Ageing hydrothermal

Torgersen, T., Clarke, W. B. (1992) Geochemical constraints on formation fluid ages, hydrothermal heat flux, and crustal mass transport mechanisms at Cajon Pass. J. Geophys. 

Torgersen T, Clarke WB, Zoback MD, Lachenbmch AH (1992a) Geochemical corrstraints on formation flttid ages, hydrothermal heat flttx, and cmstal mass transport mecharrisms at Cajon Pass. J Geophys Res 97 5031-5038... 

Zeolites. A large and growing industrial use of aluminum hydroxide and sodium alurninate is the manufacture of synthetic zeoHtes (see Molecular sieves). ZeoHtes are aluminosiHcates with Si/Al ratios between 1 and infinity. There are 40 natural, and over 100 synthetic, zeoHtes. AH the synthetic stmctures are made by relatively low (100—150°C) temperature, high pH hydrothermal synthesis. For example the manufacture of the industriaHy important zeoHtes A, X, and Y is generaHy carried out by mixing sodium alurninate and sodium sHicate solutions to form a sodium alurninosiHcate gel. Gel-aging under hydrothermal conditions crystallizes the final product. In special cases, a small amount of seed crystal is used to control the synthesis. 

The American cordillera extending from Alaska to BoUvia has been the most productive source of silver wherever it is associated with Tertiary age intmsive volcanic rocks, mosdy concentrated by hydrothermal action. The largest producing mine in the cordillera is at Potosi, BoUvia, where the total silver output since the 1500s is estimated at over 31,000 metric tons. 

Because the chemical reaction is faster at higher temperature, aging can be accelerated by hydrothermal treatment, which increases the rate of the condensation reaction (8). 

In203 has the C-type M2O3 structure (p. 1238) and InO(OH) (prepared hydrothermal ly from In(OH)3 at 250-400°C and 100-1500 atm) has a deformed rutile structure (p. 961) rather than the layer lattice structure of AIO(OH) and GaO(OH). Crystalline In(OH)3 is best prepared by addition of NH3 to aqueous InCl3 at 100° and ageing the precipitate for a few hours at this temperature it has the simple Re03-type structure distorted somewhat by multiple H bonds. 

General overview and classification of hydrothermal ore deposits of Neogene age... 

Main hydrothermal ore deposit types of Neogene age that formed in and around the Japanese Islands are Kuroko deposits and epithermal vein-type deposits. This classification is based on the form of the deposits. 

The age of formation of epithermal vein-type deposits can be estimated from K-Ar ages of K-bearing minerals (adularia, sericite) in veins and in hydrothermal alteration zones nearby the veins. A large number of K-Ar age data have been accumulated since the work by Yamaoka and Ueda (1974) who reported K-Ar age data on adularia from Seigoshi Au-Ag (3.7 Ma) and Takadama Au-Ag deposits (8.4 Ma). Before their publication on the K-Ar ages of these deposits it was generally accepted that epithermal... 

Figure 1.65. Histogram of K-Ar ages of hydrothermal ore deposits in the Shakotan-Shikotsu district, Hokkaido (Sawai and Itaya, 1996).

However, in contrast to these geologic and tectonic studies, very few studies on the relationship between tectonics and hydrothermal system in Neogene age have been carried out. Therefore, these studies are briefly summarized and then the relationship between geologic and tectonic evolution and evolution of hydrothermal system associated with the mineralizations (Kuroko deposits, epithermal veins) are considered below. 

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. 

Therefore, the wider time range from middle Miocene to present is considered below based on available age data on hydrothermal ore deposits (Kuroko deposits, epithermal vein deposits) and hydrothermal alteration in the mine areas in Northeast Japan. 

High Zn, Cu and Ba contents of the Nishikurosawa Formation also indicate that the intense hydrothermal activity occurred at these ages. 

The ages of Neogene mineralization and hydrothermal alteration in and around the Northeast Honshu and Hokkaido have been determined by K-Ar data on K-minerals (K-feldspar, sericite). These data are summarized in Fig. 1.147 and Table 1.26. 

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. 

