Hons Thesis

Variations in carbonate mineralogy and
mineral chemistry of the Griquatown
and upper Kuruman Iron Formations
and their possible controls
By:GordonAllanBallantyne
Supervisor:ProfessorHarialosTsikos
Thesis submitted in partial fulfilment of the requirements for degree of Bachelor of Science in
Honours in the Department of Geology, Rhodes University, Grahamstown

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Rhodes University G. Ballantyne 2016
Declaration
I declare that this thesis, titled “Variations in carbonate mineralogy and mineral chemistry of
the Griquatown and upper Kuruman Iron Formations and their possible controls” is my own
work, and sources of information from publications and other references is adequately cited.
The submission of this thesis is in compliance for the fulfilment of the Bachelor of Science in
Honours degree in the Department of Geology at Rhodes University, Grahamstown, South
Africa.
__________________________ __________________________
Name of candidate Signature
Signed on ________ day of __________________ 2016.

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“That's the thing about rocks--they don't break easily. When I held them,
I wanted to be like them-strong and steady, weathered but not broken.”
― Ellen Dreyer, The Glow Stone

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Table of Contents
Acknowledgements................................................................................................................. viii
Abstract......................................................................................................................................x
List of abbreviations.................................................................................................................. xi
Chapter 1. Introduction .............................................................................................................1
1.1 Regional Geology – The Transvaal Basin.........................................................................1
1.2 Geology of the Griqualand West Basin..........................................................................2
1.2.1 Ghaap Group (Griquatown and Kuruman iron formations) ........................................4
1.3 Aims and objectives .............................................................................................................5
2. Methodology..........................................................................................................................6
2.1 Sampling strategy.............................................................................................................6
3. Petrography ...........................................................................................................................8
Sample: Lo 01 (127.75m) .......................................................................................................9
Sample Lo 01 (127.75 m) .....................................................................................................10
Sample Lo 03 (145.70 m) .....................................................................................................11
Sample Lo 12 (249.50 m) .....................................................................................................12
Sample Lo 12 (249.50 m) .....................................................................................................13
Sample Lo 15 (284.70 m) .....................................................................................................14
Sample Lo 18 (320.90 m) .....................................................................................................15
Sample Lo 20 (345.45) .........................................................................................................16
Backscattered images ..........................................................................................................17
Evidence for a low diagenetic effect on the Griqualand West Basin ..................................19
4. Geochemistry.......................................................................................................................20
4.1 Introduction ...................................................................................................................20
4.2 Sampling strategy and analytical methods....................................................................20
4.3 Results............................................................................................................................22

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4.3.1 XRF ..........................................................................................................................22
4.3.2 Traces......................................................................................................................24
4.3.3 EPMA data...............................................................................................................27
4.3.3.1 Ankerite................................................................................................................27
4.3.3.2 Siderite.................................................................................................................28
4.3.4 Ratio relationships ..................................................................................................33
4.3.5 Summary.................................................................................................................37
5. Discussion.............................................................................................................................39
5.1 BIF research -the road thus far ......................................................................................39
5.2 Anoxygenic phototrophic Fe(II)-oxidation – a possible mechanism for BIF deposition?
..............................................................................................................................................40
..............................................................................................................................................41
5.3 A new look at the formation of the Griqualand West BIFs ...........................................41
5.3.1 Accommodating the geochemical data from this study.........................................41
5.4 Implications of this study...............................................................................................45
6.Conclusion.............................................................................................................................47
6.1 Significances of this study..............................................................................................47
6.2 Proposed future research ..............................................................................................47
7. References ...........................................................................................................................48
Appendices..................................................................................................................................i

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Table of Figures
FIGURE 1. DISTRIBUTION AND GROSS STRATIGRAPHIC SUBDIVISION OF THE TRANSVAAL SUPERGROUP IN THE STRUCTURAL BASINS OF
GRIQUALAND WEST AND TRANSVAAL. FROM BEUKES (1983)....................................................................................2
FIGURE 2. LOG OF THE LO SECTION EXAMINED IN THIS STUDY. RED TRIANGLES INDICATE POINTS OF SAMPLING. LOGS WERE PROVIDED
COURTESY OF PAUL OONK (2016), PHD STUDENT, RHODES UNIVERSITY, GEOLOGY DEPARTMENT....................................6
FIGURE 3. GREEN STAR INDICATES THE LOCALITY OF THE LO DRILL CORE IN CLOSE PROXIMITY TO THE KALAHARI MANGANESE FIELD
WITH THE LOCAL REGIONAL GEOLOGY. FROM TSIKOS (2015)......................................................................................7
FIGURE 4. SAMPLE LO 01 IN THE UPPER STRATIGRAPHY OF THE EXAMINED SECTION. OCCURRING MINERALS ARE: MAGNETITE, CHERT,
STILPNOMELANE AND CARBONATE. SCALE BAR AT THE TOP OF THE IMAGE......................................................................9
FIGURE 5. SAMPLE LO 01 FROM THE UPPER STRATIGRAPHY OF THE EXAMINED SECTION. SAME THIN SECTION AS PREVIOUS FIGURE
(FIGURE 4) NOT HOW QUICKLY THE MODAL ABUNDANCES OF THE MINERALS CHANGE. SCALE BAR AT THE TOP OF THE IMAGE.10
FIGURE 6. SAMPLE LO 03 FROM NEAR THE TOP OF THE EXAMINED STRATIGRAPHY. THIN SECTION CONTAINS CARBONATE, MAGNETITE,
STILPNOMELANE, QUARTZ AND HEMATITE. THIS WAS THE ONLY HEMATITE OBSERVED THROUGHOUT THE ENTIRE EXAMINED
SECTION. SCALE BAR AT THE TOP OF THE IMAGE......................................................................................................11
FIGURE 7. SAMPLE LO 12 IS SAMPLED AROUND MID-WAY IN THE STRATIGRAPHY OF THE EXAMINED SECTION. NOTE THE 'SEA' OF
CHERT. OTHER MINERALS INCLUDE MAGNETITE AND CARBONATE. SCALE BAR AT THE TOP OF THE IMAGE. ..........................12
FIGURE 8. SAMPLE LO 12 FROM AROUND MID-WAY IN THE STRATIGRAPHY. NOTE HOW THERE IS AN FE-SILICATE AND OXIDE RICH
BAND COMPARED TO A FE-SILICATE AND OXIDE POOR BAND LYING IN SUCCESSION TO ONE ANOTHER. MINERALS INCLUDE:
MAGNETITE, CARBONATE, CHERT, RIEBECKITE AND STILPNOMELANE. SCALE BAR AT THE TOP OF IMAGE..............................13
FIGURE 9. SAMPLE LO 15 IS FROM AROUND MID-WAY IN THE EEXAMINED STRATIGRAPHY. NOTE THE CHERT RICH MATRIX AND
SEEMINGLY HOW THE CARBONATES ARE 'FLOATING' ON IT. SCALE BAR IS AT THE TOP OF IMAGE........................................14
FIGURE 10. SAMPLE LO 18 IS STARTING TO RANSITION INTO THE KURUMAN IF. THE RIEBECKITE IS VERY WHISPERY AND FIBROUS.
OTHER MINERALS INCLUDE: CARBONATE, CHERT AND STILPNOMELANE. SCALE BAR AT THE TOP OF IMAGE..........................15
FIGURE 11. SAMPLE LO 20 IS NEAR THE BASE OF THE STRATIGRAPHY IN THE EXAMINED SECTION. NOTICE HOW COARSE THE RIEBECKITE
HAS BECOME. THERE IS ALSO A HIGH ABUNDANCE OF CALCITE HERE. OTHER MINERALS INCLUDE: CARBONATE AND MAGNETITE.
SCALE BAR IS AT THE TOP OF IMAGE. ....................................................................................................................16
FIGURE 12. (ON THE NEXT PAGE) MINERAL OCCURRENCES AND TEXTURAL RELATIONSHIPS OF THE GRIQUATOWN AND KURUMAN IRON
FORMATION. SCALE AT THE BOTTOM OF IMAGES. ...................................................................................................17
FIGURE 13. MAJOR OXIDE CONCENTRATIONS IN WT% FOR FE2O3, MN3O4, MGO AND CAO. NOTE THE SPIKE IN MN3O4 NEAR THE
TOP OF THE STRATIGRAPHY OF THE EXAMINED SECTION............................................................................................23
FIGURE 14. REE DIAGRAM NORMALISED AGAINST PAAS. THE PROFILE SHOWS A RELATIVELY FLAT SLOPE WITH A POSITIVE EU
ANOMALY THAT VARIES THROUGHOUT THE STRATIGRAPHY........................................................................................24
FIGURE 15. MN3O4 FROM XRF ANALYSIS PLOTTED AGAINST NI, CU AND CO TO SEE IF ANY OF THESE TRACE METALS ARE BEHAVING IN
A SIMILAR FASHION TO MN. ...............................................................................................................................25

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FIGURE 16. BA AND ZR APPEAR AS IF THEY ARE BEHAVING IN A SIMILAR FASHION TO MN. HOWEVER, BA LIKES ENTERING
CARBONATES SO THIS COULD HAVE TO DO WITH THE CARBONATE FRACTION AND ZR IS A KNOWN DETRITAL ELEMENT...........26
FIGURE 17. EPMA MAJOR OXIDE (FEO, MNO, MGO, CAO) COMPOSITIONAL VARIATIONS FOR ANKERITE AGAINST STRATIGRAPHY.
NOTE THE SPIKE OF INCREASED ABUNDANCE IN MN UP STRATIGRAPHY........................................................................30
FIGURE 18. EPMA SIDERITE MAJOR OXIDE (FEO, MNO, MGO, CAO) COMPOSITIONAL VARIATIONS AGAINST STRATIGRAPHY. NOTE
THE SPIKE OF INCREASED ABUNDANCE IN MN UP STRATIGRAPHY................................................................................32
FIGURE 19. FEO VERSUS MNO RELATIONSHIPS FOR ANKERITE A), AND SIDERITE B)................................................................34
FIGURE 20. UNEXPECTED ANTI-CORRELATION BETWEEN MGO AND MNO SUMMED VERSUS FEO FOR ANKERITE A), AND SIDERITE B).
NOTE HOW MUCH BETTER THE R2
ARE IN THIS RELATIONSHIP COMPARED TO THE MNO VERSUS FEO RELATIONSHIP. ...........35
FIGURE 21. JUXTAPOSITION OF ANKERITE AND SIDERITE MG + MN : FE RATIO PROFILES AGAINST STRATIGRAPHIC HEIGHT WITH BULK
ROCK MN:LOI FROM XRF ANALYSIS. DUE TO THE RELATIVELY LOW RESOLUTION OF THE DATA IN THIS STUDY THERE ARE ONLY A
FEW REFERENCE POINTS FOR THE EPMA DATA, IF THERE WERE MORE THE LIKELY HOOD OF THE THREE PROFILES LOOKING
SIMILAR WOULD BE GREATER..............................................................................................................................37
FIGURE 22. DIRECT MICROBIAL FE (II) OXIDATION VIA ANOXYGENIC FE(II)-OXIDIZING PHOTOTROPHY (MODIFIED FROM POSTH ET AL.,
2010A). ........................................................................................................................................................41
FIGURE 23. RED BARS REPRESENT AVERAGE VALUES FOR THE EON WHICH THEY REPRESENT, NAMELY: ARCHEAN, MID-PROTEROZOIC
AND NEOPROTEROZOIC-PHANEROZOIC. C. THE PRESENCE OF SIGNIFICANT MO ENRICHMENTS IN THE ARCHAEAN (ARROW)
SUGGESTS THE PRESENCE OF OXIDATIVE PROCESSES AT LEAST AS FAR BACK AS 2.5 GYR AGO. FROM LYONS ET AL., (2014). ..44

