Thin sections polishing

The minerals found in United States coals continue to be studied with the availability of improved instrumental procedures such as x-ray diffraction, infrared absorption, and scanning electron microscopy beyond the traditional optical and chemical mineralogical techniques as applied to thin sections, polished pellets, and isolated particles. The minerals may be grouped into the silicates (kaolinite, illite montmorillonite, and chlorite), the oxides (quartz, chalcedony, hematite) the sulfides (pyrite, marcasite, and sphalerite) the sulfates (jarosite, gypsum, barite, and numerous iron sulfate minerals) the carbonates (ankerite, calcite, dolomite, and siderite) and numerous accessory minerals (apatite, phosphorite, zircon, rutile, chlorides, nitrates, and trace minerals). 

Figure 9. SEM photographs of polished, etched thin sections of modem Acropora palmata coral (after Edwards 1988). The scale bar in a is 100 microns. Visible in a are large macroscopic pores in the skeleton and well as the textnre of the very fine aragonite crystals, b is the same section as a bnt at higher magnification. The scale bar is 10 microns. Individnal aragonite crystal fibers are visible in b. ...

The reflected light from polished surfaces permits ready distinction between many opaque minerals on the basis of brightness, colour, and anisotropy. This feature is very important in the study of ore minerals and host rocks. Transparent minerals (especially in rocks) are commonly studied by transmitted light. In this case, polarized light is passed through thin sections or through fragments mounted in oil. 

All of the samples analyzed were standard one-inch diameter polished thin sections. Whenever feasible the samples received a final, cleansing polish with 1 pm diamond compound made from commercial graded diamonds embedded in "vaseline". Commercial diamond paste has proved unsatisfactory due to high levels of K, Na, Cl, Si, F, and Ca. Samples are then cleaned with carbon tetrachloride, rinsed in ethanol, and coated with vacuum evaporator. This sample preparation technique was developed during our studies of minor elements [16,17] and has proved to produce consistently contamination-free samples. 

Polished thin sections were made in the absence of water to prevent dissolution of soluble phases. Mineral composition was determined using a combination of X-ray diffraction, electron microprobe analysis, and scanning electron microscopy with... 

Polished thin sections or iron oxides grains polished in epoxy mounts were analyzed using Universite Laval CAMECA SX-100 5-VVDS electron microprobe under a beam of 15 kV at 100 nA, using a range of natural and synthetic standards. After counting over the peak for 20 to 30 sec, background is measured on both sides for 10 sec. These settings yield minimum detection limits (mdl) as low as 20 ppm for elements such as K, Ca, Al, Si, Ti and Mg, 50 ppm for Mn, Cr and V, 200 ppm for Cu,... 

Several minerals have been identified in polished thin sections of various rock types including massive sulphide, gossan, intermediate crystal-lapilli tuff, and felsic ash tuff (Fig. 2). These minerals include apatite, monazite, zircon, allanite, titanite, xenotime, magnetite, cassiterite, cobaltite-gersdorffite, rutile, ilmenite, goethite, sphalerite, galena, arsenopyrite, chalcopyrite, pyrite, and pyrrhotite. These minerals range in size from 20 pm to 250 pm and represent potential Indicator minerals. 

Petrographic observations were made on polished thin sections, for 313 outcrop samples. Average sample spacing was one sample per 1 km within a radius of 15 km or less from the known porphyry Cu-Mo deposits, and one sample per 2 km outside this area. Five rock types are distinguished in the district andesites, diorites, granodiorites, dacites, rhyolites and sandstones. Rhyolites and dacites dominate in the zone of known porphyry Cu-Mo deposits. Sandstones are much less common and were not studied. 

One hundred samples were collected from drillholes, consisting of different lithologies, alteration, and mineralization. Polished thin sections were made from 70 samples of Chehelkureh rocks. Carbonates were analyzed for K, Na, Ca, Mg, Fe, Mn, Pb, Zn, Y and Sr using a JEOL-733 electron microprobe at the University of New Brunswick. An accelerating voltage of 15 kV with a beam current of 30 nA was applied (1pm beam) for a maximum count-time of 30 seconds. 

The rock samples were cut and polished into thin sections to be used on the SEM at Juniata College. The SEM was used for petrographic textural analysis. 

Polished thin sections of the host mineralized granite, SB-2671, and pegmatite with minor mineralization, SB-2670B, were selected for U-Th-Pb chemical monazite dating using to the method of Montel etal. (1996). 

Note These (maceral) constituents can be identified and quantitatively measured by examining thin sections or polished surfaces under a microscope, and reflect the nature of the primordial source material as well as the conditions under which it was deposited. Vitrinites derive from humic gels, wood, bark and cortical tissues eoi lnites are the remains of fungal spores, leaf cuticles, algae, resins and waxes and inertinites comprise unspecified detrital matter, "carbonized" woody tissues and fungal sclerotia and mycelia. 

