Hydrothermal mineralization

It seems clear by comparing Fig. 1.159 with Table 1.26 that the ages of hydrothermal mineralization and alterations determined by K-Ar age dating are consistent with those of sedimentary rocks affected by hydrothermal activity in the Oga. Hydrothermal activities were intense at ca. 14-13 Ma, 12.6 Ma, 10.5 Ma, and 8.2 Ma. 

The changes in stress fields, and intensities of igneous and hydrothermal activities except 12.6 Ma seem correlate to oscillatory motion of the Pacific plate (Jackson s episodes Jackson and Shaw, 1975 Jackson et ah, 1975) (Masuda, 1984). Masuda (1984) and Takeuchi (1987) pointed out that the oscillatory motion of Pacific plate during the last 42 Ma correlates with magmatism, the intensity of tectonism, the change in stress field and the history of sedimentary basin in arc-trench system (Fig. 1.147). The above argument also suggests that the hydrothermal mineralizations in arc and back arc systems relate to the oscillatory motion of the Pacific plate. 

Shimizu, M., Shikazono, M. and Tsunoda, K. (1995) Sulphur isotopic characteristics of hydrothermal mineral deposits in the southern Fossa Magna region, Japan Implications for the tectonic and geologic evolution in the southern Fossa Magna region after middle Mioceme age. Memoirs Fac. Ed. Yamanashi U., 46, 40-48. 

Taylor, H.P. Jr. (1997) Oxygen and hydrogen isotope relationship in hydrothermal mineral deposits. In Barnes, H.L. (ed.). Geochemistry of Hydrothermal Ore Deposits, 3rd ed. Wiley and Sons, pp. 229-302. Terada, T. (1934) On bathymetrical features of the Japan Sea. Bull Earths. Re.s. Inst., 12, 650-656. 

Fig. 2.29. Hydrothermal mineral occurrences related to arc-back-arc. systems of the western Pacific. Numbers are li.sted in Table 2.12 (Ishiba.shi and Urabe, 1995).

Several hydrothermal sites have been discovered on the seafloor of Izu-Bonin arc that is located at the eastern margin of the Philippine Sea plate (Fig. 2.32). This arc has been formed, related to the westward subduction of the Pacific plate (Fig. 2.32). Hydrothermal mineralization occurs both in back-arc depression and volcanic chain (Shichito-Iwojima Ridge). Hydrothermal venting and mineralizations are found... 

Hydrothermal mineral occurrences in arc-back-arc systems in the Western Pacific (Ishibashi and Urabe, 1995)... 

North Fiji Basin, Station 14 (18°50 S, 173°30 E) 2720 Collapsed lava lake on flat rise crest of fast spreading south-central segment. No sediment cover. Warm (T = 5.2°C) fluid discharge through mussel bed. No hydrothermal minerals. Site of megaplume (Noriji et al., 1989). None. 

The vesicle volume of the Kuroko basalt is large (average 20%) and vesicles are filled with hydrothermal minerals (epidote, calcite, chlorite, pyrite, quartz) which formed... 

Each of these solid phases can be described in terms of their mineralogy. This classification scheme is based on crystal structure and chemical composition. The most common minerals found in marine sediments are listed in Table 13.2. Most are silicates in which Si and O form a repeating tetrahedral base unit. Other minerals common to marine sediments are carbonates, sulfates, and oxyhydroxides. Less common are the hydrogenous minerals as they form only in restricted settings. These include the evap-orite minerals (halides, borates, and sulfates), hydrothermal minerals (sulfides, oxides, and native elements, such as gold), and phosphorites. 

In this chapter, we consider the mineral composition of the hydrogenous minerals and how they fitrm. The evaporite minerals have already been covered in Chapter 17. The hydrothermal minerals (polymetallic sulfides) are discussed further in Chapter 19. 

One of the most notable features of seawater is its high degree of saltiness. In previous chapters, we have discussed various sources of this salt, these being rivers, volcanic gases, and hydrothermal fluids. These elements have ended up in one of four places (1) as dissolved ions in seawater, (2) as sedimentary minerals, (3) as hydrothermal minerals, and (4) as volatiles that reside in the atmosphere. The minerals are recycled via geologic uplift and subduction. Upon return to Earth s surface, these minerals are chemically weathered via acid attack by the atmospheric volatiles remobilizing the salts for return to the ocean in river runoff. 

