Official journal of Japan Association of Mineralogical Sciences (JAMS), focusing on mineralogical and petrological sciences and their related fields. Journal of Mineralogical and Petrological Sciences (JMPS) is the successor journal to both “Journal of Mineralogy, Petrology and Economic Geology” and “Mineralogical Journal”.
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Datolite [CaBSiO4(OH)] was discovered in an eclogite–facies calcite marble collected from the Eastern Iratsu body in the Sanbagawa metamorphic belt of central Shikoku. The marble was composed of calcite, diopside, and garnet that contained inclusions of omphacite. Enclosed in the marble is a pod composed mainly of quartz, with subordinate calcite, diopside, and garnet that has inclusions of datolite. The formation conditions of the datolite were estimated on the basis of mineral assemblage and the Raman elastic geobarometer to be approximately 400–650 °C and 0.8–1.3 GPa, which coincide with the conditions of the eclogite juxtaposition with the non–eclogite units in the Besshi district. Our study records the highest pressure–temperature conditions as the metamorphic datolite formation. Our findings provide evidence for the occurrence of B–rich fluid infiltration during the juxtaposition of eclogite unit with the non–eclogite unit in the Besshi district.
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.
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.
Structural analysis of Ce– and Nb–perovskites containing Fe, Zr, Nb, and rare earth elements (REEs) in CaTiO3 perovskite was performed using single–crystal X–ray diffraction and X–ray absorption near–edge structure (XANES) analyses. Based on chemical analysis results, XANES measurements and the site–occupation of elements at A– and B–sites showed the chemical formula:
Al3+0.002Ge4+0.001W6+0.001)3.996+1.003O3 for Ce–perovskite and
for Nb–perovskite. In Ce– and Nb–perovskites, the total charges at the A– and B–sites achieved near–ideal divalent and tetravalent states such as Ca2+Ti4+O3, respectively, due to complex elemental substitutions. Local distortions around Ti in the perovskite solid solutions were greater, and the pre–edge features of the Ti atoms in Ce– and Nb–perovskites were different from those in pure CaTiO3. The valence states and local structures of Fe in Ce– and Nb–perovskites were significantly different. The existence of divalent Fe2+ at the B–site in Ce–perovskite was confirmed. It is presumed that the displacement ellipsoids of all atoms and local irregularities in Ce–perovskite increase owing to the radiative decay of the actinoid element Th. We reconfirmed that the composition and three–dimensional structure of perovskite–type structures were flexible and caused various electrical, structural changes.
Lithium–bearing sodium amphibole (Li2O = 0.01–1.02 wt%) was found in a specimen of schistose manganese ore from the Iimori region in the Sanbagawa metamorphic belt, central Japan. The ore is composed mainly of quartz, albite, amphibole, Na to Na–Ca pyroxene, and braunite. The amphibole occurs as prismatic crystals with lengths of up to 400 µm and consists of a pale–green core and an orange–red rim observed in hand specimen. The chemical formulae of averaged compositions of the core and rim, based on 24(O, OH, F, Cl) with (OH, F, Cl) = (2 − 2Ti) atoms per formula unit, are
Σ5.000TSi8.000O22W[(OH)1.737F0.157O0.106]Σ2.000, respectively. Consequently, the core amphibole has an intermediate composition between magnesio–arfvedsonite and potassic–magnesio–arfvedsonite, whereas the rim amphibole is potassic–magnesio–arfvedsonite.
The Hida granites, classified into the pre–Jurassic and Jurassic plutons in this study, are important components of the Hida belt, which is a Paleozoic–Mesozoic basement of the Japan arc and underwent Permian to Triassic metamorphism during the collision between the North and South China blocks. This study performed zircon U–Pb dating and whole–rock geochemical analyses for the Hida granites from the major plutonic bodies to reveal the geotectonic history and the origin of the Hida belt. Obtained 238U–206Pb weighted mean ages exhibit 239.1–238.3 Ma for the Katakaigawa body (augen granite) and 200.5–180.9 Ma for the other bodies (non–deformed granitoids), and these ages can be correlated to the pre–Jurassic and Jurassic plutons, respectively. Geochronological results suggest that the mylonitization forming augen granites of the pre–Jurassic plutons occurred during its intrusion and indicate that the Jurassic plutons are distributed widely in the Japan Sea side of the Hida belt. Meanwhile, geochemical characteristics of whole–rock major and trace element compositions indicate that the pre–Jurassic and Jurassic plutons seem difficult to distinguished geochemically and suggest that both of them are adakitic and non–adakitic granites generated in subduction zone.
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