Finally, microscopic examination of samples often requires their preparation as cross sections or thin sections, or by mounting the sample on a glass slide by means of a mounting medium. For preparing thin and cross sections, samples are embedded in a polymer solution. After curing of the polymer, the thin or cross section is obtained by polishing the embedded sample with SiC abrasive disks. Aluminum suspensions or diamond paste are occasionally employed in a final polishing step. 

Reflected light microscopy can be used either on thin sections or thicker polished sections. Reflected light is used primarily for identifying opaque minerals such as metals, sulfides, and some oxides. Each of these minerals has a unique appearance in reflected light. 

Petrographic Studies. Polished thin sections were examined by optical methods to determine original mineralogy and alteration phases. The sections were taken and oriented in such a manner to allow comparison of the microscopic mineralogy with the results of the autoradiography experiments The shale was too fine-grained to be characterized in detail. 

The observations are performed with a Leitz Ortholux polarizing microscope equipped with the ftOpak illuminator, lamps for reflected and transmitted light, immersion objectives, and verniers. Characteristics of the polished thin sections and of the nuclear emulsion plates are observed in transmitted light with the same immersion optics after removing the Berek prism. 

Polished sections and polished thin sections are prepared according to the usual techniques of coal petrography. They are mounted permanently on quadrangular pieces of transparent Lucite for location purposes. We have described elsewhere a graphical method of micro-surveying which allows an observer to locate any specific autoradiograph on nuclear emulsion plate of a given point in an opaque section (13). 

The physical or petrographic components of coal are defined or described in various ways. In one system, which depends on microscopic observation, the principal components are called exinite, vitrinite, micrinite, and fusinite. Transparency of these in a thin section decreases in that order, whereas reflectance from polished surface increases in the same order. Vitrinite, the major component of most coals, occurs in bands or strands and is usually uniform in appearance, though sometimes shows cell structure exinite consists of the remains of plant spores, pollen, and cuticles with characteristic shape micrinite occurs in very fine granular form or massive structureless, irregular form fusinite shows characteristic fibrous, cellular structure. Semifusinite is transitional between vitrinite and fusinite. On a macroscopic scale, vitrain and... 

The studies carried out consist of the megascopic description of the master columns study of thin sections for maceral assessment, determination of maceral composition on polished blocks in reflected light, determination of mean maximum reflectance values on polished pellets, proximate analyses of selected petrographic zones, hot stage studies on vitrinoids to determine the thermal behavior at various temperatures, electron microprobe and spectrochemical studies of selected zones to determine the nature of ash forming elements, analyses of certain zones petrographically important to determine the variation of total carbon, and hydrogen and microhardness determinations on certain macerals. 

Microscopic Description of the Seams. The zones delimited by observing the polished columns were studied further, both in transmitted and reflected light. A set of 40 thin sections from Seam 4 and 35 sections from Seam 2 were... 

Semifusinite is also included in the vitrinoid group of macerals. It is distinguished from fusinite by a degree of translucence in thin section and lower reflectivity in polished specimens. Semifusinites may be subgrouped according to appearance, which however was not attempted. The semifusinites very often occur as a transition stage between vitrinoids and fusinoids. 

Peter A. Hacquebard The differentiation of various vitrinic compounds so beautifully shown in the Brandon lignite—e.g., between cell wall material and cell-content material, can also be observed in bituminous coals. I have been able to show this on polished sections by using an etching technique. How has Dr. Spackman shown this in thin sections, and what would be the effect of rank increase on the existence of these two types of vitrinite—i.e., types derived from cell walls and cell contents ... 

Polished pellets and thin sections were made of each incremental fraction across the xenolith for reflected and transmitted light microscopic examination. Thin sections revealed little because of the opacity of the coke. However, the pellets, which were made by mounting the coke in plastic, were invaluable to the study. 

Optical microscopy is another method that has been used to determine the distribution of minerals in coal. This method is based on the detailed microscopic examination of polished or thin sections of coal in transmitted and/or reflected light. In principle, observing several of its optical properties, such as morphology, reflectance, refractive index, and anisotropy, makes identification of a mineral type possible. 

Petrographic Work. Petrographic studies required preparation of thin sections. Briefly, rectangular blocks of material were treated with ethanol to remove water and then infiltered with hard grade LR White resin, a low viscosity resin developed for biological work. Following this, the block was mounted on a petrographic slide and a polished thin section produced (see Bailey and Blackson (26) and Blackson and Bailey (27)). A total of 57 sections were produced in this way, at least 1 from each thinner lithofacies unit and 2 from thicker lithofacies units. 

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