See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/288925884 Use of breccias in IOCG(U) exploration Article · January 2010 CITATIONS READS 9 2,116 1 author: Michel Jébrak Université du Québec à Montréal 149 PUBLICATIONS 2,018 CITATIONS SEE PROFILE Some of the authors of this publication are also working on these related projects: Quelle acceptabilité sociale pour les projets miniers de la transition énergétique ? L’influence de l’usage et des valeurs collectives sur le développement minéral au Québec View project Auriferous volcanogenic massive sulfide, a new type of deposit in the Guiana shield? View project All content following this page was uploaded by Michel Jébrak on 18 July 2016. The user has requested enhancement of the downloaded file. USE OF BRECCIAS IN IOGC(U) EXPLORATION MICHEL JÉBRAK DIVEX network, Université du Québec à Montréal; jebrak.michel@uqam.ca Abstract Breccia are key elements of the polymetallic iron oxide copper-gold (Co-Ag-Bi-U) (IOCG) deposits worldwide. Their use is however difficult either in regional mineral exploration or in production mapping. Recent studies on breccias in magmatic-hydrothermal systems show that genetic information may be determine from quantitative geometric parameters (shape and spatial organization of fragments) and composition. Breccia maturity could be determined from several parameters et could be use for targeting mineralization. In IOGC(U) ore deposits, breccias occurs in all geological environments and at different depths. Corroded breccia fragments and chaotic particle size distribution are more abundant than in other types of ore deposits, underlying the role of solution process in this class of deposits. Résumé Les brèches sont des éléments essentiels dans les gisements d’oxydes de fer polymétalliques à cuivre-or (Co-Ag-Bi-U). Leur utilisation reste cependant difficile, aussi bien en exploration régionale que lors de la cartographie au cours de la production. Les études récentes sur les brèches dans les systèmes magmatiqueshydrothermaux ont montré qu’il était possible d’obtenir de multiples informations génétiques à partir d’analyses géométriques détaillées sur la forme et l’organisation spatiale des fragments en tenant compte de la composition. La maturité d’une brèche peut se mesurer selon différents paramètres et peut servir de vecteur vers la minéralisation. Dans les gisements IOGC(U), les brèches apparaissent dans tous les environnements et à diverses profondeurs. Les fragments des brèches sont plus corrodés et la granulométrie est plus chaotique que dans d’autres types de gisements, ce qui souligne l’importance des processus de dissolution dans ces gisements. Introduction Iron-oxide copper-gold uranium deposits are recognised as a more and more important type of ore deposit, with numerous variations in their geological setting and the composition of economic ore. These copper-gold deposits are characterized by the abundance of iron oxides (magnetite, hematite), with cobalt, uranium, rare-earths, barium, fluorine constituting minors elements. The emplacement of the ore is associated to various styles of permeability, such as veins, breccias or replacements, controlled by structural and plutonic factors. Alteration are ubiquitous, mostly alkaline (sodic, calcic, potassic) and chlorine-rich (Corriveau et al., 2008). IOGC constitute therefore a rather diverse class of ore deposits, sharing more of a mineralogical and geochemical assemblage than a common lithological package or a specific geodynamic context. Early description of this association may be found in the eba paragenesis described in Central Europe. However, it is only after the discovery of the Olympic Dam deposit in South Australia that the necessity of a distinction of specific class of ore deposits appeared clearly. Several ore deposits were furthermore discovered, such as Salobo (Brazil, 1977), Starra (Australia, 1980), La Candelaria (Chile, 1987), Osborne (Australia, 1988), Ernest Henry (Australia, 1991) and Alemao (Brazil, 1996). Several apatite-rich deposits were also attached to the group, and especially the Kiruna and Bayan Obo deposits. These deposits represent presently less than 5% of the copper and 1% of the gold produced every year. However, several deposits play a major economic role such as Olympic Dam, first Uranium mine in the world, Bayan Obo, first REE producer, or Kiruna, the largest mine in Europe. Breccias are very abundant in this type of deposit, and host most of the mineralization in major deposits such as Olympic Dam and Ernest Henry (Australia), and La Candelaria (Chile). They have been considered as one of the key elements of this family of deposits (Hitzman et al., 1992). The formation of these breccias has been related to numerous processes, from physical (explosion, comminution) to chemical (dissolution). Several hypotheses have been proposed in order to explain their formation from explosive alkaline explosion to fault rocks formation and dissolution by surficial waters (Hitzman et al., 1992; Barton and Johnson, 1996; Williams, 1999, Mark et al., 2006). However, these breccias display complex relationships to the