1 
Introduction and Research Overview 
 
 
1.1. Introduction to Iron Oxide-Copper-Gold Mineralisation 
 
The class of deposits known as iron oxide-copper-gold (IOCG) is associated with 
felsic igneous rocks in most cases, commonly potassic igneous magmatism, with 
the deposits being commonly ~2.2 ?1.5 Ga in age.  They tend to be enriched in 
Ca, Fe, Mn and P, with a large number of deposits exhibiting an additional 
distinctive enrichment in F.  The group as a whole is variably enriched to 
economic levels of Fe, Cu, Zn, Nb, Ag, Rare Earth Elements (REE), Au, Pb and 
U.  They occur in a range of tectonic settings, such as along subduction-related 
continental margins, regions of orogenic basin collapse, or regions of anorogenic 
magmatism, and have been recognised in many localities around the world 
(Figure 1.1). 
 
The IOCG class of deposits represents a family of loosely related ores that share 
a pool of common characteristics, controlled principally by chemical affinities; 
but for these similarities there are as many differences, which have led to 
contention in the past as to which deposits should be included in this class.  
 
From an ore genesis perspective, IOCG deposits and their associated polymetallic 
mineralisation are poorly understood.  Which deposits belong in this class and 
how they are related remains controversial.  However, they are highly significant 
as they represent a dominant source of iron ore, for example in Chile and Mexico,  
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                                                                   ___________________________                      ____ Chapter 1 ? Introduction 
 
Figure 1.1. Distribution of some recognised IOCG deposits worldwide. (modified after Hitzman, 
2000) 
 
 
as well as in Sweden where deposits, such as those found at Kiruna-Aitik, have 
formed the basis of industrial development.  The discovery of the giant Olympic 
Dam deposit - at Roxby Downs, South Australia, in 1975, attested to the greater 
potential of this style of mineralisation.  Olympic Dam is host to a voluminous 
polymetallic suite of Fe-Cu-U-(Au-Ag) with approximately 2 billion tonnes of 
ore at 2.5 % Cu, as well as 0.6 g/t Au, 0.02 % Co, 6 g/t Ag, 0.5 % LREE, and 0.8 
kg/t U3O8, (Williams 1999), and it is currently the fifth largest low-grade copper 
producer in the world.  The deposit was concealed underneath 300 m of post-
 Proterozoic sedimentary cover and was discovered during an exploration 
program for sedimentary-hosted stratiform copper mineralisation. It was only 
through somewhat predictive geological techniques that is was identified.  With 
regard to these sorts of ore-bearing systems it should be borne in mind that the 
economic portions may have highly subdued, or even no geophysical signatures. 
 
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                                                                   ___________________________                      ____ Chapter 1 ? Introduction 
A magmatic-hydrothermal continuum has been suggested for IOCG 
mineralisation with Williams and Blake (1993) proposing two broad groups for 
these mineralisation styles based on their detailed host rock and geochemical 
associations. One of these groups may be referred to as Olympic Dam-type, 
which exhibits an Fe (-oxide) ? REE ? U ? Au ? Cu association. According to 
Hitzman et al (1992), deposits of this association may be quite diverse in detail 
but are linked by similar processes and tectonic setting with the differences 
controlled by local wall rock and structural controls.  Other world-class 
polymetallic deposits that may belong to this class of deposits include Caraj?s, 
northern Brazil; Cloncurry, Australia; Pea Ridge, Missouri; Cerro Mercado, 
Mexico; Bayan Obo, Mongolia; Crixas, Brazil; and Vergenoeg in South Africa 
(Pollard & Williams, 1999).  The other group, which may be referred to as 
Broken Hill-type, has a Pb-Zn-Ag association distinguished by Fe/Mn silicate 
and calc-silicate host rocks. 
 
Many of these deposits exhibit intermediate characteristics of this continuum.  
These deposits characteristically contain anomalous amounts of Rare Earth 
Elements (REE), copper, gold, silver, cobalt and uranium with associated iron 
oxides and commonly associated fluorite. 
 
A characteristic feature of all IOCG districts is the abundant occurrence of barren 
ironstones, dominated by large accumulations of magnetite or hematite that only 
contain anomalous amounts of the associated metals (e.g. Kiruna barren 
ironstones) (Barton & Johnson, 2004). The number of barren Fe-oxide-rich 
occurrences exceeds the Cu (-Au) ones by many times. The absence of metals in 
these instances may in fact provide insight into the formative processes required 
to produce large polymetallic deposits, representing variable conditions of the 
system or unsatisfied conditions relating to metal trap sites. Economic copper-
 gold mineralisation is thought to be a later feature in the regional development of 
these deposits (Barton & Johnson, 2004). It is generally considered that in IOCG 
formation an early sulphide-poor magnetite stage precedes a subsequent metal-
 bearing hematite stage. It appears that a necessary requirement for the formation 
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                                                                   ___________________________                      ____ Chapter 1 ? Introduction 
of large polymetallic deposits is the presence of sulphur during the latter stage, in 
spite of the sulphur-poor characteristics of the system, such that metals may be 
precipitated. This will be considered in greater detail later.  Regardless, the 
presence of these barren ironstones becomes an important indicator of 
prospective terranes for IOCG mineralisation. 
 
The realisation within economic geology discussions that most deposits do not, in 
fact, satisfy all conditions of any given ore model, and that most deposits have 
been affected episodically by multiple processes over longer periods of time, 
tends to be the rule and not the exception. This consideration is important when 
dealing with the IOCG continuum where a great many more factors appear to be 
influential in the formation of its deposits. 
 
 
Characteristics of IOCG Mineralisation and Proposed Models 
 
With the recognition of IOCG deposits as a separate class of deposits, it was 
quickly determined that no simple descriptive model would adequately 
encapsulate the diversity of the systems included in this family. However, a 
number of features are common to most descriptions of IOCG and related 
systems, and a number of other characteristics appear to be recurrent, although 
not necessarily universally present (Table 1.1). 
 
Three tectonic settings have been identified in which IOCG deposits occur. These 
relate to regions of extension along subduction-related continental magmatism, 
intra-continental orogenic basin collapse or intra-continental anorogenic 
magmatism (Figure 1.2). All of these are likely to have relatively oxidised source 
rocks, igneous activity related to mantle underplating, and high heat flow 
(Hitzman, 2000). The presence of evaporites in some districts may have been 
important in the formation of saline brines, which are commonly associated with 
IOCG mineralisation (Barton & Johnson (2000). The combination of tectonic 
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                                                                   ___________________________                      ____ Chapter 1 ? Introduction 
setting and host lithology affect the geological signatures relating to alteration 
and mineralisation. 
 
