Kimberlite, Varty Lake (Canada)

Varty Lake Kimberlite dyke, near Belleville, Ontario (Canada) (Fig.7) intrude limestones of the Ordovician Black River and Trenton groups. The Varty Lake dike is exposed over a distance of 150 m in five prospect pits near the northwest comer of Varty Lake. In the most complete exposure, the dike is 1.5 m wide and is vertical, with a strike of 120°. The limestone host rocks are flat lying in the area but beds have been tilted up about 15° on either side of the dike.
The Varty Lake dike has two distinct zones: a fine-grained marginal zone with rare phlogopite phenocrysts nearest the wall rocks on either side, and a much coarser central region with abundant phlogopite phenocrysts. Samples from the coarse-grained central region contain between 20% and 30% phlogopite phenocrysts up to 3.0 mm in size and a lesser amount of serpentinized phenocrysts.
The groundmass consists of phlogopite, spinel, chlorite, apatite needles, and massive to euhedral perovskite aggregates all set in a serpentine-calcite matrix. The phlogopite phenocrysts optically exhibit two and often three concentric zones. Some phenocrysts have kink bands. possibly indicating some degree of deformation during emplacement. The bipyramidally terminated outline of some serpentinized phenocrysts suggests the former presence of olivine. However, the rounded edges of most of these serpentinized phenocrysts imply mechanical abrasion or absorption of original olivine during emplacement.

The Varty lake dike show fine-grained marginal zones that exhibit sharp contacts with the central parts of the dike, indicating that these marginal zones represent injections of volatile-rich fractionated liquid (Clement 1975) rather than flow differentiation products (Hon 1970). Primary magmas of the dike probably had high H20-CO2 contents similar to those of kimbelite. The rarity of xenocrysts and cognate nodules implies a limited degree of crystal fractionation of the magmas. This is supported by the primitive chemistry of the dike, involving high concentrations of the compatible elements (Ni, Co, and Cr), and by the high Mg(Mg+ Fe+) ratios.

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Fig.1: Geological map of the Lake Ontario region showing the locations of the Varty Lake dike. From Barnett (1984).





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kimberlite. Note the large green Cr-diopside megacrysts



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kimberlite, Sloan Ranch, Colorado. Note the large pyrope megacryst



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kimberlite breccia with macrocrysts of serpentinized olivine.





Sample kindly given to me by Graham Wilson (Turnstone Geological Services)


Bibliography



• R.L.Barnett; M.Arima; J.D.Blackwell; C.D.Winder (1984): The Picton and Varty Lake ultramafic dikes: Jurassic magmatism in the St. Lawrence Platform near Belleville, Ontario. Can. J. Earth Sci. 21, 1460-1472
• M. Arima; R.Kerrich (1988): Jurassic kimberlites from Picton and Varty Lake, Geochemical and stable isotopic characteristics. Contrib Mineral Petrol 99:385-391
•E.M.W.Skinner (2009): Devolopments in Kimberlite emplacement theory. The S.African Institute of Mining and Metallurgy Diamonds-Source to Use 2009


Photo
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Phlogopite and serpentinized olivine crystals (white) set in a groundmass composed by perovskite (rounded, brown crystals) and secondary minerals. PPL image, 2x (Field of view = 7mm)
kimberlite(canada)(2).jpg

Phlogopite and serpentinized olivine crystals set in a groundmass composed by secondary minerals. XPL image, 2x (Field of view = 7mm)
kimberlite(canada)(3).jpg

Phlogopite and serpentinized olivine crystals (white) set in a groundmass composed by perovskite (rounded, brown crystals) and secondary minerals. PPL image, 2x (Field of view = 7mm)
kimberlite(canada)(4).jpg

Phlogopite and serpentinized olivine crystals set in a groundmass composed by secondary minerals. XPL image, 2x (Field of view = 7mm)
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Phlogopite and serpentinized olivine crystals (white) set in a groundmass composed by perovskite (rounded, brown crystals) and secondary minerals. PPL image, 2x (Field of view = 7mm)
kimberlite(canada)(6).jpg

Phlogopite and serpentinized olivine crystals set in a groundmass composed by secondary minerals. XPL image, 2x (Field of view = 7mm)
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Phlogopite and serpentinized olivine crystals (white) set in a groundmass composed by perovskite (rounded, brown crystals) and secondary minerals. PPL image, 2x (Field of view = 7mm)
kimberlite(canada)(8).jpg

Phlogopite and serpentinized olivine crystals (white) set in a groundmass composed by perovskite (rounded, brown crystals) and secondary minerals. PPL image, 2x (Field of view = 7mm)
kimberlite(canada)(9).jpg

Phlogopite and serpentinized olivine crystals set in a groundmass composed by secondary minerals. XPL image, 2x (Field of view = 7mm)
kimberlite(canada)(10).jpg

Phlogopite and serpentinized olivine crystals (white) set in a groundmass composed by perovskite (rounded, brown crystals) and secondary minerals. PPL image, 2x (Field of view = 7mm)
kimberlite(canada)(11).jpg

Phlogopite and serpentinized olivine crystals set in a groundmass composed by secondary minerals. XPL image, 2x (Field of view = 7mm)
kimberlite(canada)(12).jpg