ore, due to multiple episodes of fragmentation. This cause several difficulties for the recognition and mapping of breccia in a large orebody, where several geologists are involved and where the variability of facies at all scales may cause some shortcuts in the description of the breccia during the production phase of the mine. In this paper, we present a semi-quantitative methodology for the description and the interpretation of breccia in IOGC(U). The approach has been developed for field geologists, either in exploration or production, and does not require any specific instrument. Describing a breccia Some previous works A variety of approaches have previously been taken on the classification of breccia. The numerous attempts have ranged from purely descriptive to genetic and have used a wide variety of criteria. Sibson (1986) reviewed the structural brecciation processes in fault zones and proposed a classification for the definition of fault rocks using textural features (e.g., roundness), internal clast deformation, clast size distribution, and clast and matrix composition. Sillitoe (1985) used a practical classification for breccias in plutonic and hydrothermal systems within magmatic-arc environments using the abundance and petrographic composition of the matrix or cement, the shape of the elements, and the overall organization of the brecciated units. Laznicka (1988) made a thorough review of breccia structures and associated rocks. He examined the wide range of settings for breccias in different geological environments and proposed a fully genetic classification and a descriptive approach. Taylor and Pollard (1993) and Taylor (2003 a, b) developed a field approach focussing on intrusive and extrusive breccias, beautifully illustrated by photographs showing specific characteristics such as discrete pressurized slurry vein, ion skin textures (probably hypogene exfoliation), decompressive shock textures, sheeted fractures, shingle texture, and collapse. Jébrak (1997) used a quantitative approach similar to the one used in sedimentology. Although it was developed for hydrothermal breccias, it could be used for different styles of fragmentation process. Four key parameters were recognized and should be theoretically self-sufficient for a total understanding of the shape of a breccia: particle size distribution, shape of the fragment, dilation ratio, and fragment fabric. Fragmentation may occur in response to either physical constraint or to chemical disequilibrium. The same approach was used by Clark et al. (2006) for understanding the formation of magmatic hydrothermal breccias in the Curnamona Province (eastern South Australia). Mineralogy, fractal analysis of clast shapes and clast size distributions analysis were able to distinguish two styles of breccia and indicate that fluid pressure fluctuations played a significant role, though to differing degrees, in the initiation of the brecciation process. Billi et Storti (2004) showed the fractal distribution of the fragments in a fault zone, whereas Storti et al. (2007) studied in great details the shape of the fragments in faults within limestone and detailed the mechanisms related to the interactions between particles. Loucks (1999) suggested a classification of the cave breccias and sediment fills. Loucks et al. (2004) showed the possibility to analyse the paleocaverns in limestone, in terms of paleocavefacies classification, from disturbed strata facies to fine and coarse class chaotic breccias. The same approach was transferred to the Dent fault, England, by Woodcock et al. (2007) where chaotic breccias are related to incremental void formation in a reverse-oblique fault. Eliassen and Talbot (2005) recognized also two main styles of breccia in sedimentary evaporitic reservoirs, horizontal, stratabound, and thick, crosscutting breccia. Some of the facies encountered show strong similarities with breccia in IOGC(U). The descriptive approach We advocate a multi-faceted, descriptive approach to studying brecciated rocks. The fragmentation variables are of three types: (1) composition of the fragments and of the matrix; (2) shape of the fragments; (3) spatial organization of the fragments. From the early rigorous description of the breccia, different styles of brecciation can be defined based on the dominant process and its intensity, allowing characterizing the maturation of the breccia. FIGURE 1. Six geometric parameters are needed for an efficient description of brecciated rocks; the distinction between monomict and polymict breccias is also essential. (1) Composition of the fragments and of the matrix Nature of fragment and of the matrix is the first key element of a description. A breccia may be monomict or polymict, and at different degrees of heterogeneity. Monomict breccia could be in situ or transported (Pl. 1, Fig. a1). Polymict breccia usually indicates some amount of transportation of the fragments, either up- or downward. However, the distance of transportation is usually difficult to assess, because it is strongly dependant of the variability of the host rocks. Transportation of several hundred meters, up and