Results 181 to 190 of about 220,175 (263)
Chemical aspects of hydrothermal alteration with emphasis on hydrogen metasomatism
Economic Geology, 1964 The ratio of cation to hydrogen-ion concentration is used as a basis for coordinating many observed varieties of silicate rock alteration. Low ratios drive alteration from feldspar through sericite, montmorillonite, or paragonite, toward kaolinite or pyrophyllite.
J. J. Hemley, W. R. Jones
semanticscholar +4 more sources
Economic Geology, 2004 The genesis of banded iron formation (BIF)-hosted high-grade hematite deposits has been debated for nearly a century. Recent worldwide recognition of magnetite- and/or hematite-, carbonate-, and talc-rich mineralization, deep below the modern weathering in these deposits, and recognition of Mg-Fe metasomatism in wall rocks implies that hydrothermal ...
H. Dalstra
semanticscholar +5 more sources
Geology, 1989 On Santa Catalina Island, southern California, bluechist to amphibolite facies metasedimentary, metamafic, and meta-ultramafic rocks show veining and alteration that reflect fluid flow and mass transfer at 25-45 km depths in an Early Cretaceous subduction zone. Synkinematic and postkinematic veins record fluid transport and metasomatism during prograde
Gray E. Bebout, Mark D. Barton
semanticscholar +4 more sources
Journal of African Earth Sciences, 1997 Abstract The granite at Arba'at shows many of the chemical features of a metallogenetically specialised A-type granite, although no economic mineralisation has yet been found there. The specialised character is, however, only strong within the aphyric granites of low density forming the interior of the intrusion.
D. C. Almond +2 more
semanticscholar +4 more sources
Geological Magazine, 1929 In Teesdale and Weardale, at all exposures that have been examined, the Whin Sill is cut by a system of approximately vertical, sweeping, joint planes. These are distinct in general character from, and are on a larger scale than, the columnar jointing which is conspicuous in all vertical scars of Whin Sill. The pattern of the larger scale jointing on a
L. R. Wager
semanticscholar +4 more sources
The Canadian Mineralogist, 2012 Secondary mineral assemblages in komatiites of the south-western Abitibi greenstone belt reflect the tectonic evolution of the region. Changes in mineralogy were accompanied by changes in fluid chemistry over time. Hot, plume-generated komatiites (2719–2704 Ma) were hydrated by hot fluids (200–300 oC), replacing the primary olivine and pyroxenes by ...
Eva S. Schandl, M. P. Gorton
semanticscholar +4 more sources
Economic Geology, 1999 The Ventersdorp contact reef is an auriferous conglomerate horizon and economic orebody on top of the Late Archean Witwatersrand Supergroup in South Africa. It differs from the other conglomerate beds (reefs) in the Witwatersrand basin in having a massive metabasalt sequence as its hanging wall and by its intense post-depositional alteration.
V. H. Gartz, Hartwig E. Frimmel
semanticscholar +4 more sources
Seawater-metasomatism in hydrothermal sediments (Escanaba Trough, northeast Pacific)
Chemical Geology, 1995 Abstract Hydrothermal sediments from the NESCA vent-field, Escanaba Trough, are enriched in a number of typical “vent-fluid” metals for which fluid data for the same, sediment-hosted, site exhibit anomalous depletion. These results are consistent with cooling of rising fluids and precipitation of various metal sulphide, sulphate and oxide phases in ...
Christopher R. German +5 more
+5 more sources
Magnesium metasomatism during hydrothermal alteration of new oceanic crust
Geology, 1978 A semiquantitative calculation of the amount of Mg fixation during greenschist-facies metamorphism of a 1-km-thick section of the oceanic crust beneath mid-ocean ridge crests shows that it is of the same order of magnitude as the “excess” (unbalanced) input of this element to the ocean.
Salman Bloch, Albrecht W. Hofmann
openalex +3 more sources