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Amertcan Mineralogist, Volume 66, pages 507-525, 1981
Mineralogy and petrology of parts of the Marra Mamba IronFormation, Hamersley Basin, Western Australia
CoRNnI-n KrBn aNo MaRrrN J. GoLB'
Department of Geology, Indiana UniversityB lo omington, I ndiana 4 7 40 5
Abstract
The Marra Mamba Iron Formation, of early Proterozoic age (probably about 2.5 G.y.), isthe lowermost member of the Hamersley Group of Western Australia. It shows well-devel-oped mesobanding and abundant fine-scale laminations. This study characterizes the bulkchemistry, mineralogy and petrology of two distiactly different units within the iron-forma-tion. The uppeflnost part consists of magnetite-rich associations which include: quartz, mag-netite, minnesotaite, riebeckite, stilpnomelane, dolomite (or ankerite), calcite, and traces ofpyrite. The lowermost part is sulfide-rich and contains variable amounts of: quartz, siderite,dolomite (or ankerite), stilpnomelane, minnesotaite, pyrrhotite and/or pyrite, and smallamounts of carbon. Quartz is commonly microcrystalline, but the carbonates and magnetiteare sub- to euhedral and medium- to coarse-graiaed, the result of recrystallization. Stilp-nomelane and pyrite are also considerably coarser grained than quartz. Fibrous minnesotaitecommonly cuts across carbonates and stilpnomelane reflecting its origin during late diagen-esis or very low grade metamorphism of the assemblages. Petrologic studies in closely asso-ciated, underlying volcanics (of the Fortescue Group) reflect a range of burial metamorphicconditions within the prehnite-pumpellyite facies. The iron-formation assemblages, at verylow temperatures of metamorphism, do not appear to be as sensitive to relatively small tem-perature changes as do very low grade metamorphic volcanics. The iron-formation assem-blages may have originated over a temperature range of 100 to a maximum of about 300oC.
Introduction and geologic setting
The Marra Mamba Iron Formation is the lower-most unit of the Proterozoic Hamersley Group in thenorthwestern part of Western Australia (see Fig. l).Its areal distribution is shown in Figure 2. It con-formably overlies the Roy Hill Shale Member of theJeerinah Formation and is overlain by the Witte-noom Dolomite. The age of the iron-formations inthe Hamersley Basin has been determined to beabout 2.5 G.y. (Compston et al., in preparation).
The Marra Mamba Iron Formation varies consid-erably in thickness, as based on sections measured inthe field; however, not enough drill hole data areavailable to provide a quantitative assessment of itsthickness variation throughout the HamersleyRange. Trendall and Blockley (1970) repoft a thick-ness range of 183 to 229 m based on sections mea-
rPresent address: Department of Geology, Georgia State Uni-vcrsity, Atlanta, Georgia 30303.
0003-004x/8 I /0506-0507$02.00
sured in the western part of the Hamersley Range(see Fig. 2). Others report thicknesses that rangefrom a minimum of 15 m (Kriewaldt and Ryan,1967) to 183 m (Macleod, 1966) for sections in dif-ferent parts of the Hamersley Range.
The Marra Mamba lron Formation is underlainby the Jeerinah Formation which is the uppermostmember of the Fortescue Group. This group may beas much as 3660 to 4270 m thick (Trendall andBlockley 1970, and Macleod, 1966) and consists ofshales and cherts in the upper part (Jeerinah Forma-tion), of basaltic lavas and pyroclastics in the middlepart (Mt. Jope volcanics), and of sandstones, con-glomerates and basic lava flows in the lower part(Hardey Sandstone). The Fortescue Group is thebasal unit of the Proterozoic sequence and uncon-formably overlies the Archean basement (see Fig. l).
The Marra Mamba Iron Formation has been in-formally subdivided into three parts (Trendall andBlockley, 1970). These are l) the lower banded iron-formation member of about 137 m thickness, 2) the
507
508 KLEIN AND GOLE: IRON-FORMATION. WESTERN AUSTRALIA
Boolgeedo lronFormolion
Woongorro
Vo lcon ic s
middle "shaly" member with a thickness of about 37m, and 3) an upper banded iron-formation memberofabout 6l m thickness.
On account of the pervasive lateritic weathering inmuch of Western Australia and the generally pooroutcrop of the Marra Mamba Formation, a studysuch as this must be based on carefully selected,unaltered material from diamond drill cores. Twodiamond drill cores which partly transect the MarraMamba Iron Formaiton were sampled for this study.The drill cores were made available by the Ham-ersley Exploration Pty. Limited in Wittenoom, W.A.(for location, see Fig. 2). One hole, D.D.H. no. 270,located 38 km west of Wittenoom, is 201 m deep, ofwhich the upper 167 m consist of Wittenoom Dolo-mite and the remaining 34 m of the upper part of theMarra Mamba Iron Formation. This section containsfresh, unaltered iron-formation. The other hole,D.D.H. no. 182, also from the Wittenoom region, is195 m deep of which the upper 172.5 m transects theMarra Mamba Iron Formation and the remaining 22m the upper part of the underlying Jeerinah Forma-tion. The upper 107 m of the Marra Mamba in thishole are heavily weathered, but the remainder of thecore is fresh. This study is based on samples from theuppermost 34 m and the lowermost 65.5 m of theMarra Mamba Iron Formation and the upper 225 mof the underlying Jeerinah Formation.
The banded iron-formations of the Hamersley Ba-sin have been studied in great detail with respect totheir stratigraphy, chemical composition, and sedi-mentary and diagenetic structural features (e.g.,Trendall and Blockley, 1970). It is the purpose of thisstudy to characterae the various assemblages and thecompositions of the individual minerals, and to eval-uate the possible metamorphic history of the lower-most unit of the iron-formations.
Methods of study
Materials were selected from the two diamond drillcores on the basis of their apparent freshness, theirdiversity of mineral assemblages as reflected by pro-nounced color banding, and on the basis oftexturalvariations, such as sfoanges in mesobanding or micro-banding, and grain size. Nine rock samples of theMarra Mamba Iron Formation and three of theJeerinah Formation were analyzed by a combination
Fig. l. Stratigraphic column of the Hamersley Group in thec€ntral part of the Hamersley Basin (after Trendall and Blockley,1970). The approximate stratigraphy of the underlying FortescueGroup is after Macleod, 1966.
Feel
2000
Meters
600
Weel i Wol l iFormol ion
Ml. lvlcRoeSho le
3OO _+- loo0
Yondicoogino
shote lv lbr
JoffreM e m b e r
Brockmon l ron Irormolron I
WholebockShole Mbr.
0oles GorgeMember
Formot ion
Wi l ienoomDolomi te
Nlor ro Mombol ron Formot ron
'
z
509KLEIN AND GOLE: IRON.FORMATION, ITESTERN AUSTRALIA
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5 1 0 KLEIN AND GOLE: IRON-FORMATION, WESTERN AUSTRALIA
of gravimetric, flame photometric, and colorimetrictechniques. Approximately 170 thin and polishedthin sections were used for detailed petrographicstudy of the mineral assemblages and their texturalrelations prior to electron probe microanalysis.Chemical analyses for nine oxide components in sili-cates, carbonates and oxides were performed on 80polished thin (l' diameter) sections using a 3-spec-trometer Etec Autoprobe. Approximately one thou-sand mineral grains were analyzed in this manner.Operating conditions and analytical procedures areoutlined by Klein (1974).
Bulk chemical analyses
Chemical analyses for twelve rock samples, eachincluding several bands of different mineral composi-tion, are given in weight percentage in Table l. Nineof these are of the Marra Mamba lron Formationand three of the immediately underlying JeerinahFormation. Each analysis represents the averagecomposition of a quartered section of diamond drillcore with a length of about 12.5 cm. Samples Ithrough 4 are from the upper part of the MarraMamba Iron Formation in D.D.H. no. 270 (fieldnumbers are preceded by a B); samples 6 through l0are from the lower part of the Marra Mamba lronFormation in D.D.H. no.282 (field numbers are pre-ceded by an A), which directly overlies the JeerinahFormation; and samples ll through 13 are from theRoy Hill Shale Member in the upper part of theJeerinah Formation. The total Fe content of the ninesamples of the Marra Mamba Iron Formation rangesfrom 18.05 to 4A0 percent. Samples l0 and l2 of theRoy Hill Shale Member of the Jeerinah Formationare sulfide-rich and shale-like (high Al,O, and KrO,but low total Fe), but sample I I represents a carbon-ate-rich iron-formation band within the JerrinahFormation. Samples I to 4 contain considerableamounts of magnetite (see assemblage listings in thefootnote to Table l) whereas samples 6 to l0 and 12generally contain no magnetite (or only a trace) butshow considerable pyrite and/or pyrrhotite contents.Such assemblage differences are clearly reflected inthe Fe3*/(Fe2* + Fe'*) ratios of the bulk analyses.The average of the four magnetite-rich samples canbe compared with analysis no. 5 which is an averageobtained by Ewers and Morris (1980) from 15 com-posite samples of BIF sections in the same DDH#270 corc. Although their average sample is trulyrepresentative of the average bulk chemistry of partof the Marra Mamba Formation, our average of fourselected sections is remarkablv close to their results.
The variable AlrO, contents and their considerablerange, 0 to 5.297o (sample no. 8) for the MarraMamba samples are a reflection of their variablestilpnomelane contents. In samples ll and 13 themuch higher AlrO, contents reflect the abundantpresence of K-feldspar, chlorite and muscovite. TheMgO contents of the iron-formations show a relz-tively restricted range, 1.96 to 7.39 percent. CaO ishighly variable, 0 to 9.41 percent, and its variationsare sympathetic with the CO, content of the samples,as carbonates are the only minerals in which Ca oc-curs. NarO and KrO occur both in relatively smallamounts (maximum NarO is 0.83 and maximumKrO is 1.05 percent). NarO occurs mainly in riebeck-ite but is also a lesser component of stilpnomelanewhich is the host for all of the K,O in feldspar-freeassemblages. KrO is very high in the two samples ofthe Jeerinah Formation on account of their abundantK-feldspar and muscovite. Sulfur is present in vari-able amounts in the Marra Mamba Iron Formationsamples, reflecting the presence or absence of pyriteand/or pyrrhotite. Carbon is present in a graphite-like form which was identified as such only in themost C-rich samples by reflected light microscopy.Large amounts of sulfur and carbon are present inthe Jeerinah Formation samples. In these, the sulfuroccurs in medium- to coarse-grained pyrite- and pyr-rhotite-rich bands. Abundant, very fine-grained car-bon in these samples makes the fine-grained silicatehost almost opaque in thin section.