down, has been documented in fault and breccia-pipe systems (Pl. 1, Fig. a2). The matrix could be crushed, hydrothermal (cement), or magmatic. In the case of the crushed matrix, it could be difficult to recognize the fragments from the matrix because of the fractality (self-similarity) of the system. (2) Shape of the fragments The shape of the fragments may be defined using three sub-parameters: aspect ratio (i.e. ratio between length and wide), roundness, and complexity. Aspect ratio (or elongation) varies from equidimensional to a very elongate shape (Pl. 1, Fig. b1, b2). Roundness (or sphericity) is related to the general shape of the fragments whereas complexity describes the detailed structure of the shape. Although there is a mathematical continuity between these two shape parameters, early observations show that a gap in scale may occurs, resulting in a bi-fractal distribution (Orford and Whalley, 1983; Jébrak, 1997). It is therefore easier for the aim of field recognition to do a distinction between the overall shape (roundness) and the detail of the boundary of the particles (complexity). Roundness could be either of mechanical or of chemical origin. In the former, it is related to abrasion process such as milling. Pebble dykes are exceptional example of this process (Pl. 1, Fig. b2). In the latter, dissolution processes are recognized by the formation of indentations, lobes and cupules (pl. 1, Fig. c1). Experiments show that such dissolution may take several tenths of years to occur; exceptionally, in pseudotachylite, roundness of clasts is indicator of flash frictional melting (Lin, 1999). Complexity is almost completely related to solution processes affecting the surface of the fragments. The only exception would be some rocks that display originally a complex shape of fragmentation because of the granular composition. Complexity (or surface roughness) can be computed by several methods, such as Fourrier Transform (FFT) or by fractal analysis (Fig. 2). The boundary fractal dimension is a relatively easy parameter to measure and it evaluates the complexity of the outline. The Euclidean Distance Mapping method (Berubé and Jébrak, 1999) is a robust method where ribbons of increasing thickness are computed from the particle outline. A high fractal dimension value indicates a high complexity related to dissolution where kinetic regime is dominant (Sahimi and Tsotsis, 1987). Such kinetic regime is characterized by a consumption rate that is limited only by the chemical reaction rate. The concentration of the reactants outside the solid is the same everywhere and the external surface of the solid is totally exposed to the reactants. This regime leads to a progressive increase in the complexity of the external surface. The diffusion-limited regime is governed by the diffusion rate of the reactants and only the most exposed parts of the solid, such as the corners, are reached by these reactants. This regime is therefore surface dependant and may lead to rounding or smoothing of the external surface (Jébrak, 1997). FIGURE 2. Two types of evolution during chemical corrosion of a particle. Diffusion Limited Regime increases rounding and indicates usually a slow process. Kinetic regime increases complexity and indicates a strong chemical disequilibrium. Numbers indicate the value of the Boundary Fractal Dimension, computed by the method of Berubé and Jébrak (1999). (3) Spatial organization of the fragments The spatial organization of the fragments could be described by three parameters: dilation ratio, PSD, and fabric. Dilation ratio corresponds to the percentage in volume of the matrix, giving an approximation of the porosity at the time of formation. A low dilation-ratio corresponds to a « clast-supported » model whereas a high dilation-ration is equivalent to the « matrix-supported » model (pl.2, Fig. e1 and e2). The dilation ratio is the more useful for distinctions between crackle breccia, mosaic breccia and chaotic breccia (Mort and Woodcock, 2008). The average degree of rotational misfit of the clasts is strongly related to breccia class: crackle breccia involves less then 10° average rotation, mosaic breccia, 10-20°, and chaotic breccia more than 20° rotation. Mort and Woodcook (2008) provide comparison charts for semi-quantitative classification of fault breccias. PSD vary from normal to log-normal/fractal distribution. It can be summarized by another fractal dimension, Ds, that represents the slope of the cumulative particle size distribution in a log-log diagram, or more intuitively the ratio between small particles on large fragments. High Ds will be significant of the impact of heterometric distribution such as in volcanic breccias whereas low Ds indicate that the fragments have roughly the same size. Plate 2 (Fig. d1 and d2) shows two end members with fractal and almost isometric distribution in IOGC(U) deposits. Fabric varies from one to random orientations of the fragments. It designs the overall orientation of the fragments, with low value for an orientation and high value for a random distribution (Pl. 2, Fig. f1 and f2). (4) Brecciation maturity During its