Breccias

Vein Deposits. The vein deposits of uranium are those in which uranium minerals fill cavities such as cracks, fissures, pore spaces, breccias, and stockworks. The dimensions of the openings have a wide range, from the narrow pitchblende-fiHed cracks, faults, and fissures in some of the ore bodies in Europe, Canada, and AustraHa to the massive veins of pitchblende at Jachymov, Czech RepubHc (15). 

Collapse Breccia Pipe Deposits. The primary occurrence of coUapse breccia pipe deposits is in circular, vertical pipes fiUed with down-dropped fragments. Uranium is concentrated in the permeable breccia matrix and in the accurate fracture zones enclosing the pipe. An example of... 

The Chilean nitrate deposits are located in the north of Chile, in a plateau between the coastal range and the Andes mountains, in the Atacama desert. These deposits are scattered across an area extending some 700 km in length, and ranging in width from a few kilometers to about 50 km. Most deposits are in areas of low rehef, about 1200 m above sea level. The nitrate ore, caUche, is a conglomerate of insoluble and barren material such as breccia, sands, and clays (qv), firmly cemented by soluble oxidized salts that are predominandy sulfates, nitrates, and chlorides of sodium, potassium, and magnesium. Cahche also contains significant quantities of borates, chromates, chlorates, perchlorates, and iodates. 

Triimmer, n.pl. fragments fission products remains debris wreck, ruin, -achat, m. brecciated agate, -gestein, n. breccia conglomerate rubble, -masse, /. debris, detritus. 

Maguire. J.M., Pemberton, D. and Collett, M.H. 1980 The Makapansgat Limeworks grey breccia hominids, hyenas, hystricids or hillwash Palaeontologio Africana 23 75-98. 

Menaichizawa, Sasahata), is composed mostly of brecciated andesite lavas and andesitic hyaloclastics. This formation is conformably overlain by the formation (Hotakizawa, Sunakobuchi) composed of thick sequence of basaltic lavas and tuff breccias with minor intercalations of mudstone and felsic tuff. 

The formation which is mostly composed of dacite lavas, tuff breccia and mudstone (Hanaoka, Yukisawa, Uwamuki formations) conformably overlies the Hotakizawa and Sasahata formations. The thickness of these formations is 300-400 m. Kuroko ore deposits occur at the upper part of this formation. White rhyolite lava domes characterized by intense sericite alteration have a close spatial relationship with Kuroko deposits. 

Figure 1.34. Frequency histogram for MgO/FeO ratios (in wt%) of chlorite from the basalt studied (A) and MORE (B). Data sources are Shikazono and Kawahata (1987), Humphris and Thompson (1978) (M Mid-Atlantic Ridge) and Kawahata (1984) (C Costa Rica Rift, Galapagos Spreading Centre). The data on chlorite from MORE are taken from typical metabasalt and not from quartz-chlorite breccia and veins which formed in a hydrothermal upflow zone (Shikazono et al., 1987).

Negative Eu anomaly is observed for hydrothermally altered dacite underlying the Kuroko ores and anhydrite in the dacitic tuff breccia. 

Koshimoda Andesite andesite lava volcanic breccia +500tn... 

Koshimoda Volcano (andesite lava, volcanic breccia)... 

Se-type Sanru 6.7 40 6.0 1925-1974 12.4 0.6 Rhyolitic tuff, tuff breccia,... 

As already noted, most epithermal Au-Ag vein-type deposits are hosted by young (late Miocene-Pliocene) volcanic rocks and by sedimentary rocks, but dominant host and country rocks for base-metal vein-type deposits are submarine sedimentary and volcanic rocks. Submarine felsic tuff, tuff breccia, dacite lava, intrusive rocks and mudstone are dominant host and country rocks of Kuroko deposits. 

Tertiary rocks are distributed widely. They are composed of alternations of sandstone, mudstone, andesitic and dacitic tuff, tuff breccia and lava. These rocks are intensively and extensively altered and are called as Green tuff. Tertiary volcanic rocks are variable in composition. Andesite, dacite and basalt are found. Quaternary volcanic rocks are dominantly andesite lava and are abundantly distributed in the northern part of the province (Fig. 1.148). 

The veins are composed mostly of quartz and a small amount of sulfide minerals (pyrite, pyrrhotite, arsenopyrite, chalcopyrite, sphalerite, and galena), carbonate minerals (calcite, dolomite) and gold, and include breccias of the host rocks with carbonaceous matters. Layering by carbonaceous matters has been occasionally observed in the veins. Banding structure, wall rock alteration and an evidence of boiling of fluids that are commonly observed in epithermal veins have not been usually found. 

The Nigorikawa (Mori) geothermal system is located in southwest Hokkaido (Fig. 2.15). The area is composed of basement rocks (sedimentary rocks such as limestone), and Tertiary andesitic rocks (Yoshida, 1991). The area is characterized by a Krakatoan-type caldera which was formed by volcanic activity about 12,000 to 20,000 years ago (Sato, 1988). The caldera is filled with sediments consisting of clays, conglomerate, and fall back materials (tuff and tuff breccia). The rock formations surrounding the caldera consist of pre-Tertiary rock which are unconformably overlain by the Neogene Tertiary formation in thicknesses of 300-700 m. 

Breccia complex The main representative of this type is Olympic Dam deposit in South Australia. Deposits in Zambia, Zaire, and Aillik group in Labrador, Canada, may also belong to this group. 

Collapse breccia pipe Deposits in the Arizona strip in Arizona, USA. 

A. Breccia, B. Esposito, G. B. Frata-docchi, A. Fini, /. Microwave Power Electromagn. Energy 1999, 34, 3—8. 

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