Table 1.1. Characteristics of IOCG Systems (after Barton & Johnson, 2004). 
 
 
Generally accepted distinguishing characteristics 
? an abundance of Cu and Au 
? extensive alkali-rich alteration of both sodic-calcic [Na(Ca)] and potassic [K] types (Hitzman et al. 
1992; Barton & Johnson, 1996) 
? voluminous low-Ti magnetite and/or hematite 
? a distinctive suite of minor elements, i.e. REE, Co, Ag, + U, + P 
? prominent structural control including localisation along high- to low-angle faults, generally splays off 
major crustal scale faults (Hitzman, 2000) 
 
Potentially key characteristics 
? adjunct coeval magmatism 
? associations with distinctive magmas, e.g. high-K granitoids (Pollard, 2000) or alkaline magmatism 
(Meyer, 1988) 
? non-magmatic brines, e.g. evaporitic fluids or basinal brines (Barton & Johnson, 1996; Haynes, 2000) 
? distinctive tectonic environments, e.g. extensional or compressional settings (Hitzman, 2000) 
? distinctive ages of formation, e.g. Mesoproterozoic (Meyer, 1988) 
 
 
 
Significant and extensive hydrothermal alteration is evident in all IOCG terranes. 
This manifests predominantly as alkali-rich alteration of both sodic-calcic/albitic 
[Na (Ca)] and potassic [K] types (Hitzman et al. 1992; Barton & Johnson, 1996) 
on a regional scale, and is commonly of the order of 10s to 100s of km2.  
 
Sodic-calcic alteration tends to occur in the deeper and more peripheral zones 
and its affects may be on the order of 100s of km2. It typically removes base 
metals and ferrous metals (Dilles & Einaudi, 1992; Williams, 1994; Johnson, 
2000).  
 
Potassic alteration/metasomatism manifests as two broad types. The first type 
contains secondary biotite or K-feldspar, and commonly with associated calcic 
phases such as amphibole or clinopyroxene. This type is typically associated with 
the introduction of magnetite or hematite and any of copper, gold, REE, and other  
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                                                                   ___________________________                      ____ Chapter 1 ? Introduction 
 
Figure 1.2. Tectonic setting of iron oxide-Cu-Au deposits (taken from Hitzman, 2000) 
 
 
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                                                                   ___________________________                      ____ Chapter 1 ? Introduction 
elements (Barton & Johnson, 2004).  It forms in inferred upflow zones of a 
maximum dimension of a few kilometres or less (Barton & Johnson, 2004). The 
second type is associated with recharge zones of certain continental and 
transitional marine settings (Barton & Johnson, 2000) which tend to be oxidised 
(hematite stable), K-feldspar dominated (with typically >8 % K2O), and more 
laterally extensive on a scale of 10s of km2 (Barton & Johnson, 2004). 
 
Acid alteration, consisting of sericitic or chloritic alteration with accessory 
hydrothermal quartz, is common but tends to occur in closer proximity to 
mineralisation, of a few kilometres in extent. 
 
Copper-gold mineralisation (chalcopyrite + bornite) occurs within or near iron-
 oxide accumulations, of both hematite and magnetite character; where the 
hematite-dominated mineralisation is distal and shallow, and the magnetite-
 dominated mineralisation is deeper and earlier. 
 
All IOCG models recognise the iron-oxide rich, sulphur-poor nature of the 
systems responsible for the formation of these deposits. It thus follows that fluids 
are requisitely saline, sulphide-poor, and relatively oxidised and may have been 
of either magmatic or non-magmatic derived sources (Figure 1.3, Barton & 
Johnson, 2004). In truth, it is likely often a variable combination of the two (see 
Table 1.2 for a synopsis of these differing genetic models). These characteristics 
may be extrapolated and used to evaluate Fe-oxide (-Cu-Au) bodies in the 
Bushveld Complex. 
 
 
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                                                                   ___________________________                      ____ Chapter 1 ? Introduction 
 
 
Figure 1.3. Schematic illustration of flow paths and hydrothermal features for alternative models 
for IOCG deposits. Shading in arrows indicates predicted quartz precipitation (veining) for 
different paths in different quartz-saturated rocks which provides a useful first-order indication of 
path (cf. Table 1.2.) (modified from Barton & Johnson, 2004).  
 
 
 
 
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                                                                   ___________________________                      ____ Chapter 1 ? Introduction 
Table 1.2. Synopsis of alternative genetic models for IOCG systems (cf. Figure 1.3.) (taken from 
Barton & Johnson, 2004). 
 
Non-magmatic 
Fluid Source Magmatic 
Basin/Surface Metamorphic 
Fundamental 
Process 
? Release of S=-poor metal-
 bearing brine from magma; 
rise of buoyancy 
? Cooling, wall-rock reaction + 
fluid mixing provide trap 
? Thermal convection of non-
 magmatic brines; wall rock 
reaction provides metals 
? Cooling, wall-rock reaction or 
fluid mixing provide trap; 
second fluid may provide 
metals 
? Metamorphic release of brine 
components by 
devolatillisation or reaction 
with other aqueous fluids; rise 
by buoyancy 
? Cooling, wall-rock reaction + 
fluid mixing provide trap 
Igneous 
Associations 
? High-K, oxidised suites ranging 
in composition from diorites to 
granites 
? Carbonatite and strongly 
alkaline connections proposed 
by some 
? Igneous rocks diverse (gabbro 
to granite); non-magmatic 
examples known 
? Key heat source in most 
? Material source, diversity 
reflected in geochemistry 
? No necessary connection, 
though commonly present 
? Could be heat source in some 
settings 
? Can be material source 
Hydrothermal 
alteration in 
feldspathic 
hosts 
? Na(Ca) and other types (K, H+) 
link to magmas 
? Regional Na(Ca) coincident 
but not directly related to Cu(-
 Au) 
? K (type I), H+ + Na(Ca) in 
upwelling zones 
? Na(Ca) + K (type II) in 
recharge zones 
? Primarily K and H+ alteration 
associated with deposits 
? Regional Na(Ca) association 
reflects sources 
Relationship of 
Fe-oxides to 
Cu(-Au) 
? Some Fe-oxides with Cu(-Au), 
may be deeper or higher-T 
equivalents 
? Barren Fe-oxides may form 
from distinct fluids and 
commonly older hydrothermal 
systems in same area 
? Mt-rich are deeper, earlier, 
higher T parts of ore-forming; 
Mt or Hm also typical with Cu 
? Barren Fe-oxides represent 
lack of S trap for Cu or lack of 
second Cu-bearing fluid 
? Fe-oxides present, but 
relatively minor (Bi or Chl 
common); Fe-oxides 
commonly generated by 
breakdown of mafic minerals 
rather than Fe introduction 
Local setting: 
depth/ structure 
? Shallow to mid-crustal levels; 
commonly along regional 
structures but near causative 
intrusions 
? In (mainly) brittle upper crust; 
plumbing provided by regional 
or volcano-tectonic structures 
? Mid- to shallow crustal levels 
near or on major structures; 
surface fluids require shallow 
levels 
Global setting 
? Arcs or extensional 
environments that produce 
characteristic magmas 
(oxidised high-K or alkaline) 
? Regions with appropriate brine 
sources (arid settings or older 
Cl-rich materials), plumbing 
systems, and thermal drives 
? Regions with Cl-rich low- to 
intermediate-grade source 
rocks; compressional setting 
(e.g. basin collapse) or 
prograde metamorphism 
Key references ? Hauck (1989), Pollard (2000), Groves & Vielreicher (2001) 
? Barton & Johnson (1996, 
2000), Haynes et al. (1995), 
Haynes (2000) 
? Williams (1994), De Jong et al. 
(1998), Hitzman (2000) 
 