Phlogopite and serpentinized olivine crystals (white) set in a groundmass composed by perovskite (rounded, brown crystals) and secondary minerals. PPL image, 2x (Field of view = 7mm)
kimberlite(canada)(13).jpg

Phlogopite and serpentinized olivine crystals (white) set in a groundmass composed by perovskite (rounded, brown crystals) and secondary minerals. PPL image, 2x (Field of view = 7mm)
kimberlite(canada)(14).jpg

Phlogopite and serpentinized olivine crystals set in a groundmass composed by secondary minerals. XPL image, 2x (Field of view = 7mm)
kimberlite(canada)(15).jpg

Phlogopite and serpentinized olivine crystals (white) set in a groundmass composed by perovskite (rounded, brown crystals) and secondary minerals. PPL image, 2x (Field of view = 7mm)
kimberlite(canada)(16).jpg

Phlogopite and serpentinized olivine crystals set in a groundmass composed by secondary minerals. XPL image, 2x (Field of view = 7mm)
kimberlite(canada)(17).jpg

Phlogopite and serpentinized olivine crystals (white) set in a groundmass composed by perovskite (rounded, brown crystals) and secondary minerals. PPL image, 2x (Field of view = 7mm)
kimberlite(canada)(18).jpg

Phlogopite and serpentinized olivine crystals set in a groundmass composed by secondary minerals. XPL image, 2x (Field of view = 7mm)
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Phlogopite and serpentinized olivine crystals set in a groundmass composed by secondary minerals. XPL image, 2x (Field of view = 7mm)
kimberlite(canada)(20).jpg

Phlogopite and serpentinized olivine crystals set in a groundmass composed by secondary minerals. XPL image, 2x (Field of view = 7mm)
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Phlogopite and serpentinized olivine crystals (white) set in a groundmass composed by perovskite (rounded, brown crystals) and secondary minerals. PPL image, 2x (Field of view = 7mm)
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Phlogopite and serpentinized olivine crystals (white) set in a groundmass composed by perovskite (rounded, brown crystals) and secondary minerals. PPL image, 2x (Field of view = 7mm)
kimberlite(canada)(44).jpg

Phlogopite and serpentinized olivine crystals (white) set in a groundmass composed by perovskite (rounded, brown crystals) and secondary minerals. PPL image, 2x (Field of view = 7mm)
kimberlite(canada)(45).jpg

Phlogopite and serpentinized olivine crystals (white) set in a groundmass composed by perovskite (rounded, brown crystals) and secondary minerals. PPL image, 2x (Field of view = 7mm)
kimberlite(canada)(46).jpg

Phlogopite and serpentinized olivine crystals set in a groundmass composed by secondary minerals. XPL image, 2x (Field of view = 7mm)
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Phlogopite and serpentinized olivine crystals set in a groundmass composed by secondary minerals. XPL image, 2x (Field of view = 7mm)
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Phlogopite and serpentinized olivine crystals set in a groundmass composed by secondary minerals. XPL image, 2x (Field of view = 7mm)
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Phlogopite and serpentinized olivine crystals set in a groundmass composed by secondary minerals. XPL image, 2x (Field of view = 7mm)
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Phlogopite and serpentinized olivine crystals (white) set in a groundmass composed by perovskite (rounded, brown crystals) and secondary minerals. PPL image, 2x (Field of view = 7mm)
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Phlogopite and serpentinized olivine crystals (white) set in a groundmass composed by perovskite (rounded, brown crystals) and secondary minerals. PPL image, 2x (Field of view = 7mm)
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Phlogopite crystal set in a groundmass composed by perovskite (rounded, brown crystals) and secondary minerals. PPL image, 10x (Field of view = 2mm)
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Phlogopite crystal set in a groundmass composed by secondary minerals. XPL image, 10x (Field of view = 2mm)
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Phlogopite crystal set in a groundmass composed by perovskite (rounded, brown crystals) and secondary minerals. PPL image, 10x (Field of view = 2mm)
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Phlogopite crystal set in a groundmass composed by secondary minerals (with calcite). XPL image, 10x (Field of view = 2mm)
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Phlogopite crystal set in a groundmass composed by perovskite (rounded, brown crystals) and secondary minerals. PPL image, 10x (Field of view = 2mm)
kimberlite(canada)(33).jpg

Phlogopite crystal set in a groundmass composed by perovskite (rounded, brown crystals) and secondary minerals. PPL image, 10x (Field of view = 2mm)
kimberlite(canada)(34).jpg

Phlogopite crystal set in a groundmass composed by secondary minerals. XPL image, 10x (Field of view = 2mm)
kimberlite(canada)(35).jpg

Phlogopite crystal set in a groundmass composed by perovskite (rounded, brown crystals) and secondary minerals. PPL image, 10x (Field of view = 2mm)
kimberlite(canada)(36).jpg

Phlogopite crystal set in a groundmass composed by secondary minerals. XPL image, 10x (Field of view = 2mm)
kimberlite(canada)(37).jpg

Phlogopite crystal set in a groundmass composed by perovskite (rounded, brown crystals) and secondary minerals. PPL image, 10x (Field of view = 2mm)
kimberlite(canada)(38).jpg

Phlogopite crystal set in a groundmass composed by secondary minerals. XPL image, 10x (Field of view = 2mm)
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Groundmass composed by perovskite (rounded, brown crystals) and secondary minerals. PPL image, 10x (Field of view = 2mm)