Volatiles volcanic

Selenium in rainfall is derived principally from earth-surface volatilization, volcanic sources, fossil-fuel combustion (especially coal), and the incineration of municipal wastes. Few determinations of selenium in atmospheric precipitation have been reported, but concentrations are usually very low. Hashimoto and Winchester (1967) found concentrations in the range 0.04-1.4 p,gL (Table 9). 

There are areas (22) where selenium levels in the soil are very low these include regions of volcanic activity like that adjacent to the Cascade mountains in the Pacific Northwest states of the United States and the central north island of New Zealand. There, because the heat of emption volatilized the selenium, the residual soil parent material is virtually devoid of selenium. Other areas of low soil-selenium reflect leaching of selenium out of the top soil, as in the Canterbury plain on New Zealand s south island. Areas of selenium deficiency have negative implications for animal and human health. 

Volcanic activity has a significant effect on the mobilization of metals, particularly the more volatile ones, e.g., Pb, Cd, As, and FFg. Effects of volcanism are qualitatively different from those of the weathering and other near-surface mobilization processes mentioned above, in that volcanism transports materials from much deeper in the crust and may inject elements into the atmospheric reservoir. 

As is true today, most phosphate in the primordial crust must have been sequestered in nearly insoluble calcium phosphates and carbonates or in basalts, and only dissolved monomeric phosphate was produced by weathering. [201] However, the volatile polyphosphate P4O10 is known to be a component of volcanic gases. [205] This material originates from the polymerization of phosphate minerals in mag-... 

Arsenic occurs primarily in sulphide minerals associated with copper ores, and to a lesser extent with zinc, lead and gold ores. Arsenic is produced as a by-product of the smelting of these metals. Primary arsenic production has now ceased in the USA and Europe, and most arsenic is now imported from China and Mexico. The volatility of arsenic represents a significant concern, and there is at present no known natural mechanism by which arsenic is immobilized in the environment. Anthropogenic activities account for an input of some 19000 tonnes into the atmosphere, compared with 12000 tonnes from natural processes, such as volcanism and forest fires (Ayres and Ayres, 1996). 

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. 

Large, R.R., Allen, R.L., Blake, M.D., Herrmann, W. 2001a. Hydrothermal alteration and volatile element haloes for the Rosebery K Lens volcanic-hosted massive sulfide deposit. Western Tasmania. Economic Geology, 96, 1055-1072. 

The isotope composition of magmatic volatiles and related isotope fractionation processes can be deduced by analyses of glasses, volcanic gases, and hot springs. The main process that can cause isotope fractionation of volatile compounds is degassing... 

Snyder G, Poreda R, Hunt A, Fehn U (2001) Regional variations in volatile composition isotopic evidence for carbonate recycling in the Central American volcanic arc. Geochem Geophys Geosystems 2 U1-U32... 

At a later stage of volcanism, volatile components are supplied from the magma and crystals of sulfur or hematite crystallize around volcanic fumaroles or in fissures of surrounding rocks. Compared with crystallization in pegmatite, the environment is much more open, and the crystals of sulfur and hematite grow due to the chemical reaction occurring when the components supplied in the vapor phase oxidize at the Earth s surface. This crystallization therefore corresponds to... 

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