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List of Tables
TABLE 1. STRATIGRAPHY OF THE GRIQUALAND WEST TRANSVAAL SEQUENCE. NOTE THAT THE SHADED BOXES REFER TO THE
STRATIGRAPHY THAT WAS EXAMINED IN THIS STUDY. MODIFIED AFTER (TSIKOS, 1999; RAFUZA, 2015; FRYER, 2016) .........3
TABLE 2. IDENTIFIED MINERAL GROUPS IN THE GRIQUATOWN AND UPPER KURUMAN BIFS ARE PRESENTED IN THE TABLE BELOW.
RELATIVE ABUNDANCES ARE DESIGNATED BELOW (FORMAT ADAPTED FROM RAFUZA, 2015)............................................8
TABLE 3. PARAGENETIC SEQUENCE AND EXPECTED GRADE OF DIAGENESIS OF BIF MINERAL ASSEMBLAGES EXPECTED FOR THE
RESPECTIVE METAMORPHIC GRADES. MODIFIED AFTER KLEIN (1983) AND RAFUZA (2015) ...........................................19
TABLE 4. ANKERITE MAJOR-OXIDE CONCENTRATIONS WITH STRATIGRAPHIC HEIGHT FOR THE LO DRILL CORE. TOTALS ARE CALCULATED
BY THE SUM OF MAJOR ELEMENT CONCENTRATIONS EXCLUDING CO2.........................................................................29
TABLE 5 SIDERITE MAJOR-OXIDE CONCENTRATIONS WITH STRATIGRAPHIC HEIGHT FOR THE COLLECTED LO DRILL CORE SAMPLES.
TOTALS ARE CALCULATED BY THE SUM OF MAJOR ELEMENT CONCENTRATIONS EXCLUDING CO2.......................................31

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Acknowledgements
I would firstly like to thank my parent Allan and Leanne Ballantyne for their unconditional
love and support that they have bestowed upon me my entire life. It is thanks to them that I
have had all the essentials I have ever needed through their continued dedication as parents.
Thank you for always giving me courage and support when I am down and for instilling the
values I have today, I would not be the person I am if it wasn’t for parents like you.
I would like to thank South32 from the Hotazel Manganese mines for making the Lo drill core
available for this project. Your continued support of research will inspire a new generation of
researchers.
Thank you to the honours class of 2016 that has displayed an absolutely impeccable meaning
of fellowship throughout the year. It has been a real honour getting to know each one of you
personally. I will forever cherish the fond memories that were made and the fun times that
were had on the honours field trip.
I would also like to thank my best friend John de Bruyn who continually demonstrates what
it is to be a compassionate and considerate human being. Your support throughout the year
both in and out of the academic realm has been truly astounding. I hope that our friendship
will continue to grow and one-day lead to bigger endeavours in the working world.
Andrea, Chris and Thulani are thanked as part of the technical team for processing my
samples and making thin sections. As well as Deon for his expertise and guidance on the
probe. Your contribution to this thesis is great appreciated.
All the lecturing staff of the geology department are thanked for their continuous efforts
throughout my undergraduate years as well as honours year. None of the research and
knowledge instilled in us would be possible without you.
Lastly I would like to thank my supervisor, Professor Hari Tsikos for his contribution to this
thesis both physically and emotionally. Your passion and enthusiasm is something that has

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always inspired me. I would also like to thank you for your willingness and time that you have
given me and this project. It has been a privilege to be part of the PRIMOR team. I wish you,
your current and future research candidates all the best with the future research that lies
ahead.

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Abstract
Analytical techniques have improved immensely over the past few decades which
have allowed us to answer complex questions that were once not considered possible. Such
techniques have allowed the growth of research along with the ability to challenge current
theories. In this thesis rocks of the Transvaal Supergroup were examined from the Griqualand
West Basin in the Northern Cape province, South Africa with special focus on the Griquatown
and upper Kuruman iron formations. The aim of this study is to establish whether Mn and Fe
produce an antithetic relationship or not when entering the structure of carbonates (i.e
ankerite and siderite) as well as the mechanism of formation – diagenetic or primary?
Geochemical analyses were conducted via XRF on bulk rock powder samples, ICP-MS for trace
elements and finally electron probe micro-analyser (EPMA) to target specific carbonate
grains. The purpose of these analyses was to gain a better understanding of the high and
somewhat anomalous increase in manganese abundance that is apparent towards the top of
the stratigraphy with respect to the Mn/Fe ratio and attempt to gain insight on the formation
mechanism with regard to carbonates. There was no antithetic relationship between Mn and
Fe via, EPMA analyses, however it was found that the antithetic behaviour of these elements
when entering carbonates is best described by Mg summed with Mn versus Fe i.e.
Mg + Mn/Fe. The rare earth elements displayed a ‘flat’ profile suggesting a seawater
environment with a positive Eu excursions suggesting a hydrothermal source, however, these
excursions were not constantly of the same magnitude suggesting another component/s was
at play with mixing taking place. It appears that the atmosphere was not oxidative at the time
of formation of the studied BIFs according to the trace elements. Ba and Co did show slight
correlations with respect to Mn however, this could be attributed to other processes taking
place. It is proposed that the formation of carbonates is not a diagenetic one due to the
behaviour of the trace metals, i.e. Mn and Fe were in the sediment as oxides but rather
formed as carbonates via a primary process of precipitation out of the water column.
Keywords: banded iron formation, BIF, Northern Cape, South Africa, Griquatown, Kuruman,
carbonate, ankerite, siderite, water column, diagenetic.

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List of abbreviations
1. BIF – banded iron formation
2. Calcite – Cal
3. Carbonate – Cb
4. GOE – great oxidation event
5. Hematite – Hem
6. IF – iron formation
7. Magnetite – Mag
8. Quartz – Qtz
9. Riebeckite – Rbk
10. Stilpnomelane – Stp
11. PAAS – post Archean average shale

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Chapter 1. Introduction
1.1 Regional Geology – The Transvaal Basin
It is believed that the 2.65 to 2.05 Transvaal Supergroup, which is essentially a sequence
perched on a platform, consists of a package of chemical sedimentary rocks that developed
over a large part of the Kaapvaal Craton which is said to form the core of Southern Africa
(Beukes 1983, Moore et al, 2001; McCarthy and Rubidge, 2005). The Transvaal Supergroup is
developed in two spatially adjacent basins (Figure 1), the Transvaal Basin which is located in
the central part of the Kaapvaal Craton and the Griqualand West Basin which is located along
the western edge of the craton (Beukes and Gutzmer, 2008; Moore et al, 2001). The former
basin confines the Bushveld Complex towards the east, whereas the latter basin is confined
at the western Kaapvaal margin which extends sub-surface beneath younger Kalahari
deposits into southern Botswana (Beukes and Gutzmer, 2008; Moore et al, 2001). The focus
of this thesis will comprise of banded iron formations (BIFs) from the Griqualand West Basin
with particular emphasis on carbonate mineralogy with relation to manganese. From a
petrographic point of view, the stratigraphy that will be examined is of the Griquatown and
upper Kuruman iron formations. According to Knoll and Beukes (2009) the Griqualand West
Basin has been severely eroded and most likely covered the entire Kaapvaal Craton at the
time of formation and in some areas had a stratigraphic thickness up to 11Km.
The stratigraphy of the Transvaal Supergroup is diverse in a textural as well as chemical sense.
It contains a large variety of lithologies that demonstrate complex lateral and vertical facies
disparities across the basin (Fryer, 2016). An analysis of these facies changes show that the
individual formations of the Transvaal Supergroup were deposited in environments that
ranged from deep-water basinal settings right through into very shallow platform settings
above normal wave base (Klein and Beukes, 1989; Beukes and Klein, 1990; Klein, 2005; Beukes
and Gutzmer, 2008). This thesis as a whole draws on the idea of a shallowing up system as
well as plausible cycles of transgression and regression.

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This thesis will give particular attention and will only deal with the rocks of the Griqualand
West basin that host the Transvaal Supergroup in the Northern Cape Province, with specific
emphasis on its lower portion that hosts the Griquatown and Kuruman iron formations of the
Asbesheuwel Subgroup.
1.2 Geology of the Griqualand West Basin
As mentioned earlier, the Griqualand West basin is located along the western edge of the
Kaapvaal Craton. In Table 1 below, the stratigraphy of the basin is shown in a relatively simple
format.
Figure 1. Distribution and gross stratigraphic subdivision of the Transvaal Supergroup in the
structural basins of Griqualand West and Transvaal. From Beukes (1983).

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Table 1. Stratigraphy of the Griqualand West Transvaal Sequence. Note that the shaded boxes refer
to the stratigraphy that was examined in this study. Modified after (Tsikos, 1999; Rafuza, 2015;
Fryer, 2016)
Two major groups can be found within the Griqualand West sequence namely: The Ghaap
group, which is located in the lower stratigraphy, and the Postmasburg group which is located
in the upper stratigraphy (table 1 above). The Ghaap group will be discussed in the coming
sections especially with respect to the Asbesheuwels Subgroup with special emphasis placed
on the Griquatown and Kuruman iron formations.
Supergroup Group Subgroup Formation Lithology
Approx.
thickness
(m)
Transvaal
Postmasburg
Voëlwater
Mooidraai
Carbonate
± Chert
300
Hotazel BIFs, Mn Ore 250
Ongeluk Andesite 500
Makganyene Diamictite 50 - 100
Ghaap
Koegas
(2.415 Ga)
Nelani
Siliciclastic,
BIF + Mn Ore
240 - 600
Rooinekke
Naragas
Kwakwas
Doradale
Pannetjie
Asbesheuwels
Griquatown
Clastic
Textured BIF
200 - 300
Kuruman Microbanded
BIF
150 - 750

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1.2.1 Ghaap Group (Griquatown and Kuruman iron formations)
Since the early 70’s a considerable amount of work and research has gone into the research
of the Griqualand West Basin with regard to the sedimentology, stratigraphy, depositional
palaeo-environment and geochemistry of the Ghaap group which is located in the lower
stratigraphy of the Transvaal Supergroup (see table 1 above) (Beukes, 1983, 1987), Klein and
Beukes (1989), and Beukes and Klein (1990). This work was conducted in order to clarify
stratigraphic transitions between the lower Campbellrand Subgroup and Asbesheuwels
Subgroup as well as stratigraphic transitions between the Kuruman and Griquatown iron
formations that form part of the Asbesheuwels Subgroup. Beukes and Klein (1990) have
thoroughly described the transitions from the Kuruman to the overlying Griquatown iron
formation. The base of the transition is comprised of the Riries member, which following on
the relatively chert-rich underlying Groenwater member, is a chert-poor greenalite-siderite
rhythmite.
Beukes (1983, 1984) and Beukes and Klein (1990) reported in their research that the
Asbesheuwels subgroup (table 1 above) is divided into two texturally different iron
formations which form the subject of this thesis, namely, the lower microbanded 150-750m
thick Kuruman iron formation, and the clastic-textured orthochemical and allochemical 200-
300m thick Griquatown iron formation. However, the Kuruman and Griquatown iron
formations are hard to distinguish geochemically from one another even though they have
blatant textural differences between them and their genesis is therefore interpreted to be
under broadly similar palaeo-environmental conditions (Beukes and Klein, 1990).
Beukes and Klein (1989) and Klein and Beukes (1990) have described the development of the
Ghaap Group as an evolving depositional system. Drowning of the basin later led to the
deposition of the conformably overlying Kuruman iron formation, which is comprised of finely
laminated BIF which are mostly rich in magnetite and Fe-silicate minerals (see petrography
section). Following this, shallowing continued of the basin and ultimately logged the transition
to the Griquatown iron formation (Beukes and Klein, 1990).

