3T sericite has been found in altered wall rocks of the Porgera gold deposit in Papua New Guinea. It occurs as fine-grained, clayey material forming aggregates of minute flakes replacing both argillaceous matter in calcareous siltstone and igneous components in breccia. It is closely associated with quartz, dolomite and/or calcite, subordinate pyrite and fluorite. Chemically the material is K-dominant dioctahedral mica with appreciable octahedral Fe and Mg (exactly intermediate between ideal muscovite and phengite). Although intermixed with 2M₁ sericite in small quantities, the X-ray powder diffraction pattern is satisfactorily indexed with a hexagonal cell: refined cell parameters by least squares calculation are a=5.203(1)Å, c=29.945(7)Å and V=702.04(26)ų, which are in good agreement with the phengitic composition. The chemical composition is correlated with infrared and thermal properties.
Crystallinity, chemical composition (phengitic substitution) and modes of occurrence are variable among common 1M and 2M₁ and rarer 3T sericite minerals in this deposit, reflecting diversity of genesis and origin. Local activity of high temperature hydrothermal to pneumatolytic fluid may be responsible for the formation of the 3T sericite, which is extremely well crystallized and closely associated with fluorite.

抄録全体を表示

The electron microprobe analysis of tinticite from the Suwa mine, Nagano Prefecture gave Fe₂O₃ 50.49, P₂O₅ 29.57, V₂O₅ 0.60, SO₃ 0.38, yielding the empirical formula Fe³⁺_5.95 (P_3.92V_0.06S_0.04)_Σ4.02O₁₉ on the basis of O=19. The original formula Fe³⁺₃(PO₄)₂ (OH)₃ · 3.5H₂O requires H₂O 19.16, thus the sum being 100.20%. The X-ray powder pattern is indexed on an orthorhombic cell with a=20.85Å, b=13.51Å, c=15.82Å, Z=16. The calculated density is 2.76 g/cm³, close to the original value, 2.8 g/cm³. The discrepancy to the monoclinic cell derived by Melgarejo et al. (1988) is accounted for. It occurs on thin coating or massive filling on void walls in rough goethite-jarosite ores that precipitated from a hydrothermal solution replacing andesitic volcanic and pyroclastic rocks. Tinticite is the later product than them. In weathered surface of the ore, masses of tinticite become partially loose or is veined by goethite due to loss of phosphorus.

抄録全体を表示

Syntheses of monazite (RPO₄, R=La, Ce, Nd, or Sm) were carried out by heating the mixture of [RCl₃, R₂O₃, Ce(NO₃)₃, or CeO₂] and [(NH₄)₂HPO₄, K₂HPO₄, Na₂HPO₄, or H₃PO₄)] with the atomic ratio (P/R) of 1 at 200–1000°C for 1 day. Products observed were monazite-(La, Ce, Nd, or Sm), hexagonal RPO₄·nH₂O, Ce(PO₃)₃, Ce(PO₃)₄, and CeP₂O₇. Single monazite-(La, Ce, Nd, or Sm) phase was synthesized by heating (1) the mixture of [RCl₃ or R₂O₃] and H₃PO₄ at 400–1000°C or (2) the mixture of [CeCl₃ or Ce(NO₃)₃] and [(NH₄)₂HPO₄, K₂HPO₄, or Na₂PO₄] at 200°C, or (3) the poorly crystallized monazite-(Ce) (synthesized from the mixture of CeCl₃ and (NH₄)₂HPO₄ at 200°C at 400–1000°C. The method (1) is most convenient.

抄録全体を表示

Phase relation among serpentine, brucite and forsterite was examined by test-tube type hydrothermal synthetic experiments at water pressures from 200 to 500 atm. It was confirmed that the tie line change reaction curve of serpentine + brucite _←^→ forsterite + water passes through the points of 200±20 atm and 310±20°C, 300±20 atm and 325±20°C, and 500±20 atm and 350±20°C.

抄録全体を表示