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51.
Based on the equation recently determined, formation pressures of skarn-type ore deposits were estimated from the composition of sphalerite coexisting with pyrite and hexagonal pyrrhotite. As criteria for equilibrium among sphalerite, pyrite and hexagonal pyrrhotite, the following three points were carefully checked on each specimen: 1) the presence of hexagonal pyrrhotite, 2) no time sequences among the formation of sulfide minerals, and 3) no compositional variation in sphalerite. Most of the Cu-Fe skarn deposits studied were formed under pressures of more than 1 kb, whereas Zn-Pb(-Cu-Fe) deposits tend to have formed at relatively shallow environments, namely under less than 1 kb. The calculated pressures are qualitatively consistent with the depth of formation of deposits estimated from the geological evidences. The sphalerite geobarometry is quite sensitive even at low pressure ranges, and it is applicable to the deposits formed under shallow conditions. 相似文献
52.
53.
N. Shimizu 《Earth and Planetary Science Letters》1975,25(1):26-32
Six pairs of coexisting garnets and clinopyroxenes were separated from the sheared and granular garnet lherzolite nodules in kimberlites and analyzed for rare earth elements (REE). The sheared and granular nodules can be distinguished in terms of REE pattern of both clinopyroxene and garnet. However, there are no significant differences in REE partitioning between clinopyroxene and garnet, indicating that the partitioning may be insensitive toP, T and composition. REE partition coefficients between garnet and liquid were estimated by using clinopyroxene-liquid partition coefficients found in the literature and clinopyroxene-garnet partitioning reported here. The estimated values agree with those reported by Philpotts et al. (1972). The estimated whole-rock REE pattern for the sheared nodules is similar to a chondritic pattern suggesting that the sheared nodules appear to be close to the primary mantle material. The REE data suggest that the granular nodules were originally garnet-free assemblages equilibrated with kimberlitic or nepheline-melilite basalt-like liquid, and later recrystallized as a garnet lherzolite assemblage. 相似文献
54.
A suite of basanitoids and alkali olivine basalts from Grenada, Lesser Antilles were analyzed for rare earth elements. The REE concentrations of these rocks are characterized by a small variation in the heavy REE (7 to 9 times chondrite) and a large variation in the light REE (17 to 93 times chondrite). Among the possible mechanisms to account for the REE variations, fractional crystallization processes at low and high pressures, and partial melting processes (both batch melting and fractional melting) were examined, using the partition relationships of REE among silicate minerals and melts. It is suggested that the observed REE variations are best explained by variable degrees of batch partial melting, in which garnet is present as one of the solid phases through 2 to 17% melting of a garnet lherzolite parent rock. 相似文献
55.
Overview of the MITI Nankai Trough Wells: A Milestone in the Evaluation of Methane Hydrate Resources 总被引:4,自引:0,他引:4
Yoshihiro Tsuji Hisashi Ishida Masaru Nakamizu Ryo Matsumoto Satoshi Shimizu 《Resource Geology》2004,54(1):3-10
Abstract. Bottom-simulating reflectors suggestive of the presence of methane hydrates are widely distributed below the ocean floor around Japan. In late 1999, drilling of the MITI Nankai Trough wells was conducted to explore this potential methane hydrate resource and a Tertiary conventional structure. The wells are located in the Northwest Pacific Ocean off Central Japan at a water depth of 945 m. A total of six wells were drilled, including the main well, two pilot wells, and three post survey wells at intervals of 10–100 m. All wells except the first confirmed the occurrence of hydrates based on logging-while-drilling, wire-line logging and/or coring using a pressure and temperature coring system in addition to conventional methods. Based on the various well profiles, four methane hydrate-bearing sand-rich intervals in turbidite fan deposits were recognized. Methane hydrates fill the pore spaces in these deposits, reaching saturation of up to 80 % in some layers. The methane hydrate-bearing turbiditic sand layers are less than 1 m thick, with a total thickness of 12–14 m. The bottom depth of high hydrate concentration correlates well with the depth of the bottom-simulating reflector. Based on these exploration results, the Japanese government inaugurated a 16-year methane hydrate exploitation program in 2001. 相似文献
56.
