0.337
0.664 16.34
Nd 1.03
Sm 0.054
0.09 0.267
3.94 0.191
0.332 0.142
1.26 Eu
0.006 0.03
0.059 1.30
Gd 0.067
0.124 0.418
4.65 0.296
0.222 0.052
Tb 0.756
0.077 0.024
0.012 0.363
0.078 1.40
0.166 0.524
4.60 Dy
0.305 0.083
0.018 Ho
0.989 0.12
0.041 0.234
0.059 0.840
0.127 0.336
2.77 Er
Tm 0.130
0.011 0.024
0.052 0.417
0.039 0.854
0.259 0.165
2.74 0.347
Yb 0.071
0.043 0.013
0.129 0.029
0.057 0.409
Lu 1.470
REE 1.082
2.332 4.016
83.981 3.988
1.859 1.756
2.613 LaSm
n c
1.461 1.922
0.688 1.388
1.181 2.414
1.537 0.567
2.969 LaYb
n
M .S
. Stone
, W
.E .
Stone Precambrian
Research
102 2000
21 –
46
31
Table 4 Continued 45.9
57.7 45.1
45.5 53.7
52.5 49.5
45.7 45.2
45.3 44.6
54.2 44.0
49.5 44.2
SiO
2
wt 0.264
0.353 0.647
0.524 0.274
0.294 0.419
TiO
2
0.374 0.92
0.396 0.528
0.158 0.274
0.236 0.373
5.63 7.23
13.1 10.6
5.14 6.15
8.43 6.98
7.52 16.5
8.27 11.2
Al
2
O
3
4.83 5.14
3.05 0.427
0.02 0.342
0.420 0.125
0.210 0.287
0.317 0.441
0.395 0.479
0.281 0.252
0.287 0.371
Cr
2
O
3
11.2 12.0
10.4 10.3
10.5 11.2
12.7 FeO
t
12.1 7.60
12.9 9.79
8.28 10.5
11.5 12.2
0.18 0.19
0.15 0.16
0.14 0.16
0.21 0.15
0.20 0.14
0.20 0.14
0.17 MnO
0.11 0.15
26.5 5.72
32.6 27.1
12.0 15.8
25.2 30.5
24.3 25.9
26.4 14.2
43.6 25.2
35.5 MgO
0.215 0.181
0.025 0.061
0.165 0.195
0.136 NiO
0.159 0.016
0.155 0.067
0.293 0.165
0.247 0.169
4.43 6.72
6.38 7.86
8.80 5.46
7.73 7.22
7.65 7.33
6.43 6.07
CaO 2.83
8.80 0.10
0.06 3.11
B 0.01
0.21 3.3
2.0 B
0.01 B
0.01 0.37
0.27 0.13
3.35 0.06
B 0.01
B 0.01
Na
2
O 0.03
0.07 0.01
0.01 B
0.01 0.03
0.01 B
0.01 K
2
O B
0.01 0.87
0.01 B
0.01 B
0.01 B
0.01 0.01
0.02 0.04
0.09 0.06
0.02 0.05
0.06 0.03
0.04 0.19
0.04 0.08
P
2
O
5
0.02 0.02
B 0.01
0.046 B
0.01 0.060
0.007 0.009
B 0.005
B 0.005
0.078 0.005
0.027 0.013
0.022 0.045
B 0.005
0.075 S
8.7 6.6
9.9 27.4
20.3 12.9
10.9 10.3
L.O.I. 10.7
2.3 5.1
18.7 4.9
11.0 5.8
99.73 100.10
100.18 100.58
99.36 99.62
99.56 99.59
99.54 99.97
99.65 99.85
Total
b
98.98 100.08
99.86 81.1
59.8 85.3
81.8 69.7
75.3 86.0
84.4 79.2
80.9 80.3
74.2 91.3
82.6 85.9
Mg c 4
5 B
2 B
2 B
2 3
B 2
Rb ppm B
2 19
B 2
B 2
B 2
B 2
B 2
B 2
12 11
12 19
5 9
19 7
13 5
5 9
12 Ba
281 6
17 453
12 32
49 30
12 10
37 23
18 10
B 2
12 61
Sr 97
104 55
69 78
98 99
Co 103
33 89
68 103
78 101
102 1692
1426 194