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1.3 Aims and objectives
This study will be focussing on the Lo drill core from the Griqualand West basin of the
Transvaal Supergroup in the Northern Cape, South Africa. Essentially this Lo drill core
represents the Griquatown and upper most Kuruman iron formations of the Asbesheuwels
Subgroup. The main aim will be to examine the distribution of carbonates i.e. siderite and
ankerite in the selected samples and compare to previous work done to establish whether
results are reproducible basin wide. This will be achieved through petrographic XRF, ICP-MS,
and microprobe analysis. Ultimately, the author wishes to constrain whether the two
carbonates are entirely diagenetic or possibly primary in origin and if they are primary in
origin ascertain whether an active carbon cycle was in operation during the formation of BIF
in the Palaeoproterozoic ocean.

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2. Methodology
2.1 Sampling strategy
A single drill core was sourced from London farm, Kalahari Manganese field, Hotazel
Manganese mines, South32 for this study (see log below in Figure 2). This specific drill core is
designated as ‘Lo’. It was sourced within 10s of kms of other drill cores from past and ongoing
studies.
GriquatownFmKurumanFm
Transition to Kuruman
Figure 2. Log of the Lo section examined in this study. Red triangles indicate points of sampling. Logs
were provided courtesy of Paul Oonk (2016), PhD student, Rhodes University, Geology Department.

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The green star in Figure 3 below shows the location of where the Lo drill core originates from.
Regional geology is also shown.
Figure 3. Green star indicates the locality of the Lo drill core in close proximity to the
Kalahari Manganese Field with the local regional geology. From Tsikos (2015).

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3. Petrography
According to Rafuza (2015), many of the Archean-Palaeoproterozoic iron formations studied
around the world through the decades, are suggested to have undergone only very low grade
metamorphism. These include those of the Transvaal Supergroup and Hamersley Group of
Australia. In areas where BIF is preserved it most commonly contains mineral assemblages
that barely enter the low grade greenschist facies of metamorphism which are typical of late
(burial) diagenesis (Klein 1983, 2005). Table 2 below documents the minerals identified in the
examined section.
Table 2. Identified mineral groups in the Griquatown and upper Kuruman BIFs are presented in the
table below. Relative abundances are designated below (format adapted from Rafuza, 2015).
Key: XXX: Synonymous to abundant component (>20%)
XX: Common component (>5%)
X: Trace component
This chapter deals primarily with the examination of the mineral assemblages in a
petrographic context studied under transmitted light.
Mineral Group
Mineral Formula Griquatown Kuruman
Carbonates
Ankerite [Ca(Fe2+
,Mg,Mn)(CO3)2] XXX XX
Siderite (Fe2+
(CO3) XXX XX
Calcite CaCO3 X X
Oxides Magnetite [Fe2+
Fe2
3+
O4] XX XXX
Hematite [Fe2
3+
O3] X X
Silicates Greenalite [(Fe2+
,Mg)6Si4O10(OH)8] X X
Minnesotaite (Fe2+
,Mg)2Si4O10(OH)2 X XX
Stilpnomelane [K0.6(Mg,Fe2+
,Fe3+
)6Si8Al
(O,OH)27.2-4H20] XXX XX
Riebeckite Na2(Fe2+
3Fe3+
2)Si8O22(OH)2 XXX XXX
Chert (Quartz) SiO2 XXX XXX
Sulphides Pyrite FeS2 X X

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Sample: Lo 01 (127.75m)
Sample Lo 1 contains magnetite, carbonate, chert and stilpnomelane. The relative modal
abundance of these minerals are: magnetite ~35%, carbonate ~25%, chert ~25% and
stilpnomelane ~15%. This sample is relatively fine grained. The magnetite grains are sub-
hedral to euhedral in shape and appear to be randomly distributed with no particular
orientation. They range in size from 200 to 400 µm. The carbonate fraction in this sample is
very fine grained (~100 µm) and appears to be associated with the Fe-silicates and oxides
which is made up of stilpnomelane and magnetite respectively. Stilpnomelane occurs as
reddish brown masses. All the mineralogy appears to ‘float’ on a chert matrix. See Figure 4
below.
Mag
Stp
Cb
Chert
Figure 4. Sample Lo 01 in the upper stratigraphy of the examined section. Occurring
minerals are: magnetite, chert, stilpnomelane and carbonate. Scale bar at the top
of the image.

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Sample Lo 01 (127.75 m)
This is the same sample as the previous one. Note the variability in the same sample between
two consecutive bands. Sample Lo 1 contains: carbonate, chert, magnetite and trace amounts
of Stilpnomelane. The relative modal abundances of these minerals are: carbonate ~50%,
chert ~47%, magnetite ~2%, and stilpnomelane ≪1%. This sample contains a much higher
carbonate fraction (~double the amount of carbonate) and very little Fe- silicates and oxides.
The carbonates range in size (~100 to 200 µm) and appear to be sub-hedral in shape.
Magnetite grains have a similar size range to that of the carbonates (~100 to 200 µm) and
appear to be euhedral in shape. Stilpnomelane occurs in trace amounts and plays an
insignificant role with respect to the mineralogy in this band of the thin section. This is another
example of where all the mineralogy appears to be ‘floating’ on a chert rich matrix. See Figure
5 below.
Cb
Mag
Chert
Stp
Figure 5. Sample Lo 01 from the upper stratigraphy of the examined section. Same
thin section as previous figure (Figure 4) not how quickly the modal abundances of
the minerals change. Scale bar at the top of the image.

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Sample Lo 03 (145.70 m)
Sample Lo 03 contains stilpnomelane, magnetite, carbonate, quartz and hematite. The
relative modal abundances of these minerals are: stilpnomelane ~45%. magnetite ~25%,
carbonate ~15%, quartz 14% and hematite <<1%. Stilpnomelane occurs as relatively well
defined grain boundaries, it has coherent anhedral grains that are yellowish red in colour and
the grain range in size from ~50 to 250 µm. Magnetite grains exhibit a sub-hedral grain shape
and appear to be randomly orientated. The carbonates in this sample are relatively large (~50
to 20 µm), but not as abundant as the previous sample before this (Lo 01). This sample has
quartz in it rather than chert which means it is slightly coarser grained. This was the only thin
section in the entire section studied to contain hematite, however, only in trace amounts. The
hematite occurs as bright red grains but look more like specks in thin section. See Figure 6
below.
Stp
Mag
Hem
Cb
Qtz
Figure 6. Sample Lo 03 from near the top of the examined stratigraphy. Thin
section contains carbonate, magnetite, stilpnomelane, quartz and hematite. This
was the only hematite observed throughout the entire examined section. Scale
bar at the top of the image.

P a g e | 12
Sample Lo 12 (249.50 m)
Sample Lo 12 contains chert, carbonate and magnetite. The relative modal abundances of
these minerals are: chert ~95% carbonate ~3%, magnetite ~2%. This sample contains a
considerably large amount of chert making it a matrix rich rock. Note that this thin section
has no Fe-silicates and a minimal amount of oxides. The carbonates appear to be sub-hedral
in shape and range from 100 to 200 µm in size. These grains appear to be at random and do
not have any preferred orientation. The magnetite grains seem to be sub to euhedral in shape
in have a size of ~100 µm. See Figure 7 below.
Chert
CB
Mag
Figure 7. Sample Lo 12 is sampled around mid-way in the stratigraphy of the
examined section. Note the 'sea' of chert. Other minerals include magnetite and
carbonate. Scale bar at the top of the image.

P a g e | 13
Sample Lo 12 (249.50 m)
This is the same sample as the previous one. Note the variability in the same sample between
two consecutive bands. This sample (Lo 12) contains: chert, magnetite, carbonate,
stilpnomelane, riebeckite. The relative modal abundances of these minerals are: chert ~35%,
magnetite ~30%, carbonate ~25%, stilpnomelane ~8%, riebeckite ~2%. Here banding can
be seen. The oxides and Fe-silicates are all together i.e. magnetite and stilpnomelane as well
as riebeckite with some chert, while the carbonates and remaining chert are together in the
next consecutive band. The magnetite occurs as sub-hedral grains and ranges from 50 to 400
µm in size. Stilpnomelane occurs in what appears to be aggregated masses and appears to be
closely associated with the magnetite. Riebeckite grains appear to be bladed in crystal habit,
are highly pleochroic and appear to be overprinting stilpnomelane. Average riebeckite size is
~200 µm. See Figure 8 below.
Mag
Stp
Rbk
Chert
Cb
Figure 8. Sample Lo 12 from around mid-way in the stratigraphy. Note how there
is an Fe-silicate and oxide rich band compared to a Fe-silicate and oxide poor
band lying in succession to one another. Minerals include: magnetite, carbonate,
chert, riebeckite and stilpnomelane. Scale bar at the top of image.

P a g e | 14
Sample Lo 15 (284.70 m)
Sample Lo 15 contains chert, quartz and carbonate. The relative modal abundances of these
minerals are: chert ~43%, quartz ~18%, carbonate ~38%, magnetite <<1%. With a
considerable amount of chert, this section of rock is matrix supported. A small pocket of
quartz is present with grains averaging ~30 to 40 µm. Carbonate grains are large relative to
the surrounding mineralogy with ankerite grains averaging ~200 µm and are euhedral in
shape. It appears that the ankerite is being replaced/altered by another mineral. EPMA
analyses conducted on these carbonates (both ankerite and siderite) suggest that no
replacement or alteration has taken place and the analyses returned a good reading for
carbonate. One small grain of anhedral magnetite can be seen, it is approximately 10 µm in
size. See Figure 9 below.
Qtz
Cb
Chert
Figure 9. Sample Lo 15 is from around mid-way in the eexamined stratigraphy.
Note the chert rich matrix and seemingly how the carbonates are 'floating' on it.
Scale bar is at the top of image.