Chemical variation in mineral compositions
Of the major rock-forming minerals in the MarraMamba Iron Formation, quartz and magnetite showno compositional deviations from the establishedpure end-member formulas, SiO, and FerOo, respec-tively. Pyrrhotite, pyrite, and chalcopyrite, as well asilmenite, which sporadically occurs in trace amountsin very stilpnomelane-rich assemblages, were not an-alyzed in sufficient numbers to establish conposi-tional ranges, ifindeed such are present. The carbon-ates, st i lpnomelane, and minnesotai te showconsiderable solid solution. and riebeckite. andgreenalite, and chlorite show limited compositionalvariations. The extent of these substitutions will bediscussed in the following section.
Carbonates
In the assemblages of the upper part of the MarraMamba Formation (B samples in Table l), calciteand members of the dolomite-ankerite series are
KLEIN AND GOLE: IRON.FORMATION. WESTERN AUSTRALIA
Table l. Chemical analyses of four samples of the upper part (nos. l-4), and five of the lower part (nos. 6-10) of the Marra Mamba IronFormation. Averages for these distinctly different parts are shown. Analysis no. 5 is based on 15 composite samples of BIF sections in themagnetite-rich part of D.D.H. no. 270, from Ewers and Morris, 1980. Three analyses of the underlying Jeerinah Formation are also
given. Column no. 12 represents an Fe-rich band in the Jeerinah Formation (see assemblage listing in footnote).
Marra MaJriba Iron Pormati .on -Jeerinah Fomation-
D D H 2 7 0 D D H I 8 2
5 l l
Avg .r - 4 L 3I 2t l1 0
A v g .5 - I 0
s i o 2
Tio2
A I 2 O 3
F e 2 O 3
Feo
MnO
Mso
CaO
N a 2 0
Kzo
H 2 O ( + )
H 2 0 ( - )
P 2 o s
co2
c
Total
1 0 t a r l e
1 3 . 3 t 2 . 5 1 8 . 5 2 3 . 2 1 6 . A 7
. 1 . 3 * , o . 5 o 0 . 4 9 0 . 5 4 0 . 5 9 0 . 5 5( F e z t + F e r + )
4 5 . 3 5 4 . 0 4 4 . 9 2 5 . 6 4 2 . 4 5 4 1 . 4 9 3 7 . 1
0 . 7 9 n . d . * 0 . 0 2 4 n . d . * 0 . 2 0 0 . 0 I 0 0 . 0 3 I
n . d . * 0 . 3 2 0 , 4 3 0 . 8 6 0 . 4 0 0 . 2 5 2 . 0 3
1 4 . ' ? 1 3 . r 2 4 . 5 3 7 . 1 2 2 . 5 0 3 5 . 9 t * 4 . 5 8
4 l . r 2 7 . 9
n . d . * 0 . 3 I
4 . 4 3 6 . 4 4
0 . 1 3 0 . 2 8
1 1 )
n . d . * 3 . 4 2
0 . 6 4 0 . 4 4
1 . 0 5 0 . 6 8
4 . 9 6 2 . 9 9
3 . 1 9 2 . 0 0
0 . 0 4 3 0 . o 7 1
3 . 6 5 1 7 . 0
0 . 5 0 0 . 0 2 9
I . 7 4 I . 2 8
r 0 0 . 0 1 9 9 . 7 2
2 3 . 2 3 2 5 . 1 8
0 . r l 0 . r 8 0 . 0 6
A 3 7 A 4 2 A 4 A
1 5 2 . 1 1 5 4 . 6 1 6 4 . 4
6 2 . t 4 5 . 9 5 4 . 0
0 . 1 4 0 . I 2 0 . 0 4 8
0 . 5 9 2 . 2 3 t ' t . 9
L . 5 7 3 , 4 0 n . d . *
2 r . 8 2 ? . 2 7 . 0 2
0 . 0 5 4 0 . 1 2 0 . 0 r 3
2 . 5 2 4 . 9 s 1 . 8 3
2 . ' 7 4 r . 4 6 0 . 0 9 2
0 . 0 5 ? 0 , 2 6 0 . 0 4 0
0 . 2 4 0 . 5 4 8 . 8 0
3 . 4 5 3 . 5 8 r . 9 6
0 . 2 3 | . 2 6 0 . 1 7
0 . 0 4 1 0 . 0 4 9 0 . 0 6 4
3 . 9 0 7 . 7 3 n . a l . *
n . d . * 0 . 4 7 5 . 0 5
o . 2 t 0 . 6 7 3 . 2 8
9 9 . 6 8 9 9 . 9 4 I 0 0 . 2 7
1 8 . 0 5 2 3 . 5 2 5 . 4 6
5 I . 7 4 7 . 4
0 . 0 7 0 0 . 0 4 5
0 . 8 6 1 6 , 0
0 . 9 I 0 . 7 8
1 6 . 4 0 9 . 7 6
0 . 3 5 0 . t 2
5 . r 7 t . 7 5
) . f J r . J 6
o . o 4 ? 0 . 0 8 0
0 . 1 4 7 . 5 0
0 . 2 9 0 . 1 8
0 . 0 3 1 0 . 0 9 I
I 7 . 4 1 . 3 5
0 . 4 s 8 , 6 6
9 9 . 8 6 r 0 0 . 1 8
1 3 , 3 9 8 . 1 4
0 . I 5 0 . 1 4 0 . 1 2 0 . 0 5 8 0 . I 2 0 . 1 3 6 0 . 0 8 6
5 . 2 0 1 . 9 6 3 . 4 1 4 . 5 7 3 . 7 8 3 . 3 6 3 . 8 0
9 . 4 1 8 . 4 4 2 , 7 5 2 . 6 5 5 . 8 1 5 . 5 2 0 . 7 0
0 . 6 3 0 . 8 3 0 . I 1 0 . 1 4 0 . 4 3 0 . 2 3 ? 0 . 1 4
0 . I 5 0 . 0 9 0 . 2 3 0 . 1 s 0 . 1 . 5 0 . 1 3 2 0 . 5 6
I . 5 2 r . I 2 L . 4 4 L . r 2 1 . - 1 0
0 . 2 4 0 . 0 7 0 . 2 3 0 . 1 3 0 . 1 7
2 . 2 4
0 . 8 0
0 . 0 7 9 0 . 0 3 0 0 . 1 1 0 . 1 5 0 . 0 9 5 0 . o 7 2 0 . 0 6 5
' 1 . 9 0 6 . 8 0 3 . 4 s 2 . A 5 5 , 2 5 6 . 0 4 1 4 . 0
0 . 0 ? 6 0 . I 3 0 . 0 2 8 0 . 1 3 0 . 0 9 0 . 0 8 s 1 . 7 5
0 . 0 9 0 . 0 2 0 . 1 7 0 . I 7 0 . I l _ 0 . 1 3
9 9 . 5 3 9 9 . 5 5 t o o . 4 o 9 9 . 4 g 9 9 . 7 3 g g . r ; f r o o . 3 l
2 0 . 6 2 1 8 . 8 8 3 l - . 5 2 4 4 . 4 0 2 8 . 8 5 2 5 . 1 3 2 8 . 3 r
F i e T d n
Depth(meters )
0 . 1 1 0
A 7 A ] 5
1 I 3 . 4 I 2 r . 3
B 3
I 7 6 . 0
B 5
1 8 1 . 4 t 8 5 . 0 1 8 9 . 0
0 . I 0 0 0 . 0 5 0 . 0 7
A 5 4 A 5 8 A 6 I
1 7 5 . 1 1 8 6 . 3 1 9 2 . 5
n . d . ' E n o n e d e t e c t e d , M . E " c o l l e r , a n a l q s x t o r a 1 l a n a l g s e s o f t h i s s t u d q i + a 7 7 E e r e c a l c u l a t e d a s F e 2 0 3 ; + j D c l u d e s
l o s s o n j g n i t j o n = 5 . 6 6 o / o .a s s e h b l a g e s ( n i n e r a l s l i s t e d i n d e c r e a s i n g o r d e r o t a b u n d a n c e ; t h o s e i n t r a c e a n o u n t s a r e i n p a r e n x b e s e s ) l : q t 2 - n a q - r i e b -
d o l ( t o a n k ) - c a 1 - s t i l p - ( t c ) , 2 : q t z - d a q - r i e b - s t i l p - a n k ( t o d o t ) - c a t - n i n n - ( p g ) , 3 : q t z - n a g - d o 1 ( s o n e a n k ) - s t i 7 p - r i e b - n i n n ; 4 ! n a g -q t 2 - d o l - r i e b - s t i ) p - t c - ( p y ) t 5 : a v e r a g e f o r t 5 B I F s u b d i v i s i o n s o f t h e M a r r a M a n b a ( E v e r s a n d M o r r i s , 1 9 8 0 ) , 6 : s t i T p - s i d - p 9 -
n i n n - ( n a q a n d p o i n p s ) ; 7 : n i n n - q t z i 8 : s t i t p - r i p - d o t - p o - c a r b o n - ( i l n ) - ( c p ) r 9 ' d o l - s t i l p - s i d - c a r b o n - ( p o ) - ( i 1 n ) ; f 0 : q t z - n j n n -
a n k - s t i l p - ( c a r b o n ) - ( p o ) - ( i l n ) t 1 t : K s p a r - q t z - c h 1 - p g - n v s c - c a r b o n - ( p o + c p ) - ( c a r b ) r 1 2 : d o l - s i d - s t i l p - q t 2 - p o - c a r b o n i 1 3 ! q t z - K s P a r -
m u s c - p g - c a r b o n - c a r b - c h 1 - ( c p ) . A s s e n b l a g e s 1 l a n d f 3 a r e e x t r e n e f q f l n e - q r a i n e d e x c e p t f o r t h e s u T f i d e s r t h e i r s i l i c a t e s w e t e
i d e n t i f i e d b 9 x - r a g d i f f t a c t o n e t e r .
M i n e r a l
a n k = a n k e t i t e
c a l = c a T c i t e
c a r b = c a r b o n a t e
c a r b o n = c a r b o n a c e o u s ( g r a p b i t i c ) n a t e r i a j
c h T o r = c h T o r i t e
c p = c h a l c o P y r i t e
d o i - d o l o n i a eg r e e n - g t e e n a l j t e
i l n = l l n e n i t e
K s p a r = p o t a s s i u n f e T d s P a r
t u i n n = n i n n e s o t a i t e
n u s c = m u s c o v i t ep o = p g r r h o E i L e
q t z - q l a t t z
r i e b = r i e b e c k i t e
t i p = r i p i d o i i t e
s i d = s i d e t i t e
s t i f p = s t i T p n o n e l a n e
commonly major constituents. Pairs of coexisting cal-cite and dolomite (or ankerite) are also abundant.Such carbonates tend to be medium- to coarse-grained, commonly with almost euhedral outlines,reflecting considerable recrystallization. The carbon-ate grains may form relatively continuous, thin bandsbetween bands of magnetite or Fe-silicates, or theymay be irregularly distributed among silicate-mag-netite-carbonate assemblages. Representative elec-tron microprobe analyses showing the range of cal-cite compositions encountered in this study are given
in Table 2; Figure 3a shows their complete composi-tional range graphically.