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1.2. Iron Oxide-Copper-Gold Examples ? Olympic Dam & Caraj?s 
 
 
The general characteristics of IOCG deposits were introduced above. A spectrum 
of deposits was identified, linked principally by a common chemical affinity. 
Deposits may differ slightly in host rocks, metallogeny, fluid compositions, depth 
of formation or any number of other features.  
 
The two deposits assessed in this chapter were chosen for likenesses to the 
Bushveld-type mineralisation discussed in this study. The Olympic Dam deposit, 
South Australia, is considered the type-deposit for the IOCG class of deposits and 
shares a great many common characteristics. The Caraj?s district of northern 
Brazil contains many deposits of differing characteristics (as in the Bushveld 
granites), and focus will be made on deposits, such as Salobo, that most closely 
resemble other members of the IOCG class of deposits. 
 
 
Olympic Dam Cu-U-Au-Ag-REE Deposit, South Australia 
 
The Olympic Dam Cu-U-Au-Ag-REE deposit is located approximately 520 km 
NNW of Adelaide, South Australia (lat. 30? 27? S, lon. 136? 53? E) (Figure 1.4).  
It is hosted by the Roxby Downs granite that is Mesoproterozoic in age (1 588 + 
4 Ma; Creaser & Cooper, 1993) and is a coarse-grained, A-type syenogranite. 
Iron-rich breccias host mineralisation that closely followed the emplacement and 
cooling of the Roxby Downs granite (Johnson & Cross, 1995). 
 
The deposit is concealed beneath 300 m of Neo-Proterozoic and Cambrian 
sedimentary cover of the Stuart Shelf Sequence, and was discovered during an 
exploration program for sedimentary-hosted stratiform copper mineralisation 
using the integration of geology, magnetic and gravity data and the delineation of  
 
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Figure 1.4. Regional geological map of the interpreted subsurface geology of the Gawler Craton. 
Olympic Dam located top right (from Reynolds, 2000). 
 
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                                                                   ___________________________                      ____ Chapter 1 ? Introduction 
well-defined structural corridors (Pirajno, 2000). The deposit is located on the 
eastern margin of the Gawler Craton. The oldest basement rocks are the 
metasedimentary rocks of the Palaeoproterozoic Hutchison Group and deformed 
granites of the Lincoln Complex (Figure 1.4). These rocks are intruded by 
Mesoproterozoic granitoids of the Hiltaba Suite and subsequently by the bimodal 
volcanics of the Gawler Range Volcanics of the same age (Flint, 1993).  
 
Mineralisation is characterised by hydrothermal hematite-quartz breccia that is 
somewhat dyke-like in occurrence, up to 100 m wide; known as the Olympic 
Dam Breccia Complex (ODBC) (c.f. Oreskes & Einaudi, 1990; and Reeve et al. 
1990). The breccia complex forms an elongate zone approximately 5 km long and 
1.5 km wide (Figure 1.5), and is loosely zoned from granite breccia on the 
periphery of  
 
 
 
 
 
Figure 1.5. Simplified geological plan of the Olympic Dam Breccia Complex (ODBC) showing the 
general distribution of the major breccia types. Note the broad zonation from the host granite at the 
margins of the breccia complex to progressively more hematite rich lithologies in the centre (from 
Reynolds, 2000). 
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                                                                   ___________________________                      ____ Chapter 1 ? Introduction 
 
the deposit (Plate 1.1 (a)), passing into a heterolithic breccia (Plate 1.1 (b)), 
hematite-quartz microbreccia (Plate 1.1 (c)) and fine-grained massive hematite-
 quartz in the central portions. The central hematite-quartz breccia zone is noted 
as being essentially barren of copper-uranium mineralisation (Reynolds, 2000). 
The heterolithic microbreccia consists of fragments of hematite and altered 
granite in a matrix of quartz-hematite-sericite-siderite-chlorite (Pirajno, 2000). 
 
Textural evidence indicates polycyclic alteration and brecciation events 
(Reynolds, 2000). The variation in breccia nature and composition is attributed to 
the proposed processes responsible for their formation: hydraulic fracturing, 
tectonic faulting, chemical corrosion, phreatomagmatism and gravity collapse 
(Reeve et al., 1990). Margins between breccia types may be gradational on the 
scale of metres to tens or hundreds of metres or may be abrupt (Reynolds, 2000). 
The ODBC is considered to have formed by the progressive hydrothermal 
brecciation and iron metasomatism of the Roxby Downs host granite (Oreskes & 
Einaudi, 1990). The Complex represents a pipe-like structure that dips steeply to 
sub-vertical. Drilling has indicated that it extends to a depth in excess of 1 400 m 
(the limits of drilling). 
 