P a g e | 15
Sample Lo 18 (320.90 m)
Sample Lo 18 contains chert, quartz and carbonate. The relative modal abundances of these
minerals are: chert ~65%, riebeckite ~21%, carbonate ~13%, stilpnomelane <<1%. With a
considerable amount of chert, this section of rock is matrix supported. The dominant chert
matrix gives the appearance that all the other minerals are ‘floating’ on the matrix. Riebeckite
in this section of the rock appears to be whispery/fibrous almost having the texture of a
feather. Riebeckite crystals range from ~100 to 200 µm and are a deep blue colour in PPL.
Carbonates are euhedral in shape and are ~100 µm in size. Some of the carbonates appear
to be zoned. There is a small amount of stilpnomelane that appears to occur in an aggregated
mass, however, there is hardly enough to affect the modal abundances. See Figure 10 below.
Chert
Stp
Rbk
Cb
Figure 10. Sample Lo 18 is starting to ransition into the Kuruman IF. The riebeckite is
very whispery and fibrous. Other minerals include: carbonate, chert and
stilpnomelane. Scale bar at the top of image.

P a g e | 16
Sample Lo 20 (345.45)
Sample Lo 20 contains riebeckite, calcite, carbonate and magnetite. The relative modal
abundances of these minerals are: riebeckite ~55%, carbonate ~25%, calcite ~15%,
magnetite ~15%. Riebeckite displays a blade like crystal habit that is randomly orientated.
The riebeckite seems to be overprinting all the other mineralogy except the magnetite.
Riebeckite is strongly pleochroic and has a high birefringence. The riebeckite crystals range
from ~100 to 600 µm. This sample has a large amount of calcite, which is relatively rare for
this package of rocks. Due to the chemical similarity of carbonates i.e. ankerite and siderite
relative to calcite it makes it difficult to tell them apart, therefore this was done using EPMA
analysis. Magnetite consists of relatively finer grains (~50 to 200 µm) and are euhedral in
shape. See Figure 11 below.
Rbk
Mag
Cb
Cal
Figure 11. Sample Lo 20 is near the base of the stratigraphy in the examined
section. Notice how coarse the riebeckite has become. There is also a high
abundance of calcite here. Other minerals include: carbonate and magnetite.
Scale bar is at the top of image.

P a g e | 17
Backscattered images
A) Major contrast between ankerite and magnetite
B) Large ankerite (darker grains) with smaller siderites (bright grains) showing
coexistence of the two carbonates
C) Ankerite grains which have a euhedral shape with calcite which is anhedral in shape.
Riebeckite it present as whispery fibres.
D) Coexistence of ankerite and siderite with what looks like could be a replacement
texture?
E) Ankerite with minnesotaite, notice the very characteristic bow-tie texture of the
minnesotaite.
F) Ankerite banding in the presence of minnesotaite.
Figure 12. (on the next page) Mineral occurrences and textural relationships of the Griquatown and
Kuruman iron formation. Scale at the bottom of images.

P a g e | 18
A B
C D
E F

P a g e | 19
Evidence for a low diagenetic effect on the Griqualand West Basin
In the context of this study the degree of diagenesis and/or metamorphism that has taken
place is important. The less diagenesis and/or metamorphism that has taken place the more
confidently the original primary environment can be deciphered. According to Rafuza (2015),
iron silicates are particularly useful as indicators of metamorphic grade, as opposed to Fe-
oxides and carbonates. Klein (1983) studied various iron formations around the world which
had been exposed to various degrees of metamorphism and was able to determine the
paragenetic sequence of these iron formations and listed them in order of increasing grades
of metamorphism (Table 3). The prograde metamorphism of iron-formations produces
sequentially Fe-amphiboles, then Fe-pyroxenes, and finally (at highest grade) Fe-olivine-
containing assemblages. Such metamorphic reactions are isochemical except for
decarbonation and dehydration (Klein, 2005).
According to Klein’s (2005) paragenetic sequence as well as the observed mineralogy studied
in this thesis, these BIFs have undergone very little metamorphism.
Low
Siderite
Riebeckite
Greenalite
"Fe3O4∙H2O" magnetite
Grade of Metamorphism
Medium High
Diagenetic Biotite
Zone
Garnet
Zone
Staurolite-Kyanite
and Kyanite Zone
Siliminite Zone
Early Late
Chert Quartz
Stilpnomelane
Talc - Minnesotaite
Dolomite - Ankerite
Calcite
Table 3. Paragenetic sequence and expected grade of diagenesis of BIF mineral assemblages
expected for the respective metamorphic grades. Modified after Klein (1983) and Rafuza (2015)

P a g e | 20
4. Geochemistry
4.1 Introduction
Tsikos et al., (2010) suggested that older BIFs in the lower Transvaal Supergroup (i.e. the
Griquatown and Kuruman iron formations) may very well record a progressive enrichment in
contained Mn as a precursor signal to the major Mn anomaly in the Hotazel strata.
Work conducted by Fryer (2016) and Rafuza (2015) was carried out based on the above
suggestion of Tsikos et al. (2010) of Mn abundances in the Griquatown and upper Kuruman
BIF from drillcore intersections similar to the Lo core studied here. The results from these two
studies both indeed show a Mn enrichment recorded in the upper Griquatown BIF, although
Mn is hosted entirely within the carbonate fraction of the rock. This study effectively aims to
further contribute to the work of Fryer (2015) and Rafuza (2015) by understanding the
significance of the Mn signal, in light of prevailing models that interpret BIF carbonates as
entirely diagenetic in origin. Furthermore, to whether geochemical data is reproducible
throughout the Griqualand West basin. For these reasons, the majority of samples that were
examined petrographically in the previous chapter were also analysed geochemically via
three methods. The first being major element analyses by X-ray fluorescence (XRF) of bulk
rock sample powders (at Stellenbosch University). Secondly, trace elements were analysed
via ICP-MS where they were scrutinised on REE plots and depth profiles. Lastly, microprobe
analyses of the two carbonate species (conducted in house using the Electron Probe
Microanalyser) namely ankerite and siderite; Interpretations will be made by focussing on the
key mineral-specific elemental oxide abundances together with the trace elements and their
distribution across stratigraphy, together with the petrographic and mineralogical
observations.
4.2 Sampling strategy and analytical methods
8 carbon coated thin sections were chosen from the section studied here in order to gain
analytical results in a broad sense for the examined stratigraphy in this thesis. These thin
sections were used in the EPMA analysis. As an additional aid to using the microscope in
determining the mineralogical make-up of the carbonate fraction in the chosen thin sections,
a combination of EPMA data along with accompanying back-scattered images was used to

P a g e | 21
identify coexisting carbonates from one another. As mentioned earlier, the goal of this
exercise was to capture and cross-examine any stratigraphic signal in manganese distribution
with respect to ankerite and siderite or both if they are in coexistence with one another as it
was with the findings of Fryer (2016) and Rafuza (2015). Rafuza (2015) outlined four common
obstacles that hindered the achievement of optimum data towards the above goal, these
obstacles were also present in this study and can be listed as the following:
 occasionally substandard polishing and coating some samples;
 the very fine-grained nature of the carbonate grains, especially with regards to
siderite;
 mixed analytical data, particularly through the detection of Si related to the
groundmass surrounding carbonate grains;
 the occurrence of only a single carbonate (specifically ankerite) in many sections.
EPMA data as well as those of XRF and ICP-MS were used with objective of revealing any
broad trends in manganese distribution across stratigraphy. With respect to the EPMA, XRF
and ICP-MS data, these were all used and in conjunction with one another and an attempt
was made from all angles in as much detail as possible with the data on hand to establish the
stratigraphic and mineral-specific behaviour of manganese and other carbonate associated
components (FeO, MgO and CaO) in the examined thin sections and bulk-rock powders.

P a g e | 22
4.3 Results
4.3.1 XRF
The method of X-ray fluorescence (XRF) was employed in order to establish quantitatively the
wt% via Fe ore fusion of the manganese present as well as the other carbonate associated
components (i.e. Fe2O3, MgO and CaO from the bulk-rock powders obtained from the Lo
drillcore. This analysis was conducted by Stellenbosch University in Stellenbosch, South Africa.
Table 4 provides the major elements weight percents (as oxides) for the XRF analysis.
From the plots of Figure 13, it is evident that Fe2O3, MgO and CaO all show an overall increase
upwards in stratigraphy. Mn3O4 values range from 0.07-5.04 wt% with an average of 0.69
wt%. Interestingly, Mn3O4 specifically shows relatively low values at the base of the examined
section (averaging around 0.4 wt%) and appears to continue to gradually increase up section,
finally reaching a value of circa 1 wt% near the top. A distinct spike of Mn3O4 is present at
circa 128m depth below surface. Both Fryer (2016) and Rafuza (2015) report this spike in
Mn3O4 and record a two-prong excursion towards high Mn3O4 separated by a plateau of lower
values. This is difficult to see here because of the relatively low resolution of the data
collected.
Fe2O3 exhibits a similar profile to Mn3O4 at the start in the lower stratigraphy, increasing
gradually upwards until about halfway through the examined section. The values then appear
to decrease temporarily and then increase again towards the top. Values of the Fe2O3 XRF
analysis range from 18.01-52.70 wt%, with an average of 36.65 wt%. Highest Fe2O3 value
(52.70 wt%) occurs circa midway through the section at circa 237 m. The MgO values of the
XRF analysis range from 1.52-8.56 wt%, with an average of 3.56 wt%. The stratigraphic profile
shows a characteristic “zig zag” pattern of sharply fluctuating values over short stratigraphic
intervals, with distinct MgO minima towards the base of the examined section. Like the Mn3O4
profile, MgO also records an increase stratigraphically upwards, however, this is broadly
speaking and appears to be only a very slight increase. The highest MgO (8.56 wt%) is
recorded circa three quarters of the way up the stratigraphy at circa 176m. CaO appears to
be pointing to two-prong excursion towards high CaO separated by a plateau of lowers values.
However, CaO does not display any obvious stratigraphic trend but varies rather greatly on
either side of the plateau. CaO values range from 0.35-15.96 wt%, with an average of 4.07

P a g e | 23
wt%. Scrutinising the data in Figure 13 it would appear that overall the stratigraphic patterns
of increasing Mn3O4, MgO and broadly speaking Fe2O3 suggest a broad modal increase up
section in the carbonate component, which according to Rafuza (2015) would account for the
increased manganese in the rocks.
110
160
210
260
310
360
15 25 35 45 55
Depth(m)
Fe2O3(wt%)
110
160
210
260
310
360
0 2 4 6
Depth(m)
Mn3O4(wt%)
110
160
210
260
310
360
1 3 5 7 9
Depth(m)
MgO(wt%)
110
160
210
260
310
360
0 5 10 15 20
Depth(m)
CaO(wt%)
Figure 13. Major oxide concentrations in wt% for Fe2O3, Mn3O4, MgO and CaO. Note the spike in
Mn3O4 near the top of the stratigraphy of the examined section.