Members of the dolomite-ankerite series occur inmost of the Marra Mamba samples but dolomite (orankerite)-calcite pairs occur only in the upper part ofthe Marra Mamba Formation (B samples in Tables;Figure 3a) and dolomite (or ankerite)-siderite pairsonly in the lower (sulfide-rich and magnetite-free)part of the Formation (A samples in Tables; Figure3b). The compositional range of the very abundantmembers of the dolomite-ankerite series is shown bv
512
Table 2. Representative electron probe analyses of calcite in theMarra Mamba Iron Formation.
KLEIN AND GOLE: IRON-FORMATION, WESTERN AUSTRALIA
F e O 0 . 9 4
M n o O . 2 5
M g O 0 . 2 4
c a o 5 3 . 0 2
T O T A L 5 4 . 4 5
F e O . O 2 7
M n 0 . 0 0 7
M g 0 - 0 1 2
c a 1 . 9 5 4
rcTAL 2 000
F i e l d I A J A
i A n a l g s i s o f c o e x i s t i n q d o f o i l i t e g i v e n i n l a b l e J . A s s e r D l a q e s( n i n e r a l s l i s t e d i b o r d e r o t d e c . e a s i n g a b u n d a n c e ; t h o s e i n t t a c ea n o u n t s a r e i D p a r e n t h e s e s ) : t t i e b - c a 7 - d o t - ( n a q ) ; 2 a o f - c a r - s t i 7 p -( p V ) ; 3 . s c i l p - q t z - c a 1 - h a g - ( d o t ) - ( r i e b ) ; 4 d o t - r t e b - c a 7 - q a z - ( s t i l p ) -( n a g ) | 5 , n a q - q t z - s t i l p - c a f - d o 1 ; 6 , q t z - n a q - . t i t p - d o t ; 7 . c a l - t i e b -( s t i l p ) - ( n a q ) , I c a 7 - r i e b - d o l - n a q
o . 9 7 r . 0 0 1 . 0 8 1 . 3 8 r . 5 3 1 . 5 5 2 . O 3
0 . 9 9 r . I 4 0 . 4 2 1 , 0 1 0 . 4 3 1 . 8 6 0 . 4 1
0 . 4 9 0 . 4 2 0 . 5 1 0 . 5 6 0 . 4 9 0 . 6 7 0 . 4 7
5 4 , 0 3 5 5 . 4 9 5 4 . 4 1 5 3 . 4 5 5 5 . 8 8 5 2 . 4 5 5 2 - 2 1
5 5 , 7 3 5 8 . 0 5 5 6 . 4 2 5 6 , 4 1 5 8 . 3 3 5 6 , 6 3 5 5 , 1 8
r e c a l c u l a t s e d o n t h e b a s i s o f 2 ( F e , M n , M 9 , C a )
0 . o 2 7 0 . 0 2 8 0 . 0 3 0 0 . 0 1 9 0 . 0 4 1 0 . 0 4 6 0 . 0 5 8
0 . 0 2 8 0 . 0 1 2 0 . 0 I 2 0 . 0 2 9 0 , 0 1 2 0 . 0 5 2 0 . 0 f 2
0 . 0 2 4 0 . 0 2 1 0 . 0 2 5 0 . 0 2 8 0 . 0 2 1 0 . 0 3 3 0 . o 2 4
1 . 9 2 1 I . 9 6 9 1 . 9 3 3 r - 9 0 4 r . 9 2 4 1 . 8 5 9 r . 9 0 6
2 . 0 0 0 2 . 0 0 0 2 . 0 0 0 2 . 0 0 0 2 . 0 0 0 2 . 0 0 0 2 . 0 0 0
E 9 B 3 A B 7 B B 7 A B 3 A B 2 B B 2 O A
plete compositional range, which extends fromFeroMgro to just short of the Fe end-member compo-sition, is shown in Figure 3b. The most Fe-rich sid-erites are also the most Ca-rich (up to 2.43Vo CaO).
Similar calcite-ankerite, and ankerite-sideritepairs are common in the Sokoman Iron Formation inLabrador, Canada (Klein and Fink, 1976), the Biwa-bik Iron Formation, Minnesota (French, 1968), andthe Gunflint Iron Formation, Ontario, Canada (Flo-ran and Papike, 1975). Haase (1979) reports a fewcalcite-ankerite and ankerite-siderite pairs from theleast metamorphosed part of the Negaunee Iron For-mation in northern Michigan. The compositionalrange of the carbonates from the above referencedoccurrences is more restricted to the Fe-rich side ofthe diagrams in Figure 3, than is that of the carbon-ates in the Marra Mamba Iron Formation; many ofthe carbonates in this study are more magnesian thanin other iron-formations.
Stilpnomelane
Stilpnomelane is the most cornmon Fe-silicate inthe magnetite-rich, upper part of the Marra MambaIron Formation (B samples) as well as in the sulfde-rich, magnetite-free, lower part of the formation (Asamples). Where stilpnomelane is present as a majorconstituent the rock is dark brown. Where present aslayers between carbonate- or magnetite- or sulfide-
representative electron probe analyses in Table 3.The complete range of these carbonates is shown inFigures 3a and b. The tieline distribution betweendolomite (or ankerite)-siderite pairs shows consid-erable consistency although there are some tielinesthat cross the general trend.
Siderite was found only in the lower part of theMarra Mamba Formation. Representative electronprobe analyses are given in Table 4, and the com-
Table 3. Representative electron probe analyses of members of the dolomite-ankerite series. Analysis no. I is for a sample from theWittenoon Dolomite but the other samples are all from the Marra Mamba Iron Formation.
5 * 6 * * 7 * 8 * * 9 * * 1 0 I 41 3L 21 I
F e O 2 . 3 6 1 0 . 6 1
M n o 0 . 9 8 0 . 3 0
M g o 2 1 . 0 I 1 4 . 8 2
C a O 2 8 . 9 7 2 7 . 9 0
T o t a L 5 3 . 3 9 5 3 . 6 3
C a 0 . 9 5 I 0 . 9 7 9
T o r a l 2 . 0 0 0 2 . 0 0 0
I L . 7 7 1 2 . 4 6 t 2 . 9 7
0 . 5 2 0 . r 9 0 . 9 2
1 3 . 9 r L 2 . L 4 L 0 . 4 4
2 ' 1 . 2 7 2 7 . 3 I 2 6 . L 2
5 3 . 4 7 5 2 . L O 5 0 . 4 5
0 . 9 7 0 1 . 0 1 0 1 . 0 I 5
2 . 0 0 0 2 . 0 0 0 2 . 0 0 0
1 5 . 9 3 1 6 , 8 2 I 6 . 8 5
0 . 4 5 0 . 9 8 0 . 4 2
1 1 . 1 5 9 . 3 0 l r . 1 8
2 6 . 0 6 2 6 . 4 3 2 6 . 7 3
f J . b u ) J - f J ) 5 . r d
r 6 . 8 8 1 8 . 2 1 L 8 . 7 ' 1
0 . 4 5 0 . 2 5 0 . 7 8
1 0 . 1 9 1 0 . 1 9 7 . 4 6
2 7 . 4 5 2 6 . 4 L 2 6 . - ? 3
5 4 . 9 7 5 5 . 0 6 5 3 . ' 7 4
2 0 . 3 1 2 L - 1 5 2 3 . L L
0 . 8 2 0 . 0 2 0 . l 8
7 . 7 4 7 . 5 7 6 - 3 4
2 6 . 4 7 2 5 . 9 2 2 5 . 4 5
5 5 . 3 4 5 4 . 6 6 5 5 . 4 8
F e
Mn
Mg
r eca l cu la ted on t he bas i s o f 2 (Fe ,Mn ,Mg 'Ca )
0 . 0 6 0 0 . 2 9 0 0 . 3 2 7 0 . 3 6 0 0 . 3 9 3 0 . 4 5 7 0 . 4 9 3 0 . 4 7 2 0 . 4 ' 7 8 0 . 5 1 7 0 . 5 5 0 0 . 5 9 0 0 . 6 2 3 0 . 6 8 3
0 . 0 2 5 0 . 0 0 8 0 . 0 1 5 0 . 0 0 5 0 . 0 2 8 0 . 0 1 3 0 . 0 2 9 0 . 0 1 2 0 . 0 1 3 0 . 0 0 7 0 . 0 2 3 0 . o 2 4 0 . 0 0 r 0 . 0 0 5
0 . 9 6 4 0 . 7 2 3 0 . 6 8 8 0 . 6 2 5 0 . 5 6 4 0 . 5 ? r 0 . 4 8 6 0 . 5 5 8 0 . 5 1 4 0 . 5 1 6 0 . 3 9 6 0 . 4 0 r 0 . 3 9 7 0 . 3 3 4
F i e l - d # B 1 A 2 6 A 2 3 B A 8
0 . 9 5 9 0 . 9 9 2 0 . 9 5 8 0 . 9 9 5 0 . 9 6 0 1 . 0 2 1 0 . 9 8 5 O . 9 7 9 0 . 9 7 8
2 . 0 0 0 2 . 0 0 0 2 . 0 0 0 2 . 0 0 0 2 . 0 0 0 2 . 0 0 0 2 . 0 0 0 2 . 0 0 0 2 . 0 0 0
A 5 8 A B 7 B A ] . O B A 2 4 A T O B B 5 A 8 6 B A 2 A A 6 4B 3 A
* A n a T g s i s o f c o e x i s t i n g c a f c i t e g i v e n i n T a b f e 2 . * * A n a f g s i s o f c o e x i s x i n g s i d e r i t e g i v e n i n T a b f e4 . A s s e n b T a g e s ( m i n e . a J . s . l i s t e d i n o r d e t o f d e c t e a s i n g a b u n d a n c e ; t h o s e i n x r a c e a m o u n x E a t e i n p a r e n t h e -
s e s ) . ' 7 . W i t t e n o o m D o T o m i t e 3 d o l - ( q t z ) - ( p g ) - ( c a r b o n ) ; 2 . q t z - d o 7 , 3 . q X z - d o f - p 9 - ( s t i 7 p ) ; 4 . d . o 7 - E t i l - p -g r e e n - p g - ( p o ) ; 5 . s t i L p - q t z - c a 1 - n a g - ( d o 1 ) - ( t j e b ) ; 6 . d o 7 - s i d - s t i 7 p ; 7 . d o f - t i e b - c a 1 - q t z - ( s t i f p ) - ( n a g ) ,8 . q t z - s i d - d o L - ( n i 4 n ) - ( s t i 7 p ) , 9 . d o J . - s i d - p o - p g - s t i T p i f o . q t z - s i d - d o L - ( n i n n ) - ( s x i l p ) ; 1 7 . m a g - a n k - s x i L p -q t z ; 7 2 . q t z - a n k - s t i 7 p - m a g i L 3 , s t i T p - a n k - p 7 - ( n i n n ) - ( c p ) , 1 4 . m i n n - a n k .
