Tuffaceous rocks

The Maze Lake area is underlain primarily by massive mafic volcanic flows and lesser pillowed, and amygdaloldal flows and tuffaceous rocks In the southern and central portions of the property, and along the extreme northern edge. Minor... 

The geological environments for these assemblages are those of weather ing, deep-sea floor sediments and continental shelf sediments, or shallow burial of these materials as sedimentary or tuffaceous rocks. 

SURDAM (R.C.) and PARKER (R.L.), 1972. Authigenic aluminosilicate minerals in the tuffaceous rock of the Green River Formation, Wyoming. Bull. Geol. Soc. Ame. fL3, 689-700. 

White, A. F., and Claassen, H. C. Geochemistry of ground water associated with tuffaceous rocks. Oasis Valley, Nevada,... 

Introduction actinide solubilities in reference waters. In this section, the environmental chemistry of the actinides is examined in more detail by considering three different geochemical environments. Compositions of groundwater from these environments are described in Tables 5 and 6. These include (i) low-ionic-strength reducing waters from crystalline rocks at nuclear waste research sites in Sweden (ii) oxic water from the J-13 well at Yucca Mountain, Nevada, the site of a proposed repository for high-level nuclear waste in tuffaceous rocks and (iii) reference brines associated with the WIPP, a repository for TRU in... 

The Arcturus Formation is structurally over-lain by felsic volcanic rocks and volcaniclastic sedimentary rocks (Passaford and Lower Shamva formations) and intercalated graphitic argillites (Mount Hampden Formation). Tuffaceous rocks and volcanic breccias occur in close association with porphyry stocks. All are andesitic to dacitic in composition. Associated epiclastic sedimentary rocks are poorly sorted massive, structureless and planar-bedded deposits. Clasts are felsic in composition and include crystal tuff, porphyry and chert, suggesting a very localized provenance. This felsic volcanism has been dated at 2643 8 Ma (Figs 2a and 3g, Wilson et al. 1995) and is associated with the emplacement of late-tectonic... 

Tuff and tuffaceous rocks of late Tertiary and Quaternary age... 

Tuff and tuffaceous rocks in numerous formations of late Tertiary and Quaternary age Tuffaceous sandstone in the Santa Margarita (3, 70, 118, 119, 123) (37)... 

Mordenite was recognized only recently as a rock-forming constituent of sedimentary deposits in the United States. In 1964, mordenite was reported from tuffaceous rocks of California (118) and Nevada (83). Since then, occurrences of mordenite have been recorded from Cenozoic tuffs in many of the western states (Table II, Figure 3). Although mordenite occurs in lacustrine rocks, most occurrences are in rocks from other depositional environments. Clinoptilolite and opal are commonly associated with mordenite in the sedimentary deposits. 

Phillipsite was found long ago in deposits on the sea floor (89). Since the discovery by Deffeyes (22) of phillipsite in lacustrine tuffs of Nevada, this zeolite has been reported commonly as a rock-forming constituent in tuffaceous rocks of the western United States (Table II, Figure 3). Phillipsite occurs in sedimentary rocks that range in age from Cretaceous to Holocene, but it is especially common in lacustrine deposits of late Cenozoic age, particularly those deposits of saline, alkaline lakes. Extensive and relatively pure beds of phillipsite are reported from southeastern Oregon, southeastern California, and Nevada. 

Ever since the discovery of analcime in tuffaceous rocks, most workers have assumed that the analcime formed directly from vitric material. The presence of vitroclastic texture and pyrogenic crystals in some anal-cimic tuffs seemed sufficient evidence however, these criteria do not necessarily prove that the glass altered directly to analcime. Hay (48) and Sheppard and Gude (123) concluded from a study of tuffs in saline-lake deposits that analcime commonly formed from alkalic, silicic zeolite precursors. Formation of analcime from clinoptilolite and phillipsite was documented in tuffs of the Miocene Barstow Formation. Relict fresh... 

Snellings, R., L. Machiels, G. Mertens and J. Elsen (2010). Rietveld Refinement Strategy for Quantitative Phase Analysis of Partially Amorphous Zeolitised Tuffaceous Rocks . Geologica Belgica 183-196. 

Geological Setting The area is underlain by Birimian meta-volcanic and meta-sedimentary rocks that have been intruded by granites. The meta-volcanic rocks are of basaltic and gabbroic compositions and most have been altered to various schists. The metasedimentary rocks consist of sandstones, siltstones, tuffs, carbonaceous phyllites, tuffaceous phyllites, cherts and maganeferous rocks (Leube et al. 1990). 

Another type of analcime concentrations in sedimentary rocks are analcimolites. These are rocks composed almost entirely of granular, spherulitic analcime. Beds up to 1 to 2 m thick have been described in Jurassic formations of Georgia (9). Similar rocks have been found by Buryanova (10) among analcime tuffs and tuffaceous sandstones of early Carboniferous deposits of Tuva. Analcimolites are structurally similar to the rocks described by Vanderstappen and Verbeek (11) in Cretaceous and Jurassic rocks of the Congo. These authors assumed a sedimentary... 

The uranium that is found in roll-front deposits is generally believed to be derived from the dissolution and leaching of host minerals by soil water and ground water (2 3). Typical source rocks for the uranium are granites, tuffs, and tuffaceous sandstones that have relatively high concentrations of uranium in... 

Chabazite was unknown from sedimentary deposits prior to its discovery by Hay (47) in tuffs and tuffaceous clays at Olduvai Gorge, Tanzania. Since then, authigenic chabazite has been recognized in silicic tuffs from Arizona, California, Nevada, and Wyoming (Table II, Figure 3). Most of the occurrences are in lacustrine rocks of late Cenozoic age. There are no reported occurrences of chabazite in rocks older than Eocene in the United States. Monomineralic beds of chabazite are rare, but extensive and nearly pure beds have been reported from lacustrine... 

Tuff and tuffaceous sedimentary rocks in the Danforth Formation of Pliocene age (148)... 

Tuff and tuffaceous sedimentary rocks of late Oligocene or early Miocene age (149)... 

The Glasgow Formation consists primarily of volcanic breccia which reaches a thickness of 2,5(X) m at the type locality on Mt. Glasgow (71°08 S, 162°55 E). The composition of the volcanic rocks ranges from basalt to andesite but does include rhyolites. The volcanic breccias grade into debris flows and tuffaceous sediment of the Molar Formation. The presence of pillow basalt and marine fossils indicates that the eruptions occurred primarily in a subaqueous and marine environment The volcanic rocks were altered by seawater to form spUites and keratophyres composed of quartz, albite, chlorite, epidote, actinolite, and varying amounts of caldte and leucoxene (Stump 1995). 

Uranium in epigenetic sandstone deposits is believed to have come from such varied sources as weathering of granitic rocks, siliceous tuffs or other uraniferous rocks in the source area for the sandstone devitrification of tuffaceous sediment in or interbedded with the sandstone hydrothermal solutions from nearby magmas and recycling and redistribution of earlier-formed uranium deposits. 

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