Joint Characteristics and Spatial Distribution

Of the diamond boreholes drilled within this assemblage, the only orientated holes are NDDH0614, NDDH07001 and NDDH07002. Within these boreholes; 46% of all joints were recorded to contain no infill or mineral coating on the joint plane. 23% were calcite coated joints, 15% chlorite coated, 14% quartz coated and 2% talc coated. The mean orientation of joints with no infill is dipping 06° to the E. Another set is dipping 85° to the NE (Figure 3.51). Calcite coated joints are scattered but are mostly shallowly dipping (Figure 3.51). Other minor sets are dipping 60° to the ENE and dipping 52° to the NNW. Although scattered,

Magnesite Fault Eastern Contact Fault

Drillhole Collar Eastern Splay Fault Legend:

Eastern Splay Assemblage Postulated continuation of the Eastern Splay

Assemblage

L L’

East Wall Assemblage West Wall Assemblage

Main Host Assemblage

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chlorite coated joints are orientated at a mean orientation of 18°/080° (Figure 3.51). Quartz coated joints are mostly dipping to the NE or shallowly dipping. There is only one data point for talc coated joints; this is dipping 10° to the E (Figure 3.51).

Figure 3.51. Pole plot showing orientation data of joints with no infill, calcite (CC), chlorite (CH),

quartz (QZ) and talc (TC) within the Eastern Splay Assemblage.

A three dimensional terrain model (DTM) was generated of the 15m high pit face on the 80RL looking SE using photogrammetry. An additional twelve joints were selected and their orientations were generated by photogrammetry (Figure 3.52). Although many of the joints were too high up the face to see infill type and joint roughness profiles, the majority of these joints had no infill. The additional joint orientation data were plotted on a stereonet (Figure 3.52) using the Adam Technology 3DM™ Photogrammetry in-built stereonet generator.

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Figure 3.52. A- DTM of the 80RL. Blue halos denote joints. Looking SE. B – Pole/contour plot

showing joint orientation from A. The more persistent the joint in the model above, the larger the pole

within the stereonet below.

Many of the joints recognised using the photogrammetry technique are dipping 40° to the W. This is the orientation of a common set of unfavourably dipping joints seen within the East Wall Assemblage (‘Ski-jump joints’). These joints are of particular slope stability concern for the mine, acting as basal slip planes for recent failures on the E wall (refer to Section 3.3.2). Although remaining a slope stability concern within the Eastern Splay Assemblage, the difference in the strike of the pit face reduces the risk of failure on these discontinuities. The unfavourably oriented joints are on the eastern end of the face. A damage zone of intensely jointed rock is visible to the E of the Eastern Contact Fault within the Eastern Wall

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Assemblage. This damage zone extends N-S along the strike length of the Eastern Contact Fault in some areas such as within the Eastern Splay Assemblage. The unfavourably orientated joints are located within this damage zone.

Comparatively, the orientations of joints logged within boreholes (Figure 3.51) and the joints captured with photogrammetry (Figure 3.52) are different. For all other assemblages within North Pit, many more joint recordings were taken so a general orientation trend is noticeable within a large data set. For the Eastern Splay Assemblage, <70 joint recordings were taken making it more difficult for major joint orientation trends to be visible. Sampling bias also has to be taken into account when using two methods to retrieve joint data. Two boreholes were drilled E to W (NDDH0614 and NDDH07002) and one was drilled W to E (NDDH07001). The trend and plunge of the borehole presents bias within drilling and the geometry of the pit wall presents bias within photogrammetry. This could account for some of the difference in joint orientation between the two methods. The west dipping joints should have been detected in NDDH07001 but this drillhole did not penetrate through to the Eastern Splay Fault (Fig. 3.53) and was 100 m higher where it approaches the fault.

Calcite coated joints were only found within the mafic carbonate rich schist of the Eastern Splay Assemblage. No calcite coated joints were recorded within the dolomitic rich mylonitised rock types within this assemblage. The majority of calcite filled joints have an undulating and rough joint profile. This roughness profile is the most common within the MHA and WWA but an undulating and smooth profile dominates within the East Wall Assemblage. Due to the roughness, friction angles are increased along these discontinuities within the assemblage.

Chlorite coated joints were found within NDDH07001 AND NDDH07002. They are distributed throughout mafic and mylonitised dolomitic lithologies of the assemblage. The orientations of these joints differ from the foliation orientation in the assemblage. Therefore it

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is clear that foliation has not been mistaken for chlorite coated joints. Planar and smooth joint roughness profiles are the most common within this assemblage, reducing basic friction angles on the joints. This profile is the same as for chlorite filled joints in all other assemblages of North Pit.