 
Alteration 
 
Alteration around the deposit is dominated by a sericite-hematite mineralogy 
with lesser amounts of chlorite, silica, carbonate (siderite) and magnetite and is 
not associated with any sodic metasomatism (Reynolds, 2000). Like the 
brecciation episodes, hydrothermal alteration appears to be polycyclic in nature, 
but zonation patterns may be developed around the deposit and around individual 
breccia zones; the intensity of the alteration being directly proportional to the 
amount of brecciation. That is, the granite and granite breccia halo that surrounds 
the ore zone (Figure 1.5) is characterised by weak, highly variable sericite-
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                                                                   ___________________________                      ____ Chapter 1 ? Introduction 
hematite-chlorite-carbonate alteration, with intensity increasing towards the 
centre.  
 
Sericitic alteration of feldspars is widespread, and where locally intense may be 
texturally destructive of affected grains (Plate 1.1 (d)-(e)). Intense Fe-
 metasomatism may cause significant volume changes in affected granites where a 
substantial proportion of the feldspathic components are leached out during 
hydrothermal alteration (Plate 1.1 (f)).  
 
Sericite and Fe-metasomatism occur weakly in the fractured granite and become 
more intense towards breccia bodies, where sericite, hematite, chlorite and 
epidote become dominant. Towards the centre of the breccia bodies hematite 
becomes abundant and overprints all other styles of alteration. Chlorite alteration 
of the Roxby Downs granite is patchy but widespread and tends to be 
pseudomorphic of the feldspar grains (Reynolds, 2000). Chlorite alteration, 
together with siderite alteration, is more abundant at depth and on the peripheries 
of the deposit and appears to be associated with magnetite-dominated alteration 
and chalcopyrite mineralisation (Reynolds, 2000). Silicification occurs 
throughout the breccia complex but is most intense around the margins of the 
central hematite-quartz breccias. These zones are prospective for gold 
mineralisation. 
 
Veinlets occur throughout the Complex and the granite country rocks and may be 
composed of one or any of the components in a variety of combinations: 
hematite, sericite, chlorite, siderite, barite, fluorite, quartz, sulphides or 
pitchblende and only rarer tourmaline and dolomite (Reynolds, 2000). A late-
 stage overprint of the Complex, extending into the roof-rocks, produces barite-
 fluorite-siderite-sulphide veins up to several metres across, but despite their 
similar assemblage, are not considered to be associated with the development of 
the ODBC (Reynolds, 2000). 
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                                                                   ___________________________                      ____ Chapter 1 ? Introduction 
 
a b 
c d 
e 
 
f 
 
Plate 1.1. All photographs and descriptions from Reeve et al., (1990). a) Granitic breccia with 
abundant hematite-rich matrix. Fine-grained orange clasts in the upper half largely consist of fine-
 grained felted sericite, which are presumably products of extreme alteration of intensely brecciated 
granite. Chalcopyrite (tan & brass colour) disseminated throughout clasts and matrix. b) 
Heterolithic matrix-rich breccia with subequal proportions of sericite clasts (orange-brown) and 
steely grey hematite clasts. Abundant quartz fragments. c) Heterolithic hematite breccia. Hematite 
clasts include a variety of red-brown, purplish and black types, many of which are fragments of 
pre-existing breccias. Subordinate clasts of sericitised granite breccia and hematite-quartz breccia 
also present. Chalcopyrite and bornite occur as non-visible disseminations. Fluorite present (jet-
 black) d) Sericite-chlorite altered granite clasts in orange brown network of very fine-grained 
sericite, ultra-fine iron oxide and angular relict quartz fragments. e) Intensely sericitised granite 
breccia in which original granite texture preserved. f) Intensely Fe-metasomatised granite in which 
primary feldspars and ferromagnesian minerals totally replaced by vuggy hematite. 
 
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                                                                   ___________________________                      ____ Chapter 1 ? Introduction 
Mineralisation 
 
Olympic Dam is host to a voluminous polymetallic suite of Fe-Cu-U-(Au-Ag) 
with approximately 2 billion tonnes of ore at 2.5 % Cu, as well as 0.6 g/t Au, 0.02 
% Co, 6 g/t Ag, 0.5 % LREE, and 0.8 kg/t U3O8, (Williams 1999), and it is 
currently the fifth largest low-grade copper producer in the world.  Ore grades are 
represented in Table 1.3. The ore zones account for only a small portion of the 
ODBC volume but background levels of all mineralisation components are 
widespread, typically up to 0.5 % Cu, 0.2 kg/t U3O8, 0.5 g/t Au and 1 g/t Ag 
(Reeve et al. 1990). 
 
 
Table 1.3. Ores Grades of the Olympic Dam Cu-U-Ag-Ag-REE deposit, South Australia.  
 
Deposit 
(Williams, 1999) 
Reserve 
(Reynolds, 2000) 
Resource 
(Reynolds, 2000) 
2000 Mt > 600 Mt  
2.5 % Cu 1.8 % Cu 30 Mt Cu 
0.8 kg/t U3O8 0.5 kg/t U3O8 930 Kt U3O8
 0.6 g/t Au 0.5 g/t Au 1200 t Au 
6 g/t Ag 3.6 g/t Ag 6700 t Ag 
0.5% LREE 26 % Fe 10 Mt REE 
 
 
The principal copper-bearing minerals are cogenetically-precipitated 
chalcopyrite, bornite and chalcocite (Plates 1.2 (a)-(c)) (Johnson & McCulloch, 
1995) with minor native copper. Bornite and chalcocite often occur as exsolution 
intergrowths of each other (Plate 1.2 (d)-(e)). Minor gold and silver is intimately 
associated with the copper sulphides. 
 
Sulphides occur as disseminated grains or as veinlets with massive ore rare. The 
principal uranium mineral is uraninite with lesser coffinite, pitchblende and 
brannerite (Plate 1.2 (c)), and the REEs contained in bastnaesite, monazite, 
xenotime and florencite (Oreskes & Einaudi, 1990).  
 
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High-grade copper-uranium mineralisation generally correlates to more hematite 
altered rocks (Fe-metasomatised) and may be accompanied by fluorite, barite and 
REE phases. The exception is the central hematite-quartz breccia, which appears 
to be a final stage hydrothermal reworking of earlier generations of 
mineralisation. High-grade gold zones occur as narrow, complex zones around 
the silicified margins of the hematite-quartz core.  
 
