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Journal Article

The shapes of dikes: Evidence for the influence of cooling and inelastic deformation Available to Purchase

Katherine A. Daniels, Janine L. Kavanagh, Thierry Menand, J. Sparks R. Stephen
Journal: GSA Bulletin
Published: 01 July 2012
GSA Bulletin (2012) 124 (7-8): 1102–1112.
DOI: https://doi.org/10.1130/B30537.1
...Katherine A. Daniels; Janine L. Kavanagh; Thierry Menand; J. Sparks R. Stephen Abstract We provide detailed observations on the shape of dikes from well-exposed field locations in the Isle of Rum, Scotland, and Helam Mine, South Africa. The basaltic Rum dikes crop out on a smaller scale than...
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Location and distribution of dyke thickness measurements from Helam Mine: (a) Plan view and (b) east–west plane projection with depth below the current surface level. The measurements have good coverage and are well distributed through the mined cavity. The data are grouped into depth-dependent mining levels, ranging from Level 16 to 23 (E, Edward; J, John).

Location and distribution of dyke thickness measurements from Helam Mine: (... Available to Purchase

Published: 15 June 2011
Fig. 2. Location and distribution of dyke thickness measurements from Helam Mine: ( a ) Plan view and ( b ) east–west plane projection with depth below the current surface level. The measurements have good coverage and are well distributed through the mined cavity. The data are grouped into depth
Image
Figure 1. A: Plan view of Main kimberlite dike array at Helam Mine (Muil and Changehouse dikes occur within several meters of Main dike). All three dikes occur as series of en echelon segments (inset shows locations of Venetia and Helam Mines). B:Cross-section view of Helam Mine with approximate stratigraphy. Mining excavation corresponds approximately with geometry of dikes. Dikes appear to taper in width at the shale-quartzite boundary. Mine workings are not shown.

Figure 1. A: Plan view of Main kimberlite dike array at Helam Mine (Muil an... Available to Purchase

Published: 01 September 2007
Figure 1. A: Plan view of Main kimberlite dike array at Helam Mine (Muil and Changehouse dikes occur within several meters of Main dike). All three dikes occur as series of en echelon segments (inset shows locations of Venetia and Helam Mines). B:Cross-section view of Helam Mine with approximate
Image
Detail of dykes at Helam Mine. Due to the close proximity of the Main, Male and Changehouse dykes within any given segment, only the Main dyke is shown. Below are Thickness (cm) vs. Distance from Dyke Centre (m) plots (TvD-1 to TvD-7) with data extending from the dyke centre to the mined terminations of the dykes (highlighted by narrow grey boxes). At right are basic orientation data (poles to dyke contacts, lower hemisphere plots) for Main (n=179), Male (n=18) and Changehouse (n=20) dykes. As for dykes on the Star Mine, the dykes display very small angular variations or twists from the array trend.

Detail of dykes at Helam Mine. Due to the close proximity of the Main, Male... Available to Purchase

Published: 01 December 2003
Figure 5. Detail of dykes at Helam Mine. Due to the close proximity of the Main, Male and Changehouse dykes within any given segment, only the Main dyke is shown. Below are Thickness (cm) vs. Distance from Dyke Centre (m) plots (TvD-1 to TvD-7) with data extending from the dyke centre
Image
(A) Surface outcrop map of the John and Edward kimberlite dike segments, Helam Mine, South Africa. (B) Contour plot of dike thickness for the John and Edward dike segments plotted against depth below the current surface and distance easting. The shaded area indicates locations where data were collected. The approximate stratigraphy and unit contacts (dashed line) are shown: quartzite (Qtz), shale (Sh), and dolerite (Dol). The map inset indicates the location of Helam Mine in southern Africa (25.594°S, 26.659°E).

(A) Surface outcrop map of the John and Edward kimberlite dike segments, He... Available to Purchase

Published: 01 July 2012
Figure 3. (A) Surface outcrop map of the John and Edward kimberlite dike segments, Helam Mine, South Africa. (B) Contour plot of dike thickness for the John and Edward dike segments plotted against depth below the current surface and distance easting. The shaded area indicates locations where
Image
Histograms showing the dyke thickness distribution of the Swartruggens kimberlite dyke array for (a) John and (b) Edward dyke segments, and (c) Edward and John dyke segments from Helam Mine.