KLEIN AND GOLE: IRON.FORMATION, WESTERN AUSTRALIA
FeO+MnO
Mso Sider i le;159 onolyses FeO*MnO
Fig. 3. Range of carbonate compositions and the chemistry of carbonate pairi (indicated by tielines) in (a) the upper, magnetite-rich
part of the Marra Mamba Iron Formation and the Wittenoom Dolomite, and (b) the lower, sulfide-rich part of the Marra Mamba Iron
Formation. The number of analyses comprising each compositional field is shown.
5 1 3
rich bands the rock appears well laminated. Stilp-nomelane also occurs as well-crystalhzed sprays andglobular aggregates.
Representative analyses of stilpnomelane are givenin Table 5. The major chemical variation is in theFel(Fe+Mg) ratio, 0.587 to 0.825. Al,O3 contentsrange from 2.85 percent to 6.10 percent. The stilp-
nomelane compositions of the magnetite-rich part ofthe Marra Mamba lron Formation (B samples) showa greater range in Fel(Fe+Mg) ratios and a generallylower A1 content than the stilpnomelanes in the mag-netite-free, and sulfide-rich, lower part (A samples).These chemical relations are shown graphically inFigure 4. One of the assemblages (no. Bl0B) in the
CoO
Anker i te
%
CoO
5r4 KLEIN AND GOLE: IRON-FORMATION, WESTERN AI]STRALIA
magnetite-rich part of the Marra Mamba lron For-mation contains a 0.3 mm thick veinlet of a very fine-grained, light brown, matted, biotite-tke materialthat cuts across a medium-grained assemblage of fer-roan dolonrite (Fel(Fe+Mg) : 0.433) and stilpnome-lane. Two representative analyses, given in Table 5(nos. 9 and l0) show very high KrO, TiO, and Al,O,contents as compared with stilpnomelane (see alsoFig. a). Normal biotites tend to have somewhathigher KrO contents and considerably more AlrO,than this phase which appears to be intermediate incomposition between stilpnomelane and biotite. TheMgO content is very much larger than that of any ofthe stilpnomelane analyzed in this study.
Riebeckite
Riebeckite is commonly present in the magnetite-rich, upper part of the Marra Mamba lron Forma-tion, but not as a major constituent of the samplesstudied. Old crocidolite workings within the MarraMamba Formation indicate, however, that it is lo-cally abundant (Trendall and Blockley, 1970). It ismost commonly present as randomly distributed ag-gregates and sprays, although in places grains andpatches may be aligned to form a poorly definedlamination. Table 6 lists representative analyseswhich have been recalculated by the method of pa-pike et al. (1974) to evaluate the Fe3* content. Al-
though there is some range of Fel(Fe+Mg) contentsin the analyses, the general compositional range is re-markably small, as shown in Figure 5.
Minnesotaite and Talc
Sprays of minnssslaite are present in many of theassemblages, typically cutting quartz-carbonate- andstilpnomelane-rich assemblages. Table 7 gives repre-sentative electron microprobe analyses of minnesota-ite and talc. The minnesotaite analyses show a largerange of Fel(Fe+Mg) ratios, 0.632 to 0.842. Thisrange is similar to that of minnesotaite in the Soko-man lron Formation (Klein, 1974) which rangesfrom about 0.64 to 0.92 (Fe+Mn)/(Fe+Mn+Mg)(Lesher, 1978). Two assenblages contain tirlc with anFel(Fe+Mg) ratio of 0.392 (analysis no. 7, able 7).The talc has a somewhat more coarsely bladed habitthan is generally seen in the needlelike minnesotaite.Talc in iron-formation assemblages has also been re-ported by Floran and Papike (1975) from the Gun-flint lron Formation, by Lesher (1978) from theSokoman lron Formation , and by Gole and Klein(1981) from Archean iron-formations in WesternAustralia.
Greenalite and Chlorite
Greenalite is a very rare constituent of the MarraMamba Iron Formation and is present in only two
Mso so Feo +MnoFig. 4' Range of stilpnomelane compositions and that of a biotiteJike phase in the Marra Mamba Iron-Formation, in terms of
molecular percentages of MgO' Feo + MnO, and Al2O3. Note that the Al2o3 corner repr€sents 20 molecular percent. The number ofanalyses comprising each compositional field is shown.
A l 2 0 3
134 onolyses(A somples)
KLEIN AND GOLE: IRON.FORMATION, WESTERN AUSTRALIA
Table 4. Representative electron probe analyses of siderite in the Marra Mamba Iron Formation.
5 t 5
l lI O6 *2 *
F e o 3 6 . 0 9 4 3 ' 8 7 4 4 . 0 2 4 7 . 0 0 5 0 . } 4 4 9 . 9 6 5 1 . 9 8 5 0 . 1 6 5 3 . 0 7
M n o t . 4 l 0 . 9 0 0 . 8 4 0 . 3 5 0 . 2 7 O ' 2 L O ' 0 5 0 ' 8 4 0 ' 0 7
r ' 1 s o 1 9 . 6 8 1 2 . 0 8 1 0 . 0 6 9 . 5 0 9 . 4 5 7 . o 4 5 ' 3 s 2 ' 2 7 0 ' ? 8
C a O 0 . 1 6 0 . 1 6 0 . 1 7 0 . 5 3 0 . 3 0 0 . 4 8 0 ' I 9 2 ' 7 I 2 ' 4 3
T o t a l 5 7 . 3 4 5 7 . 0 1 5 5 . 0 9 5 7 . 3 8 6 0 . 1 6 5 7 . 6 9 5 7 ' 5 7 5 5 ' 9 8 5 6 ' 3 5
r e c a l c u l a t e d o n t h e b a s i s o f 2 ( F e , M n , M 9 ' C a )
f 4 . ) f , f o . u o
0 . 0 s 0 . 0 0
0 . 9 0 1 . 0 8
1 . 8 7 1 . 0 3
5 7 . 3 7 5 8 . 1 7
F e 0 . 9 s 2 1 . 0 1 1 I . 3 9 7 l 4 4 7 L . 4 8 2 1 . 5 ? 8 I . 6 8 2 I . 1 I 4 1 . 8 4 2 1 . 8 6 I I ' 8 9 I
M n 0 . 0 3 9 0 . 0 2 I 0 . 0 2 7 0 . 0 1 1 0 . 0 0 8 0 . 0 0 7 0 . 0 0 2 0 . 0 2 9 0 . 0 0 2 0 . 0 0 2 0 . 0 0 0
M s 0 . 9 6 3 0 . 4 9 6 0 . 5 6 9 0 . 5 2 1 0 . 4 9 8 0 . 3 9 5 0 . 3 0 8 0 . I 3 8 0 . 0 4 8 0 . 0 5 5 0 ' 0 6 5
c a 0 . 0 0 6 0 . 4 7 2 0 . 0 0 7 0 . 0 2 I 0 . 0 1 2 0 . 0 1 9 0 . 0 0 8 0 . I 1 9 0 ' 1 0 8 0 . 0 8 2 0 . 0 4 4
T o t a l 2 . 0 0 0 2 . 0 0 0 2 . 0 0 0 2 . 0 0 0 2 . 0 0 0 2 . 0 0 0 2 . 0 0 0 2 ' 0 0 0 2 ' 0 0 0 2 ' 0 0 0 2 ' 0 0 0
F i E f d # A 5 8 A A 5 8 A A 4 3 B A 3 1 A 1 3 A f O B A 7 A 2 4 A 7 A A 7 B A 7 7 B
* A n a f g s i s o t c o e x i s t i n g d o l - o n i t e a t a n k e r i t e g i v e n i n T a b l e 3 . A s s e n b T a q e s ( n i n e r a l s T i s t e d i n
o r d e r o l d e C r e a s i n g a b u n d a n c e ; t h o s e i n t r a c e a m o u n t s a t e i n p a t e n t h e s e s ) : 7 . q t z - d o f - s i d - p o - ( C a t b o n ) i
2 . d o t - s i d - s t i J . p ; J . q t z - s l d - d o 7 ; 4 . q t z - s i d - m i n n ; 5 . s i d - a n k - s t j l p - q t z - ( n i n n ) ; 6 . q X z - s i d - d o 7 - ( n i n n ) -
( s t i l p ) ; 7 . s t i f p - s i d - n i n n - p g ; 8 . d o f - s i d - p o - p v - s t i f p i g . s i d - s t i 7 p - m i n n ; f o . s t i f p - s i d - p g - m i n n ;
f f . s i d - s t i f p - p 9 .
assemblages (A8 and BllB). In the A sample it oc-curs as light green, somewhat bladed (chlorite-like)patches that are closely intergrown with medium-grained stilpnomelane. The grain size of this green-alite is somewhat coarser than that of the typicallycryptocrystalline variety that appears almost ani-sotropic in doubly polarized light (e.9., Klein, 1974;Zajac, 1974; znd Floran and Papike, 1975; Gole,1980). In the B sample it occurs as medium-grained,light brownish green blotchy masses that are closelyintergrown with irregular patches of pyrite and pyr-rhotite. Feathery minnesotaite has grown at the ex-pense of some of the greenalite. The habit of thisgreenatte is again not that of the usual cryptocrystal-line variety, but as shown by the analyses in Table 8,it is compositionally very similar to greenalite ana-Iyzedby Floran and Papike (1975), Klein (1974) andGole (1980).
Chlorite was found in only two samples (A37 andA37A) in which it occurs as very dense and fine-grained intergrowths with finely dispersed stilpnome-lane. An analysis of this relatively Mg-rich phase isgiven in Table 8 (analysis no. 4).
