Replies to post #14041 on Alkane Inc (ALKN)

[Shaun Spelliscy]

There are several groups and classifications of lamprohyres.

If the lamprohyre is a minette’ i.e. a mica lamprophyre it should be studied by someone specialized in this field, such as one of the authors of the paper outlined below.

Diamondiferous Volcaniclastic debris flows of Wawa, Ontario, Canada

Lefebvre* NS, Kopylova MG, Kivi KR and Barnett RL

Historically diamonds are recovered from Proterozoic to Cenozoic magmatic rocks such as kimberlite, and lamproite, and occasionally from lamprophyre and basalt. An atypical, highly diamondiferous occurrence has recently been discovered in the western section of the Michipicoten greenstone belt, within the Wawa subprovince of the Superior craton. The Wawa rocks are unique because they represent an Archean aged diamondiferous occurrence. They have been metamorphosed and deformed, and little evidence of their primary magmatic nature is preserved. The aim of this study is to determine if these rocks are metamorphic equivalents of known diamondiferous deposits or a new, previously unrecognized, deposit type.

Two diamond-bearing rock types have been recognized in the Wawa area and are interpreted as: polymict volcaniclastic breccia and younger lamprophyric rock which contain rare fragments of the volcaniclastic breccia. Both rock types have been metamorphosed to upper greenschist facies.

The matrix- to clast-supported breccia forms thick (~60 to 70 m) units. It contains dominantly angular, granule to large boulder-sized fragments with a wide variety of lithologies, including metamorphosed mantle ultramafic rocks with high Cr and Ni content. Irregular and oval shaped, aphanitic fragments and similar aphanitic rinds around lithic fragments are present in some breccia areas. These are believed to be juvenile and cored lapilli, and their presence implies incorporation of a pyroclastic component in the breccias. The breccias are interpreted to be volcaniclastic debris flow deposits based on the stratigraphy, the wide range in fragment lithologies, poor sorting, and lack of sedimentary structures. The fine-grained matrix of the breccia is comprised of the typical upper greenschist mineral assemblage for rocks of mafic composition. Two foliations, termed S1 and S2, are present and are defined by the alignment of actinolite grains. No obvious igneous textures and minerals have been preserved. Occasional oscillatory zoned hornblende, biotite and unknown mineral pseudomorphed by epidote are microstructurally pre- to syn-S1. Large, euhedral, oscillatory zoned hornblende are interpreted as possible relict phenocrysts and probably the only primary phase preserved.

The lamprophyre occurs as dikes which cross-cut the breccia. In other areas the relationship between the lamprophyre and the breccia, is unclear where it overlies the breccia along straight, long, parallel contacts that may be depositional in origin. The lamprophyre contains commonly 5-10% fragments of surrounding country rock, occasional altered ultramafic mantle xenoliths, and rare breccia. It is petrographically and compositionally similar to the breccia matrix.

The pre- to syn- S1, oscillatory zoned hornblendes in the breccia and the lamprophyre were classified as tschermakite, pargasite, edenite, and magnesio-hornblende. Assuming these hornblendes retained their magmatic compositions, their protoliths were petrographically close to calc-alkaline lamprophyres.

The calc-alkaline lamprophyric magma must have originated in the diamond stability field, as it incorporated diamond-bearing mantle material upon its ascent to the surface. It erupted in the Archean to produce volcaniclastic deposits and later also intruded as dikes. The Wawa diamondiferous rocks could be one of few known lamprophyric volcanoes. Lamprophyric volcaniclastic rocks may be considered a potential target for diamond exploration in the future.

[Shaun Spelliscy]

Kjarsgaard seems to be the federal government expert in the study of lamprophyres and my experience is they are more than happy to review new discoveries.

The first criteria is to establish what type of lamprophyre was actually discovered.

We know there was abundant quartz and olivine but since it is not only a new discovery but a new discovery in a new area it will require a lot of work to make a correct classification.

Kimberlite Mineralogy, Petrology and Geochemistry
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B.A. Kjarsgaard
Geological Survey of Canada, Ottawa

Objectives And Description:

Objectives:

To characterize mantle-derived potassic rocks (kimberlites, minettes) in Alberta and their entrained crustal and mantle xenoliths on a mineralogic, petrologic, geochemical and isotopic basis and compare with other Canadian occurrences.
To evaluate the economic potential of the kimberlites on the basis of the above listed parameters.
Establish a kimberlite heavy mineral database for Alberta.

Description of work:

Petrography is being used to provide a textural-genetic facies classification of collected samples. In conjunction with the petrography, electron microprobe analysis of individual minerals (megacrysts, phenocrysts, groundmass) has been conducted. Major and trace element whole-rock geochemistry, including REE analysis has been completed at the GSC. Whole-rock radiogenic isotope analyses on selected samples has been completed by the GSC and by contracted laboratories. In order to evaluate the economic potential of the kimberlites, geochemical analysis of kimberlite heavy mineral concentrates will be completed using both the electron microscope at the GSC and the proton microprobe at the University of Guelph. MRD's Exploration Geophysics Subdivision will characterize representative kimberlite samples by performing bench tests for resistivity, conductivity, magnetic susceptibility and gravity response.