A sulphide zonation has been identified laterally and vertically from pyrite-
 chalcopyrite at depth and towards the periphery of the deposit, grading inwards 
and upwards to bornite and the chalcocite (Reeve et al., 1990; Oreskes & 
Einaudi, 1990) and may be hypogene in origin suggesting multi-stage 
introduction of fluids (Reeve et al., 1990). A distinct boundary is identified 
between chalcopyrite and bornite mineralisation (Figure 1.6) 
 
Fluorite mineralisation occurs together with sulphides in the mineralised breccias 
as disseminations, clasts and veins that may comprise up to 1-2 % of the rock. 
Barite characteristically occurs in the hematite-granite breccia and central 
hematite-quartz breccia core of the deposit, which contain lesser amounts of 
sulphide mineralisation. 
 
Magnetite generally only occurs at depth or in less evolved breccia systems in the 
periphery of the deposit, however, relict magnetite in commonly found in the 
cores of hematite grains (Plate 1.2 (f)) implying that magnetite was the earliest 
phase of iron oxide mineralisation, and had been subsequently overprinted by 
widespread hematite alteration. Hematite alteration tends to be more abundant 
and intense towards the centre of the rock and affects virtually any of the primary 
granitic components or vein minerals. 
 
Secondary barite and hematite in the upper portions of the deposit indicate 
surface or near-surface exhalative activity (Pirajno, 2000). Generalised alteration 
and mineralisation patterns are shown in Figure 1.7. 
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                                                                   ___________________________                      ____ Chapter 1 ? Introduction 
 
a 
 
b 
 
c 
 
d 
 
e 
 
f 
 
Plate 1.2. All photomicrographs and descriptions from (Hagni, unpubl.) a) Rounded chalcopyrite with 
coating of bornite then partial coating of later chalcopyrite. Subsequent fine-grained hematite has 
preferentially replaced parts of the bornite layer. Reflected light x 150; oil immersion. b) Rounded bornite 
in matrix of hematite. Reflected light x 150; oil immersion. c) Bornite partially replaced by subsequent 
uranium-bearing fluids. Bluish tinted coffinite with fine-grained disseminations of covellite. Brannerite is 
locally formed in association with the abundant anatase. Although U mineralization shown here formed 
late, uranium was present in the early ore fluids indicated by the presence of trace amounts of uranium in 
hematite. Reflected light x 500; oil immersion. d) Exsolution intergrowth of bornite and chalcocite. 
Reflected light x 150; oil immersion. e) Exsolution intergrowth between bornite and chalcocite showing 
smooth boundaries between the two minerals that are typical for such exsolution intergrowth. Hematite 
occurs especially along the margins of the sulphide grain and probably occurs as a partial replacement of 
the sulphide grain. Reflected light x 500; oil immersion. f) Large pseudomorphic crystal of martite after 
magnetite, characterized by its fine-grained polycrystalline nature. Small remnants of magnetite remain in 
most martite grains. Bornite and chalcopyrite occur as veins and along the martite grain boundaries Finer 
grained hematite occurs in the groundmass between the martite. Reflected light x 150; oil immersion. 
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                                                                   ___________________________                      ____ Chapter 1 ? Introduction 
 
 
Figure 1.6.  Schematic E-W cross section through the ODBC, showing generalised lithological 
relationships and the location of the bn-cp interface (from Reeve et al., 1990). 
bn bn 
cp cp 
 
 
 
 
Figure 1.7. Generalised alteration and mineralisation patterns within the ODBC with some 
typical mineral assemblages. More common components of the ODBC shown in solid lines; 
neither absolute nor relative abundances are implied. mt=magnetite; hem=hematite; ser=sericite; 
chl=chlorite; sid=siderite; flu=fluorite; bar=barite; sil=silicification; py=pyrite; cp=chalcopyrite; 
bn=bornite; cc=chalcocite; Cuo=native copper; Auo=free gold; ura=uraninite; bra=brannerite; 
cof=coffinite; REE=lanthanum and cerium (from Reynolds, 2000). 
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                                                                   ___________________________                      ____ Chapter 1 ? Introduction 
Fluid Characteristics 
 
Two fluid sources were recognised based on fluid inclusions and stable isotopes 
(Oreskes & Einaudi, 1992). The first fluid was of magmatic origin (high-
 temperature) and characterised by high ?18O = ~10 ?, and a homogenisation 
temperature of ~400 ?C. The production of the abundant magnetite is attributed 
to this fluid. The second fluid was found to be lower temperature (200-400 ?C) 
with ?18O <9 ?. Salinities for these fluids ranged from 7 wt% to 42 wt% NaCl 
equivalent. It is presumed that this fluid contained some meteoric component and 
was implicated in the hematisation overprint, similar to that in the Bushveld 
granites. 
 
 
Deposit Model 
 
The ODBC is considered to have formed in a high-level environment, which may 
have formed a phreatomagmatic volcanic structure at surface (Figure 1.8) (Reeve 
et al., 1990). Brecciation initiated at structurally determined position within the 
Roxby Downs granite and was accompanied by alteration, veining, 
phreatomagmatic activity and mineralisation that occurred polycyclically 
(Reynolds, 2000). 
 
An estimated 500 m of the ODBC is considered to have eroded during Meso- to 
Neoproterozoic glaciations to the present unconformity level. Subsequent 
deposition of the overlying Stuart Shelf Sequence occurred at around 700 Ma 
(Pirajno, 2000), with little subsequent geological modification of the deposit 
taking place.  
 
Haynes et al., (1995) proposed a fluid-mixing model as the dominant process 
responsible for the generation of the ores. The model suggests the occurrence of 
three distinct fluid sources: magmatic, deep meteoric and near-surface oxidised 
meteoric fluids. Cu-Au-U mineralisation was thought to have occurred in a saline 
- 20 - 
                                                                   ___________________________                      ____ Chapter 1 ? Introduction 
groundwater reservoir, which introduced Cu, Au, U and S and mixed with hotter 
fluids, which introduced Fe, F, Ba and CO2. The model relies on sulphate 
reduction and ferrous iron oxidation (Fe2+ ? Fe3+) for the precipitation of iron 
oxides and sulphides. Barton & Johnson (1996) invoked an evaporitic source for 
saline fluids in a similar model. 
 
Oreskes & Einaudi (1992) proposed a two-stage model involving an early fluid, 
likely of magmatic origin, responsible for abundant magnetite production, and a 
significantly later fluid of lower temperature, responsible for ore mineralisation 
and Fe-metasomatism, which destructively overprinted the earlier magnetite 
generation. This fluid is proposed to have had some meteoric component. 
 