Assemblages and textures
The assemblages from the upper part of the MarraMamba Iron Formation (B samples) are distinctlydifferent from those of the lower section (A samples)
(see Table 9). The majority of the B assemblages con-tain major amounts of quartz2 and magnetite, andlesser and variable amounts of min-nesotaite, rie-beckite, stilpnomelane, dolomite (or ankerite), cal-cite, and traces of pyrite. The A samples, on the otherhand, contain no iron oxides and no calcite. Theyconsist of variable amounts of quartz, siderite, dolo-mite (or ankerite), stilpnomelane, minnesotaite, pyr-rhotite and pyrite, and small amounts of carbon' Thelisting of coexistences in Table 9 illustrates the diver-sity of minerals that are intimately associated in thetwo complex types of iron-formation. The B sampleswould normally be classified as oxide-rich and the Asamples as sulfide-rich (or type) iron-formation. Bothtypes, however, contain abundant carbonates and sil-icates. The diversity of assemblages is caused mainlyby fine scale banding and laminations in which alter-nating bands tend to have distinctly diferent miner-alogies. Representative assemblages of both parts ofthe Marra Mamba Iron Formation are depicted inFigs. 6 and 7 . The most common assemblages in theupper part (B samples) arei qtz-ma9-do1-stilp-rieb-caland qtz-mag-ank-stilp-rieb-minn (see Figs. 6a and
2 Most of what is refemed to as quartz has a grain size of <50
microns. As such it is a microcrystalline, finely granular quartz
verv similar to what is often referred to as chert.
5 1 6 KLEIN AND GOLE: IRON-FORMATION, WESTERN AUSTRALIA
Table 5. Representative electron probe analyses of stilpnomelane and a biotite-like phase in the Marra Mamba Iron Formation(columns 9 and l0).
l 0
s io2
T iO2
A l 2 0 3
FeO
IvlnO
Mgo
CaO
Na2O
K20
Tota l
4 7 . 4 4 4 7 . 8 3 4 8 . 0 4
0 . 0 0 0 . 0 0 0 . 0 7
4 . 8 r 3 . 9 9 4 . 0 3
3 3 . 4 5 3 3 . 0 8 3 0 . 7 5
0 . 0 6 0 . l s 0 . 0 5
3 . 9 8 4 . 0 8 5 . 7 3
0 . 0 2 0 . 0 4 0 . 1 0
0 . 3 4 0 . 1 1 0 . 1 1
I . 4 4 0 . 9 5 r . 0 4
9 1 . 5 s 9 0 . 2 3 8 9 . 9 3
recalculated
3 . 7 6 4 3 . 8 3 0 3 . 8 1 s
o . 2 3 6 0 . 1 - 7 0 0 . 1 8 5
4 . 0 0 0 4 . 0 0 0 4 . 0 0 0
4 8 . 6 7 4 8 . 8 2
0 . 0 1 0 . 0 0
3 . 9 9 4 . 6 9I
3 0 . 9 1 2 9 . 5 I
0 . 0 5 0 . 0 6
5 . 8 4 7 . O 9
0 . r 0 0 . 1 8
1 . 1 3 0 . 2 2
1 . 9 3 I . 5 0
9 2 . 6 3 9 2 . 0 7
o n t h e b a s i s o f
3 . 7 8 4 3 . 7 6 5
0 . 2 L 6 0 . 2 3 5
4 . 0 0 0 4 . 0 0 0
4 5 . 5 8 4 8 . 1 5 5 1 . 3 3
0 . 0 0 0 . 0 0 0 . 0 0
5 . l 0 5 . 4 0 2 . 8 5
2 9 . 2 6 2 7 . 5 9 2 9 . 6 4
0 . 0 8 0 . 0 7 0 . 0 5
7 . 4 6 7 . 5 5 1 0 . s 4
0 . o 2 0 . 2 9 0 . 0 7
0 . 7 8 0 . 1 6 0 . 3 0
1 . 0 3 2 . 9 9 0 . 7 3
9 0 . 4 1 9 2 . 2 0 9 2 . 5 2
I l oxygens ( to ta l Fe as
3 . 5 0 8 3 . 7 I 4 3 . 8 s t
0 . 3 9 2 0 . 2 8 5 0 . 1 4 9
4 . 0 0 0 4 . 0 0 0 4 . 0 0 0
4 2 . 6 2 4 3 . 4 0
0 . 9 2 0 . 8 1
8 . 7 8 9 . 1 3
r 6 . 3 1 1 5 . 0 8
0 . 0 I 0 . 1 9
t 7 . 2 7 1 7 . 4 3
0 . 1 0 0 . 0 2
0 . 1 7 0 . 0 0
6 . 5 8 6 . 7 8
9 2 . 7 6 9 2 . 8 4
F e 2 + o n l y )
3 . 2 L 0 3 . 2 4 L
0 . ' ? 7 9 0 . 7 5 9
3 . 9 8 9 4 . 0 0 0
0 . 0 0 0 0 . 0 4 5
0 . 0 5 2 0 . 0 4 5
r . 0 2 8 0 . 9 4 2
0 . 0 0 0 0 . 0 1 2
1 . 9 3 9 1 . 9 4 0
0 . 0 0 8 0 . 0 0 1
0 . 0 2 5 0 . 0 0 0
0 . 6 3 2 0 . 6 4 6
3 . 6 8 4 3 . 6 3 r
0 . 3 4 6 0 . 3 2 7
B ] . O B 8 7 O B
s i
A1
I
A1
Ti
Mn
M9
Ca
K
x
0 . 2 r 4 0 . 2 0 7
0 . 0 0 0 0 . 0 0 0
2 . 2 2 0 2 . 2 I 5
0 . 0 0 4 0 . 0 r 0
0 . 4 7 1 0 . 4 8 7
0 . 0 0 1 0 . 0 0 3
0 . 0 5 2 0 . 0 1 7
0 . 1 4 6 0 . 0 9 7
3 . 1 0 8 3 . 0 3 6
0 . L 9 2 0 . r 5 0
0 . 0 0 4 0 . 0 0 1
2 . 0 4 3 2 . 0 1 0
0 . 0 0 4 ' 0 . 0 0 3
0 . 6 7 8 0 . 6 7 7
0 . 0 0 8 0 . 0 0 8
0 . 0 1 7 0 . r 7 0
0 . 1 0 5 0 . 1 9 1
3 . 0 5 1 3 . 2 1 0
0 . I 9 2 0 . 1 7 6
0 . 0 0 0 0 . 0 0 0
1 . 9 0 4 1 . 9 3 3
0 . 0 0 4 0 . 0 0 5
0 . 8 1 5 0 . 8 7 8
0 . 0 I 5 0 . 0 0 2
0 . 0 3 3 0 . I 2 0
0 . r 4 8 0 . 1 0 4
3 . t r 1 3 . 2 r 8
0 . 2 0 4 0 . 1 0 3
0 . 0 0 0 0 . 0 0 0
1 . 7 8 0 L . 6 7 2
0 . 0 0 5 0 . 0 0 4
0 . 8 6 8 1 . 1 7 8
0 . 0 2 4 0 . 0 0 5
o . o 2 4 0 . 0 4 4
0 . 2 9 5 0 . 0 7 0
3 . 2 0 0 3 . 0 7 6
F a
I F " + M g I 0 . 8 2 s 0 . 8 2 0 0 . 7 5 1 0 . 7 4 8 0 . 7 0 0 0 . 6 8 8 0 . 6 7 2 0 . s 8 7
F i e T d # A B B J 3 B B L I B A t t B A 3 5 B A 5 B A A 3 A B f 2 A
A s s e m b l a g e s ( m i n e r a T s - l i s t e d i n o t d e r o f d e c t e a s i n g a b u n d . a n c e ; t h o s e i n t r a c e a m o u n t sa r e i n p a r e n t h e s e s ) . ' l ' . d o L - s t i 7 p - g r e e n - p g - ( p o ) ; 2 . a n k - s t i 7 p - m a g - m i n n - q t z ; 3 . q t z - m a g -a n k - s t i 7 p - m i n n ; 4 . s i d - s t i 7 p - p g - m i n n - ( c p ) ; 5 . s t i t p _ a n k _ p o _ ( m i n n ) _ ( q t z ) ; G . d o l _ s i d _s t i T p ; 7 . d o f - q x z - s t i l - p ; B . d o I - r i e b - m a g - s t i l , p - q t z - p g ; g a n d 1 0 . d o l _ s t i l p _ ( n a g )t t a v e t s e d b g v e i n J e t o f b i o t i t e - l i k e m a t e r i a j .
KLEIN AND GOLE: IRON.FORMATION. WESTERN AUSTRALIA 517
s i o 2 5 2 . I r
T i o 2 0 . 3 8
A I 2 O 3 0 . 0 7
F e O 3 1 . 0 2
M n o 0 . 0 3
M g O 4 . 3 8
C a O 0 . 4 6
N a 2 O 7 . 1 5
K z O 0 . 0 3
F e r O ? i 1 3 . 5 1r e 6
- 1 8 . 8 6
rotal 96lTE
5 r . 6 5 5 3 . 6 0 5 2 . 8 A
0 . 0 0 0 . r 3 0 . 0 0
0 . 0 8 0 . I 9 0 . 0 1
3 0 . 9 6 3 0 . 4 r 2 9 . 4 4
0 . 0 2 0 . 1 5 0 . 0 0
4 . 8 5 5 . 3 8 5 . 0 8
0 . 4 1 0 . 7 5 0 . 5 9
? . 6 8 6 . 4 8 6 . 2 6
0 . 0 0 0 . 0 r 0 . 1 5
9 5 . 5 5 9 7 . 1 0 9 5 . 4 1
1 I . 0 8 1 5 . 8 9 1 5 . 5 82 0 , 9 9 1 6 , 1 r 1 5 . 4 0
5 2 . 4 7 5 2 . 9 0
0 . 0 ? 0 . 1 6
0 . 1 4 0 . 0 4
2 9 . 3 A 2 6 . 2 9
0 . 0 7 0 . 0 1
5 . 9 8 1 . ' t L
0 . 3 3 0 . 2 9
6 . 3 1 ? . 3 0
0 . 0 8 0 . 0 4
9 5 . 8 3 9 4 . t 4
1 I . 2 8 1 3 . 5 8t 9 . 2 3 1 3 . 9 8
Table 6. Representative electron probe analyses of riebeckite inthe magnetite-rich part of the Marra Mamba Iron Formation (B
samples only).