Electron microprobe analyses of individual mineral phases of mantle xenoliths for thermobarometric studies are being used to constrain mantle paleogeothermal gradients that existed beneath Alberta. Whole-rock major, trace, REE and radiogenic isotope studies on selected fresh xenoliths have been completed to assist in understanding the subcontinental upper mantle underlying Alberta. Mineral analyses from mantle xenoliths will be compared with heavy mineral separates obtained from kimberlites.

Geochemical and isotopic characterization of crustal xenoliths will assist in interpreting the crystalline basement of Alberta in areas of poor exposure or regions with Phanerozoic sedimentary cover.

Outputs:

Kimberlite, Lamproite, Diamond.

Kjarsgaard, B.A., 1993 (abstr.). Calgary Mineral Exploration Group Society, Calgary Mining Forum, March 3-4, Program and Abstracts Volume, p. 6.

Petrology of the Sweetgrass Minettes, Southern Alberta.

Kjarsgaard, B.A., 1993 (abstr.). Canadian Institute of Mining Bulletin, vol. 86, no. 968, March, 1993, p. 57.

Recalibration of the Ni Garnet/Olivine Exchange Thermometer, with Applications.

Kjarsgaard, B.A., 1993 (abstr.). Canadian Institute of Mining Bulletin, vol. 86, no. 968, March, 1993, p. 69; also

Geological Association of Canada/Mineralogical Association of Canada Joint Annual Meeting, Edmonton, Alberta, Program and Abstracts Volume, p. A-53.

Potassic magmatism in the Milk River area, southern Alberta: petrology and economic potential.

Kjarsgaard, B.A., 1993. In Current Research 1994-B, Geological Survey of Canada, p. 59-68

A Rb-Sr phlogopite-whole rock isochron age for olivine minette from the milk River area, southern Alberta.

Davis, W.J, and Kjarsgaard, B.A. In Current Research 1994-F, Radiogenic Age and Isotopic Studies, Report 8, Geological Survey of Canada, p.11-14.

An overview of the occurrence and distribution of kimberlites in Canada.

Kjarsgaard, B.A. ,1995. Geological Survey of Canada, Forum 1995, Abstracts, p.19 (poster presentation).

Justification And Benefits:

Presently, more than 50% of world natural diamond production is from mines commissioned within the past 35 years in countries which formerly were not major producers (e.g. the former U.S.S.R., Botswana, Australia). Diamond is a very important strategic commodity with a high market value. Diamondiferous kimberlites are generally restricted to regions of old (>2.4 Ga) thick crust which was cratonized by 1.5 Ga. Alberta is a prime exploration site in which to find economically viable kimberlites as major crustal domains older than 2.5 Ga (Slave, Hearne, Rae, Medicine Hat Block, Loverna Block, etc.) occur both exposed and in the subsurface. Furthermore, the regional tectonic events predate 1.7 Ga, implying that cratonization was complete long before 1.5 Ga.

Modern diamond prospecting has become much more sophisticated, and it is now apparent that although diamond deposits around the world have many similarities, there are also important regional differences. A significant prospecting tool used for kimerlites is indicator mineral sampling. Recent advances in geochemical characterization of heavy mineral concentrates have illustrated that indicator minerals can provide important information about the economic potential for diamonds of a kimberlite. A database of indicator mineral compositions for Alberta kimberlites is being constructed for comparison to other North American kimberlites (e.g. Stateline Field, Wyoming; Missouri Breaks, Montana; Northwest Territories and Saskatchewan) as well as other well documented examples from other parts of the world.

Because studies of mantle and crustal xenoliths can provide important insights into the crystalline basement and upper mantle beneath Alberta, investigation of the Sweetgrass intrusives (minettes) is an important component of the project and provides a link with kimberlite-related xenolith studies. The Sweetgrass rocks have never been studied by modern petrologic methods, and are known to contain both abundant Precambrian crustal xenoliths and mantle xenoliths. The study of crustal xenoliths should provide important information about the buried Archean Medicine Hat Block.

Plans For Fiscal Year 1995-96:

Complete and submit manuscript on origin and diamond potential of the minettes of southernmost Alberta, for inclusion in the GSC Alberta MDA Bulletin.

Prepare a journal paper on the petrology of Sweet Grass minettes.

Summary

Minettes and lamproites, which are closely related to kimberlites, are igneous rocks that originate in the earth's mantle, commonly at depths greater than 100 km. Because of these great depths, the rocks commonly contain minerals formed at high pressures. Diamonds are the best-known example, but relatively few kimberlites contain diamonds of commercial quality or amount. In 1992, seven minette bodies were examined in the Sweetgrass Hills of the Milk River area in southern Alberta. Earlier work suggested that the Sweetgrass minettes were dykes radiating from the main intrusive centres in northern Montana, but the 1992-93 studies indicated the Sweetgrass minettes represent discrete, small volcanic vents. Combined whole-rock major and trace element chemistry, mineralogy and mineral chemistry studies confirm that these rocks are minettes and are similar to other minettes from the Montana alkaline province.

Classifying the Sweetgrass intrusives as minettes suggests that there is low potential for diamonds in these rocks. However, this does not eliminate the potential for diamond-bearing lamproite or kimberlite in the Archean Medicine Hat Block in the adjacent portion of southern Alberta. This work has been reported in a GSC Current Research paper and several related oral and poster presentations.