Petrology of Dikes Emplaced in the Ultramafic Rocks of Southeastern Quebec and Origin of the Rodingite

Abstract

The ultramafic rocks of the Appalachian region in the Eastern Townships of Quebec consist mainly of serpentinized harzburgite and dunite. They are intruded by dikes of dioritic rocks, quartz monzonites (adamellites), pegmatite, and albitite. Near contacts with the dikes the serpentinite with 7-A serpentines has been transformed to a zone with 14-A chlorites with higher Al/Si ratio; serpentinite may also be converted into diopside, talc, anthophyllite, and so forth, indicating dehydration and loss of water into the intruding dike. The granitic and dioritic rocks are modified especially at the borders to assemblages consisting of grossularite, diopside, vesuvianite, prehnite, zoisite, and calcite, forming a rodingite.In general, the water-rich and silica-deficient environment of serpentinized ultramafic rock is responsible for affecting the normal sequence of crystallization of the dikes. This leads to the conversion of pyroxene to hornblende and finally to chlorite and (or) biotite; at the same time the crystallizing plagioclase becomes albitic. The lime and alumina that would normally form clinopyroxene or hornblende and plagioclase remain in the residual hydrous melt to form abundant lime-rich hydrothermal minerals. The lime in these rodingites is, therefore, not derived by serpentinization of the ultramafic wall rocks. PETROLOGY OF DIKES AND ORIGIN OF RODINGITE, QUEBEC 491Thetford Mines on a large peridotite-dunite body is the Jeffrey mine, located in the mining town called Asbestos. DIKE ROCKS Granitic RocksThe granitic rocks are the commonest dike rocks of the area. Granitic pegmatite dikes are also common. There are two main types of granitic rocks: (a) biotitemuscovite quartz monzonite, the most abundant granitic rock, particularly common in the Black Lake area; and (b) a leuco-quartz monzonite found in the Normandie mine, Black Lake, and hence termed the Normandie quartz monzonite. Several rock types have been produced by the desilication and subsequent albitization of the granitic rocks, out of which syenodiorite and albitite are noteworthy.These dikes were emplaced in the epizone (Buddington, 1959, p. 677-690) by wedging along the shear zone, fractures, and joints in the serpentinized ultramafic rocks.Both the above types of quartz monzonite consist of plagioclase An24_12, potash feldspar Or77 Ab(+An)23, and quartz. The micas are the important constituents, and a biotite of red-brown variety (Ny = 1.643 ± .001; d (060) = 1.543 A) is widely developed. A second generation of plagioclase, An0_10, is commonly present.The chemical, normative, and modal compositions of the granitic rocks show that the specimens of biotite-muscovite quartz monzonite and of the leuco-quartz monzonite are all typical quartz monzonites (adamellites); chemical analyses of two specimens (nos. 194 and 548) are given in Table 1. The normative quartz, orthoclase, and albite content of these two specimens (194 and 548), recalculated to 100, are 41.6, 33.0, 25.4; and 39.0, 26.8, 34.2, respectively. They fall close to

The Unique Granite Gorge in Mountainous Adygeya, Russia: Evidence of Big and Complex Geosite Disproportions

“…Igneous type: Late Paleozoic granitoids, including granites and granodiorites with aplite dikes (Ig1), very peculiar rodingite dikes (rodingite is a rare, garnet-bearing rock closely related to ultramafic complexes, and its nature is somewhat debatable [21][22][23][24][25][26]) (Ig2).…”

Exposing the “Myth” of ABC, “Anything But Chrysotile”: A critique of the Canadian asbestos mining industry and McGill University chrysotile studies

“…The most likely source of this crocidolite was the local mine ore, not imported fibers. Two geological surveys found that mines from both areas contained blue fibrous riebeckite, otherwise known as crocidolite [De, 1961;Hebert, 1980]. How did the McGill researchers miss this information on crocidolite contamination of ore?…”

“…As discussed earlier, tremolite and other fibers released during the mining process end up in the bags of end product. Therefore, it is likely that current and past shipments from the Jeffrey mine, as well as from all other Quebec mines, were contaminated with tremolite, crocidolite, and amosite [De, 1961;Gibbs, 1972]. This conflicts with information dispensed to the public under The Asbestos Institute logo [Browne, 2000].…”

“…This conflicts with information dispensed to the public under The Asbestos Institute logo [Browne, 2000]. The Asbestos Institute does not mention the fact that crocidolite and amosite are also present in the mine ore, and claims that tremolite is removed through various mining and milling processes [De, 1961;Browne, 2000]. This is simply untrue.…”

Rodingite formation from diorite in the Samothraki ophiolite, NE Aegean, Greece

“…However, other authors (e.g. De 1972;Hall and Ahmed 1984) have argued that the Ca necessary to produce the calc-silicate assemblages in rodingites need not have been derived by serpentinization of ultrama®c rocks, but by introduction of Ca-rich hydrothermal solutions and/or leaching of gabbroic lithologies. Rodingitization involves metasomatism of ophiolites due to in®ltration of hydrothermal¯uids, which add Ca and remove Si and alkali elements from the precursor.…”