formation, breccias evolve and their shapes reflect the intensity of the brecciation processes, physic or chemical. Such maturity of breccia is an important character to determine because mineralization is usually associated to the most evolved part of a breccia system. Even if a general pattern may be proposed (Fig. 3), there is no general consensus for the best parameter to observe for targeting the ore. It obviously depends of the nature of the processes involved in breccia formation. FIGURE 3. Maturity in a breccia system, and evolution of fragmented rocks. The three stages of the fragmentation process, with the different style of breccia associated (from Jébrak, 1997): (a) represents the initiation of the fragmentation, with mechanical continuity; (b) represents the stage of mechanical discontinuity and hydraulic continuity; (c) represents both mechanical and hydraulic discontinuities. In the Athabasca sandstone U deposits, ball zones are composed of altered sandstone fragments wrapped in red, green, yellow and/or white massive clay (illite) locally displaying flow texture. Their maturity, characterized by the matrix percentage, increased toward the unconformity and at fault intersections (Lorrilleux et al., 2003). Ball zones are hydrothermal breccias developed in sandstones some tens of meters from unconformity-type uranium ore bodies. They formed during peak diagenesis at temperatures between 240 and 280 oC. In a fault zone, the evolution of a breccia system could be followed using the particle size distribution. Billi and Storti (2004) studied in detail carbonate cataclastic rocks from the Mattinata Fault, Southern Apennines, Italy. They showed that the PSD follows a fractal law with fractal dimensions (D) cluster around the value of f2.5. High D-values pertain to gouge in shear bands reworking the bulk cataclastic rocks of the fault core. Low D-values characterise immature cataclastic breccias. Intermediate D-values are typical of the bulk fault core. The development of particle size distributions with D>2.6–2.7 in shear band occurred by a preferential relative increase of fine particles rather than a selective decrement of coarse particles, and reflect intense comminution enhanced by slip localisation progressed by rolling of coarse particles whose consequent smoothing produced a large number of fine particles. Mort and Woodcock (2008) used a geometric classification of fault breccia in the Dent Fault, northwest England. They demonstrated that maturity could be quantified by clast rounding correlated with surface roughness. However, PSD shows no correlation with the breccia classes. Interpretation The genesis of breccia in plutonic hydrothermal system may be related to numerous processes (Fig. 4). In fault systems, comminution and hydraulic breccias are the more commons. Dissolution processes, followed by collapse are ubiquitous and occur not only in soluble host-rocks, but also in silica-rich environments. In IOGC(U) deposits, such process is frequently observed because of the high capacity of dissolution of sodi-calcic hydrothermal solution (Hecht and Cuney, 2000; Le Carlier de Veslud et al., 2007). Explosion and fluidization processes are more specific and usually related to subvolcanic environments (Oliver et al., 2004). FIGURE 4. Main classes of process involved in breccia formation. All the cases have been observed in IOGC(U) deposits. From field to laboratory Field mapping is an absolute requisite for any breccia study, and, therefore, most of the steps for breccia identification are to be applied in the field. Mapping of breccias remains difficult because of the variability of facies, the numerous styles of brecciation, and the multiplicity of classification. In the field, the following steps should be followed: Look for major evolution and gradient in the six geometric parameters, composition of fragments and matrix; Search for the less evolved breccia in order to define the end members; this usually means to quit the main zone of mineralization; Organize your observations by giving explicit names to the different styles of breccias, connecting geometric and compositional observations; Search for pocket organization as numerous hydrothermal system and IOGC display several generations of breccias; Search for chronology, determined by breccia in breccia and crosscutting relationships; Take some samples and high-definition photographs of the main evolution observed. Back in the lab, it could be necessary to prepare polished slab for a better observations of the samples, and especially the composition of the cement, the nature of the dissolution processes, the relation between ore deposition and breccia formation. More detail work could be performed using semi-quantitative or quantitative approaches. Geoscientists have been trying for long to develop automatic recognition of breccias, including Fourrier transform analysis, computation of fractal dimensions, fabrics analysis, etc. (Berubé et Jébrak, 1999; Heilbronner et Keulen, 2006; Storti et al., 2007). These approaches are however limited because of the distinctions of the fragments, of the matrix that remains