 
 
Figure 1
 U-Au m
 Deeper le
 fluid types 
chalcopy
 based on
 2000). 
SCC alteration 
CAM  
alteration 
.8. 
ine
 ve
 rite
  R
 H
  
 Schematic cross section of an Olympic Dam style hydrothermal system, showing Cu-
 ralisation associated with hematite-sericite-chlorite-carbonate alteration (HSCC). 
l and/or distal calcsilicate-alkali feldspar-magnetite alteration (CAM), and alternative 
that may have been active in the system, are also shown. The interface between 
-pyrite (cpy-py) and bornite-chalcocite (bn-cc) assemblages is indicated. Geology 
eeve et al. (1990) and Haynes et al. (1995). (from Skirrow, 1999; Skirrow et al., 
- 21 - 
                                                                   ___________________________                      ____ Chapter 1 ? Introduction 
Caraj?s District, Northern Brazil ? Salobo Deposit 
 
The Caraj?s Mineral Province (CMP) of northern Brazil is one of the most 
endowed mineral districts in the world and hosts a diverse suite of commodities 
including iron, copper, manganese, gold, nickel, bauxite and PGEs. The iron 
deposits are some of the largest in the world are reported to contain on the order 
of 18 Gt of high grade hematite ore at an average grade of 67 % Fe (Dalstra & 
Guedes, 2004). The CMP is situated on the southeastern margin of the Southern 
Amazonian Craton in the Brazilian Central Shield in possibly the largest A-type 
granitoid province in the world (Figure 1.9). 
 
 
 
 
Figure 1.9. Location of the Caraj?s Mineral Province on the margin of the Southern Amazonian 
Craton (redrawn from Groves, 2004). 
 
 
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                                                                   ___________________________                      ____ Chapter 1 ? Introduction 
IOCG mineralisation is contained in various supercrustal sedimentary and 
volcanic assemblages that compose the Itacai?nas Belt formed on the Archean 
granite-gneiss basement (Figure 1.10). These rocks belong to the 2.76 ? 2.6 Ga 
Itacai?nas Supergroup (consisting of the Igarap? Salobo Group, Salobo-Pojuca 
Group, Gr?o Par? Group and Igarap? Bahia Group) (Souza & Viera, 2000). 
Deposition of these groups is considered to have taken place within a tectonic 
environment of extensional continental crust, accompanied by ocean basin 
formation (Wirth et al., 1986) that has been further described as a pull-apart rift 
basin (Pinheiro et al., 1991; Ara?jo & Maia, 1991). 
 
The supercrustal rocks were intruded by granitoids of the 2 573 + 2 Ma Granito 
Estrela Complex and by the 1 800 ? 1 900 Ma A-type Central Granite of the 
Caraj?s Suite (Machado et al., 1991). Gabbros of various ages (2.6 Ga and 
younger) and numerous Proterozoic-Phanerozoic dykes also cut the sequence.  
 
A number of important deposits (>100 Mt) are located in the Itacai?nas Belt 
including Salobo, Igarap? Bahia, Alem?o and Serra Pelada. The Salobo IOCG 
deposit is located on the north-western end of the Belt, and is developed among a 
sequence of amphibolites, banded iron formations, metagreywackes and 
quartzites belonging to the Salobo-Pojuca Group (Farias & Saueressig, 1982; 
Lindenmayer, 1990), which ranges in thickness from 300 to 600 m. Shearing is 
observed along the basal contact with underlying basement gneisses. The lower 
portion of the Salobo Group, consisting of metagreywackes and amphibolite 
layers and lenses (originally of tholeiitic basaltic composition, Requia & 
Fontbot?, 1999), is host to the mineralisation. The upper portion of the Group 
consists entirely of quartzites. The Salobo rocks underwent amphibolite facies 
metamorphism at 2763 ? 2759 Ma, with a peak metamorphism at 650 ?C and 3 
kbar, with subsequent retrograde greenschist facies metamorphism with a 
temperature of 350 ?C (Requia et al., 1995). 
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                                                                   ___________________________                      ____ Chapter 1 ? Introduction 
According to Machado et al., (1991), the Salobo deposit is situated in a duplex 
structure bounded by two convergent shear zones. These shears developed a sub-
 vertical mylonitic fabric that affected all lithologies except the younger 
intrusives. 
 
 
 
 
Figure 1.10. Simplified Geological Map of the Itacai?nas Belt of the Caraj?s Mineral Province, 
northern Brazil (redrawn from Groves, 2004).   
 
- 24 - 
                                                                   ___________________________                      ____ Chapter 1 ? Introduction 
Alteration 
 
Alteration effects were determined from amphibolite precursors, composed 
primarily of Ca-amphibole and plagioclase, with subordinate biotite, 
cummingtonite, quartz and chlorite, and minor tourmaline, titanite, 
stilpnomelane, epidote, sericite and calcite (Requia & Fontbot?, 1999). 
 
Alkali metasomatism predominates with an initial event of Na-metasomatism 
indicated by albitisation of Ca-plagioclase. This was followed by extensive K-
 metasomatism resulting in replacement of plagioclase by K-feldspar or by the 
formation of biotite, in the absence of K-feldspar. Intense potassic alteration was 
observed spatially related to mineralisation suggesting a link (Requia & Fontbot?, 
1999). Alkali metasomatism appears to be post-dated by sericitisation and 
propylitisation, which occur among all alteration types. 
 
Chloritisation of mafic minerals is widespread throughout the Caraj?s region and 
is likely a regional metamorphic background effect (Requia & Fontbot?, 2000). 
 
 
Mineralisation 
 
The Salobo IOCG deposit represents the largest Brazilian copper deposit with a 
resource of 1 200 Mt @ 0.86 % Cu and an included reserve estimated at 450 Mt 
@ 1.15 % Cu and 0.5 g/t Au (Requia & Fontbot?, 2000).. The deposit extends 
approximately 4 000 m along strike and is between 100 ? 600 m in width (Souza 
& Viera, 2000). It is recognised to depths of 750 m below surface from drilling. 
 