P a g e | 24
4.3.2 Traces
In addition to the XRF data presented in the foregoing section, trace elements were also
analysed from the bulk rock powders using ICP-MS at Stellenbosch University, Western Cape
province, South Africa. Trace elements are present in concentrations of <0.1% and are
expressed in ppm. Trace elements are also useful in understanding the environment of
formation and this case Rare Earth Element (REE) plots were used to further understand the
environment of the Griquatown and upper Kuruman BIFs. REE diagrams are a useful way of
displaying data because the REE behave geochemically in a similarly. In Figure 14 below are
the REE plots for the rocks examined in the section in this study.
All REE were normalised to PAAS, PAAS values from Cai (2010), in order to establish how
enriched or depleted a certain element is. In this case Figure 14 above shows that Eu has a
positive anomaly, therefore it is enriched relative to the other REEs. This particular profile is
also relatively flat and highly suggestive of a seawater environment. After quantifying Eu by a
ratio of where it is and where it should be, it was found on average to be 1.16 times higher
than it should be while the highest individual case was 2.4 times higher. A positive Eu anomaly
of this sort is indicative of a hydrothermal origin. It would be expected that the Eu anomaly
be constant throughout the stratigraphy if it were a single component system, however, this
0,01
0,10
1,00
10,00
La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
PAAS-Normalised REE diagram
Figure 14. REE diagram normalised against PAAS. The profile shows a relatively flat slope with a
positive Eu anomaly that varies throughout the stratigraphy.

P a g e | 25
is not the case. Therefore, it is evident that a pure hydrothermal origin is not at play here and
the system has an additional component/s and depending on how they are mixed then
determines the observed variations in the Eu anomaly.
Trace metals were also used in order to try and establish a relationship with manganese. This
was done by comparison using depth profiles against Mn3O4 from the XRF bulk rock powder
analysis. Geochemical analyses conducted on manganese nodules in the modern ocean will
almost certainly display an enrichment in trace metals such as Ni, Cu and Co. These
enrichments are caused when manganese oxides precipitate and essentially behave as
‘garbage bins’ by absorbing a lot of other trace metals as well as adsorbing trace metals to
110
160
210
260
310
360
0 2 4 6
Depth(m)
Mn3O4(wt%)
110
160
210
260
310
360
0 5 10 15 20
Depth(m)
Ni(ppm)
110
160
210
260
310
360
0 100 200 300 400
Depth(m)
Cu(ppm)
110
160
210
260
310
360
0 5 10
Depth(m)
Co(ppm)
Figure 15. Mn3O4 from XRF analysis plotted against Ni, Cu and Co to see if any of
these trace metals are behaving in a similar fashion to Mn.

P a g e | 26
the surface via ionic bonding. Figure 15 above shows Mn3O4 and the concentrations of Ni, Cu
and Co stratigraphically.
From figure 15 above it is evident that Ni and Cu have no relationship with Mn which shows
that they weren’t acting in concert. The only trace metal to show an increase up stratigraphy
with Mn is Co. Another mechanism is possibly at play here because it is highly improbable
that Co gets adsorbed to the surface otherwise similar patterns would be observed with Ni
and Cu as is observed in the modern ocean. Below in figure 16 are the trace elements Ba and
Zr.
From Figure 16 above it is also apparent that there is an increase in Ba and Zr up stratigraphy.
It is apparent that Ba is behaving very similarly to Co (Figures 16 & 17). Ba is a trace element
that is commonly found in carbonates thus, it is likely to be associated with the carbonate
fraction of the rocks and therefore could have an association with Mn which is not yet well
documented and understood. Zr on the other hand is a known detrital trace element that also
seems to be increasing up stratigraphy like Mn. This increase of Zr is more likely to be
suggesting an increased detrital fraction and therefore possible shallowing of the ocean
environment. The other above mentioned traces (Co and Ba) could also therefore be
associated with an increased detrital fraction and not necessarily be associated with the Mn.
110
160
210
260
310
360
0 20 40 60 80
Depth(m)
Zr(ppm)
110
160
210
260
310
360
0 50 100
Depth(m)
Ba(ppm)
Figure 16. Ba and Zr appear as if they are behaving in a similar fashion to Mn.
However, Ba likes entering carbonates so this could have to do with the
carbonate fraction and Zr is a known detrital element.

P a g e | 27
4.3.3 EPMA data
The trace data presented in the foregoing section is now followed by EPMA data in which
individual ankerite and siderite grains were targeted in order to understand their mineral
chemistry through the stratigraphy. This was done with the intention of establishing
distinctive geochemical patterns, if any, which when used in conjunction with the XRF data
and preceding petrography may help clarify the potential cogenetic origin of the carbonates
and confine their formation to a specific environment. Due to ankerite’s relatively high
abundance in the examined section compared to siderite, ankerite will be dealt with first then
siderite will follow immediately thereafter. Data that was considered pure for analysis were
averaged for the appropriate elemental oxide (i.e. MnO, FeO, MgO and CaO). It must be
reiterated that the data for this study is of relatively low resolution compared to previous
work done (e.g. Fryer, 2016; Rafuza, 2015).
4.3.3.1 Ankerite
EPMA data for ankerite are shown in Table 4 and plotted in Figure 17. Data which is presented
is averaged from multiple analyses of ankerite grains in a given sample. Values for FeO exhibit
a profile with generally higher but variable values over most of the section, however,
stratigraphically these values suddenly decrease at the top. FeO ranges from 14.73-24.10
wt%, with an average of 20.64 wt%. MgO values vary highly throughout the stratigraphy with
a “zig zag” pattern, ranging from 6.43-12.95, with an average of 8.34 wt%. CaO has a much
smaller range of 28.14-30.13 wt%, with an average of 28.98 wt%.
MnO in ankerite overall reveals a relatively contrasting profile when compared to the other
carbonate oxide components with values increasing generally with stratigraphic height. In
absolute terms of the data, the MnO content of the data ranges substantially, from 0.48-3.98
wt%, with an average of 1.49 wt%. However, with this overall increasing upward trend there
is a bulge of MnO in ankerite near the base of the examined section which then decreases
higher up in the stratigraphy and then increases again to a maximum at the top of the
examined section. This sort of behaviour suggests that MnO in ankerite does not become
progressively richer up section because stratigraphically at lower levels high values are
recorded. The study of Rafuza (2015) which had a much higher resolution data set suggest
that high Mn “spikes” may be masked in bulk rock or in this case XRF geochemical data (see

P a g e | 28
by comparison the XRF profile for Mn in the previous section) if the modal abundance of such
ankerite in respective samples is relatively low.
4.3.3.2 Siderite
EPMA data for siderite are shown in Table 5 and plotted in Figure 18, as was done with the
ankerite data above. Data which is presented is averaged from multiple analyses of siderite
grains in a given sample. With regard to the profiles for siderite, they are not as richly
populated with data as compared to those with ankerite, due to siderite been
characteristically finer grained and less abundant in the examined rocks as was also noted by
Rafuza (2015). This made obtaining a large population of data for siderite difficult and
therefore practically not possible.
It appears that certain parallels can be drawn of the profiles for siderite chemistry of major
oxide stratigraphic variations to those presented for ankerite. Values for MgO and CaO depict
like for ankerite a similar variable stratigraphic pattern. It may however be argued that
siderite starts off quite calcic in the lower stratigraphy, decreases in calcic content when
moving up stratigraphy then ends off very calcic at the top again. Ankerite on the other hand
starts off with a low calcic content and ends with a relatively low calcic content. In absolute
terms of the data, Mgo ranges from 5.27-6.79 wt%, with an average of 6.26 wt%; while CaO
ranges from 0.43-1.00 wt%, with an average of 0.66 wt%.
FeO values exhibit a profile which appear to have high values at the lower sections of the
stratigraphy as well as at the mid sections which then gradually curve away towards lower
values at the top of the stratigraphy. In absolute terms, the FeO content ranges from 50.01-
58.27 wt%, with an average of 54.85 wt%. With regard to MnO, it displays a similar profile to
ankerite, however, it starts at moderate values at the base of the stratigraphy which then
curves towards lower values at the mid sections and then curves back out again to a maximum
at the top of the stratigraphy. The most likely cause of this profile is due to the lack of
measurable siderite grains in the basal part of the section. Therefore, the siderite grains do
not resolve a high MnO peak as it does for the corresponding ankerite profile. In terms of
absolute values for siderite there appears to be a substantially large range from 0.84-6.05
wt%, with an average of 2.29 wt%.

P a g e | 29
Table 4. Ankerite major-oxide concentrations with stratigraphic height for the Lo drill core. Totals are
calculated by the sum of major element concentrations excluding CO2.
Ankerite major oxide concentrations (wt%)
Sample
Stratigraphic
height (m) MgO MnO FeO CaO Totals
Lo 01 127,75 8,06 3,98 18,62 28,14 58,80
Lo 03 145,7 12,95 1,14 14,73 30,13 58,95
Lo 07 191,15 6,78 0,48 24,10 29,10 60,45
Lo 12 249,5 8,25 0,64 21,72 29,27 59,88
Lo 15 284,7 9,42 1,60 18,46 28,21 57,69
Lo 18 320,9 6,43 1,76 23,24 28,59 60,02
Lo 20 345,45 7,66 1,58 20,87 29,79 59,90
Lo 21 355,6 7,14 0,71 23,39 28,58 59,82

P a g e | 30
110
160
210
260
310
360
14 19 24 29
Depth(m) FeO(wt%)
110
160
210
260
310
360
0 1 2 3 4
Depth(m)
MnO(wt%)
110
160
210
260
310
360
6 8 10 12 14
Depth(m)
MgO(wt%)
110
160
210
260
310
360
28 29 30 31
Depth(m)
CaO(wt%)
Figure 17. EPMA major oxide (FeO, MnO, MgO, CaO) compositional variations for ankerite against
stratigraphy. Note the spike of increased abundance in Mn up stratigraphy.

P a g e | 31
Table 5 Siderite major-oxide concentrations with stratigraphic height for the collected Lo drill core
samples. Totals are calculated by the sum of major element concentrations excluding CO2.
Siderite major oxide concentrations (wt%)
Sample
Stratigraphic
(m) MgO MnO FeO CaO Totals
Lo 01 127,75 6,30 6,05 50,01 0,78 63,14
Lo 03 145,7 6,79 1,81 55,78 0,73 65,11
Lo 07 191,15 5,27 0,84 58,27 0,46 64,84
Lo 12 249,5 6,30 0,99 56,75 0,55 64,59
Lo 15 284,7 6,55 1,37 53,29 0,43 61,65
Lo 20 345,45 6,34 2,64 54,98 1,00 64,96

P a g e | 32
110
160
210
260
310
360
48 50 52 54 56 58 60
Depth(m)
FeO(wt%)
110
160
210
260
310
360
0 2 4 6 8
Depth(m)
MnO(wt%)
110
160
210
260
310
360
5 6 7
Depth(m)
MgO(wt%)
110
160
210
260
310
360
0 1
Depth(m)
CaO(wt%)
Figure 18. EPMA siderite major oxide (FeO, MnO, MgO, CaO) compositional variations against
stratigraphy. Note the spike of increased abundance in Mn up stratigraphy.

P a g e | 33
4.3.4 Ratio relationships
From the XRF data presented in the preceding sections it is evident that it is useful in terms
of the studied intersection (i.e. the Griquatown and upper Kuruman BIFs) to provide a simple
technique in terms of analysing the behaviour of Mn in a stratigraphic sense. It appears that
Mn is hosted exclusively in the carbonate fraction of the rocks, as was also suggested by
Rafuza (2015) where speciation analyses were conducted on the rocks. If this is the case, then
it is assumed that the XRF data obtained here with respect to manganese comes from the
carbonate fraction of the rocks and may provide a meaningful record of Mn distribution in
the examined section of this study. The further use of microprobe application on the
individual carbonates, i.e. ankerite and siderite, is able to quantify and give further support
to the XRF results on a more targeted and precise mineral specific level. For these data (i.e
XRF and mineral chemical) to have any relevance they must be plotted in such a way that they
are assessed fully. This can be achieved through the use of ratio diagrams where the relative
abundances for Mn and Fe contained in the carbonates (ankerite and siderite) as well as bulk
carbonate from XRF is depicted. This may become evident through the respective binary plots
of Figure 19 as both ankerite and siderite display a broadly antithetic behaviour between Mn
and Fe. Ratio diagrams are also depicted in a stratigraphic ratio profile form in Figure 21.

