On the Occurrence of Silician Magnetites

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 Al2O3, 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-Fe2SiO4 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.

Generation and Evolution of Ore Fluids for Porphyry Cu‐Au Mineralization of the Santo Tomas II (Philex) Deposit, Philippines

“…This is higher than the previously reported silicianmagnetite analyses (e.g., 5 wt% from the Kamaishi skarn deposit, Japan, Shiga, 1988Shiga, , 1989; 4 wt% from the Ansil massive sulfide deposit, Canada, Westerndorp et al, 1991). No Si-bearing magnetite has been encountered from other porphyry Cu-Au deposits in the western Pacific rim, including the Lepanto-FSE, the Dizon, and the Mamut deposits (A. Imai, unpublished data); whereas silician magnetite has been commonly found from a number of skarn deposits (Shimazaki, 1998;Imai and Anan, 2000).…”

Mineralogical Characteristics of Exsolved Spinel in the Panzhihua V‐Ti Magnetite Deposit, Sichuan: Implications for the Mineralization Process

“…substitution. The magnetite solid solution becomes unstable as the temperature decreases and solute elements exsolve from it in the form of new minerals (Shimazaki, 1998;Dare et al, 2012;Nadoll et al, 2012;Hu Hao et al, 2014).…”

Geological, geochronological, and mineralogical constraints on the genesis of the Chengchao skarn Fe deposit, Edong ore district, Middle–Lower Yangtze River Valley metallogenic belt, eastern China

“…The compositions of magnetite within the Chengchao skarn Fe deposit are given in Table 3 indicating substitution of Si into the magnetite structure, as has been documented in other skarn Fe deposits (e.g., Shiga, 1989;Westendorp et al, 1991;Shimazaki, 1998;22 22 Ciobanu and Cook, 2004).…”