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Magnetic metacrysts

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Journal Article
Published: 01 November 2005
The Journal of Geology (2005) 113 (6): 707–713.
... this feature is masked by dark coloration. Hematite is replaced by magnetite in prograde regional metamorphic settings (LaBerge 1964 ; Jansen and Schuiling 1976 ). Hence, medium- to high-grade metaquartzites are typically white or black, and the latter may be highly magnetic. Metaquartzite is occasionally...
FIGURES
Journal Article
Journal: GSA Bulletin
Published: 01 November 2000
GSA Bulletin (2000) 112 (11): 1635–1649.
... obtained gravimetrically using bromoform, and further fractionated using a magnetic separator. Grain mounts of each magnetic fraction were prepared so that many grains of each mineral species could be studied. To facilitate discussion, the zircon terminology of Carroll (1953) is used. Selected thin...
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Journal Article
Published: 01 January 2004
Exploration and Mining Geology (2004) 13 (1-4): 15–23.
... with biotite metacrysts, and are occasionally feldspar phyric. The second type of mafic intrusive rock is Proterozoic diabase present as dikes. These medium-grained dikes have a strong magnetic signature, are typically 5 m to 20 m thick, and generally trend 160°. Northeast-trending, medium- to coarse...
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Journal Article
Published: 01 October 2003
Russ. Geol. Geophys. (2003) 44 (10): 979–992.
... gold of basites by granitoid magma, supply of this gold together with iron into the enclosing rocks, and formation of an aureole of high magnetization (from 50–100 to 700–2000 g and more) and gold content (from 3–5 to 10–20 and, sometimes, up to 50 ppb) around the massif or its satellite. The gold...
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Journal Article
Published: 01 March 2012
The Journal of Geology (2012) 120 (2): 203–216.
... and is present in the center of the synform ( fig. 2 ). The black willemite zone occupies much of the cross member and extends into the west limb. It is composed of black to gray willemite and magnetic franklinite disseminated in manganoan calcite. The average grain size of noncarbonate minerals is about 5...
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Journal Article
Published: 01 May 2017
The Journal of Geology (2017) 125 (3): 351–366.
...-ICP-MS zircon U-Pb dating. Zircons were separated with magnetic and heavy-liquid separation methods and then hand-picked under a binocular microscope. Zircon grains were mounted in epoxy and then polished for subsequent cathodoluminescence observation and LA-ICP-MS analysis. Southeast China...
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Journal Article
Published: 01 August 2016
Russ. Geol. Geophys. (2016) 57 (8): 1171–1190.
... interact with earlier formed native gold if it were present in the ore-forming system. The borders of some pyrite metacrystals are rough and wavy, which is typical of metasomatic-replacement or metamorphic structures. Dissolution and recrystallization of pyrite containing invisible gold and silver...
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Journal Article
Published: 01 June 2018
Mineralogical Magazine (2018) 82 (3): 539–575.
... ). However, Ashwal et al . ( 2005 ) defined the Main-Upper Zone boundary in the northern limb on the appearance of disseminated magnetite as detected by magnetic susceptibility measurements. This parameter placed the boundary ~50 m below the first cumulus magnetite in the Bellevue drill-core. These changes...
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Journal Article
Published: 01 December 2020
Russ. Geol. Geophys. (2020) 61 (12): 1354–1373.
... in pyrite is 0.58 ppm ( Chanyshev and Stepanov, 1987 ). Pyrrhotite occurs as scattered dissemination and small lenses in rocks; less often, it forms veins of two generations: magnetic and nonmagnetic. It is usually younger than pyrite. Other sulfides (galena, sphalerite, and chalcopyrite) form fine...
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Journal Article
Published: 01 May 2020
The Journal of Geology (2020) 128 (3): 275–301.
... isotope analysis. Conventional heavy-liquid and magnetic techniques were used to separate zircons from two samples. Handpicked zircon grains were mounted in epoxy resin and then polished for the cathodoluminescence (CL) image observation and LA-ICP-MS U-Pb dating and in situ Hf isotope analysis. All...
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Journal Article
Journal: AAPG Bulletin
Published: 01 November 1949
AAPG Bulletin (1949) 33 (11): 1791–1829.
... , 86 ) to a depth of 750 feet, in the southeastern part of the dome, and production from the mine, called the Kleer Mine, began in January, 1931. An account of the dome to 1934 was given by Hanna ( 36 ), and recently magnetic and gravity investigations were made in the mine ( 66 ). Cleavage...
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Journal Article
Published: 01 December 2001
Clays and Clay Minerals (2001) 49 (6): 559–585.
..., for associated siderite metacrysts. The larger amounts of Mg in the first type of berthierine in comparison with the sparry siderite probably reflect the high Mg concentration in pore-water (trapped marine water with some hydrothermal input). Plotting onto the diagram in Figure 4d all chemical analyses...
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Journal Article
Journal: GSA Bulletin
Published: 02 May 2019
GSA Bulletin (2020) 132 (1-2): 334–352.
... to these in the host rocks ( Figs. 2E and 2F ). All zircons for U-Pb dating were separated using conventional heavy liquid and magnetic separation techniques. Zircon grains were handpicked and mounted in epoxy resin, and then polished to half their thickness and coated with gold. The internal morphology...
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Journal Article
Journal: Economic Geology
Published: 01 March 2005
Economic Geology (2005) 100 (2): 225–252.
... of its reverse geometry design. An electrostatic mass analyzer downstream of the magnet permits third-order focusing, resulting in improved mass resolution ( Williams, 1996 ; Bacon et al., 2000 ). Forty-seven zircon analyses were obtained from sample RIDN99 from Ridgeway ( Table 3 ). Scattered 206...
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Series: Special Publications of the Society of Economic Geologists
Published: 01 January 2020
DOI: 10.5382/SP.23.25
EISBN: 9781629496429
... et al., 2015 ; Ivanov, 2017 ). The Bodaibo synclinorium, which hosts most of the gold, coincides with the thickest part of the passive margin sequence, as can be seen on the regional gravity map ( Fig. 5 A). On the magnetic map, the gold deposits cluster along magnetic lows ( Fig. 5 B). Fig. 5...
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Series: Special Publications of the Society of Economic Geologists
Published: 01 January 2020
DOI: 10.5382/SP.23.10
EISBN: 9781629496429
... of the Olympiada cluster ( Fig. 5 B). It has two sulfide-rich lithologic horizons, clearly visible near Olympiada as magnetic highs ( Fig. 4 B) due to the presence of pyrrhotite. The lower horizon consists of mica-quartz-carbonate schist with lenses of marbleized rock. Its thickness varies between 320 and 415 m...
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