Histograms showing the dyke thickness distribution of the Swartruggens kimb... Available to Purchase

Published: 15 June 2011
Fig. 7. Histograms showing the dyke thickness distribution of the Swartruggens kimberlite dyke array for ( a ) John and ( b ) Edward dyke segments, and ( c ) Edward and John dyke segments from Helam Mine.
Image
East–west plane projection with depth, showing variation of dyke thickness across the length and breadth of the John and Edward dyke segments at Helam Mine. Measurements are colour coded according to thickness in metres. An approximate stratigraphy of quartzite (Qtz.), shale (Sh.), dolerite (Dol.) and their contacts (dashed lines) is shown for the intruded horizons.

East–west plane projection with depth, showing variation of dyke thickness ... Available to Purchase

Published: 15 June 2011
Fig. 10. East–west plane projection with depth, showing variation of dyke thickness across the length and breadth of the John and Edward dyke segments at Helam Mine. Measurements are colour coded according to thickness in metres. An approximate stratigraphy of quartzite (Qtz.), shale (Sh
Image
(a) Main kimberlite dyke emplaced into dolerite (Dol) host-rock with close-spaced dyke-parallel fractures. See accompanying sketch to the right for details. Side view, up direction is at the top of the image. (b) Fractures in host-rock adjacent to Muil dyke walls are asymptotically parallel to the dyke. The sketch to the right highlights these features. Up direction is into the page. All photographs taken at Helam Mine underground at c. 750 m depth.

( a ) Main kimberlite dyke emplaced into dolerite (Dol) host-rock with clos... Available to Purchase

Published: 15 June 2011
parallel to the dyke. The sketch to the right highlights these features. Up direction is into the page. All photographs taken at Helam Mine underground at c . 750 m depth.
Journal Article

Insights of dyke emplacement mechanics from detailed 3D dyke thickness datasets Available to Purchase

J.L. Kavanagh, R.Stephen J. Sparks
Published: 15 June 2011
Journal of the Geological Society (2011) 168 (4): 965–978.
DOI: https://doi.org/10.1144/0016-76492010-137
...Fig. 2. Location and distribution of dyke thickness measurements from Helam Mine: ( a ) Plan view and ( b ) east–west plane projection with depth below the current surface level. The measurements have good coverage and are well distributed through the mined cavity. The data are grouped into depth...
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Figure 2. A: Angular shale breccia (br) intruded by kimberlite stringers (kd) (side view, propagation direction is vertical). Note blunt termination of dike against breccia. Kimberlite magma occurs in pore space of breccia immediately above dike termination. Thin kimberlite stringer in far left. B: Spheroidal altered dolerite in Helam Mine. Main kimberlite dike has split into series of thin stringers within dike jog (side view, propagation direction is vertical). Spheroidal clasts are prominent left of center. 25 cm shown on rule.

Figure 2. A: Angular shale breccia (br) intruded by kimberlite stringers (k... Available to Purchase