Joints with no infill are the most common within this assemblage. This is a common trend for all assemblages. These joints, although evident at regular intervals down-hole, are concentrated close to the Eastern Contact Fault (Figure 3.53). Undulating and rough joint profiles are the most common, which is different to the undulating and smooth profiles which dominate joints with no infill within the other assemblages.

Figure 3.53. Cross Section L-L’ showing the distribution of joints with no infill within the Eastern

Splay Assemblage; as light grey discs down-hole. Section: 8649 m N (looking N). Refer to digital Appendix 8 for a complete lithological legend.

Quartz coated joints are only distributed within one 10m interval in NDDH07002. The joints are in both mafic and dolomitic lithologies. The proportion of quartz coated joints within the Eastern Splay Assemblage is higher than within other assemblages but with the small sample set this is probably not significant. Undulating and rough joint profiles are the most common,

L L’

Legend:

Eastern Contact Fault Eastern Splay Fault North Pit August 2012 surface

Collar Location and drillhole ID Joints with no infill down-hole

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increasing basic friction angles of these discontinuities.

3.6.3 Vein Characteristics and Spatial Distribution

A small volume of veins were recorded within the Eastern Splay Assemblage. 86% were calcite veins and only one quartz vein was recorded. The calcite vein orientation, although scattered, were shallow and or dipping to the E. Dips range from 10° to 75° (Figure 3.54).

Figure 3.54. Pole plot showing orientation data of calcite (CC) veins and quartz (QZ) veins within the

Eastern Splay Assemblage.

Calcite veins occur within carbonate-bearing mafic assemblages of the Eastern Splay Assemblage. The veins are concentrated within a zone 25 m W of the Eastern Splay Fault. The quartz vein was detected within a mafic lithology next to the quartz coated joints described in Section 3.6.2. The quartz veins are strongly deformed, boudinaged and brecciated within this assemblage (Figure 3.55). Calcite veins are not as thick, not deformed and generally are orthogonal to the quartz veins; overprinting them.

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Figure 3.55. Vein types within the Eastern Splay Assemblage. A – Boudinaged quartz veins within mafic schist.

B – Deformed quartz vein within a dolomite rich lithology. C – Flat lying undeformed calcite vein within mafic schist. Geological hammer is approximately 35 cm in length.

Abbreviations: QTZ- Quartz, CC- Calcite, MXR- Mafic carbonate schist and SLO- Dolomitic lithology.

3.6.4 Foliation Characteristics

Only a small number of foliations were recorded within the Eastern Splay Assemblage. All the foliations within the boreholes were FO2 (moderate foliation). Refer to Section 3.2 for an overview of foliation logging parameters. There are two main sets of foliation orientation; steeply dipping to the W and moderately dipping to the SE (Figure 3.56).

3.6.5 Failure Modes of the Eastern Splay Assemblage

Failure mechanisms within the Eastern Splay Assemblage are lithologically controlled, similar to the MHA and WWA. Due to the variable structural and strength characteristics of the rocks within the Eastern Splay Assemblage, overhang of massive rocks is a geotechnical

A C B QTZ QTZ QTZ SLO CC MXR MXR 5 cm

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Figure 3.56. Pole plot showing orientation data of foliations recorded within the Eastern Splay Assemblage.

problem. Massive magnesite lenses outcrop within the assemblage (Figure 3.57 – A) in a similar manner to those within the WWA. The kernels of massive magnesite are surrounded by intensely foliated, puggy chlorite rich lithologies which falls down the face after heavy rainfall, leaving the magnesite block protruding and at risk of failure. Similar to the MHA and WWA, weak foliation planes or joints facilitate toppling failures on benches. Figure 3.57 – B and C show how the 140 RL within this assemblage is presenting tension cracks, a sign that there is movement on the wall below. Lithologically, structurally and geotechnically the Eastern Splay Assemblage is very different from the East Wall Assemblage. The East Wall rocks are strong, joint dominated with areas of intense foliation. Puggy, chloritic seams are not observed in these rocks neither are magnesite lenses or variable foliation orientation. The Eastern Splay Assemblage are softer and more schistose than the East Wall rocks, but the failure mechanisms and rock mass behaviour are similar to the MHA and WWA. Persistent hematite coated joints were not found and therefore planar failure is not as much a slope stability concern for this assemblage as for the East Wall. Due to the area originally being

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mapped as part of the East Wall Assemblage, caution is advised for future planning in this area.

Figure 3.57.A – Magnesite lens within the Eastern Splay Assemblage on the 80RL. Looking SE. B – The 140RL berm within the Eastern Splay Assemblage. Looking SW. C – Tension cracks on the 140RL berm.

5 m 5 m 20 cm 140RL A B C

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