Least-altered metavolcanic samples have Na20 and MgO contents of 1.8-4.0 wt. % and 4-25 wt. %, respectively, whereas strongly altered samples (having greater than 30% hydrothermal minerals by volume, in dense net-textured veins, in places obscuring primary textures) contain less than 1.5 wt. % Na20 and 11-23 wt. % MgO. 

Markl, G., Lahaye, Y., Schwinn, G. 2006. Copper isotopes as monitors of redox processes in hydrothermal mineralization. Geochimica et Cosmochimica Acta, 70(16), 4215 228. 

Lithogeochemistry of the Meguma Supergroup, Nova Scotia, Canada petrographic constraints, depositional environments and alteration haloes about sediment hosted hydrothermal mineral deposits... 

Proper watershed delineation provided an effective framework for interpretation and analysis of multidisciplinary data and relies on the quality of the original DEM. In the flat, vegetated lowlands, the resultant watersheds tend to be small, whereas in the alpine areas they are larger and more favourable to the detection of hydrothermal minerals by the Landsat imagery because of sparse vegetation. 

Automated feature extraction using The Spectral Geologist provides a fast means to obtain abundant and valuable data pertaining to mineral alteration. However, the automated spectral mineral identifications of foliated rocks proved strongly biased towards the phyllosylicates that define tectonic foliations, and were not sufficient to model hydrothermal mineral alteration zoning. 

Chlorine is the major anion in surface- and mantle-derived fluids. It is the most abundant anion in hydrothermal solutions and is the dominant metal complexing agent in ore forming environments (Banks et al. 2000). Despite its variable occurrence, chlorine isotope variations in natural waters conunonly are small and close to the chlorine isotope composition of the ocean. This is also true for chlorine from fluid inclusions in hydrothermal minerals which indicate no significant differences between different types of ore deposits such as Mississippi-Valley and Porphyry Copper type deposits (Eastoe et al. 1989 Eastoe and Guilbert 1992). 

By direct measurement of fluid inclusions contained within hydrothermal minerals... 

Despite the close association of intnisions with many ore deposits, there is still debate about the extent to which magmas contribute water and metals to ore-forming fluids. Many early studies of the stable isotope composition of hydrothermal minerals indicated a dominance of meteoric water (Taylor 1974), more recent studies show that magmatic fluids are commonly present, but that their isotopic compositions may be masked or erased during later events such as the influx of meteoric waters (Rye 1993 Hedenquist and Lowenstem 1994). 

The dissolved solids and gases in geothermal fluids have been divided into two types, reactive and conservative components (Giggenbach 1991). Temperature-dependent equilibria between solution and hydrothermal minerals fix the aqueous concentrations of the reactive components, at least if temperatures exceed some 100 C (e.g., Giggenbach 1980, 1981 Arnorsson et al. 1983). 

Karingithi, C. W. 2002. Hydrothermal Mineral Buffers Controlling Reactive Gases Concentrations in the Greater Olkaria Geothermal System, Kenya. MSc thesis, University of Iceland, 94 pp. 

Naboko, S. I., Glavatskikh, S. F., Hydrothermal Minerals of Goryachi Plyazh (Kunashir I.), in Mineralogiya Gidrotermarnykh Sistem Kamchatki i KuriFskikh Ostrovov, Nauka, Moscow, 1970. 

Itakura, T., Sasai, R. and Itoh, H. (2006) Arsenic recovery from water containing arsenic ions by hydrothermal mineralization. Chemistry Letters, 35(11), 1270-71. 

Taylor, H.P. Jr., 1970. Oxygen isotope studies of hydrothermal mineral deposits. In Geokhimiya gidrotermal nykh rudnykh mestorozhdeniy (Geochemistry of Hydrothermal Ore Deposits). Izd. Mir, Moscow, pp. 101-128 (in Russian). H.L. Barnes (Editor), Pennsylvania Univ., Holt, Rinehart and Winston, Inc. (1967, pp. 109-142, in English). 

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