484 1298
1532 1064
1325 1248
123 1215
529 Ni
1951 1298
2310 47
41 B
5 34
103 69
27 B
5 36
35 B
5 247
B 5
27 B
5 Cu
53 62
69 72
36 52
74 68
55 65
Zn 88
26 36
60 64
124 169
220 178
107 139
187 141
168 107
165 201
115 V
152 66
2998 152
2407 2963
885 1487
2023 2223
3097 2769
3367 1977
1778 2023
2616 Cr
7 9
11 7
4 8
7 Ga
7 23
10 11
2 4
3 6
5 8
22 20
4 7
10 6
6 8
9 16
Y B
1 4
2 22
112 14
18 70
60 16
17 24
23 21
51 9
16 19
Zr B
0.5 B
0.5 B
0.5 B
0.5 B
0.5 B
0.5 B
0.5 B
0.5 Nb
B 0.5
8 2
B 0.5
B 0.5
B 0.5
B 0.5
0.293 0.349
3.81 3.04
0.332 0.246
0.228 0.391
La ppm 1.34
0.883 1.07
9.83 8.28
0.740 0.691
Ce 0.984
0.157 0.212
1.46 1.21
Pr 0.123
0.144 0.186
0.268 1.02
1.26 6.92
5.70 1.52
Nd 1.03
0.868 0.635
0.650 0.487
0.622 2.22
1.77 0.247
0.403 0.472
Sm 0.200
0.224 0.624
0.453 Eu
0.092 0.112
0.201 0.263
0.849 1.08
3.00 2.35
1.01 Gd
0.750 0.683
0.434 0.186
0.164 0.199
0.530 0.419
0.076 0.126
0.137 Tb
1.08 1.40
3.53 2.73
Dy 0.551
0.891 0.954
1.28 0.245
0.317 0.766
0.598 0.281
Ho 0.214
0.193 0.129
0.792 0.710
0.883 2.22
1.75 0.374
0.549 0.576
Er 0.105
0.138 0.337
0.266 Tm
0.064 0.082
0.088 0.120
0.690 0.892
2.21 1.71
0.775 0.416
0.563 0.530
Yb 0.116
0.105 0.140
0.346 0.265
0.069 0.080
0.087 Lu
6.988 5.046
37.799 30.541
REE 4.196
5.580 6.574
4.852 0.378
0.353 1.083
1.078 0.379
0.443 LaSm
n c
0.627 0.356
0.286 LaYb
n
0.264 1.167
1.201 0.400
0.290 0.399
0.341
a
Rx type; amp gb, amphibole gabbro; cpx, clinopyroxenite. All data recalculated to 100 volatile-free L.O.I. and S. FeO
t
, total iron as FeO.
b
Total = XRF+L.O.I.−O=S.
c
n, normalised to primitive mantle Hofmann, 1988. Data available on request.
Fig. 4. A Discordant spinifex veins intruding the lower olivine cumulate komatiite zone of a flow. Hammer for scale is 40 cm in length. B Photograph of a thin auto-brecciated bx komatiitic basalt flow. Hammer for scale is 40 cm in length. C Fine-grained
subhedral and coarser grained, more skeletal relict olivine grains Fo
91.7
; Table 3 set in an altered glassy groundmass of an orthocumulate komatiite. Field of view is 6 mm. D Coarse-grained, randomly-oriented serpentine pseudomorphs of skeletal olivine
in the top of a differentiated komatiite flow. Coin for scale is 1 cm in diameter.
5. Geochemical modelling