octahedral outline unless the grains are severelycrowded together in essentially continuous micro-bands or laminations (see Figs. 9b to c). Stilpnome-lane occurs as discontinuous laminations of finelymatted intergrowths of thin sheaves (see Fig. 9a), andalso as coarser grained sprays and rosettes of sub-hedral sheaves (Figs. 8a and c). Minnesotaite dis-plays its typical habit of randorrly distributed ro-settes of needles in carbonate and quartz (or chert)matrices. Its cross-cutting relations with stilpnome-lane and carbonates are clear evidence for it havingformed subsequent to the minerals it transgresses. Acoarser grained variety is found in close associationwith pyrite grains (Fig. 8b). Riebeckite ranges fromfine- to medium-grain size and occurs as randomlydistributed grains in qtz-dol(or ank)-stilp-mag matri-ces, or as thin laminations that parallel quartz-mag-netite microbands. Frequently the riebeckite needlesare very fine and elongate (see Fig. 8e) and cut across
Table 7. Representativc O..jll"ril:* analyses of minnesotaite
s i o 2 4 8 . 8 7 4 9 . 2 O 5 0 . 6 s 5 r - 3 5 s 2 . r 3 5 1 . 6 1 5 4 . 4 0
T i O 2 0 . 0 0 0 . 0 0 0 . 0 0 0 . 0 2 0 . 0 0 0 . 0 5 0 . 0 0
A l 2 o 3 I . 1 5 0 . 6 7 0 . 4 9 0 . 5 7 0 . 5 6 0 . 8 4 1 . 0 9
F e o 3 7 . 5 9 3 6 . 3 6 3 3 . I I 3 2 . 7 3 3 0 . 9 1 2 9 . s 9 2 0 . 2 0
l { n o 0 . 0 r 0 . 0 0 0 . 0 4 0 . 1 9 0 . 0 ? O . 2 4 0 . 0 8
M g o 3 . 9 4 4 . 5 7 7 . 0 0 ? . 8 0 8 . I 8 9 , 6 5 L i . 5 5
C a O 0 . 0 0 0 . 0 I 0 . 0 0 0 . 0 0 0 , 0 C 0 . 0 1 0 . 0 0
N a 2 o 0 . 0 0 0 . 0 2 0 . 1 9 0 . 0 0 0 . 0 0 0 . 0 3 0 . 0 0
K z O 0 . 4 2 0 . 2 2 0 . 3 2 O . 4 4 0 . 4 7 0 . 6 ? 0 , L 2
T o t a l 9 0 . 9 8 9 I . 0 5 9 1 . 8 0 9 2 , 5 1 9 2 . 3 2 9 2 . 6 4 9 3 . 4 4
recalculated on the basls of 1I oxygens (re total as Fe2+ only)
s i
A]
r 3 . 9 9 9 4 . 0 0 0 4 . 0 0 0 4 . 0 0 0 4 . 0 0 0 4 . 0 0 0 3 . 9 7 9
A 1 0 . 0 0 0 0 . 0 r 4 0 . 0 0 5 0 . 0 r r 0 . 0 4 2 0 . 0 0 2 0 . 0 0 0
T i 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 0 . 0 0 r 0 . 0 0 0 0 . 0 0 3 0 . 0 0 0
F e 2 . 5 5 4 2 . 4 4 L 2 . 1 6 4 2 . O 1 L 1 . 9 1 9 I . 8 8 3 I . 2 0 7
u n 0 . 0 0 I 0 , 0 0 0 0 . 0 0 2 0 , 0 1 3 0 , 0 0 5 0 . 0 I 5 0 , 0 0 4
M 9 0 . 4 7 A 0 . 5 4 7 0 . 8 1 6 0 . 8 9 6 0 . 9 3 4 r . 0 9 4 1 . 8 6 9
c a 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 0 , 0 0 0 0 . C 0 0 0 . 0 0 1 0 . 0 0 0
N a 0 . 0 0 0 0 . 0 0 3 0 . 0 2 8 0 . 0 0 0 0 . 0 0 0 0 . 0 0 4 0 . 0 0 0
K 0 . 0 4 4 0 . 0 2 3 0 . 0 3 2 0 . 0 4 4 0 , 0 4 6 0 . 0 6 1 0 . 0 1 1
t 3 . 0 7 7 3 . 0 2 8 3 . 0 4 7 3 . 0 3 6 3 . 0 0 6 3 . 0 6 3 3 . 0 9 1
- - I 9 - o . a 4 2 0 . 8 r ? o . 7 2 6 0 . 6 9 8 0 . 6 7 9 0 . 6 3 2 o . 3 g 2t ! e+Mg)
F i e l d I A 7 B A 6 A A 2 A A B f T B B 1 3 A B 5 A B 2 B
A s s e n b T a g e s h i n e r a l s T i s t e d i n o t d e r o f d e c r e a s l n q a b u n d a n c e i
t h o s e i n E t a c e a n o u n t s a r e i n P a r e n t h e s e s ) : L 6 c i 7 p - s i d - p g - n i n n i
2 . n i n n - a n k ; 3 . q t z - n i n n - s t i 7 p - a n k - p o , 4 . q t z - n i n n - g t e e n - p o - P g r
5 . a n k - n i n n - q t z - n a g t 5 . q t z - n a g - n i n n , 7 . d o l - q x 2 - s t i l P - t c - ( n a q ) '
r e c a l . c u l a t s e d o n t h e b a s i s o f 2 3 o x y g e n s
s i 7 . 9 9 3 7 . 9 9 2 7 . 9 4 6 1 . 9 9 9 1 . 9 8 7 | . 9 9 6A r 0 , 0 0 ? 0 . 0 0 8 0 . 0 1 4 0 . 0 0 1 0 . 0 1 3 0 . 0 0 4r 6:Trd 6.-nd E.-ad fiTIT 6.-Id E-Td
A I 0 . 0 0 6 0 . 0 0 7 0 . 0 1 9 0 . 0 0 1 0 . 0 1 2 0 . 0 0 3T i - 0 . 0 4 4 0 , 0 0 0 0 . 0 1 5 0 . 0 0 0 0 . 0 0 8 0 . 0 1 8F e r ' I . 5 5 0 L . 2 9 0 1 . . 7 8 1 1 . 7 5 3 1 . 2 9 2 I . 5 5 ?F e 2 + 2 . 4 2 0 2 , 1 1 6 2 . 0 0 8 1 . 9 7 2 2 . 4 4 8 r . ' t 6 7h 0 . 0 0 4 0 . 0 0 3 0 . 0 1 9 0 . 0 0 0 0 . 0 0 9 0 . 0 0 IMe l.9E l.+: l4:9 L'3J9 l.:91 r=4!. 5 . 0 J ) r . I J 5 5 . 0 J 6 5 . 0 9 6 5 . J 5 3 5 . 0 8 3
x o c r 0 . 0 3 5 0 . 1 3 5 0 . 0 1 6 0 . 0 9 6 0 . 3 5 3 0 . 0 8 3C a 0 . 0 7 5 0 . 0 6 8 0 . 1 2 0 0 . 0 9 6 0 . 0 5 4 0 . 0 4 7N a 1 . 8 9 0 1 . 1 9 7 I . 8 4 4 I . 8 O B I . 5 9 3 I . 8 7 0
-d'td r.-d!-o' tJno z.Tnd ,.TtT z:TnE
N a 0 . 2 3 7 0 . 5 0 7 0 . 0 2 8 0 , 0 2 1 0 . 2 6 9 O . 2 7 OK 0 . 0 0 5 0 . 0 0 0 0 . 0 0 2 0 . 0 2 9 0 . 0 1 6 0 . 0 0 8
f:245 0':5n7 0:Tl5' blT56-' o-:ZE d:Tl€
T o t a l L 5 . 2 7 8 1 5 . 5 0 7 1 5 . 0 3 0 1 . 5 . 0 5 6 1 5 . 2 8 5 t 5 . 2 7 A
f f i t r* o .7es o .782 0. ?60 0 . 73r o . io2 o .6s7
F i e f d # B 1 4 C B 4 C B l 3 A B I 2 A B 2 B B 4 C
' E e 2 0 3 c o n t e n t e s t i n a t e d b V t h e n e t h o d ' o f P a p i h e e t . a 7 .( 1 9 7 4 ) -
A s E e n b l a g e s ( n i n e r a l s a r e T t s t e d i n o r d e r o f d e c r e a s i n ga b u n d a n c e ; t i o s e j n t t a c e a n o u n t s a r e i n p a r e n x h e s e s ) t 7 . c a f -r i e b - ( s t i f p ) - ( p 9 t i 2 . q t z - r i e b - d o t - c a 1 - n a q r 3 . c a 7 - d o l - q t z -( r i e b ) - ( p 9 ) t 4 , d o l - r i e b - n a g - s t i l p - q t z - p g i s . c a l - r i e b - ( s t i l p ) -( n a g ) , 5 . q t z - t i e b - d o t - c a L - n a g .
b). The most common types in the lower section ofthe Marra Mamba (A samples) are: qtz-dol(or ank)-stilp-sid-py-po and qtz-dol(or ank)-sid-stilp-minn-po-py (see Figs. 7a and b). The assemblages shown inFigs.6 and7, and listed in Table 9 may.not all beequilibrium assemblages. It has been impossible forus, at the very low temperatures these assemblageshave undergone, to di-fferentiate equilibrium and dis-equilibrium coexistences.
The grain sizes of the assemblages are mainly fineto very fine. Quartz is often microcrystalline andchert-like in handspecimen as well as in grain size intransmitted [ght. The carbonates are generally con-siderably coarser grained than quartz (or chert) andtend to have euhedral, rhombohedral outlines (seeFigs. 8c to e). Magnetite shows a range of grain sizesfrom fine- to medium-grained, and generally good
3 . 8 8 9 3 . 9 5 1 3 . 9 5 9 3 , 9 5 9 3 . 9 9 r 3 . 9 2 7 3 . 8 8 7
0 . 1 1 0 0 . 0 4 9 0 . 0 4 1 0 . 0 4 1 0 . 0 0 9 0 . 0 7 3 0 . 0 9 2
5 1 8 KLEIN AND GOLE: IRON-FORMATION, WESTERN AUSTRALIA
Mgo FeOFig. 5. Range of riebeckite compositions in the magnetite-rich, upper part of the Marra Mamba Iron Formation, in terms of weight
percentage of Na2O, MgO, and FeO (total Fe and FeO). The number of analyses comprising the compositional field is shown.
other minerals, such as quartz and carbonates. pyriteand pyrrhotite are common constituents of the sul-fide type iron-formation. Pyrite is commonly me-dium-grained and euhedral, whereas pyrrhotite is an-hedral, mostly granular in habit (see Fig. 8f). Bothsulfrdes may occur together and generally define thin(< I mm thick) discontinuous bands, parallel to thebanding of other surrounding rock types.