Published: 01 September 2007
: Spheroidal altered dolerite in Helam Mine. Main kimberlite dike has split into series of thin stringers within dike jog (side view, propagation direction is vertical). Spheroidal clasts are prominent left of center. 25 cm shown on rule.
Image
Macroscopic features
 a) Photo-mosaic of an approximately 5m long extent of Burns dyke (hangingwall) (11 Level East, Cross-Cut 9, Star Mine). The dyke is 60cm across at its widest. The opposite contacts of the host shale display a high degree of similarity, in terms of their irregular, zigzag pattern and asperities (AP) that extend into the kimberlite. Note the in-situ breccia (ISB) in two areas and the overall breccia-free nature of the kimberlite.
 b) Sympathetic fracture cleavage (SC) on either side of 35cm-wide East Star dyke (K), which is hosted by a dolerite sill (HR = host rock) in this area (11½ Level Centre, Star Mine). In this exposure, the cleavage zone extends for up to 80cm to the south of the dyke (left on photograph) and a minimum of 20cm into the poorly-exposed northern wall of the dyke. Width of exposure is 180cm.
 c) Closely-spaced fracture cleavage (SC), exhibiting extreme spalling into mined-out areas (K - at right). Fracture spacing varies from about 5 to 50cm (8 Level East, Cross-Cut 46, Helam Mine). Length of pen is 15cm.
 d) Internal high-aspect ratio breccia clast of bioturbated sandstone where the Burns dyke splits into multiple stringers prior to terminating. The in-situ breccia (ISB) displays almost no movement with respect to the adjacent host rock (HR), and is separated by a thin (2cm wide) kimberlite stringer (KS) to the north and a 6cm wide stringer to the south (13 Level East, Cross-Cut 11, Star Mine). Length of hammer head is 13cm.
 e) Highly fractured in-situ breccia (ISB) within the Burns dyke, hosted by Ecca shales. The ISB is separated from the main host rock by a thin kimberlite stringer (KS). Note the matching morphology of the opposite sides (N-left and S-right) of the shale host rock (11 Level East, Cross-Cut 9, Star Mine). Width of dyke is 60cm.
 f) Fibrous calcite veinlets at the edge of the zoned M8 dyke, which has olivine macrocryst-rich margins. In this instance, the left-stepping, overlapping format of the veins mimics that of the overall kimberlite array in the area (West wall of the Marsfontein pipe, Klipspringer system). Scale in centimetres.
 g) Multiple, fine calcite fibres, orthogonal to the host rock, in an anastomosing set of fibrous veinlets (FV) (East Star dyke - K, 10½ Level Centre, Star Mine). Scale in centimetres.
 h) Highly brecciated kimberlite-free zone parallel to the Main dyke in a dyke overlap area (21 Level, Helam Mine). Length of pen is 15cm.
 i) Highly brecciated zone (B) within shale host rock (HR) near kink or change in strike of the Main dyke (18 Level, Helam Mine). Width of exposure is 150cm.
 j) Large cavity at a step or offset in the Leopard dyke, Klipspringer Mine, extending from 3 to 4 Level. Height of cavity is approximately 2m. Note the abundant stalactites.
 k) Wedge-shaped kimberlite apophysy (AP), trending at approximately 70° to the main Burns dyke (at right Main dyke - K). The apophysy indicates bending of the host rock bridge (HR) between two adjacent, dilating overlapping dyke segments (11 Level East, Cross-Cut 9, Star Mine).
 I) Example of shale breccia with a kimberlite matrix, from a “roll”, wherein the kimberlite steps laterally or assumes a near-horizontal attitude in mine workings (Wynandsfontein dyke, Star Mine sample collection). The scale is in cm.

Macroscopic features
 a) Photo-mosaic of an approximately 5m long extent of... Available to Purchase

Published: 01 December 2003
), exhibiting extreme spalling into mined-out areas ( K - at right). Fracture spacing varies from about 5 to 50cm (8 Level East, Cross-Cut 46, Helam Mine). Length of pen is 15cm.
 d) Internal high-aspect ratio breccia clast of bioturbated sandstone where the Burns dyke splits into multiple stringers prior
Image
(a) Fracture-bound spheroidal altered dolerite (Dol) adjacent to Muil dyke. The hard resistant round cores and onion-skin style weathering of the host rock should be noted. (b) The Main kimberlite dyke has split into a series of stringers at the dyke jogs. The magma was intruded along fracture planes and partially wraps around the spheroidal blocks of altered dolerite. Ruler length is 1 m. Side view, up direction is at the top of the image. (c) Enlarged section of (b). Ruler length shown is c. 65 cm. All photographs taken at Helam Mine underground at c. 750 m depth. Sketches provided to the right of the photographs for clarity.

