著者

Mariko NAGASHIMA Daisuke NISHIO–HAMANE Shuichi ITO Takahiro TANAKA

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

vol.116, no.3, pp.129-139, 2021 (Released:2021-07-17)

参考文献数

23

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Ferriprehnite (IMA2020–057), ideal formula Ca2Fe3+(AlSi3)O10(OH)2, is a new mineral that was found as secondary mineral in druses developed in the hydrothermal altered dolerite from Kouragahana, Shimane Peninsula, Japan. Ferriprehnite is an Fe analogue of prehnite. The crystals consisting of ferriprehnite and prehnite occur as a radial aggregate. The tabular crystals are up to 300 µm long, 100 µm wide, and 50 µm thick. Ferriprehnite is colorless to pale green with white streak and vitreous luster. It has a Mohs hardness of 6½. Its cleavage is good on {100}. The calculated density is 2.97 g/cm3. The empirical formula of ferriprehnite on the basis of 10O + 2OH using the result obtained by electron microprobe analysis is Ca1.99(Fe3+0.66Al0.34)Σ1.00(Al1.02Si2.98)Σ4.00O10(OH)2. Structure refinement converged to R1 = 4.64%. Its space group is orthorhombic Pma2 with unit–cell parameters a = 18.6149(10) Å, b = 5.4882(3) Å, c = 4.6735(3) Å, and V = 477.46(1) Å3. The determined site occupancy at the octahedral M site is Fe0.637(9)Al0.363 indicating that the M site is predominantly occupied by Fe. <M–O> increases with increasing Fe content leading to isotropic expansion of MO6 octahedra. The a– and c– dimensions of ferriprehnite are longer than those of prehnite due to Fe substitution for Al at the M site.

著者

Mariko NAGASHIMA Yukina MORISHITA Yuji IMOTO Teruyoshi IMAOKA

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

pp.200818, (Released:2021-02-10)

被引用文献数

1

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Mineral assemblages and chemical compositions of ore minerals from the Eboshi deposit, the historical Naganobori copper mine, Yamaguchi Prefecture, Japan were investigated in order to clarify its characteristics as a skarn deposit. Some Bi–, Ag–, and Te–bearing minerals are newly identified, which contribute updating the mineralization sequence of this deposit. Samples collected from the mine dump are one massive magnetite ore, and copper ores associated with skarn gangue minerals. Skarns are categorized as clinopyroxene skarn, garnet skarn, and wollastonite skarn, and the clinopyroxene skarn is the most dominant. The major ore minerals are chalcopyrite, cobaltite, and early–stage pyrite (Py–I) and later stage pyrite (Py–II). Py–II is enriched in arsenic (~ 5.19 As wt%). The Bi–, Ag–, and Te–bearing minerals, such as native bismuth, bismuthinite, wittichenite, emplectite, tsumoite, kawazulite, hessite, and matildite are minor ore minerals. Based on the mineral assemblages and textures of the specimens examined, four ore mineralization stages were recognized; the ore mineralization stage I is characterized by the major ore minerals such as chalcopyrite, bornite, pyrrhotite, sphalerite, and Py–I. The stage II is defined by the mineralization of cobaltite, Py–II, and Bi(–Cu)–bearing sulfides such as native bismuth, bismuthinite, and wittichenite. The mineralization stage III is characterized by the Ag– and/or Te–bearing ore minerals such as matildite, kawazulite, tsumoite, and hessite. The stage IV is characterized by chalcopyrite veins cutting the main skarn masses and the host limestone. The mineralogical properties and mineralization process of the Eboshi deposit is similar to those of the skarn deposits in the Yamato mine and the Tsumo mine, and consistent with common skarn–type deposits associated with ilmenite–series granitoids in the San–yo Belt, which are characterized by the occurrence of minor Ag– and/or Te–bearing ore minerals.

著者

Teruyoshi IMAOKA Jun–Ichi KIMURA Qing CHANG Tsuyoshi ISHIKAWA Mariko NAGASHIMA Natsuki TAKESHITA

出版者

Japan Association of Mineralogical Sciences

雑誌

Journal of Mineralogical and Petrological Sciences (ISSN:13456296)

巻号頁・発行日

pp.200721, (Released:2021-02-10)

被引用文献数

4

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We report in situ major and trace element and Li isotope analyses of murakamiite and Li–rich pectolite in an albitite and whole–rock analyses of the albitite and host granite from Iwagi Islet, SW Japan. The albitite forms small bodies that are several tens of centimeters to tens of meters in size, disseminated in a host granite of Late Cretaceous age. The studied murakamiite–bearing albitite contains albite, sugilite, aegirine–augite, quartz, murakamiite–Li–rich pectolite, microcline, katayamalite, and accessory minerals. It shows conspicuous strain–induced textures. The murakamiite and Li–rich pectolite form a solid solution with Li × 100/(Li + Na) atomic ratios ranging from 44.2 to 60.1, and the Na line profiles show a zoning structure in which Na decreases from core to rim. Major and trace element compositions of murakamiite–pectolite normalized to that of albitite indicate the enrichments of some elements, particularly in Mn, Ca, Li, Sr, and REEs, roughly on the same order of magnitude (~ 10 times). The albitite–normalized element concentrations vary systematically with ionic radius of the element; the normalized concentrations of cations with the same valence roughly form a simple convex parabolic curve when plot against the ionic radius. This indicates that the element partitioning of murakamiite and pectolite during metasomatism to form albitite took place under a strong control of crystal structure, quasi–equilibrated with metasomatic fluids and coexisting minerals. The δ7Li values of murakamiite and Li–rich pectolite show a wide range from −9.1 to +0.4‰ (average −2.9‰), and no obvious correlation with Li contents was observed. These δ7Li values should have resulted from hydrothermal fluid–rock interactions at the temperatures of 300–600 °C. The very low δ7Li values down to −9.1‰ may have originated from intra–crystalline Li isotope diffusion, or involvement of deep–seated, Li–Na–enriched subduction–zone fluids with low δ7Li values.