Geochemical environment

Continental Shelf. Most consohdated mineral deposits found on the continental shelf are identical to those found on land and are only fortuitously submerged. Exceptions include those laid down in shallow marine seas or basins in earlier geochemical environments such as bedded ironstones, limestones, potash, and phosphorites. 

Numerous geochemical data (fluid inclusions, stable isotopes, minor elements) on the epithermal vein-type deposits in Japan are available and these data can be used to constrain geochemical environment of ore deposition (gas fugacity, temperature, chemical compositions of ore fluids, etc.) and origin of ore deposits. 

Figure 1.189. The relationship between tAuCl / Au(HS)" temperature. Hatched and dotted areas represent the probable geochemical environment for typical Japanese gold-silver vein and auriferous vein deposits, respectively. A, mci- = 10, mK+ =2, qh2S = 10, K-feldspar/K-mica/quartz equilibrium B, mQ- = 1. niK+ =0.2, H2S = 10 - , K-feldspar/K-mica/quartz equilibrium C, mci- — 1, Wk+ =0.2, qh2S = 10, K-feldspar/K-mica/quartz equilibrium D, mci- =0.2, mK+ =0.04, oh2S = 10 , K-feldspar/K-mica/quartz equilibrium E, mci- =0.2, m <+ =0.04, uh s = 10 K-feldspar/K-mica/quartz equilibrium F, mci- =0.2, = 0.04, UHiS = 10 , K-feldspar/K-mica/quartz equilibrium. Thermochemical data for the calculations were taken from Helgeson (1969), Seward (1973), Drummond (1981), and Henley et al. (1984). (Shikazono and Shimizu, 1987).

Shikazono, N. and Shimizu, M. (1987) The Ag/Au ratio of native gold and electrum and the geochemical environment of gold vein deposits in Japan. Mineralium Deposita, 22, 309-314. 

Cu, Pb, Zn, Fe) deposition in epithermal systems. Thus, it is interesting to summarize the gold distribution in Besshi-type deposits, considering the geochemical environment of gold deposition. 

The geochemical environment of ore deposition for Besshi-type deposits is generally difficult to estimate because of the effect of metamorphism. 

Fig. 1. Approximate pH values and ranges for a selection of biochemical and geochemical environments, with their relation to successive pK values for the aminocarboxylate ligand ethylene glycol bis-(2-aminoethyl ether)-tetraacetate, egta.

Redox reactions in the geochemical environment, as discussed in previous chapters (Chapters 7 and 17), are commonly in disequilibrium at low temperature, their progress described by kinetic rate laws. The reactions may proceed in solution homogeneously or be catalyzed on the surface of minerals or organic matter. In a great many cases, however, they are promoted by the enzymes of the ambient microbial community. 

Jin, Q. and C. M. Bethke, 2005, Predicting the rate of microbial respiration in geochemical environments. Geochimica et Cosmochimica Acta 69, 1133-1143. 

Shacklette, T. H., Sauer, H. I., Miesch, A. T. (1970). Geochemical Environment and Cardiovascular Mortality rates in Georgia. U.S. Geological Survey Prof. Paper No. 574-C, Washington, pp. 1-39. 

Besides humic and fulvic substances in surface waters and soils, organic compounds occur in a variety of geochemical environments. Their role is determinant in the following processes. 

Data has been obtained from published sources and listed data held in the library of the Geological Survey of Namibia. This data has been used to assess the geochemical environment in the vicinity of channel fill and pedogenic uraniumbearing calcrete deposits. The data has been analysed by various methods and laboratories so direct comparison of the data has to be treated with caution. A summary table of the geochemistry of waters from each of the deposits is given in Table 1. 

Trace element reviews which are suggested for further reading and bibliography sources include Refs. 13, 14, 15, and 16 and the complete issue of Annals of the New York Academy of Science, Volume 199, Geochemical Environment in Relation to Health and Disease, (1972). 

Jhe distribution of beryllium, boron, titanium, vanadium, chromium, cobalt, nickel, copper, zinc, gallium, germanium, tin, molybdenum, yttrium, and lanthanum in the principal coal-producing beds of the Interior Province has been studied by the U. S. Geological Survey. Data, methods of sampling, and analyses are discussed by Zubovic and others (II, 12). This chapter discusses the occurrence of 13 of these elements with respect to geological and geochemical environments of coal deposition and chemical properties of the elements. Zinc and tin are not included in this study because they were detected in only a few samples. 

The equilibrium model allows certain inferences to be drawn concerning the geochemical environment which might have existed when sediments were formed, from knowledge of the thermodynamic properties of these sediments today. Thus, one can speculate about the evolution of the lithosphere, hydrosphere, and atmosphere, by assuming that equilibrium states were approached at various stages in geological history. 

Kutle, A., OreSCanin, V., ObhodaS, J. and Valkovid, V. (2004) Trace element distribution in geochemical environment of the island Krk and its influence on the local population. Journal of Radioanalytical and Nuclear Chemistry, 259(2), 271-76. 

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