Lakehead University Geology - Journal Yearbook (Thunder Bay, Ontario Canada)

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Mr. R. Bennett. Honours Practical Geology, Heriot Watt College. Edinburgh, Scotland . Background : Chief Laboratory Technician, 1936-1967 The Grant Institute of Geology, University of Edinburgh. Researching many kinds of technical approaches to Ph. D. studies. Presently, Chief Laboratory Technician, Lakehead University. Thin Section Making with the Aid of Araldite Epoxy Resin. Araldite Epoxy (Resin 502, Hardener 956)has the ability to penetrate into the cracks and cleavage planes of minerals and it will bond efficiently the angular particles of semi-consoli- dated sedimentary rocks, as well as recent sediments and soil samples. The adhesive properties of the Resin are such that it can be used as a mounting media, where such thermo-plastics as Lakeside 70 cannot be used or are not advisable due to the re-arrangement or twisting of the surface to be mounted. IGNEOUS ROCKS The following are some of the ways in which Araldite Resin was used in making thin sections of serpentinites from the Atlantic Ridge of the Azores. These rocks were very fragile and had a coating of manganese over the whole or part of the sample. The Preparation for the thin section: Due to the fragmental nature of the sample, it was necessary to bond a part of it even before attempting to cut it. This is done by mixing Araldite Resin ( 10 parts of resin to 2 parts hardener, by volume) in a thin-walled pliable polythene jar. The SDecimens to be cut are placed in an oven set at 60 degree Centigrade until the surface is hot to the touch. Remove from the oven and immerse the portion of the rock to be sectioned in the resin. Return the polythene jar with the specimen to a vacuum oven and impregnate the sample. When the oven chamber starts to evacuate, the resin will start to froth. This frothing is controlled by periodical closing of the vacuum and slowly allowing the air to force the resin into the sample ' s surface. Repeat this procedure until it becomes apparent that there is sufficient penetratio n of the resin into the surface of the sample, so that when cold, it can be cut without breaking. The Cutting: Remove the sample from its container. A surrounding mass of excess resin is beneficial, as it will preserve the outside edges of the sample. Clamp the unimpregnated part in the cutting machine and cut off the required part. If the specimen is holding together, then cut a second slab for future work. Wash the cut-off part and examine it under the microscope. Ensure that the surface cracks have been impregnated and if not, dry the slab and return it to the oven to complete drying and warming of the surface for coating with a fresh mix of resin. If the slab is used, it may suffice to place it on the plate to warm for surface coating. Surface coat the slab with resin, impregnating it as before if it was on the hot plate or in the oven. Allow it to set, strip off any unwanted resin with a razor blade while the slab is still hot, to save unnecessary grinding. 23

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Analysis of Material Balance in Segregated Bodies Existence of material balance is one of the most convincing evidences in favour of segregational origin of the differentiated features like veins or lenses of mineral concentrates bordered by characteristic aureoles . Analysis of material balance is therefore crucially important and it cannot be overemphasized that the methods employed for such analysis ought to be reliable as well as capable of revealing the true state of balance within the differentiated bodies. By use of spherical and triaxial ellipsoidal models of segregation the reliability of the methods commonly used for balance analysis are tested. It is demonstrated that none of them can yield correct results. The reason for this is that these methods do not take the true volume ratio of the concentrate and aureole into account. This volume ratio is an indispensable factor for correct balance analysis. Accordingly, modified procedures to evaluate the state of balance are suggested. Determination of the above mentioned volume ratio in natural specimens is extremely difficult and imposes severe restrictions on the scope of balance analysis. The state of balance across a hornblende vein surrounded by a feldspathic aureole has been deter- mined by the suggested method as well as by one of the existing methods for a comparative evaluation of their reliabilities. The results obtained by the suggested methods show that material balance exists, thus indicating the segregational origin of the vein. This agrees well with the conclusion derived from mineralogical and chemical evidences. But, as predicted from the model studies, the existing method shows a lack of material balance across the vein. GRADUATE TO FALCONBRIDGE Geologists, Geophysicists, Geochemists, Mineralogists Mining and Electronic Technologists FALCONBRIDGE NICKEL MINES LIMITED 23 TOMLINSON BLOCK SEVEN KING STREET EAST, sa n. Cumberland st. -thunder bay. ont. TORONTO 210, CANADA 22

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When the sample is cold, trim to the size of a sli ' de and grind to a very fine mounting surface, using either coated carborundum paper (400, then 600 grit) or a glass plate with the same abrasive and water. Wash the sample and ensure that the required surface is whole (not pitted) and even. The Mounting: This can be done using Lakeside 70 or Araldite resin. Use the former if the surface is hard and not likely to twist and buckle when re-heated, which would cause an uneven mount. The latter should be used if this is apt to happen. If the resin is used as a mounting media, apply a small amount to each surface (the glass slide and the sample surface) , press them together to remove all the air and allow it to set at room temperature for 24 hours. This will allow the resin to set sufficiently for grinding. The Thin Section: Cut or grind the sample down to the first stage of transparency, using either a diamond bonded wheel or the carborundum method. It is now that the bonding shows its effect. Due to the differences in structure of the silicates and the manganese crust to transmit ordinary light, it is therefore beneficial to hand grind the now thin section to completion on a glass plate with 600 grit or finer if desired, taking great care to retain the complete surface area. Having completed this stage to the required thickness, wash the section and dry it with a tissue; then remove the surplus Lakeside or Araldite. If the latter is used, trim the outer edges leaving a small border around the section edge, but do not attempt to remove all the Araldite from the thin section as this will result in the destruction of the sample. Clean the surrounding slide with a solvent such as chloroform or acetone. Clean and cover a covering slip with a reasonable amount of Canada Balsam, warm it on the hot plate until the Balsam flows outward over the cover-slip, and in the meantime warm the surface of the thin section. Do this by holding it over the hotplate without touching it, and then laying the two surfaces together. Remove the covered section from the hotplate, then carefully press down the cover-slip to remove all the air. Clean off the surplus Balsam with acetone and finally with chloroform. If the thin section is too fragile to use heated Balsam, use Permount and allow to dry at room temperature. This takes longer, but it helps to retain the structure o f the section. SEDIMENTARY ROCKS The thin sectioning of sedimentary rocks such as sandstones, sandy shales, clay shales, etc. can be difficult when their natural cementing media is a carbonate or some other material (with the exception of silica). It is therefore necessary to impregnate the rock with a material that will act as a bonding substance to retain the grains and structure of the rock in original form. If the rock matrix is a carbonate, either calcite or dolomite, the action of the cutting blade will tear away the carbonate, leaving many loose grains, and the stages of grinding prior to mounting on the slide will have a similar effect, though not so harsh. If the fine-ground slab is washed down and dried, then examined under a binocular microscope, it will be observed that the cleavage- planes of the carbonate have been irritated and are apt to be loose. There- fore, when the slide mounting media is applied to the section slab, and the slide placed in position, a gritty feeling will be observed. The result is a thin section full of holes, due to the fact that all the grain surfaces were not on an even plane. If the same sandstone were impregnated with Araldite Epoxy Resin, all the grains as well as the cleavage planes of the carbonate would be bonded together to create a solid interior which can be thin-sectioned without any difficulty. The same technique may be applied to sandy shales and the fine laminations of shales. Method : Cut the rock with a diamond blade to a thickness of no less than one quarter of an inch, as this will give a sufficient depth with which to work. Dry the slab and place it on a Teflon plate (Use Teflon because of its self- lubricating properties as well as its high melting point) and put the unit in a vacuum oven and bring it to 60 degrees Centigrade. 24