Geochemical features

They calculated the change in 8 0 values of hydrothermally altered volcanic rocks as a function of water to rock ratio by weight and temperature, assuming that oxygen isotopic equilibrium is attained in a closed system, and demonstrated that the increase in 8 0 values of altered andesitic rocks from the veins towards peripheral zones can be interpreted as a decrease in temperature from the vein system (Fig. 1.135). In their calculations, the effect of mixing of hydrothermal solution with groundwater was not considered. 

Paragenetic sequanca of tha Asahl daposit Oita pref. Matsukuma (1951) 

Paragenetic sequanca of tha NishItanI vein, NIshItanf vein group, the Ogane mine, Hokkaido. Akiba (1957) 

A Big adularia crystals with fins qusru B Aggregates of adularia and quartz C Masslve quartz with adularia P Dfusy quartz  

Qensral feature of paragenetic sequence of gangue minerals, 

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The summary of the bulk chemical compositions (major elements, minor elements, rare earth elements), Sr/ Sr (Farrell et al., 1978 Farrell and Holland, 1983), microscopic observation, and chemistry of spinel of unaltered basalt clarifies the tectonic setting of Kuroko deposits. Based on the geochemical data on the selected basalt samples which suffered very weak alteration, it can be pointed out that the basalt that erupted almost contemporaneously with the Kuroko mineralization was BABB (back-arc basin basalt) with geochemical features of which are intermediate between Island arc tholeiite and N-type MORE. This clearly supports the theory that Kuroko deposits formed at back-arc basin at middle Miocene age. 

As already noted in section 1.4.3, geochemical features of ore fluids responsible for base-metal and gold-silver types of deposits are distinct. They are summarized in Table 1.22. The differences in metals concentrated to the deposits and geochemical fectures of ore fluids responsible for both types of deposits are interpreted in terms of HSAB (hard, soft, acids and bases) principle by Pearson (1963, 1968) below. 

Geochemical features of sedimentary rocks formed in the Japan Sea as a proxy for hydrothermal activity... 

As noted already, intense submarine hydrothermal activity took place in the Japan Sea in 15-12 Ma, associated with Kuroko mineralization. However, it is uncertain that submarine hydrothermal activities associated with the Kuroko mineralization took place in the other periods from middle Miocene to present in the Japan Sea. Therefore, the geochemical features of sedimentary rocks which formed from the Japan Sea at these ages have been studied by the author because they are better indicator of age of hydrothermal activities than those of hydrothermally altered igneous rocks because the samples of continuous age of sedimentation are able to be collected and the ages are precisely determined based on microfossil data (foraminiferal, radioralian and diatom assemblages). 

Thick sedimentary pile from middle Miocene to late Pliocene is exposed in the Oga Peninsula, northern Honshu, Japan (Fig. 1.153). Age of the sedimentary rocks has been determined by microfossil data. Thus, the sedimentary rocks in the Oga Peninsula where type localities of Miocene sedimentary rocks in northern Japan are well exposed have been studied to elucidate the paleoenvironmental change of the Japan Sea (Watanabe et al., 1994a,b). Kimura (1998) obtained geochemical features of these rocks (isotopic and chemical compositions) and found that regional tectonics (uplift of Himalayan and Tibetan region) affect paleo-oceanic environment (oxidation-reduction condition, biogenic productivity). However, in their studies, no detailed discussions on the causes for the intensity and periodicity of hydrothermal activity, and temporal relationship between hydrothermal activity, volcanism and tectonics in the Japan Sea area were discussed. They considered only the time range from ca. 14 Ma to ca. 5 Ma. 

The geochemical features of the sedimentary rocks in the Oga Peninsula and the hydrothermal activity in Japan Sea deduced from these features are described below. 

Berger, B.R. (1985) Geologic-geochemical features of hot-spring precious-metal deposits. In Tooker, E. (ed.). Geologic Characteristics of Sediment- and Volcanic-hosted Disseminated Gold Deposits — Search for an Occurrence Model. U.S. Geol Surv. Bull, 1646, 47—53. 

Geological, mineralogical and geochemical features of these deposit types (distribution, age, associated volcanism, host and country rocks, fluid inclusions, opaque, gangue and hydrothermal alteration minerals, chemical features of ore fluids (temperature, salinity, pH, chemical composition, gaseous fugacity, isotopic compositions (O, D, S, Sr/ Sr, Pb), rare earth elements)) were summarized. 

Samoilov, V.S. 1991. The main geochemical features of carbonatites. Journal of geochemical Exploration, 40, 251-262. 

Gold-rich polymetallic VMS deposits such as those hosted by the Bousquet Formation represent a very attractive exploration target. Lithogeochemistry is a key tool in mapping units and tracing hydrothermal vectors towards the ore in the DBL camp. Some key geochemical features are summarized here ... 

Chapter 9 describes how crystal field energy data obtained from measurements of electronic spectra of minerals at elevated pressures and temperatures may be applied to geophysical and geochemical features of the Mantle. 

Kovalev, V.A. and Generalova, V.A., 1969. Geochemical features of the migration of iron in the recent peat bogs of Belorussia. Geokhimiya (Geochemistry), 2 210-220 (in Russian). 

The prominent niobium and lead spikes of continental materials are not matched by any of the OIBs and MORBs reviewed here. They are, however, common features of subduction-related volcanic rocks found on island arcs and continental margins. It is therefore likely that the distinctive geochemical features of the continental crust are produced during subduction, where volatiles can play a major role in the element transfer from mantle to crust. The net effect of these processes is to transfer large amounts of lead (in addition to mobile elements like potassium and rubidium) into the crust. At the same time, niobium and tantalum are retained in the mantle, either because of their low solubility in hydrothermal solutions, or because they are partitioned into residual mineral phases such as Ti-minerals or certain amphiboles. These processes are the subject of much ongoing research, but are beyond the scope of this chapter. 

Shimizu N. (1999) Young geochemical features in cratonic peridotites from southern Africa and Siberia. In Mantle Petrology Field Observations and High Pressure Experimentation (eds. Y. Fei, C. M. Bertka, and B. Mysen). The Geochemical Society, Houston, vol. 6, pp. 47-55. 

Baturin G. H. (1983) Some unique sedimentological and geochemical features of deposits in coastal upwelling regions. In Coastal Upwelling - Its Sediment Record, part B. NATO Conference Series IV, Marine Sciences lOB (eds. J. Theide and E. Suess). Plenum, pp. 11—27. 

Bustillo, M.A. Bustillo, M. (2000) Miocene silcretes in argillaceous playa deposits, Madrid Basin, Spain petrological and geochemical features. Sedimentology 47, 1023-1037. 

This paper will not be restricted to a description of geochemical features of Brazilian oil shales, since, as it was mentioned before, they are rather scarce. It will be, indeed, more of a critical discussion of Geochemistry on (using) Brazilian oil shales. 

Figure 13.15 Schematic cross-section of an idealized uranium roll-front orebody showing the zonation of elements and primary hydrologic and geochemical features. Oxidized groundwaters flow from left to right. The roll front and associated redox interface moves in the same direction. After Larson (1978).

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