P a g e | 34
From the above binary plots, it is evident that MnO and FeO are behaving in a dissimilar way
as the Mn/Fe ratio for ankerite hardly displays any relationship and therefore do not anti-
correlate with one another. Siderite on the other hand shows more evidence of an antithetic
relationship however it is not strong enough to draw any concrete conclusions. This will be
discussed in greater detail in the discussion. Further possible relationships were explored in
order to establish which of the major oxide species best display an antithetic relationship. It
is apparent that the best antithetic behaviour can be observed by the sum of MnO and MgO
versus FeO. Figure 20 below shows a binary plot of this antithetic relationship.
R² = 0,1313
0
1
1
2
2
3
3
4
4
5
14 16 18 20 22 24 26
MnO(wt%)
FeO(wt%)
R² = 0,753
0
1
2
3
4
5
6
7
49 51 53 55 57 59
MnO(wt%)
FeO(wt%)
A
B
Figure 19. FeO versus MnO relationships for ankerite A), and siderite B).

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Figure 20 above shows an unusual antithetic relationship. This has implications in terms of
the correlation between MnO and FeO suggesting that they do not actually anti-correlate and
that the actual anti-correlation is between the MnO and MgO summed versus FeO.
R² = 0,83
5
6
7
8
9
10
11
12
13
49 50 51 52 53 54 55 56 57 58 59
MgO+MnO(wt%)
FeO(wt%)
R² = 0,9749
6
7
8
9
10
11
12
13
14
15
14 16 18 20 22 24 26
MgO+MnO(wt%)
FeO(wt%)
A
B
Figure 20. Unexpected anti-correlation between Mgo and MnO summed versus FeO for ankerite
A), and siderite B). Note how much better the R2
are in this relationship compared to the MnO
versus FeO relationship.

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The (Mg + Mn)/Fe ratio profiles against stratigraphic height for both ankerite and siderite
show a common resemblance in Figure 21. From scrutinising these profiles, it is evident that
this relationship implies that with regard to the anti-correlation of MgO and Mn summed
relative to FeO in the carbonates, both ankerite and siderite record very similar signals in a
stratigraphic sense. Being very cautious, an open interpretation could suggest that the
carbonates are behaving in a certain manner whereby Mg is coupled with Mn in a similar
fashion, while Fe behaves in a passive manner. This behaviour is observed in both ankerite
and siderite and thus suggests co-genesis of the two carbonates. The similarity of the mineral
specific stratigraphic (Mg + Mn)/Fe pattern with that of the bulk rock obtained from XRF data,
show a spike at the top of the examined intersection which strengthens the case of the above
proposal that a common origin is possible for the two carbonates.

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4.3.5 Summary
A few preliminary conclusions can be drawn from the results presented above based on the
combination of XRF, ICP-MS and EPMA analytical data with regard to the carbonate fraction
in the examined BIF of the Griquatown and upper Kuruman iron formations:
 XRF analyses seem to suggest that there is an increase in MnO stratigraphically
upwards in the examined section as recorded in the bulk rock. This is characterised
110
160
210
260
310
360
0 0,5 1 1,5
Depth(m)Ank (Mg + Mn)/Fe
vs depth(m)
110
160
210
260
310
360
0 0,1 0,2 0,3
Depth(m)
Sid (Mg+Mn)/Fe vs
depth(m)
110
160
210
260
310
360
0 0,1 0,2
Depth(m)
Mn/LOI vs
depth(m)
Figure 21. Juxtaposition of ankerite and siderite Mg + Mn : Fe ratio profiles against stratigraphic
height with bulk rock Mn:LOI from XRF analysis. Due to the relatively low resolution of the data in
this study there are only a few reference points for the EPMA data, if there were more the likely
hood of the three profiles looking similar would be greater.

P a g e | 38
by two distinctive maxima Figure 6 at circa 128 and 159 m below the surface, which
are separated by a small plateau of relatively low values.
 Trace metals suggest that there were no/very little oxidative processes happening at
the time of formation of the Kuruman and Griquatown BIF.
 Trace data suggests a marine environment with a REE plot depicting a seawater
profile. Ni and Cu remain stagnant and show no relationship to Mn.
 It is apparent that according to the EPMA data on a mineral specific level, ankerite
and siderite simultaneously both display an overall and progressive increase of Mg
and Mn summed relative to Fe stratigraphically upwards which is in agreement with
Rafuza (2015). A similar sort of profile is depicted by the XRF profile for the bulk rock.
 A stronger antithetic relationship is evident between Mg and Mn summed versus Fe
which suggests that Mg and Mn are coupled while Fe behaves in a passive manner.
 Both EPMA mineral specific data as well as XRF bulk rock data record relatively high
Mg and Mn summed to Fe ratios that is observed at the top of the stratigraphy in the
examined section.
 Generally speaking the lowest (Mg + Mn)/Fe ratios and MnO values can be found the
base of the examined section.
 In broad terms it appears that the geochemical results from the rocks in the examined
section of this study are reproduced in the examined section of Rafuza (2015) and
further suggests that geochemical results may be reproducible basin wide. However,
caution must be taken here as the results of this study are of a much lower resolution
and may not be fully representative of the entire section.
In conclusion of the above summary, a preliminary conclusion may cautiously be drawn from
the above geochemical parameters. With regard to ankerite and siderite in the Griquatown
and upper Kuruman iron formations, their profiles are similar which indicates that Mn, Fe and
Mg are behaving in a similar way in the carbonates therefore they are probably forming at
the same time. Trace metals suggest that oxide deposition did not take place due to the
general dearth of trace metals in the examined section

P a g e | 39
5. Discussion
5.1 BIF research -the road thus far
Since BIF was first arbitrarily assigned by James (1954) to describe thinly laminated or bedded
formations on which this current thesis based, much has been learned about these
Neoarchean and Palaeoproterozoic deposits and is still a keen topic of research for scholars.
Since early research began into BIF, genetic modelling has been at the forefront and
subsequently involved a large variety of diverse processes and consequent evolutionary
changes of the early Earth’s oceanic and atmospheric compositions. A number of authors
when writing about BIFs in general state in their opening line that ocean chemistry as well as
atmospheric conditions that we thrive in today were vastly different during the time of BIF
formation (e.g. Crowe et al., 2008; Lyons et al., 2014 amongst others). Widespread anoxia
would have dominated the atmosphere as well as most of the ocean. To this affect it is safe
to say that BIFs worldwide have played a pivotal role in the evolution of the Earth’s
atmosphere.
With respect to studies conducted on BIFs and especially to those studied in this thesis from
the Asbesheuwles Subgroup, constrains on diagenesis and metamorphism is crucial when
trying to reconstruct the primary depositional environment of the circa 2.4 Ga old rocks from
the Griquatown and Kuruman iron formations which are also prime candidates for the pre-
great oxidation event (GOE). As mentioned earlier these rocks were subject to mostly upper
diagenetic to very low grade metamorphism. This makes it highly probable that any primary
chemical signatures that were recorded in the primary environment of formation are likely to
be unaltered which makes geochemical analysis on these rocks a vital tool of evaluation.
The dominant processes responsible for the primary formation of BIF are still a matter of
much debate and contention, although increasing evidence points towards photoferrotrophy
as a plausible oxidative mechanism, however, considering BIF mineralogy alone presents
evidence that for primary BIF formation some form of Fe(II) oxidation was necessary (Crowe
et al., 2008; Posth et al, 2010a; Rafuza, 2015). The question that now arises is: what sort of
process or mechanism is responsible for the deposition of the initial precipitates of iron
required to form these deposits of such large magnitude?

P a g e | 40
5.2 Anoxygenic phototrophic Fe(II)-oxidation – a possible mechanism for BIF
deposition?
In more recent years, biotic mechanisms have gained popularity amongst many researchers
(Llirós et al., 2015; Posth et al., 2010a; Crowe et al., 2008; amongst others). Other models have
been proposed in the past such as the oxygenic photosynthesis model by Cloud (1968) which
models microbes in BIF genesis; as well as the UV photo-oxidation model (Cairns-Smith, 1978)
as an abiotic means of BIF formation. Essentially the anoxygenic phototrophic Fe(II)-oxidation
model is a combination of the oxygenic photosynthesis model and the UV photo-oxidation
model.
In this model (Figure 22), sun light (UV) rather than free oxygen produced by cyanobacteria
and/or eukaryotes in the photic zone may have been responsible for coupling the carbon and
iron cycles via a photosynthesis mechanism. Kappler et al., (2005) reported that ferrous iron
served as the electron donor for these photothrophs which convert CO2 into biomass by using
light energy via the following reaction (Figure 22):
4Fe2+ + CO2 + 11H2O → [CH2O] + 4Fe(OH)3 + 8H2O+
Scientific data has been made available through experimental studies (modern ocean
analogues as well as lab studies) which lends support to this model (e.g. Llirós et al., 2015;
Kappler et al., 2005 amongst others). Such experiments were able to demonstrate that in
order to account for the large expansion of these deposits as seen in Superior type formations
that the organisms responsible would have been proficient in oxidising appreciable amounts
of ferrous Fe. Kappler et al. (2005) were also able to demonstrate that such phototrophs
through growth experiments could effectively oxidise Fe(II) up to a few 100 m’s of depth in
the water column.

