Geological background

As the Earth s tectonic plates drift apart, a new oceanic crust is formed from the basalt rising from the depths cold sea water acts as a cooling agent. Geologists distinguish between two types of hydrothermal systems (Holm, 1992)  

Sediment-free, on-axis systems at tectonic spreading centres, which have high temperature gradients (as they lie directly above magma chambers). The mean temperature of the ejected water is 620-640 K, the throughput 24 km3/year. 

Off-axis systems, on the flanks of spreading centres, driven by free convection due to cooling of the ocean crust, where the mean water temperature is around 420 K. 

The redox properties of these systems are vitally important for possible abiotic chemical syntheses the main minerals present in young basalt ocean basins, at depths between 300 and 1,300 m, are pyrite (FeS2), pyrrhotite (FeS) and magnetite (Fe3C 4) (the PPM system). 

At greater depths, the redox characteristics are mainly determined by another mineral system fayalite (Fe2Si04), magnetite and quartz (Si02) (theFMQ system). The buffer properties of the two systems can be expressed in terms of the following equations  

The oldest existing rocks on Earth, from the Isua supracrustal belt of West Greenland, are dated at 3.8 X 10 years (Moorbath et al., 1973) and consist of metamorphosed sediments. It has been suggested that the carbon in the Isua banded iron formation may be photosynthetic in origin (Schidlowski et al., 1979). Whether this remarkable conclusion is substantiated by further work remains to be seen. It is in any case abundantly clear from the available evidence that the conditions of deposition of the oldest known sediments were remarkably like those prevailing during the rest of the Archaean (4.6 — 2.6 X 10 years). Furthermore, with the exception of the appearance 

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Fig. 9-9 demonstrates the results of MVDA for the three investigated territories in the plane of the computed two discriminant functions. The separation line corresponds to the limits of discrimination for the highest probability. The results prove that good separation of the three territories with a similar geological background is possible by means of discriminant analysis. The misclassification rate amounts to 13.0%. The scattering radii of the 5% risk of error of the multivariate analysis of variance overlap considerably. They demonstrate also that the differences in the multivariate data structure of the three territories are only small. 

M. Wagner, H. J. Rasch, J. Piske, M. Baum. MPOG - microbial prospection for oil and gas. Field examples and their geological background Conference Cracov, Poland, AO-05, 118-121, 1998. 

First, we must underline once again the preliminary nature of this study. We would also emphasize that our objective was to establish the baseline values in roe blood of several heavy elements, taking into account various local factors but mainly the geochemical and geological background of the area. 

This classification try to analyze mine environment geological problems from the angles of geology background, sorts of mineral resources and mining methods (Figure 1), and accurately explain the causes, characteristics, seriousness and law of dynamic changes. 

Geology background can better reflect basic conditions of occurrence and distribution law of mine environment geological problems. Meanwhile, geology background concludes the storage conditions of ore body. 

Table 4. Mine environment geological problems in different geology background. 

Geology background Mine environment geological problems... 

This comprehensive classification considers the restriction of geology background, sorts of mineral resources and mining methods. 

This classification is based on the analysis of geology background, focuses on basic conditions of mine environment geological problems, specifies the inducing mechanism and major inducing factors, and analyzes these problems progressively and exactly. 

Li Yong, Huang Runqiu. Geological background of Longmenshan seismic belt and surface rupture in Wenchuan earthquake. Journal of Engineering Geology, 2009, 17(1) 3 16. 

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