Fine-scale banding and laminations are commonwithin mesobands (see Figs. 9a and b) but micro-banding as described by Trendall and Blockley(1970) and Trendall (1973) in the Dales Gorge Mem-ber and the Weeli Wolli Formation of the HamersleyGroup, is in general poorly developed (see alsoEwers and Morris, 1980). The continuity of fine lami-nations is commonly intemrpted by well-crystallized,medium-grained rhombohedral carbonates, as wellas recrystallized magnetite of medium grain size (seeFig. 9c). Although pyrite and pyrrhotite, in the sul-fide-rich iron-formation, are most commonly presentas finely disseminated grains, they also occur as well-defined bands (up to several mm in thickness) andlaminations of dense concentrations of subhedralpyrrhotite and/or pyrite grains (see Fig. 9d).
Discussion and conclusions
The magnetite-containing asserrblages of theMarra Mamba Iron Formation are very similar to
those reported for the weakly metamorphosed partsof the Sokoman (Klein, 1974 and. 1978; Klein andFink, 1976; Zajac,1974; Lesher,1978), the Negaunee(James, 1955; Haase, 1979), the Biwabik (French,1968) and Gunflint Iron Formations (Floran and Pa-pike, 1975) except for the abundant presence ofriebeckite and the general absence ofgreenalite. Theaveraged bulk composition for the nine samples ofthe Marra Mamba lron Formation versus those ofthe Sokoman or Biwabik Iron Formations (Gole andKlein, l98l) reveals a considerably higher NarO con-tenl (0.39Vo) than for the other two (Sokoman 0.17and Biwabik 0.06Vo). The average for the four mag-netite-rich samples in Table I gives a value of 0.43wt.7o NarO.
The medium- to coarse-grained, sub- to euhedraloutlines of the carbonates and magnetite are verysimilar in all of the iron-formations mentionedabove. Medium- to coarse-grained stilpnomelanepatches and sprays appear to be universal, and min-nesotaite shows cross-cutting relations with carbon-ates and stilpnomelane (as well as greenalite whenpresent) in many occurrences. Riebeckite grains arecommon as part of the fine- to medium-grained ma-trix of the Marra Mamba lron Formation or as smallrosettes and sprays of delicate and long needles, butvery rare in most of the North American occurrences.Such riebeckite, as is also the case for minnesotaite.
No2O
Fe2O3
KLEIN AND GOLE: IRON.FORMATION, WESTERN AUSTRALIA
FeO+MnO
FeO*MnO
py +(po)
Mgo 50 mtnn FeO*MnO MgO
Fig. 6. Graphical representation of asemblages in the magnetite-rich part of th€ Marra Mamba Iron Formation (B samples) in terms
of important and competing solid solution components, molecular perc€ntages of CaO, MgO' (FeO+MnO), and Fe2O3. Miaeral
abbreviations as in Table L Coexistences shown in A and B are the most conunon.
5 1 9
FerO.
mnn slrlp qr".nFeO+MnO
Al2o3
Moleculor %
s20 KLEIN AND GOLE: IRON-FORMATION, WESTERN AUSTRALIA
Moleculor %
10
+ qtz
po+ py
srd FeO+MnO
FeO*MnO Mgo FeO*MnO
lvloleculor %
10
t (cor bon)
green
py +(po)
Mgo srd Feo+Mno Mso FeO+MnOFig. 7. Graphical representation of assemblages in the sulfide-rich part of the Marra Mamba Iron Formation (A sarrples) in terms of
important an6 sompeting solid solution components, molecular perc€ntages of CaO, MgO, (FeO+MnO), and AlrO.. ihe AlrO, apexrepresents 20 mole%o. Mineral abbreviations as in Table 1. Coexistences shown in A and B are the most corrlmon.
(py)
(po)
A l2o3
Moleculor
Moleculor %
Fig. 8. photomicrographs of representative assemblages and t€xtures in the Marra Mamba Iron Formation. A' Medium-grained
siderite and light brown, fine-grained stilpnomelane oveiarinted by minnesotaite. Plane polarized light (#AllB)' B' Medium-grained
pyrite (opaque) intergrown with minnesotaite, in a fine-lrained matrix of stilpnomelane, ankerrte and extremely fine minnesotaite
needles. Minnesotaite is commonly medium- to coarse-grained whegrained, anhedral ankerite grains intergrown with medium-grainedsmall quartz inclusions but a quartz-free rim. It is not compositirankerite and smaller, euhedral grains of siderite in a fine-grainExtremely fine needles of riebeckite in a matrix of frne-grained quar
also part of this assemblage but is not pres€nt in the photograph. Plane polarized light (#B4C). F' Discontinuous bands of euhedral'
medium-grained pyrite and anhedral pyrrhotite in a matrii of fine-grained quartz and medium-grained dolomite (to ankerite)'
Reflected, plane polarized light (#A238).
Kti
'" '$i rC! 1
- . ' t - "?
, O.2 mm , O . Z m mhe Marra fiffiiffiFffi. ileffilil#A;;""* (.p"qil
l - - ^ - ^ l - - - , - - |stilpnomelane mesoband adjoining an ankerit€-stilpnomelane mesoband in which the ankerite is coanely re-crystallized. plane polarizedlight (#868). B. Magnetite laminations (opaque) across a matrix of medium-grained dolomite, with minor stilpnomelane and quartz.Doubly polarized light (#BsA). C. Medium-grained dolomite and magnetite-(opaque) euhedra in fine-grained, laminated matrix ofstilpnomelane and quanz. Plane polarized ught (#B2B). D. Fine- to medlum-grained pyrrhotite-rich mesoband adjoining a fine-grainedstilpnomelane-chlorite mesoband. Reflected, plane polarized ught (#A3?A).
Table 8. Representative electron probe analyses of greenalite(columns l, 2 and 3) and chlorite (column 4).
523
0.18) verszs those of the magnetite-rich part (0'49 to
0.55: see Table l).The primary structures of the Marra Mamba Iron
Formation are very similar to those in other mem-
bers of the Hamersley Group (Trendall and Block-
ley, 1970) and in Archean iron-formations describedby Gole (1980). Fine-scale laminations and banding
are the only sedimentary textures in the Marra
Mamba whereas oottic and granular textures are
commonly present in North Anerican sequences as
well (Gole and Klein, l98l).The question of the possible metamorphic history
of the Marra Mamba lron Formation is a difficultone. Quartz which is a major constituent is generally
microcrystalline. Unambiguous overprints of minne-
sotaite and riebeckite on earlier minerals' such as
carbonates and stilpnomelane, are abundant. Both of
these minerals have large stability fields in terms of
temperature and pressure. Talc, the Mg-rich phase
which is closely related to minnesotaite, can be
formed experimentally at 90"C and atmosphericpressure (Bricker et al., 1973). Minnesotaite, there-fore, will be stable over a wide range of pressure-
temperature conditions, ranging from a minimum of
that determined for talc to maximal conditions of
those associated with the transition from the biotite
to garnet zones, as shown by pelitic schists (Klein,
1978). Riebeckite ranges in stability from late diage-
netic (Milton and Eugster, 1959) to that of highgrades of metamorphism (Ernst, 1962). Other miner-
als of the iron-formation have similarly large, if not
larger pressure-temperature stability fields (e.g., car-
bonates, magnetite, stilpnornelane).The presence and distribution of authigenic preh-
nite, pumpellyite, epidote and actinolite as very lowgrade metamorphic minerals in basic and inter-
mediate volcanics of the Fortescue Group (which di-
rectly underlies the Hamersley Group) has been
documented by Smith (1980) and Srrith et al. (1981)'
These authors interpret four sub-greenschist togreenschist facies metamorphic zones' These are:
Zl-pumpellyite + prehnite; Zll-pumpellyite +
prehnite + epidote; Zlll-pumpellyite + prehnite *
epidote * actinolite; and ZlY----epidote * actinolite+ prehnite. The samples of the present study can beplaced within those authors' zone II by reference to
their reconstructed cross section. This would implytemperatures, during burial, in the range of 200o to
300'C and a maximum pressure of burial of aboutl.2kbar for the Marra Mamba Iron Formation. Oxy-gen isotope temperature estimates (Becker and Clay-ton, 1976) on the overlying Dales Gorge Member
KLEIN AND GOLE: IRON-FORMATION, WESTERN AUSTRALIA
S i o 2
T i o 2
Al zo :
FeO
MnO
Mgo
CaO
Na2O
K2o
Tota l
5 0 . 0 2 4 9 . 2 3
0 . 0 9
0 . 0 3
0 . 1 9
2 . 4 9
U . U J
0 . r 0
0 . 0 0
1 . 3 7
3 6 . r 3 3 4 . 9 6 3 6 . 2 6 2 9 . L 7
0 . 0 9 0 . 0 0
I . U / I f , . f , /
4 1 . 9 8 2 8 . 2 0
0 . 0 2 0 . 0 0
3 . 4 4 1 3 . 3 0
0 . 0 1 0 . 4 4
0 . 0 r 0 . 0 5
0 . 0 2 0 . 0 6
8 8 . 9 0 8 6 . 8 0
14 oxygens
4 . 2 3 5 3 . 1 4 5- 0 . 8 5 5
0 . I 4 ' 7 r . r 2 40 . 0 0 7 0 . 0 0 04 . 6 8 6 2 . 5 4 30 . 0 0 2 0 . 0 0 00 . 6 0 0 2 . r 3 70 . 0 0 2 0 . 0 5 10 . 0 0 2 0 . 0 r 30 . 0 0 3 0 . 0 0 8
0 . 0 0
3 . 0 4
0 . 0 s
0 . 0 4
0 . 0 0 0 . 0 0
8 9 . 0 8 8 8 . 6 9
o n b a s i s o f
4 . 2 7 6 4 . L 4 2S iA I
T iFeMnMg
NaK
FE
IF-eTMs)-
F i e T d #
5 . 4 4 6
0 . 9 1 8
8 7 1 B
0 . r 9 t0 . 0 0 04 .8 '790 . 0 0 00 . 5 3 70 . 0 0 70 . 0 0 90 . 0 0 0
5 . 6 2 3
0 . 9 0 r
A 8
5 . 4 4 9
0 . 8 8 6
A 8
f , . d / o
0 . 5 4 3
A 3 7 A
0 . 0 0 40 . 0 0 84 . 9 5 00 . 0 1 90 . 4 3 90 . 0 0 40 . 0 2 2
A s s e m b T a g e s ( m i n e r a T s a t e l i s t e d i n o r d e r
o f d e c t e a s i n g a b u n d a n c e ; t h o s e i n t r a c e
a m o u n t s a t e i n p a r e n t h e s e s ) : 7 - q t z - m i n n -
g r e e n - p g - p o ; 2 a n d 3 . s t i T p - p g - g r e e n - d o 1 -( m i n n ) - ( p o ) ; 4 . s t i l p - c h f - ( c a r b o n ) - ( p o ) -
( i l n ) .
appears to have formed during the late diagenetic tovery low-grade metamorphic stages of the iron-for-mation (Milton and Eugster 1959; Trendall andBlockley, 1970).