( a ) Fracture-bound spheroidal altered dolerite (Dol) adjacent to Muil dyk... Available to Purchase

Published: 15 June 2011
fracture planes and partially wraps around the spheroidal blocks of altered dolerite. Ruler length is 1 m. Side view, up direction is at the top of the image. ( c ) Enlarged section of ( b ). Ruler length shown is c . 65 cm. All photographs taken at Helam Mine underground at c . 750 m depth. Sketches
Image
Fractional distance along the breadth of the John (a) and Edward (b–c) dyke segments, Helam Mine, and East Star (d) dyke segment, Star Mine, plotted against fractional half-thickness. The measurements (open diamonds) document dyke thickness. The best-fit model ellipse (blue dashed line) and teardrop (red long-dashed line) calculate dyke thickness according to the elastic model of Pollard & Muller (1976). (a) John Level 19: n = 172, host-rock dolerite, G = 40 GPa, depth range = 34.6 m, P = 36 MPa (R2 = 0.28) and ∇P = 35 kPa m (R2 = 0.48). (b) Edward Level 20: n = 181, host-rock dolerite, G = 40 GPa, depth range = 28.7 m, P = 40 MPa (R2 = 0.51) and ∇P = 70 kPa m (R2 = 0.72). (c) Edward Levels 19 and 20: n = 342, host-rock dolerite, G = 40 GPa, depth range = 54.4 m, P = 36 MPa (R2 = 0.48) and ∇P = 62.5 kPa m (R2 = 0.71). (d) East Star Levels 6 and 7: n = 84, host-rock interbedded shales and sandstones, G = 40 GPa, depth range = 77.8 m, P = 72 MPa (R2 = 0.43) and ∇P = 263 kPa m (R2 = 0.56). See Figures 2b and 6b for level depths for Helam and Star Mines, respectively.

Fractional distance along the breadth of the John ( a ) and Edward ( b– c )... Available to Purchase

Published: 15 June 2011
Fig. 13. Fractional distance along the breadth of the John ( a ) and Edward ( b– c ) dyke segments, Helam Mine, and East Star ( d ) dyke segment, Star Mine, plotted against fractional half-thickness. The measurements (open diamonds) document dyke thickness. The best-fit model ellipse (blue dashed
Journal Article

Mechanically disrupted and chemically weakened zones in segmented dike systems cause vent localization: Evidence from kimberlite volcanic systems Available to Purchase

R.J. Brown, J. Kavanagh, R.S.J. Sparks, M. Tait, M. Field
Journal: Geology
Published: 01 September 2007
Geology (2007) 35 (9): 815–818.
DOI: https://doi.org/10.1130/G23670A.1
...Figure 1. A: Plan view of Main kimberlite dike array at Helam Mine (Muil and Changehouse dikes occur within several meters of Main dike). All three dikes occur as series of en echelon segments (inset shows locations of Venetia and Helam Mines). B:Cross-section view of Helam Mine with approximate...
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(a) Angular shale breccia (Sh, Br) intruded by Main kimberlite (K). Side view, up direction is at the top of the image. The blunt dyke termination against the breccia should be noted. Kimberlite occurs within the pore spaces of the breccia immediately above the dyke termination. Thin kimberlite stringer (K) in the far right. (b) Muil dyke emplaced into a brecciated dolerite (Br). The irregular margins of the kimberlite dyke (K) and separation into en echelon segments should be noted. Side view, up direction is at the top of the image. (c) Branched Main kimberlite dyke (K), emplaced into highly fractured dolerite (Dol) that is brecciated in the region between the dyke limbs. Sketch provided to the right for clarity. Ceiling view, up direction is into the page. (d) Kimberlite stringers (K) intruded a pre-existing fracture plane. In the top-left of the photograph the stringer is c. 1 cm thick. Sketch provided to the right for clarity. Ceiling view, up direction is into the page. All photographs taken at Helam Mine underground at c. 750 m depth.

( a ) Angular shale breccia (Sh, Br) intruded by Main kimberlite (K). Side ... Available to Purchase