P a g e | 41
5.3 A new look at the formation of the Griqualand West BIFs
5.3.1 Accommodating the geochemical data from this study
Depending on what school of thought one has when it comes to the genesis of the Griquatown
and Kuruman BIFs, it will impact on the way that the geochemical data is viewed. If these
rocks are entirely diagenetic in origin in terms of the examined carbonates in a chemical and
petrographic sense with regard to the overprinting of diagenetic textures as well as the
proposed paragenetic scheme by Klein (1983), then the preceding sections could be perceived
to adequately explain their mode of origin and mineral chemical variations.
The anomalous elevated manganese in the Griquatown BIF is a phenomenon that needs to
be adequately addressed and a conceivable explanation must be derived as this is an atypical
feature of BIF worldwide. The general lack of manganese in BIF may have been due to an
effective process such as the recycling of transient Mn oxides/hydroxides by ferrous iron
within the upper parts of the primary water column, or to no oxidation of Mn at all and its
resultant progressive enrichment in solution relative to iron (Tsikos et al., 2010). Either of
these processes taking place in the water column would have led to the development of a
distinct spike of high Mg + Mn/Fe. There is currently quite a broad range of work being done
by fellow postgraduate researchers in the Rhodes University Geology Department
surrounding this topic.
Figure 22. Direct microbial Fe (II) oxidation via anoxygenic Fe(II)-oxidizing phototrophy (modified
from Posth et al., 2010a).
4Fe2+
+ CO2 + 11H2O → [CH2O] + 4Fe(OH)3 + 8H2O+
ℎ𝑣

P a g e | 42
If the diagenetic model is correct, carbonates (i.e. ankerite and siderite) would form entirely
via a diagenetic process and the two redox sensitive species (Mn and Fe) would enter the
carbonate structure when they are reduced. A key mechanism here would be that there were
some bacteria in the sediment that could utilise the manganese and iron oxides. Presumably
these oxides would have been mixed with organic carbon which would have precipitated out
of the water column. As soon as the bacteria have reduced the manganese and iron oxides,
these reduced species would be incorporated into carbonate and a Mn bearing ankerite or
siderite would be formed. On the other hand, what complicates matters is that there is Mg
and Ca also entering the structures of the carbonates and this process is not yet adequately
understood but it is presumably through the pore fluids, if the process was diagenetic.
Therefore, when the carbonate forming reactions happen assuming that they all form
diagenetically, a carbonate mineral which is in equilibrium with the fluid chemistry will be
formed. Ca is invariant and therefore no further consideration of this species is necessary.
Because Mn and Fe are the redox sensitive species it would be reasonable to assume that if
one species is increasing in carbonate, the other should be decreasing, in other words they
would anti-correlate with one another every time because they are the redox sensitive
species and perhaps the two of them together would anti-correlate with Mg. If Mn and Fe do
not anti-correlate at least their sum should anti-correlate with Mg because then essentially
it’s the redox sensitive versus the redox non-sensitive.
However, the results of this study have brought to light an interesting relationship that was
previously unknown. According to Figure 20 under the results section suggests the actual anti-
correlation is not of the Mn and Fe redox species but rather of Mn summed with Mg versus
Fe and thus suggesting that Fe is passive. Therefore, it appears as if Mg is coupled with Mn in
some way. The question is in what fashion could Mg and Mn be behaving in if the Mn is redox
sensitive and the Mg is not? One way to suggest a possible solution to this problem is to
propose that they are sourced from a similar kind of source in that both Mg and Mn are
already at the same 2+ oxidation state which would then allow for the carbonate to draw in
both Mg and Mn. This relationship of Mg summed with Mn versus Fe was a relationship that
was found in both ankerite and siderite via the EPMA data and suggests that these two
carbonates were probably co-precipitating or both forming together which indicates that they

P a g e | 43
are not alien to one another. If the carbonates only had two species to contend with, say Fe
and Mn, then an anti-correlation would most certainly be definite.
Trace element data also proved useful in this study. The REE plot in Figure 14 displayed a
rather flat profile with the occurrence of a positive Eu anomaly throughout the stratigraphy.
The flat profile is indicative of a seawater environment while the positive Eu anomaly is
indicative of hydrothermal fluids. These hydrothermal fluids invariably break down K-feldspar
which release Eu which are carried into the water column. When the hydrothermal fluids
precipitate the Eu that was released from the K-spar will be recorded in the sediment. Having
determined that the BIFs of the Griquatown and upper Kuruman iron formations have a
hydrothermal component the Eu anomaly should be constant throughout the stratigraphy,
however, this is not the case. In this instance it is not purely hydrothermal in original but has
another component/s as well and depending on how they are mixed results in variations in
the Eu anomaly.
Manganese nodules in the modern ocean contain trace metals such as Ni, Cu, Co. These
elements were plotted and compared to manganese from the XRF bulk rock powder analysis.
It is apparent that there is no relationship with respect to manganese, however, Co does
increase up stratigraphy in a similar fashion to Mn (Figure 15). In the modern ocean,
manganese nodules are metal rich because when manganese oxides precipitate they
scavenge all other metals around them and incorporate them into their structure. This is not
observed in the Griquatown and Kuruman BIFs, therefore the presence of oxides in the
sediment is slim and most likely not to have been an operating mechanism at the time. Other
trace metals Figure 16 such as Ba and Zr also increase in concentration up stratigraphy. Zr is
a known detrital element and could suggest shallowing, therefore these other elements (Co
and Ba) could also be representative of a detrital fraction. At the same time Ba is fond of
entering the carbonate structure therefore this increase could be a direct result of Ba entering
carbonates. The results of this study alone cannot ascertain what these trace elements
represent at the time of formation. A suggestion can however be made that these trace
elements are not all necessarily linked by one process because if the environment changes
several other things might change along with it but not necessarily in the same way or under
the same forcings. For example, there may be two changes happening concomitantly that are

P a g e | 44
not related to one another but respond together to the same cause; so if there is shallowing
happening more detritus could be introduced into the system and there may be more Mn
deposition taking place. Essentially it doesn’t matter if they are of the same source, as a result
they often occur together.
Lyons et al., (2014) report trace elements as records of ocean redox evolution. Figure 23
shows a diagram of molybdenum concentrations throughout time. Every time there is a spike
in the concentration, according to Lyons et al., (2014) an oxidative process has taken place.
The arrow in Figure 23 below indicates an oxidative process at 2.5 Ga, just before the
formation of the Kuruman and Griquatown BIFs. It could therefore be possible that the trace
metals in this study that showed an increase in concentration up stratigraphy (e.g. Ba and Co)
could be responding to a much smaller or responding early to the onset of the next oxidative
process.
Figure 23. Red bars represent average values for the Eon which they represent, namely:
Archean, mid-Proterozoic and Neoproterozoic-Phanerozoic. c. The presence of significant Mo
enrichments in the Archaean (arrow) suggests the presence of oxidative processes at least as
far back as 2.5 Gyr ago. From Lyons et al., (2014).

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5.4 Implications of this study
As a result of the data presented in the foregoing section as well as the conclusions drawn in
the discussion above, it is rather imminent that an alternative mechanism be adopted in the
modelling of the carbonate fraction of the Griquatown and upper Kuruman BIFs. The
geochemical data presented as a whole can best be used to describe a scenario of primary
precipitation of carbonate mineral particle species directly from a chemically heterogeneous
but stratified water column in an ocean environment. This also includes subsequent re-
crystallisation of such particles during diagenesis with a limited degree of chemical change.
To put things simply, primary carbonate precipitation directly out of the water column as a
model, is proposed instead of a diagenetic origin for the BIF carbonates.
Certain characteristic features stand out that suggest that the carbonate fraction is not of
diagenetic origin. These features include the increase of Mn in the carbonates
stratigraphically upwards as well as the relative low trace metal abundance in the
stratigraphy. Therefore, primary precipitation of carbonates out of the water column seem
like a plausible alternative as opposed to a diagenetic mechanism. If such a process was
indeed at play in the water column at the time of BIF formation it can be envisaged that a
strong chemocline caused by a strong vertical chemistry gradient between the relative
abundances of Mn(II) and Fe(II) with depth would have developed. Such a model is
geochemically favourable against such a strongly stratified water column and can be used in
simple yet elegant explanations. Primary carbonate particles that form in the water column
will have contrasting mineral chemical signatures with respect to Mg + Mn/Fe due to the area
in terms of the stratified water column they formed in, this includes cycles of transgression
and regression. Precipitation of carbonates out of the water column would then have
recorded a unique chemical signal in terms of the stratified water column in which they
formed and would then be incorporated into the sediment on arrival from the water column.
Although there is still much contention and debate regarding the formation of BIFs around
the world, if this primary water column model were to be accepted and hold true, it would be
a great scientific breakthrough with regard to the origin of BIF and especially carbonate in
general. It would mean that we are one step closer in understanding the early
Palaeoproterozoic Earth and the systems which governed. In pre-GOE BIF settings such as

P a g e | 46
the Griquatown and upper Kuruman iron formations oxidation of Mn was not attained but
through an active biological redox cycling of Mn as well as carbon and Fe, Mn was able to
enter into carbonates that formed in the water column as Mn2+. This would have required a
continuous supply of organic matter and high valence Fe from the photic zone. Such a process
in the past would have been equivalent to a present day biological pump, the only difference
being that the ancient equivalent of a modern day biological pump would have made use of
an electron acceptor and Fe oxy-hydroxide would have been the ideal candidate. Carbonates
would effectively have acted as carbon sinks and much of the organically derived carbon
would have consequently been transferred into BIF. Summing up, it can be said that with
regard to the BIFs studied in this thesis, when it comes to the chemical signature of the
carbonates, they may well record primary water column processes especially with respect to
the long term redox behaviour of manganese during BIF genesis. At the end of the day no
matter how we define BIFs and their formation, the ‘how, when and why’ behind the Earth’s
dynamic and complex rock record will continue to motivate a generation of researchers.

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6.Conclusion
6.1 Significances of this study
With regards to the Griquatown and upper Kuruman BIF sections that were examined in this
study, a conclusion was reached that ultimately implicates the mechanism in which
carbonates are formed. After thorough examination of geochemical data from these BIFs it
appears that a diagenetic component to carbonate formation constitute a direct clash with
the results of this study. Absence of trace metals through the greater part of the stratigraphy
suggests formation as an oxide in the sediment is improbable. The author therefore argues
and is in agreement of recent research that the carbonates that were studied in this thesis,
as well as the rest from the Griqualand West Basin, originally formed from a primary
precipitation directly out of a well-stratified water column in which chemical signatures were
adopted from the water column, which was characterised by strong chemocline gradients due
to the dissolved Mg + Mn/Fe ratio. The chemical signature of the water column would then
have been successfully recorded in the precursor BIF sediment.
The exact reason to the increase in Mn up stratigraphy cannot be determined from the results
of this study alone, however, trace element data could give a little insight into why this could
be the case. Zr is a very well-known detrital elements and behaves similarly to Mn, this
increase in Mn could therefore be associated with a shallowing environment therefore
increasing the Mn content coupled with a strong Mn gradient in the water column with time.
This sort of enrichment can be explained through simple Rayleigh fractionation processes or
a slight oxygen ‘whiff’ during BIF formation.
6.2 Proposed future research
One way in which a more conclusive study could be done is to include isotope data in order
to gain more of an understanding in how these deposits were formed. Secondly a laboratory
experiment could be set up in which a study is done on how the Mg +Mn / Fe anti-correlation
works and how these elements enter the carbonate structure.