Shoji Arai Yohei Shimizu Tomoaki Morishita Yoshito Ishida 《Contributions to Mineralogy and Petrology》2006,152(3):387-398
We found fine-grained Fe-rich orthopyroxene-rich xenoliths (mainly orthopyroxenite) containing partially digested dunite fragments of Group I from Takashima, Southwest Japan. Orthopyroxenite veinlets, some of which contain plagioclase at the center, also replace olivine in dunite and wehrlite xenoliths of Group I. This shows high reactivity with respect to olivine of the melt involved in orthopyroxenite formation, indicating its high SiO2 activity. The secondary orthopyroxene of this type is characterized by low Mg# [= Mg/(Mg + total Fe) atomic ratio] (down to 0.73) and high Al2O3 contents (5–6 wt%). It is different in chemistry from other secondary orthopyroxenes found in peridotite xenoliths derived from the mantle wedge. Clinopyroxenes in the Fe-rich orthopyroxenite show a convex-upward REE pattern with a crest around Sm. This pattern is strikingly similar to that of clinopyroxenes of Group II pyroxenite xenoliths and of phenocrystal and xenocrystal clinopyroxenes, indicating involvement of similar alkali basaltic melts. The Fe-rich orthopyroxenite xenoliths from Takashima formed by reaction between evolved alkali basalt melt and mantle olivine; alkali basalt initially slightly undersaturated in silica might have evolved to silica-oversaturated compositions by fractional crystallization at high-pressure conditions. The Fe-rich orthopyroxenites occur as dikes within the uppermost mantle composed of dunite and wehrlite overlying pockets of Group II pyroxenites. The orthopyroxene-rich pyroxenites of this type are possibly common in the uppermost mantle beneath continental rift zones where alkali basalt magmas have been prevalent. 相似文献
57.
Sulfur Isotope Geochemistry of the Supergiant Xikuangshan Sb Deposit, Central Hunan, China: Constraints on Sources of Ore Constituents 总被引:2,自引:0,他引:2
Dong-sheng Yang Masaaki Shimizu Hidehiko Shimazaki Xian-hua Li Qing-lin Xie 《Resource Geology》2006,56(4):385-396
Abstract. The supergiant Xikuangshan Sb deposit is located in the Middle to Upper Devonian limestone of central Hunan, China. Primary ores are composed of early-stage stibnite and calcite with rare pyrite, early main-stage stibnite and quartz, and late main-stage stibnite and calcite. New sulfur isotope data reveal the clustering of δ34 S values (+5 ∼ +8 %) for both early and late main-stage stibnite; a single early-stage stibnite exhibits δ34 S value (+7.5 %) identical to its main ore-stage counterparts and the coexisting calcite has almost unmodified carbon isotope composition (-4.4 %). The data suggest a probable common source of sulfur for stibnite that was deposited at different paragenetic stages. A much wider variation in δ34 S values for early main-stage stibnite (+3.5 to +16.3 %, av. +7.5 %) compared to that for late main-stage stibnite (+5.3 to +8.1 %, av. +6.2 %) can be interpreted to be due to local interaction of earlier ore fluid with Devonian host rocks. The previous studies show that the Precambrian basement contains elevated Sb concentrations, and two distinctive sulfur reservoirs with δ34 Spyrite values at ca. +11 ∼ +24 % and -7.0 ∼-11 %. The homogenizing effect for sulfur hydrothermally leached from the two reservoirs might have provided ore constituents for the Xikuangshan fluids. 相似文献
58.
The effective failure modes and stability of slopes in rock mass with two discontinuity sets 总被引:3,自引:5,他引:3
Summary The stability of rock slopes in discontinuous rock mass associated with the construction of power plants, highways and open pits is always of paramount importance during the lifetime of these structures. The likely forms of instabilities observed in the excavation of rock slopes and some mathematical methods for the stability analyses are well documented in literature. Since most of the mathematical approaches used are based on the limiting-equilibrium concept, there seems a need to check the validity of these approaches under some controlled conditions. In this paper, the authors describe methods for the stability of a blocky column and discontinuous rock slopes derived on the basis of dynamic equilibrium equations and compare the results calculated according to the developed method with those of experiments on model blocky columns and model slopes in the laboratory. Test results confirm that the limiting equilibrium approache is valid and an effective way of dealing with the stability problems in discontinuous rock mass as long as the likely forms of instability are properly treated in these approaches. 相似文献
59.
The diffusivity of oxygen was determined in melts of Jadeite (NaAlSi2O6) and diopside (CaMgSi2O6) compositions using diffusion couples with 18O as a tracer. In the Jadeite melt, the diffusivity of oxygen increases from at 5 Kb to at 20 Kb at constant temperature (1400°C), whereas in the diopside melt at 1650°C, the diffusivity decreases from at 10 Kb to at 17 Kb. These results demonstrate that the diffusivity is inversely correlated with the viscosity of the melt. For the jadeite melt, in particular, the inverse correlation is very well approximated by the Eyring equation using the diameter of oxygen ions as a unit distance of translation, suggesting that the viscous flow is rate-limited by the diffusion of individual oxygen ions. In the diopside melt, the activation volume is slightly greater than the molar volume of oxygen ion, indicating that the individual oxygen ion is the diffusion unit. The negative activation volume obtained for the jadeite melt is interpreted as the volume decrease associated with a diffusive jump of an oxygen ion due to local collapse of the network structure. 相似文献
60.
Mikio Shimizu 《Astrophysics and Space Science》1979,62(2):509-513
Carbon suboxide (C3O2) polymers formed in the primitive atmosphere would have produced an organic compound soup of high concentration on the Earth. Various vestiges of C3O2 are found in the present genetic scheme, which might suggest that the living system had formed from the polymer soup. 相似文献