The principal ore assemblages are magnetite-bornite-chalcocite and magnetite-
 bornite-chalcopyrite. Magnetite dominates both assemblages with variable 
amounts of sulphides; accessory phases include hematite, molybdenite, ilmenite, 
uraninite, graphite, digenite and covellite. Native gold may occur as small 
inclusion less than ~10 ?m in copper sulphides or interstitially between magnetite 
and chalcopyrite (Requia & Fontbot?, 2000). The paragenetic sequence of the 
Salobo deposit is given in Figure 1.11. 
- 25 - 
                                                                   ___________________________                      ____ Chapter 1 ? Introduction 
 
 
Figure 1.11. Paragenetic sequence of the Salobo deposit, Carajas District, northern Brazil (Requia & 
Fontbot?, 2000). 
 
 
Fluid Characteristics & Sulphur Isotopes 
 
Two fluids were recognised from the Salobo deposit (Requia et al., 1995, Requia, 
1995). The first fluid was found to homogenise at a temperature of 360 ?C and 
contained salinities of up to 58 wt % NaCl equivalent. The other fluid 
homogenised at a range of temperatures with a tendency towards 195 ?C with 
much lower salinities of between 1-29 wt % NaCl equivalent. The interpreted 
source of these fluids is a deeper brine of magmatic-connate derivation, and an 
upper oxidised fluid probably of meteoric derivation (Requia et al., 1995, Requia, 
1995). 
 
Sulphur isotopes indicate a magmatic sulphur source for chalcopyrite and bornite 
from low ?34S values, ranging from 0.2 ? ? 1.6 ?, with an average of 1.0 ? 
- 26 - 
                                                                   ___________________________                      ____ Chapter 1 ? Introduction 
Deposit Model 
 
Ore formation has been shown to be related to the 2.573 Ga alkaline Granito 
Estrela Complex (Requia & Fontbote, 2000), with clear distinction evident 
between Cu-Au-Ag-U-F-Mo-Co-LREE enriched ironstones and depleted banded 
iron formation, indicating a hydrothermal origin. The alteration types (alkali 
metasomatism), and their distribution and the ore and fluid chemistry are 
consistent with IOCG-type deposits. The extremely low sulphur isotope values 
indicate a magmatic source. Figure 1.12 is a schematic model of the Itacai?nas 
Belt showing the proposed genetic relationship of some of the principal deposits 
of the CMP, and the influence that the steeply-dipping shears may have had on 
ore development.  
 
 
 
 
 
Figure 1.12. Schematic model of the Caraj?s Mineral Province indicating the relationships 
between major deposits in the region, including Salobo. Grades are indicated for each deposit, 
corresponding to wt % Cu and g/t Au, respectively (redrawn from Groves, 2004). 
- 27 - 
                                                                   ___________________________                      ____ Chapter 1 ? Introduction 
1.3. Previous Work & Research Objectives 
 
This study is a co-operative effort between the University of the Witwatersrand 
and Rio Tinto Exploration Ltd. It forms part of a much larger exploration and 
research program undertaken by Rio Tinto to re-evaluate known mineral 
deposits, primarily in the context of massive iron oxide-polymetallic 
mineralisation, and to identify new mineral occurrences of economic significance 
within the mineralised rocks of the Bushveld Complex. In this study, specific 
attention has been focused on the alteration and associated Fe-Cu-Au-F 
mineralisation in the western Bushveld granites. The chosen study area is located 
southeast of the town of Rooiberg, adjacent to the Rooiberg fragment; a 
sedimentary inlier to the Bushveld Complex consisting of Transvaal Supergroup 
sediments. 
 
Several models have been generated to explain the origin and characteristics of 
ore deposits found within the acid phase of the Bushveld Complex.  The principal 
aim of the greater study is to resolve whether these deposits formed from an 
immiscible, iron-rich magma (Crocker, 1985) or an unusual, low-sulphur, iron-
 rich hydrothermal fluid (Borrok et al, 1998), as well as determining the source of 
these fluids. 
 
To determine the origin of these deposits, we need to know: 
? the nature of the mineralising fluids (orthomagmatic versus hydrothermal) 
? the composition and temperature of the fluid from which these massive iron 
oxide deposits formed 
? the source of the fluids (magmatic versus meteoric), and 
? the relation between these deposits and the evolution of genetically related 
silicic magmas 
 
Extensive research was carried out by Crocker (1976; 1977; 1979; and 1985) and 
Crocker et al (1988, 2001) in the region in establishing an inventory of the 
numerous fluorite occurrences.  Crocker favoured a magmatic origin for these 
- 28 - 
                                                                   ___________________________                      ____ Chapter 1 ? Introduction 
deposits, although, the relationship between mineralisation and alteration has not 
been satisfactorily addressed. A detailed understanding of this relationship is 
imperative for the development of an effective exploration model, and critical in 
the search for new deposits of similarly styled mineralisation. 
 
Freeman (1998) examined fluids from several polymetallic-type deposits in the 
eastern Bushveld granites in comparison to the barren granites, to establish the 
characteristics of the mineralising fluid, and also attempted to place a relative 
temporal constraint on the mineralising event. It was determined that two distinct 
populations of fluids existed, namely a high temperature magmatic fluid and a 
lower temperature meteoric/connate derived fluid, with mineralisation occurring 
in the zone of fluid-mixing.  These results favoured a magmatic-hydrothermal 
model for mineralisation over an immiscible iron-rich magmatic fraction model. 
 
A study by Borrok et al (1998) performed a comprehensive fluid inclusion stable 
isotope assessment of Vergenoeg to constrain primary mineral assemblages, 
temperatures of formation, and genetic source of mineralising fluids. It too 
established a clear magmatic-hydrothermal origin of formation.  These results 
were supported by the isotopic studies of Ogilvie (1998), which demonstrated 
contaminated Sr isotopic ratios suggestive of the assimilation of country rocks; 
and fluid studies, which again demonstrated the presence of distinct meteoric and 
magmatic fluid populations. 
 
Another study by Bailie (1997) and Bailie & Robb (2004) looked regionally at 
the mineral occurrences of the eastern Bushveld granites and attempted to 
constrain these occurrences within a genetic model applicable to a broader 
exploration program.  The study evaluated the Bushveld granites in terms of 
lithology, morphology, mineralogy, relation to host rock and trace element 
indices for identifying and prioritising targets of mineralisation.  Four main types 
of deposits were identified based upon mineral associations. 
 