complex using image analysis, and because such software work mainly as black box. In order to improve breccia recognition on the field, a new approach based on a forensic science has been developed using a Breccia Digital Recognition (BDR) software (Pouradier and Jébrak, 2007). BDR is based on a Microsoft Access® database with a Java© embedded extension. Several fields are recorded, describing the geology, the mineralogy, and the alteration of breccias. A digital photograph is also recorded. A breccia simulator is generated and the user performs itself the evaluation of six geometrical parameters, three on the fragments geometry themselves and three on their organisation: complexity and roundness of the shape of the fragments, aspect ratio of the fragments, fragment/matrix ratio, fabric and particle size distribution. For each parameter, a value is given from 1 to 10, and can be correlated to absolute measurements. The estimation of these parameters is then compared to a database where several hundred samples have been characterized. Such comparison allows the user to know what environment shows similar breccias. Application to IOGC deposits One of the main characteristics of IOGC deposits is the abundance of breccias. Williams et al. (this volume) classify the IOGC clan of deposits in three groups: (1) iron oxide ± apatite deposits of types that occur in IOCG districts; Iron Oxide Apatite deposits (IOA) : Pea ridge (US), Ligthning Creek (Australia), Bafq (Iran), or apatite poor iron oxide such as Ligthning Creek and barren ironstone from Australian districts; (2) IOCG and closely affiliated deposits (i.e. low Fe oxide Cu-Au, low Cu-U-(Fe oxide), and low Cu-Co-As±U(Fe oxide); (3) Igneous affiliated Fe oxide ±apatite ±Cu ±Au ±rare metal deposits : Bayan Obo (China), Phalabowa, Vergenoeg (RSA), Faleme (Senegal). One of the main characteristics of IOGC is their strong relations with high permeability domains of the crust, illustrated by the abundance of breccias. IOGC deposits may occur at different levels of the crust (Fig. 5), in different environments, and are associated with different styles of breccias: directly in association with pluton (Kiruna, Aitik); breccias are characterized by hydraulic breccia, exceptionally explosion breccia; As iron-skarn facies (Faleme, Candelaria, Pea Ridge), showing a polyphased emplacement, including an early and inner magnetite and K-Ca assemblage followed by a latter and outer hematite and Na assemblage; breccia facies are mainly chemical pseudobreccia; As mantos styles deposits (Tennant Creek, Bayan Obo, Kwyjibo); breccias are characterized by hydraulic and dissolutioncollapse facies; As veins systems (Ernest Henry, Wallaroo, Andes), where breccias can be structural or chemical. As epithermal style deposits (Tapajos, Mt Painter, Olympic Dam, Great Bear Lake – Wenecke, or Pea Ridge (Missouri)), forming breccia pipes, and veins. Pipes can be subvolcanic, phreatomagmatic or hydrothermal. Breccias are usually of multiple origins. There are also some affinities between IOGC(U) and Besshi-type Sedex deposits, with examples such as Otjihase, Matchless, Red Sea, Guyamas. They share the same geochemical assemblage, with the abundance of iron oxides, copper, gold, cobalt, in a locally extensive environment. FIGURE 5. Conceptual geological contexts of breccias in IOGC(U) deposits. Deeper environment are usually dominated by magnetite whereas surficial deposit are more hematite-rich. BDR method may be use to assess more precisely the style of brecciation in IOGC(U) deposits and compare the results to other styles of deposit. We will present some preliminary results of a systematic study of breccias in IOGC(U) deposits. Three level of comparison were performed: between different types of deposits, between different deposits, and at the scale of a deposit. Strong differences appear between different types of deposits. For instance, the IOGC(U) breccias displays of wide range of particle size distribution whereas orogenic gold deposits are much more characterized by distribution of particles with a limited range. The same observation could be done also for Cu-Mo porphyry systems. This illustrates the variation of processes occurring in IOGC(U) deposits. Other results showed that roundness is similar to breccia in CuMo porphyry deposits, but higher than in shear zone; Fabric is characterized by an almost absence of orientation in IOGC(U) deposits, much more frequent in others types of ore-deposits; (5) Complexity could be very high (Fig. 6); the only type of ore deposits that host breccia with such high scores are magmatic breccia in PGE deposits (Lac-des-Iles, Ontario). (BFD-1); Circularity varies from angulose (0) to rounded (10). Large symbols represent average value for each deposit. FIGURE 6. Comparison of two geometric parameters of breccias in IOGC(U) and other styles of deposit. Upper histograms: comparison of the particle size distribution for breccia between IOGC(U) (South Australia, mainly Olympic Dam) and Au shear zone (SZ, Abitibi greenstone belt); 0 means equal size distribution, 10 a high fractal value. Lower histograms: comparison of the