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7. References
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basin of the Transvaal Supergroup, South Africa, in: Iron-Formations: facts and
problems, eds., Trendall, A.F., and Morris, R.C.: developments in Precambrian
Geology 6, Elsevier Sci. Pbl., p. 131-209.
Beukes, N.J. (1984) Sedimentology of the Kuruman and Griquatown iron-formations,
Transvaal Supergroup, Griqualand West, South Africa: Prec. Res., v.24, p. 47-84.
Beukes, N.J., (1987) Facies relationships, depositional environments and diagenesis in a major
early Proterozoic Stromatolitic carbonate platform to basinal sequence, Campbellrand
Subgroup, southern Africa, Sedimentary Geology, Vol. 54, pp. 1-46.
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iron formations at the Archaean-Palaeoproterozoic boundary, In: Hagemann, S., et
al., (Eds.), Banded iron formation related high-grade iron ore, Reviews in Economic
Geology, Vol. 15, pp. 5-47.
Beukes, N.J., and Klein, C., (1990) Geochemistry and sedimentology of a facies transition from
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Cloud, P.E., (1968) Atmospheric and hydrospheric evolution on the primitive Earth, Science,
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Ö., Borrego, C.M., Bouillon, S., Servais, P., Borges, A.V., Descy, J.-P., Can- field, D.E.,
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Moore, J.M., Tsikos, H., Polteau, S., (2001) Deconstructing the Transvaal Supergroup. South
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Tsikos, H., (1999) Petrographic and geochemical constraints on the origin and post-
depositional history of the Hotazel iron-manganese deposits, Kalahari Manganese
Field, 104 South Africa. Ph.D. Thesis Unpublished. Rhodes University, Grahamstown,
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Appendices
Analytical Methods
EPMA
Quantitative mineral chemical analyses were obtained by using four wavelength dispersive
spectrometers on a JEOL JXA-8230 electron probe micro-analyzer at Rhodes University. The
beam was generated by a Tungsten cathode; 15 kV accelerating potential, 15 nA current, and
1 µm beam size was applied. All elements except Ba and Sr were measured on K-alpha peaks.
Barium and Sr measured on L-alpha. Counting times were 10 seconds on the peak, and 10
total on the background, for all elements. Commercial “SPI” standards were used for intensity
calibration. The standards were Dolomite (Ca), Diopside (Mg), Plagioclase (Na, Si, Al),
Hematite (Fe), Galena (S), SrTiO3 (Sr), Rhodonite (Mn), Orthoclase (K), Benitoite (Ba).
Calibration acquisitions were peaked on the standards, while unknown acquisitions were
peaked on the samples before each point analysis. The data was collected with JEOL software.
An automated ZAF matrix algorithm was applied to correct for differential matrix effects.
Oxygen was calculated by stoichiometry.
Acknowledgements:
I would like to thank Rhodes University for access to the Electron Microprobe (the purchase
of which was partially funded by NRF National Equipment Program grant UID 74464).

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Major oxide concentrations (wt%) raw results for XRF
Sample name Fe2O3 Mn3O4 CaO MgO LOI Depth (m)
(wt%) (wt%) (wt%) (wt%) (wt%)
Lo1 49,00 1,03 5,39 2,54 8,48 118,60
Lo2 25,54 5,04 12,39 5,44 25,93 127,75
Lo2b 31,38 0,24 2,52 1,52 4,55 136,47
Lo3 36,79 0,73 3,74 4,02 16,36 142,05
Lo3b 28,92 0,58 9,60 4,54 17,31 145,70
Lo4 23,96 0,45 5,34 4,19 14,90 151,08
Lo5 33,05 3,00 5,67 4,41 20,99 158,75
Lo5b 36,41 0,55 0,80 3,32 10,65 167,55
Lo6 18,01 1,06 15,96 8,56 25,13 175,80
Lo7 41,82 0,41 1,95 3,53 15,43 178,60
Lo7b 18,29 0,23 1,66 2,05 6,36 191,15
Lo8 43,72 1,24 7,27 4,55 26,92 197,70
Lo8b 41,79 0,49 2,16 3,59 9,61 201,00
Lo9 42,27 0,68 2,62 4,73 13,42 212,95
Lo10 33,35 0,29 0,35 2,82 6,14 224,60
Lo11 52,70 0,39 0,95 4,08 11,79 236,50
Lo12 33,90 0,26 1,60 2,27 6,90 249,50
Lo13 40,85 0,13 0,44 2,20 2,79 260,80
Lo14 38,57 0,36 0,78 3,15 6,56 271,70
Lo15 44,36 0,36 1,07 3,64 7,50 284,70
Lo15b 49,84 0,07 0,99 2,91 6,27 293,05
Lo16 41,02 0,08 1,48 3,08 5,88 296,45
Lo16b 43,10 0,66 8,35 3,88 14,88 303,18
Lo16c 33,04 0,70 3,91 3,62 14,92 306,56
Lo17 46,83 0,73 2,57 3,52 8,93 309,00
Lo18 34,47 0,52 7,62 2,68 11,73 320,90
Lo18b 42,57 0,14 1,21 3,17 5,09 327,78
Lo19 35,61 0,30 2,36 3,97 8,82 332,90
Lo19b 35,00 0,36 1,87 3,72 6,54 337,80
Lo20 33,76 0,49 6,47 3,01 9,49 345,45
Lo20b 28,22 0,33 8,99 2,27 15,16 349,45
Lo21 34,76 0,28 2,00 2,94 9,99 355,60

P a g e | iii
Tabulated raw microprobe data for ankerite
CaO
(wt%)
MgO
(wt%)
MnO
(wt%)
FeO
(wt%) Total
Height
(m) sample
28,538 7,639 4,619 18,077 58,873 127.75 Lo 01
28,665 8,811 4,152 18,162 59,79 127.75 Lo 01
27,994 8,359 4,481 16,795 57,629 127.75 Lo 01
28,856 6,786 2,809 21,214 59,665 127.75 Lo 01
25,334 7,784 4,097 20,625 57,84 127.75 Lo 01
28,346 6,774 3,361 21,083 59,564 127.75 Lo 01
28,273 8,378 4,412 17,343 58,406 127.75 Lo 01
28,33 8,734 3,996 16,677 57,737 127.75 Lo 01
28,954 9,299 3,873 17,573 59,699 127.75 Lo 01
29,198 8,671 0,595 21,274 59,738 249.50 Lo 12
30,12 7,93 0,493 21,205 59,748 249.50 Lo 12
28,132 8,435 0,683 21,736 58,986 249.50 Lo 12
29,734 8,057 0,814 21,674 60,279 249.50 Lo 12
29,169 8,178 0,618 22,703 60,668 249.50 Lo 12
29,498 6,432 1,663 23,312 60,905 320.90 Lo 18
28,413 6,277 1,99 22,145 58,825 320.90 Lo 18
29,298 6,736 1,716 22,887 60,637 320.90 Lo 18
29,162 6,505 1,922 21,958 59,547 320.90 Lo 18
28,945 6,662 1,582 22,501 59,69 320.90 Lo 18
24,836 5,826 1,485 25,184 57,331 320.90 Lo 18
29,958 6,585 1,98 24,659 63,182 320.90 Lo 18
29,568 7,27 1,429 20,559 58,826 345.45 Lo 20
32,028 10,097 1,646 16,473 60,244 345.45 Lo 20
29,643 7,718 1,433 23,006 61,8 345.45 Lo 20
29,719 7,228 1,542 20,822 59,311 345.45 Lo 20
29,388 7,876 1,996 19,693 58,953 345.45 Lo 20
29,391 6,798 1,275 22,733 60,197 345.45 Lo 20
29,423 7,45 1,741 21,34 59,954 345.45 Lo 20
29,143 6,853 1,585 22,309 59,89 345.45 Lo 20
30,967 15,989 1,026 10,525 58,507 145.70 Lo 03
30,278 15,81 1,091 11,197 58,376 145.70 Lo 03
29,251 15,339 1,291 11,547 57,428 145.70 Lo 03
32,787 16,549 1,032 10,863 61,231 145.70 Lo 03
28,743 6,686 1,419 22,138 58,986 145.70 Lo 03
28,78 7,322 1,001 22,081 59,184 145.70 Lo 03
30,019 6,619 0,686 23,49 60,814 191.95 Lo 07
29,235 6,229 0,502 24,418 60,384 191.95 Lo 07
30,309 6,375 0,638 22,525 59,847 191.95 Lo 07
28,124 7,107 0,296 24,976 60,503 191.95 Lo 07
28,776 6,951 0,372 24,809 60,908 191.95 Lo 07
28,115 7,386 0,376 24,392 60,269 191.95 Lo 07

P a g e | iv
27,342 7,665 0,84 22,732 58,579 284.70 Lo 15
29,155 10,406 0,841 18,957 59,359 284.70 Lo 15
28,461 10,573 0,465 16,401 55,9 284.70 Lo 15
27,269 8,142 0,461 20,637 56,509 284.70 Lo 15
28,744 8,657 2,687 17,761 57,849 284.70 Lo 15
28,781 9,863 3,216 17,618 59,478 284.70 Lo 15
27,74 10,599 2,662 15,134 56,135 284.70 Lo 15
28,949 6,791 0,766 24,103 60,609 355.60 Lo 21
29,652 7,481 0,635 23,853 61,621 355.60 Lo 21
28,417 6,848 0,732 23,79 59,787 355.60 Lo 21
28,712 7,364 0,581 23,173 59,83 355.60 Lo 21
28,399 7,75 0,733 21,985 58,867 355.60 Lo 21
27,37 6,59 0,791 23,427 58,178 355.60 Lo 21
Tabulated raw data for siderite
CaO
(wt%)
MgO
(wt%)
MnO
(wt%)
FeO
(wt%) Total
Height
(m) sample
0,417 7,636 7,774 46,508 62,335 127.75 Lo 01
0,813 5,02 3,8 52,547 62,18 127.75 Lo 01
0,928 5,087 4,918 52,43 63,363 127.75 Lo 01
0,692 6,758 6,558 49,552 63,56 127.75 Lo 01
0,715 5,476 5,113 51,861 63,165 127.75 Lo 01
1,341 7,419 7,658 47,419 63,837 127.75 Lo 01
0,554 6,684 6,522 49,772 63,532 127.75 Lo 01
0,364 5,784 1,542 53,814 61,504 249.50 Lo 12
0,889 5,132 1,334 58,582 65,937 249.50 Lo 12
1,262 4,945 1,025 58,005 65,237 249.50 Lo 12
0,508 6,356 0,629 57,331 64,824 249.50 Lo 12
0,276 7,597 0,641 56,016 64,53 249.50 Lo 12
0,249 6,474 0,647 58,059 65,429 249.50 Lo 12
0,267 7,823 1,137 55,451 64,678 249.50 Lo 12
0,995 5,598 2,698 56,332 65,623 345.45 Lo 20
1,08 7,371 3,136 52,924 64,511 345.45 Lo 20
1,157 5,807 2,329 55,422 64,715 345.45 Lo 20
0,766 6,577 2,405 55,223 64,971 345.45 Lo 20
0,824 7,231 1,71 54,857 64,622 145.70 Lo 03
1,097 6,734 1,865 55,469 65,165 145.70 Lo 03
0,649 7,543 2,053 55,757 66,002 145.70 Lo 03
1,089 6,481 2,002 55,671 65,243 145.70 Lo 03
0,311 6,681 1,73 55,736 64,458 145.70 Lo 03
0,398 6,085 1,528 57,181 65,192 145.70 Lo 03
0,407 5,679 0,959 58,332 65,377 191.95 Lo 07

P a g e | v
0,294 4,665 0,65 54,811 60,42 191.95 Lo 07
0,467 5,23 0,976 58,458 65,131 191.95 Lo 07
0,849 5,294 0,916 58,452 65,511 191.95 Lo 07
0,261 5,313 0,882 59,443 65,899 191.95 Lo 07
0,332 5,828 0,593 59,417 66,17 191.95 Lo 07
0,615 4,899 0,895 58,945 65,354 191.95 Lo 07
0,923 6,079 1,226 56,251 64,479 284.70 Lo 15
0,319 5,828 1,346 54,81 62,303 284.70 Lo 15
0,206 8,689 1,411 50,142 60,448 284.70 Lo 15
0,328 5,802 1,262 57,057 64,449 284.70 Lo 15
0,378 6,375 1,62 48,212 56,585 284.70 Lo 15

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