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On the Occurrence of Silician Magnetites
Author(s) -
Shimazaki Hidehiko
Publication year - 1998
Publication title -
resource geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.597
H-Index - 43
eISSN - 1751-3928
pISSN - 1344-1698
DOI - 10.1111/j.1751-3928.1998.tb00004.x
Subject(s) - magnetite , ferrous , skarn , maghemite , geology , electron microprobe , mineralogy , hydrothermal circulation , mössbauer spectroscopy , ferric , mineral , precipitation , geochemistry , inorganic chemistry , materials science , metallurgy , chemistry , crystallography , paleontology , physics , fluid inclusions , seismology , meteorology
Abstract: About 120 specimens of magnetite from various localities are examined by an electron microprobe analyzer. Magnetites containing more than one weight percent of silica but lack of any other components than ferrous and ferric iron, called silician magnetites in the present paper, are recognized in 23 skarn, one vein and one thermally metamorphosed massive sulfide deposits. Thus it is confirmed that this mineral occurs in nature much more frequently than so far expected. Besides silician magnetites, magnetites with appreciable amounts of Al 2 O 3 , CaO, MgO and other components along with silica, are also recognized in some skarn deposits. Magnetites with such unusual compositions are found only in hydrothermal environments, and it is suggested that precipitation mechanisms seem to be responsible for their formation. In silician magnetites, excess electric charge brought by the replacement of ferric iron in tetrahedral site by silicon, could be compensated by the replacement of ferric iron in octahedral site by ferrous iron, known as γ–Fe 2 SiO 4 component. The natural occurrence of silician magnetites, however, gives no positive support to the existence of this component at crustal pressures. Instead a preliminary Mössbauer experiment demonstrates that one silician magnetite has a maghemite –like structure by the omission of ferrous iron from octahedral site.