Volcanism

Zeolites are tire product of a hydrotliennal conversion process [28]. As such tliey can be found in sedimentary deposits especially in areas tliat show signs of fonner volcanic activity. There are about 40 naturally occurring zeolite types. Types such as chabazite, clinoptilolite, mordenite and phillipsite occur witli up to 80% phase purity in quite large... 

Carbon dioxide, CO. Carbon dioxide is present in air and escapes from fissures in the earth in volcanic regions and where mineral springs occur. It may be prepared by ... 

The element is not found free in nature, but occurs as orthoboric acid usually found in certain volcanic spring waters and as borates in boron and colemantie. Ulexite, another boron mineral, is interesting as it is nature s own version of "fiber optics."... 

Natural diamonds are found in kimberlite of ancient volcanic "pipes," found in South Africa, Arkansas, and elsewhere. Diamonds are now also being recovered from the ocean floor off the Cape of Good Hope. About 30% of all industrial diamonds used in the U.S. are now made synthetically. 

Most of the developed hot-water fields are located by significant surface indications, particularly in the form of hot springs. Once a resource has been identified, a variety of techniques can be used to map the system and determine whether it is of a size sufficient to justify commercial development. Hidden hot-water resources are much more difficult to locate, but geologic indicators such as volcanic activity and evidence of hydrothermal alteration can be used. 

The most significant deposits are in southern Nevada, in the Lake Mead area, and in the McDermitt caldera complex on the Nevada—Oregon border. In the McDermitt caldera, lithium probably originated from volcanic sedimentary rocks deposited in the caldera moat. There is evidence that areas of the caldera were hydrothermically active contributing to enrichment of lithium (14). This and other similar deposits are not economically viable as of this writing. These deposits do represent a significant lithium reserve, however, whenever large expansion in demand occurs. 

Volcanic Deposits. Uranium deposits of volcanic deposits type are strata-bound and stmcture-bound concentrations in acid volcanic rocks. Uranium is commonly associated with molybdenum, fluorine, etc. Examples are the uranium deposits in Michelin, Canada Nopal I in Chihualiua, Mexico Macusani in Pern and numerous deposits in China and the CIS (16). 

Regulations include guidelines on geologic conditions. Of special interest is the stabiUty of the geology against faulting, volcanic action, and earthquakes. The repository is to be located in an arid region, where the water table is quite low. The host rock is to have a suitable porosity and a low hydrauhc conductivity. 

Tuff, a compressed volcanic material, is the primary constituent of Yucca Mountain, near Las Vegas, Nevada, the site selected by Congress in 1987 for assessment for spent fuel disposal. An underground laboratory, to consist of many kilometers of tunnels and test rooms, is to be cut into the mountain with special boring equipment to determine if the site is suitable for a repository. 

Site characterization studies include a surface-based testing program, potential environmental impact, and societal aspects of the repository. Performance assessment considers both the engineered barriers and the geologic environment. Among features being studied are the normal water flow, some release of carbon-14, and abnormal events such as volcanic activity and human intmsion. The expected date for operation of the repository is 2013. 

Ocean Basins. Ocean basins are primarily formed from oceanic basalts and maybe interspersed with continental remnants, ridges, seamounts, or volcanic islands rising from the depths. Average water depth is around 4000 m but the most significant mineralization is generally found at 5000 m for manganese nodules, 4000 m for biogenic oozes, and 3000 m for hydrothermal metalliferous sulfides. The area is poorly explored, however. 

Similar heterogeneous reactions also can occur, but somewhat less efticientiy, in the lower stratosphere on global sulfate clouds (ie, aerosols of sulfuric acid), which are formed by oxidation of SO2 and COS from volcanic and biological activity, respectively (80). The effect is most pronounced in the colder regions of the stratosphere at high latitudes. Indeed, the sulfate aerosols resulting from emptions of El Chicon in 1982 and Mt. Pinatubo in 1991 have been impHcated in subsequent reduced ozone concentrations (85). 

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. 

Tridymite. Tridymite is reported to be the siUca form stable from 870—1470°C at atmospheric pressure (44). Owing to the sluggishness of the reconstmctive tridymite—quart2 conversion, which requites minerali2ers such as sodium tungstate, alkah metal oxide, or the action of water under pressure, tridymite may persist as a metastable phase below 870°C. It occurs in volcanic rocks and stony meteorites. 

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. 

Sulfur constitutes about 0.052 wt % of the earth s cmst. The forms in which it is ordinarily found include elemental or native sulfur in unconsohdated volcanic rocks, in anhydrite over salt-dome stmctures, and in bedded anhydrite or gypsum evaporate basin formations combined sulfur in metal sulfide ores and mineral sulfates hydrogen sulfide in natural gas organic sulfur compounds in petroleum and tar sands and a combination of both pyritic and organic sulfur compounds in coal (qv). 

Sulfur dioxide occurs in industrial and urban atmospheres at 1 ppb—1 ppm and in remote areas of the earth at 50—120 ppt (27). Plants and animals have a natural tolerance to low levels of sulfur dioxide. Natural sources include volcanoes and volcanic vents, decaying organic matter, and solar action on seawater (28,290,291). Sulfur dioxide is beHeved to be the main sulfur species produced by oxidation of dimethyl sulfide that is emitted from the ocean. 

The flow of hydrothermal solutions iato the oceans from hydrothermal vents, ie, springs coming from the sea floor ia areas of active volcanism, and the chemical reactions occurring there by high temperature alteration of basalts ate of significance ia the mass balance of and. Eurthermore,... 

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