- 29 - 
                                                                   ___________________________                      ____ Chapter 1 ? Introduction 
Research Aims 
 
This study attempts to: 
? map in detail the distribution of mineralised bodies and describe the associated 
alteration patterns in the Rooiberg district of the western Bushveld Complex, 
near the Ruigtepoort Fluorspar mine. 
? compliment and apply existing regional results to the geology of more 
localised targets. 
? establish the relationship between mineralisation and alteration using 
petrographical and geochemical observations, and to determine whether 
alteration assemblages can be used as an effective tool for vectoring towards 
mineralisation. 
? construct a model to explain the origin and characteristics of these deposits. 
? re-evaluate the small iron oxide-fluorite deposits of the western Lebowa 
Granite Suite in the context of an IOCG magmatic-hydrothermal continuum 
framework. 
? identify new occurrences of potential economic significance. 
? establish the relationship and similarities, if any, between the Lebowa Granite 
Suite polymetallic deposits and Olympic Dam-type Fe-Cu-U-(Au-Ag) 
mineralisation. 
 
 
Significance of the Research 
 
The significance of the research can be categorised from an economic geology 
perspective as follows: 
? Massive iron oxide deposits have only recently been established as a separate 
class of ore deposits, in spite of a long history of exploitation throughout the 
world.  These deposits as a separate class of ore deposits are not yet properly 
understood. 
 
- 30 - 
                                                                   ___________________________                      ____ Chapter 1 ? Introduction 
 
? Massive iron oxide deposits represent a considerable resource of a multitude 
of commodities and include several major world-class ore deposits: 
? the numerous Australian Proterozoic Fe-oxide-(Cu-Au) deposits 
such as Olympic Dam (450 Mt @ 2.5% Cu, 0.6 g/t Au) and Cloncurry 
District deposits (195 Mt @ mean 1.3% Cu, 0.7 g/t Au) (Williams, 1999)  
? Vergenoeg, South Africa, one of the largest, single fluorite 
deposits in the world (178 Mt @ 28.1% CaF2, 195 Mt @ 42 % Fe) 
(Fourie, 2000)  
? the iron ore deposits of the Caraj?s Mineral Province, northern 
Brazil, including the Salobo copper-gold deposit with a resource of 1200 
Mt @ 0.86% Cu and reserves estimated at 450 Mt @ 1.15% Cu and 0.5 
g/t Au (Souza & Viera, 2000) 
? the iron ore deposits of the Chilean Coastal Belt such as La 
Candalaria copper-gold deposit (366 Mt @ 1.1% Cu, 0.26 g/t Au), the 
Manto Verde copper deposit (120 Mt @ 0.72% Cu, 0.1 g/t Au) and the 
Andacollo copper-molybdenum deposit (300 Mt @ 0.7% Cu, 0.25 g/t Au) 
(Williams, 1999)  
? the iron ore deposits of the N?rbotten terrane, Sweden, which 
have formed the basis of Swedish industrial development.  These include 
Aitik (450 Mt Fe-oxide @ 0.4% Cu, 0.2 g/t Au), Viscaria (25 Mt @ 2.9% 
Cu), Pahtohavare (5.4 Mt @ 2.18 % Cu, 1.28 g/t Au), and Kiruna (2 000 
Mt Fe-oxide @ 60% average Fe content, 0.9% REE) (Blake, 1999) 
? the Bayan Obo rare-earth deposit, Inner Mongolia, one of the 
largest rare earth element deposits in the world (1.5 Mt @ mean 6% REE, 
0.13% Nb) (Williams & Blake, 1993) 
? The Bushveld Complex is still an unknown entity in terms of the 
characteristics that define IOCG deposits and whether the numerous 
polymetallic deposits located in the upper portions of the granite and the roof 
rocks correspond to mineralisation of this type. 
- 31 - 
                                                                   ___________________________                      ____ Chapter 1 ? Introduction 
Methodology 
 
Basic Field Mapping 
 
The study area was mapped from 1:10 000 orthophotos with emphasis being 
given to the recognition of zonation patterns in the alteration assemblages 
associated with fluorite-hematite (-gold) mineralisation. Consideration was given 
to litho-types, structural control on mineralisation, and mineralisation in terms of 
depth of emplacement. Textural variation, as well as mineralogical changes in the 
various granitic lithologies was also mapped.  Samples were taken of both altered 
and background ?least altered? material.  Known mineral occurrences were 
revisited and new mineral occurrences identified.  Comparative samples were 
taken of variously mineralised and background unmineralised material.  A 
geological outcrop map illustrating these features was prepared and is included in 
this volume.  
 
 
Transmitted and Reflected Light Mineral Petrography 
 
Polished thin sections were prepared from over 100 samples to study the silicate 
and opaque mineral petrography of the various lithologies, styles of alteration 
and mineralisation. Sections were described in terms of primary assemblages and 
alterations thereof, and related to mineralisation. Alteration assemblages were 
considered and evaluated in terms of IOCG deposits. Digital photographs used in 
this study were taken at the University of the Witwatersrand. 
 
 
Whole Rock Geochemistry 
 
Major and trace element whole rock geochemistry was determined for a 
representative suite of 82 altered, background and mineralised samples, using a 
Phillips 1400 X-ray fluorescence (XRF) spectrometer at the University of the 
- 32 - 
                                                                   ___________________________                      ____ Chapter 1 ? Introduction 
Witwatersrand.  A suite of 58 mineralised and background samples were fire 
assayed for Au and Ag contents by Bergstr?m and Bakker Laboratories, South 
Africa.  LREE and rare metals (Sn, Mo, U, Th, Pb, As and W) analyses for a 
selected suite of samples were also determined by XRF by Bergstr?m and Bakker 
Laboratories, South Africa. 
 
Results of these analyses were compiled and modelled in the context of IOCG 
deposits, with emphasis on styles of alteration. Well-documented crystal 
fractionation trends in the Bushveld granites were considered and related to 
observed alteration and mineralisation trends. 
 
??? 
 
This chapter presented a brief overview of the prominent characteristics of 
IOCG-type mineralisation in a global context, including reviews of the Olympic 
Dam and Salobo deposits. Key similarities have been identified amongst IOCG 
deposits with respect to tectonic settings, associations with potassic magmatism, 
characteristic fluids of highly-saline magmatic character which mix with oxidised 
surficial fluids, extensive alkali-rich alteration of both sodic-calcic and potassic 
types, voluminous Fe-oxides and a distinctive suite of minor polymetallic 
elements. The next chapter will present a geological overview of the Bushveld 
Complex and its related mineralisation, with particular attention to the acid 
phase, and will draw attention to the above characteristics. 
 
- 33 -