The sulfide-rich assemblages of the Marra MambaIron Formation are an example of the sulfide-typeiron-formation, originally described as "sulfide-facies" by James (1954). These assemblages reflectconsiderably more reducing sedimentary conditionsthan the magnetite-rich associations (Klein andBricker, 1977). This is reflected in the much lowerFe'*/(Fe2*+Fe3*) ratios of the sulfide-rich part (0 to
524 KLEIN AND GOLE: IRON-FORMATION, WESTERN AUSTRALIA
Table 9' complete listing of assemblages in the magnetite-rich (B samples) and sulfidc-rich (A samples) portions of the Marra MambaIron Formation.
B samples A samples
J 4 €C ..{d o o ] o ]
F I C O - O
I q ' . . ! c o o . - { r - { J 1. l J . ( g . + J . . i t { . . { O r d O Ct t i E ' / ' E b r r . p o d 6 i i d ,
oF !
o . ; do . . { o
o ] q !d t r O O
N . r l C q J - { . 1.lJ .lJ ..1 t{ ,4 Of t o E b r o d
Xx xx xx x xX X Xx xX XX XX XX XX Xxxx (x )X XX XX XXXX
xxX X
XXXX
I
x
xxx
xxxXXxXx
xXxXxX
X X
X Xx
xxx
X XX
XX XX
X Xx
X
xxx ( x )
XxxX
XY
XxXXxxxxxXxXx
x
xx
xx xX (x )
(x ) (x )(x)xX X
xX
XX X
X
( x )
( x )
X(x )( x )
(x)x
( x )
xX X
XX XX
Xxx
xx
xXY
Xx
x
xxx
xx
x
xXxx
XX XxY
xx x
xx xx x
xY Y
xXXxx xx xxX XXx xX XX XXXxx xX XX Y Y
X XX XX Xx x
xX X
xY
xxXxI
X
xx x
xx x
x xx
x
X (X )X ( X )X
(x ) (x ) (x )(x )
xxX
x ( x )(x ) (x )
x(x)x (x )x ( x )
( x ) ( x )
(x ) (x ) (x )x (x )
X X(x )
(x )( X ) X
x (x ) (x )x x
X Xx ( x ) ( x )
xX
X Xx x xx xx x x
X XxxxX X
X XY
x xxx
x x
x (x )x
x (x )x x ( x )
x (x) x ( x )
xxX XX XX X ( X )
x (x )
Xx
Xxxx
M i n e r a l a b b t e v i a x i o n s a s j n T a b l e l , x = m a j o r c o m p o n e n t i ( x ) = t t a c ea m o u n t .
F o t r e L a t i v e l g h o m o g e n e o u s m e s o D a n d s t h e a s s e m b r a g e J i s t i n g r e f r e c t st h e m i n e r a f o g g o f a n a r e a i n a t h i n s e c t i o n o f 5 t o r 0 m n i n d i a m e t e r ;i n f i n e T g b a n d e d o r l - a m i n a t e d T o c k x g p e s t h e a s s e m b T a g e l i s t i n g n a gr e f L e c t t h e n i n e t a L o g ? o f a b a n d < 0 . 3 m m j n t h i c k n e s s .
KLEIN AND GOLE: IRON-FORMATION, WESTERN AUSTRALIA 525
and Wittenoom Dolomite indicate temperatures ofburial for those formations of 270 to 310'C. The al-most total lack of greenalite in materials of this studymight well be the result of such elevated temper-atures. The low temperature metamorphic assem-blages of iron-formation are, however, relatively in-sensitive to changes in metamorphic temperature onaccount of the large stability fields of their low tem-perature index minerals. Because of this, as well as alack of knowledge of the stability fields of e.9., green-alite, minnesotaite and stilpnomelane, the estimatedburial temperatures cannot be evaluated independ-ently in any quantitative fashion, by the use of theiron-formation assemblages. One can only say thatthey appear, on the basis of textures and mineralogy,to be of late diagenetic to very low metamorphicgrade origin.
AcknowledgmentsResearch on this project was begun during a Guggenheim Me-
morial Fellowship awarded C.K. for 1978. Diamond drill coreswere made available by the Hamersley Exploration Pty. Limitedin Wittenoom, Western Australia. We thank Messrs. Bill Burnsand John Evans of the Hamersley Exploration Pty. Ltd. for theiradvice and aid in the selection of materials. The Division of Min-eralogy of the Commonwealth Scientific and Industrial ResearchOrganization (cslRo) in Perth, Western Australia, providcd C.K.with office and laboratory space as well as field vehicles. C.K. isgrateful to Messrs. W. E. Ewers and A. J. Gaskin of the cslRo fortheir hospitality and support during his six months stay in West-ern Australia. Laboratory research was made possible by Nsrgrant EAR-76-11740 to C.K. The electron microprobe used in thisstudy was obtained by joint funding from Nsr grant GA-37109 (toC.K.) and the Indiana University Foundation. We thank Messrs.W. H. Moran, R. T. Hill, and G. R. Ringer for drafting and pho-tography of the illustrations; Mrs. Thea Brown for the typing ofthe manuscript; and W. E. Ewers, H. L. James, R. C. Morris, A. F.Trendall, and R. E. Smith for critical and constructive reviews ofthe manuscript.
ReferencesBecker, R. H. and Clayton, R. N. (1976) Oxygen isotope study of a
Precambrian banded iron-formation. Hamersley Range, West-ern Australia. Geochimica et Cosmochimica Acta, 40, 1153-I 165.
Bricker, O. P., Nesbitt, H. W. and Gunter, W. D. (1973) The sta-bility of talc. American Mineralogist, 58,6+72.
Ernst, W. G. (1962) Synthesis, stability relations, and occurrenceof riebeckite and riebeckite-arfvedsonite solid solutions. Journalof Geology, 70, 689-'1 36.
Ewers, W. E. and Morris, R. C. (1980) Chemical and mineral-ogical data from the uppermost section of the upper BIF mem-ber of the Marra Mamba lron Formation. cslRo, Institute ofEarth Resources, Division of Mineralogy, Report no. FP23.
Floran, R. J. and Papike, J. J. (1975) Petrology ofthe low-graderocks of the Gunflint Iron Formation, Ontario-Minnesota. Geo-logical Society of America, Bulletin 86, I169-1 190.
French, B. M. (1968) Progressive contact metamorphism of ttre
Biwabik Iron Formation, Mesabi Range, Minnesota. Minnesota
Geological Survey, Bulletin 45'Gole, M. J. (1980) Mineralogy and petrology of very-low-meta-
morphic grade Archean banded iron-formations, Weld Range'
Western Australia. American Mineralogist, 65' 8-25.
Gole, M. J. and Klein, C. (1931) Banded iron-formations through
much of Precambrian time. Journal of Geology, 89' 169-183
Haase, C. S. (1979) Metamorphic petrology of the Negaunee Iron
Formation, Marquette district, Northern Michigan. Ph.D.
thesis, Indiana UniversitY.James, H. L. (1954) Sedimentary facies of iron-formation. Eco-
nomic Geology, 49, 236-281.James, H. L. (1955) Regional metamorphism in the Precambrian
of northern Michigan, 66, 1455-1488.Klein, C. (1974) Greenalite, stilpnomelane, minn€sotaite, crocido-
lite and carbonates in a very low grade metamorphic Pre-
cambrian iron-formation. Canadian Mineralogist, 12, 475498.
Klein, C. (1978) Regional metamorphism of Proterozoic iron-for-
mation, Labrador Trough, Canada. American Mineralogist, 63,
898-912.Klein, C. and Fink, R. P. (1976) Petrology of the Sokoman Iron
Formation in the Howells River area, at the western edge of the
Labrador Trough. Economic Geology, 71, 45348'1.
Klein, C. and Bricker, O. P. (1977) Some aspects of the sedimen-
tary and diagenetic environment of Proterozoic banded iron-
formation. Economic Geology, 7 2, 145'l - l4'l 0'Kriewaldt, M. J. B. and Ryan, G' R. (1967) Pyramid, Western
Australia: Western Australia Geological Survey l:250,000, Geo-
logical Series Explanatory Notes'Lesher, C. M. (1978) Mineralogy and petrology of the Sokoman
Iron Formation near Ardua Lake, Quebec' Canadian Joumal of
Earth Sciences, 15, 480-500.Macl-eod, W. N. (1966) The Geology and iron deposits of the
Hamersley Range area, Westem Australia. Geological Survey
of Western Australia, Bulletin I 17'Milton, C. and Eugster, H. P. (1959) Mineral assemblages of the
Green River Formation. In P. H. Abelson, Ed', Researches in
Geochemistry, p. I l8-151. John Wiley and Sons, New York.
Papike, J. J., K. L. Cameron, and Baldwin, K. (1974) Amphiboles
and pyroxenes: characterization of other than quadrilateral
compon€nts and estimates of ferric iron from microprobe data.
Geological Society of America, Abstracts with Programs' 1053.
Smith, R. E. (1980) Recognizing the paths of metamorphic/me-
tasomatic fluids in a basic volcanic pile, Hamersley Basin, West-
ern Australia. International Geologic Congress, Paris, Abstract
Volume l, 93.Smith, R. E., Pedrix, J. L. and Parks, T. C. (1981) Burial meta-
morphism in the Hamersley Basin, Western Australia. Journal
of Petrology, in Press.Trendall, A. F. (1973) Varve cycles in the Weeli Wolli Formation
of the Precambrian Hamersley Group, W€stern Australia. Eco-
nomic Geology, 68, 1089-1098.Trendall, A. F. and Blockley, J. G. (1970) The iron-formations of
the Precambrian Hamersley Group, Western Australia. Geolog-
ical Survey of Western Australia, Bulletin I19.Zajac,l. S. (1974) The stratigraphy and mineralogy ofthe Soko-
rnan Formation in the Knob Lake area' Quebec and New-
foundland. Geological Survey ofCanada Bulletin 220.
Manuscript received, October 3, 1980;
acceptedfor publication, January 19, 1981'
