The Mitsuishi district, noted for the largest Roseki production in Japan, is generally characterized by the alteration zoning from center to margin; Quartz zone → Roseki ore (Pyrophyllite, Pyrophyllite-sericite and Sericite zones) → K-feldspar-sericite zone → Albite zone. They are overlain by Weakly propylitized zone. The filling temperatures of fluid inclusions in euhedral quartz crystals indicate the hydrothermal solution was about 300-350°C for the formation of Quartz zone. The chemical composition of the hydrothermal solution was estimated from salinity of the fluid inclusions, analytical results of altered rocks and minerals (feldspars and sericite), thermochemical calculations on the K-feldspar-albite and muscoviteparagonite solid solutions and equilibria in the Na 2 O-K 2 O-SiO 2 -Al 2 O 3 -H 2 O-HCl system, and mobility calculation on the water-rock interaction process. It is deduced that pH dramatically increased, while K and SiO 2 concentrations decreased, and Na concentration remained relatively constant in the hydrothermal solution from center to margin of the alteration zones.
Abstract:Rivers characterized by suspended load and bed load tend to build fine-grained deltas and coarse-grained deltas, respectively. Gilbert-type deltas consisting of topset, foreset, and bottomset beds are recognized in marine environments as well as in lakes. Coarse-grained deltas tend to be Gilbert-type deltas. However, fine-grained deltas built in deep-water river mouthsand in wave-dominated rivermouths are mostly Gilbert-type deltas. Bird foot, lobate, cuspate, and estuarine deltas are recognized in marine environments.In contrast, estuarine deltas do not occur in lakes, since lakes are less subjected to tidal influ encesthan seas.
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