complexity of the fragments of the breccia between IOGC(U) (South Australia, mainly Olympic Dam) and low temperature fluorite-barite vein type deposits (FIL, French Massif Central, mainly Le Rossignol); 0 means non corrosion, 10 highly corroded particles. Within the IOGC(U) class, difference on breccia styles is also significant between deposits. For instance, a quantitative analysis of the shape of the fragments, using roundness (value of sphericity) and complexity (BFD) shows that the F zone, in the North-Western part of the Olympic Dam deposit, displays much more corrosion that other deposits (Fig. 7). Such high values are clearly different from what occurs in a breccia pipe, and suggest that a large part of the breccias in this zone are related to solution process within a tectonic zone. At the scale of a deposit, large variation in particle shape distribution can also be observed. For instance, several deposits show an evolution from magmatic to hydraulic and solution breccias. Magmatic breccias are generally very early and are associated with pluton emplacement and magnetite deposition. Hydraulic breccias are associated with early hydrothermalism and Fe mobility. Explosive breccias occur in large systems. Solution breccias displaying evidence of dissolution and collapse, are associated with the development of the late hydrothermal system that is carrying most of the economic element (Cu-Au-REE-U). Tectonic breccias are usually associated to late cooling. Each stage corresponds to the progressive opening of the system that allows fluid to escape from the magma to the surface. Recognition of the degree of evolution of breccias (mixing and corrosion) can be used for an early assessment of their economic potential. A cross section in the Olympic Dam deposit for instance shows that complexity of the fragment increases strongly from the in situ hematite hydraulic-style brecciation (Pl. 1, Fig a1) to highly corroded fragments (Lei et al., 1995). Such criteria can be used easily during field traverse. Conclusion Breccias are key elements in the exploration for IOGC(U) deposits. Composition and geometric parameters allow recognition of the different generations and the evolution of each generations of breccias. Observations may be semi-quantified on the field using BDR or quantified in lab in order to define more precisely the maturation of brecciation, and define vectors to mineralization. The abundance of breccias in IOGC is related to the diversity of processes that cause fragmentation. Solution breccias in silicate system are probably one of the key elements that explains their abundance at different levels of the crust. Acknowledgment FIGURE 7. Comparison of two geometric parameters of breccias in three IOGC(U) deposits: Kwyjibo (Quebec), Faleme (Senegal) and Olympic Dam (F zone, South Australia). Fractal dimension represents the complexity The study of fragmentation processes associated to ore deposits have been supported mainly by NSERC, FQRNT, DIVEX and numerous mining exploration companies including Areva, Soquem, Sirios, Osisko, Goviex, and Iamgold. Références Barton M.D. and Johnson D. A., 1996. Evaporitic-source model for igneous related Fe-oxide-(REE-Cu-Au) mineralization. Geology, 24: 259-262. Bérubé D. and Jébrak M., 1999. High precision boundary fractal analysis for shape characterization. Computers & Geosciences, 25: 1059-1071. Billi, A. and Storti, F., 2004. 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Fe-oxyde-Au Deposits of the Olympic Dam/Ernest Henry-Type, in: New Developments in the Geological Understanding of some major ore types and environments, with implications for exploration. 1-44. Woodcock, N.H., Dickson, J.A.D., and Tarasewicz, J.P.T., 2007. Transient permeability and reseal hardening in fault zomes: evidence from dilation breccia textures. Lonergan, K., Jolly, R.J.H., Rawnsley, K., and Sanderson, D.J., eds. Geological Society, London, Special Publication, 270: 43-53. Plate descriptions PLATE 2. PLATE 1. View publication stats Compositional variations: a1: monomict breccia, Olympic Dam (South Australia); size of the photograph: 1m - a2: polymict breccia, Olympic Dam (South Australia), core; graduation in millimetres. Roundness variations: b1: low roundness, Kwyjibo (Quebec); size of the photograph: 1m - b2: high roundness, pebble dyke, Mt Gee (South Australia); size of the photograph: 1m. Complexity variations: c1: lobate fragment, Olympic Dam (South Australia), core – c2: fragments without corrosion, straight contour, Roxmere (Australia); size of the photograph: 0,5 m. Dilation variations: d1: high dilation: Prominent Hill (South Australia), core - d2: low dilation: Mary Kathleen (Australia); size of the photograph: 10 m. Particle Size Distribution variations: e1: fragments of similar size, Olympic Dam (South Australia); size of the photograph: 2m - e2: fractal distribution of fragments, Kourou Diako, KKKI, Faleme (Senegal), core. Fabric variations: f1: orientated fragments, Kwyjibo (Quebec) ; size of the photograph: 1m - f2: random orientation, Murdie Well (South Australia), core. All photographs from M. Jébrak, except c2, d2 (M. Gauthier).