Published: 15 June 2011
cm thick. Sketch provided to the right for clarity. Ceiling view, up direction is into the page. All photographs taken at Helam Mine underground at c . 750 m depth.
Image
Microscopic Textures - Stretched calcite fibrous veins
 a) Stretched calcite fibres in Main dyke, Helam Mine: highly irregular kimberlite matrix (KM) forms the host rock to calcite veins. These contain very thin, high aspect ratio calcite fibres (CF), which grow epitaxially on very fine-grained matrix carbonate and occur orthogonal to the dyke’s intrusive contact. Aligned with the calcite fibres are kimberlitic phenocrystic phlogopites (PP), which have pointed terminations centred on the contact between adjacent calcite fibres. Such phiogopite phenocrysts display very minor crack-seal growth or extension parallel to the dilation direction. The contact to the vein does not transect the indicated phlogopite macrocryst (PM). Plane Polarized Light (PPL), Horizontal Field of View (HFOV) = 1.75mm.
 b) Stretched calcite fibres (CF) in Main dyke: Description as above. Note the apatite crystal (AT) at bottom left. PPL, HFOV = 1.75 mm.
 c) Stretched calcite fibres (CF) and a single phlogopite phenocryst (PP) extending across the width of a vein in Main dyke. PPL, HFOV = 2.5mm.
 d) Description as above. Note the locally curved nature of the calcite fibres, due to growth interference with the larger curved phlogopite phenocryst. PPL, HFOV = 2.6mm.
 e) Backscatter mosaic of a vein in Main dyke. Besides the ubiquitous high aspect ratio calcite fibres (CF), completely serpentinised, elongate olivine phenocrysts (OP). The latter contains secondary opaques. High reflectance barite (B) also extends into the vein. The width of the vein is approximately 1mm.

Microscopic Textures - Stretched calcite fibrous veins
 a) Stretched calcit... Available to Purchase

Published: 01 December 2003
Figure 9. Microscopic Textures - Stretched calcite fibrous veins
 a) Stretched calcite fibres in Main dyke, Helam Mine: highly irregular kimberlite matrix ( KM ) forms the host rock to calcite veins. These contain very thin, high aspect ratio calcite fibres ( CF ), which grow epitaxially on very
Journal Article

Structural overview of selected Group II kimberlite dyke arrays in South Africa: implications for kimberlite emplacement mechanisms Available to Purchase

I.J. Basson, G. Viola
Published: 01 December 2003
South African Journal of Geology (2003) 106 (4): 375–394.
DOI: https://doi.org/10.2113/106.4.375
...Figure 5. Detail of dykes at Helam Mine. Due to the close proximity of the Main, Male and Changehouse dykes within any given segment, only the Main dyke is shown. Below are Thickness (cm) vs. Distance from Dyke Centre (m) plots (TvD-1 to TvD-7) with data extending from the dyke centre...
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Journal Article

GEM-QUALITY DIAMONDS: SOURCE DISCRIMINATION Available to Purchase

L. CONEY, A.V. MOILA, A.G. QUADLING
Published: 01 March 2012
South African Journal of Geology (2012) 115 (1): 33–46.
DOI: https://doi.org/10.2113/gssajg.115.1.33
... of diamonds, particularly those that are gem-quality, creates difficulties with scientific fingerprinting as a mechanism to discriminate diamonds. Conflict diamonds, or “blood diamonds”, are diamonds that are mined in conflict zones, and sold by rebel groups to finance wars against legitimate...
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Spectroscopic analysis of microdiamonds in ophiolitic chromitite and peridotite Open Access

Kyaw Soe Moe, Jing-Sui Yang, Paul Johnson, Xiangzhen Xu, Wuyi Wang
Journal: Lithosphere
Publisher: GSW
Published: 20 March 2017
Lithosphere (2018) 10 (1): 133–141.
DOI: https://doi.org/10.1130/L603.1
...-octahedral diamonds have been reported in nature. Diamonds from the Swartruggens dike in the Helam Mine, South Africa, exhibit cubo-octahedral growth sectors ( McKenna et al., 2004 ). Octahedral diamonds from Yakutian kimberlites have cubo-octahedral growth bands ( Bulanova, 1995 ). This growth pattern can...
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Tracking sources of selected diamonds from Southern Africa based on carbon isotopic and chemical impurities Available to Purchase

A.T. Kidane, M. Koch-Müller, M. Wiedenbeck, M. J. de Wit
Published: 01 September 2017
South African Journal of Geology (2017) 120 (3): 371–384.
DOI: https://doi.org/10.25131/gssajg.120.3.371
... sources; or Rayleigh fractionation processes within the diamond forming process ( Palot et al. 2012 ; Smart et al. 2011 ; Cartigny 2005 ; Javoy et al. 1986 ; Javoy et al. 1984 ; Deines 1980 ). The Swartruggens Group kimberlites are exploited in the Helam Mine in the west central Kaapvaal...
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