In contrast, in Southwest Japan, polymetallic veins (so-called xenothermal-type deposits in the sense of Buddington (1935) or subvolcanie hydrothermal type in the sense of Cissartz (1928, 1965) and Schneiderhohn (1941, 1955) occur. Examples of these deposits are Ashio, Tsugu, Kishu and Obira. All these vein-type deposits have formed at middle Miocene age in western part of Tanakura Tectonic Line under subaerial environment. In these deposits, many base-metal elements (Sn, W, Cu, Pb, Zn) and small amounts of Au and Ag are concentrated. These deposits are associated with felsic volcanic and plutonic rocks along the Median Tectonic Line (MTL) or south of MTL. 

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. 

Yamaoka, K. (1969) Metallic minerals of the Kuroko deposits in Northeast Japan. Proc. Symp. Mineral Constituents of Sulfide Minerals from Hydrothermal Deposits, Morioka, pp. 1-38 (in Japanese). Yamaoka, K. (1976) On the genetical problems of the vein-type deposits of the Neogene age in the inner belt of Northeast Japan. Mining Geology Special Issue, 7, 59-74 (in Japanese). 

As already noted, intense bimodal volcanic activity occurred in the Kuroko mine area at middle Miocene age and dacitic and basaltic rocks suffered hydrothermal alteration. The midoceanic ridges basalt (MORE) is widespread and sometimes hydrothermally altered. Shikazono et al. (1995) compared hydrothermally altered basalt from the Kuroko mine area and MORE and clarified the differences in the characteristics of these basaltic rocks. 

It was shown in previous chapters that intense hydrothermal activities occurred in the Neogene age in and around the Japanese Islands under the submarine and subaerial environments. In this chapter the influence of these hydrothermal activities on the seawater chemistry, and the global geochemical cycle are considered. 

The CO2 concentrations of present-day geothermal waters in terrestrial environment have been also interpreted in terms of the interaction of hydrothermal solutions with country rocks (Giggenbach, 1981 Shikazono, 1978,1985). For example, as noted in section 2.4.3, Shikazono (1985) estimated /CO2 for epithermal Au-Ag and base-metal vein-type deposits in Japan which formed in terrestrial environments at Miocene-Pliocene age and showed that fco2 controlled by the alteration minerals (Fig. 3.6). Estimated /coi" temperature range for epithermal Cu-Pb-Zn vein-type deposits are clearly similar to those for the Kuroko and back-arc deposits in which base metals (Cu, Pb, Zn) are concentrated. 

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. 

It is suggested that the mode of subduction of the Pacific Plate since the middle Miocene age related to Jackson s episode, hence oscillation of direction of lateral movement of Pacific plate. Synchronized igneous and hydrothermal activities and Jackson s episode indicate that the formations and characteristics of hydrothermal ore deposits (Kuroko and epithermal vein-type deposits) are largely influenced by plate tectonics (mode of subduction, direction of plate movement, etc.). For example, sulfur isotopic composition of sulfides is not controlled by /o and pH, but by of... 

In Chapter 3, hydrothermal and volcanic gas fluxes from submarine back-arc basins and island arc are estimated. These fluxes are compared with midoceanic ridge hydrothermal fluxes. Particularly, hydrothermal flux of CO2 is considered and the influences of this flux on global long-term carbon cycle and climate change in Tertiary-Quaternary ages are discussed in Chapter 4. 

The hydrothermal ageing of Fe-ZSM5, which represents practical operating conditions, resulted in the production of N20 at intermediate temperatures in the presence of N02 in the gas feed (Figure 9.26) [57], For Cu-ZSM5, the addition of N02 to the feed increased the N20 production significantly, the maximum value of 111 ppm found at 250°C. 

Typically, various sized LDH particles are synthesized under hydrothermal conditions by altering the aging time and reaction temperature. A clear metal solution was prepared with concentration 0.1 M, and the ratio of Mg A1 fixed at 2 1. The clear solution was titrated up to pH 9.5 with 0.5 M of NaOH solution containing Na2C03, and samples were then aged in an autoclave at various temperatures for various... 

Zeolites are formed by crystallization at temperatures between 80 and 200 °C from aqueous alkaline solutions of silica and alumina gels in a process referred to as hydrothermal synthesis.15,19 A considerable amount is known about the mechanism of the crystallization process, however, no rational procedure, similar to organic synthetic procedures, to make a specifically designed zeolite topology is available. The products obtained are sensitive functions of the reaction conditions (composition of gel, reaction time, order of mixing, gel aging, etc.) and are kinetically controlled. Nevertheless, reproducible procedures have been devised to make bulk quantities of zeolites. Procedures for post-synthetic modifications have also been described.20 22... 

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