Volcanic lava deposits

Volcanic activity. Volcanic activity includes atmospheric dust, ash, and lava flows. The relationship of atmospheric volcanic dust to quantitative mineral inputs is not known, but a review of the subject indicates that this mineral source is not generally significant from an agricultural standpoint (Lamb, 1970). Recent volcanic ash deposition and lava flows can make sizable contributions of minerals to soils on a localized basis. Maximum involvement in this respect concerns land areas bordering on or occurring as islands in the Pacific Ocean. 

Occurrence, — Selenium must be considered a rare element, although it is found widely distributed in nature. The distinctive selenium minerals are rare, and they are usually selenides, of such metals as lead, mercury, copper, bismuth, and silver. The element is also found in the free state associated with sulfur and as a selenite. The most common occurrence of selenium is in ores in which the element has partially displaced sulfur. Generally the selenium is present in very small proportions, but on account of the fact that enormous quantities of sulfide ores are used, this represents a considerable amount of selenium. It occurs also in small amounts in meteoric iron, in volcanic lavas, and in certain deposits of coal. Traces of selenium have been detected in rain and snow. Even though present in mineral ores in mere traces, it is readily concentrated either in the flue dusts or in the anode mud of the electrolytic refineries. Considerable quantities are known to exist in Hawaii, Japan,... 

Most copper deposits are (/) porphyry deposits and vein replacement deposits, (2) strata-bound deposits in sedimentary rocks, (J) massive sulfide deposits in volcanic rocks, (4) magmatic segregates associated with nickel in mafic intmsives, or (5) native copper, typified by the lava-associated deposits of the Keweenaw Peninsula, Michigan. 

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. 

The basement complex for the Patagonian desert and arid northeastern Brazil is formed by metamorphosed Precambrian rocks. Landscapes are characterized by level erosion surfaces of different ages. The landscape is dissected by a large number of valleys. Large depressions are filled with marine and continental beds of sedimentary rocks. Rocks in the Andean system, that stretches the entire length of the west side of the continent, vary greatly. Many depressions are filled with sediments. In addition, many active volcanoes are responsible for periodic lava flows and the deposition of volcanic ash. East of the Andes, the land surface is level and slopes towards the Atlantic Ocean. Broad depressions contain saline or sodic soils. 

Abstract Nash creek is the largest Zn-Pb deposit in the Tobique-Chaleurs Zone, and contains indicated and inferred resources of 7.8 Mt grading 2.72% Zn, 0.55% Pb and 18.26 g/t Ag and 1.2 Mt grading 2.66% Zn, 0.52% Pb and 18 g/t Ag, respectively. The deposit is hosted by Early Devonian bimodal volcanic and minor interlayered sedimentary rocks that were deposited in a trans-pressional rift. The host rocks sequence includes the Archibald Settlement Formation (rhyolite flows domes and related rocks), and the Sunnyside Formation (mafic lava flows and interlayered volcaniclastic and sedimentary rocks). 

In the southern TCZ only Early Devonian rocks are exposed, and all of them are assigned to the Tobique Group. The Tobique and Dalhousie groups are in part coeval and are similar in terms of rock types. The depositional environment for the Tobique Group is, for the most part, thought to be outer shelf or slope based on sedimentary bed forms and ichnofauna and the presence of abundant pillow lava and hyaloclastite in mafic volcanic units. In... 

The geologic timescale for the Earth is based mostly on stratigraphy (the depositional succession of layers from bottom to top). Most strata are sedimentary rocks. The relative ages of the sedimentary layers are determined by the sequence of deposition and by the fossils that they contain. It is not possible to use radioactive isotopes to measure the time that a sediment was deposited, because deposition does not reset radiometric clocks. However, the absolute ages of sediment layers and the fossils they contain have been determined by measuring radiometric ages of volcanic ash layers in the sequence or lavas that crosscut sedimentary strata. 

Mare basalts include lavas that erupted from fissures and pyroclastic deposits that produced glass beads. Six of the nine missions to the Moon that returned samples included basalts. The mare basalts from different sites have distinctive compositions and are classified based on their Ti02 contents, and to a lesser extent on their potassium contents (Fig. 13.3). A further subdivision is sometimes made, based on A1203 contents. Mare basalts are compositionally more diverse than their terrestrial counterparts. Volcanic glass beads, formed by fire fountains of hot lava erupting into the lunar vacuum, were found at several Apollo sites and eventually were shown to be a constituent of virtually every lunar soil. The glasses are ultramafic in composition and formed at very high temperatures. 

The volcanic centres of the LAP consist of pyroclastic deposits and a few lava flows and dyke rocks. Lavas have olivine melilitite and kalsilite meli-litite composition and show an ultrapotassic kamafugitic affinity. Pyroclastic rocks range from melilitite to phonolite. Carbonate-rich pyroclastic rocks are also present. 

Vulsini 0.6 to 0.15 - Several multicentre volcanic complexes with calderas, developed around the volcano-tectonic depression of the Bolsena Lake. Dominant pyroclastic fall deposits and ig-nimbrites and minor lavas, showing KS (trachybasalt to trachyte) and HKS (leucitite and leucite tephrite to pho-nolite) compositions. Minor melilitite. 

The Sabatini Volcanic District developed between about 0.8-0.6 Ma and 40 ka over a wide area located just to the north of Rome. Volcanism was predominantly explosive and generated widespread pyroclastic deposits with only minor lava flows, which were emitted from a large number of centres including several calderas (e.g. De Rita et al. 1983, 1993). The vol-canism occurred along a zone of crosscutting NW-SE and NE-SW faults (Di Filippo 1993). The Sabatini rocks rest over the same type of sedimentary bedrocks as at Vico, as well over the acid volcanics of Tolfa-Manziana-Cerite complex of the Tuscany Province. 

The Faete phase erupted about 6 km3 of volcanic products, which formed the Monte Faete lava and scoria cone, an intra-caldera massive pyroclastic flow deposit (Campi di Annibale pyroclastics), and some flank lava flows (Osa lava at 297 ka Capo di Bove lava at 277 ka Kamer et al. 2001 Marra et al. 2003). The activity of the Faete phase was closed by the collapse of the Campi di Annibale nested caldera and by circum-caldera strombolian eruptions. 

Roccamonfina is an asymmetric truncated composite cone, with a base diameter of about 20 km and a 6 km wide, NW-SE-elongated summit caldera that is breached on the east side (Fig. 5.7). The caldera floor, sited at about 600 m above sea level, hosts several lava flows and domes which reach a maximum altitude of about 1000 m. The volcano is composed of alternating lava flows, domes and pyroclastic deposits which were emitted both from central and parasitic vents between about 0.6 and 0.1 Ma. As shown in Fig. 5.3, rock compositions range from mafic to felsic, and from subal-kaline to alkaline potassic and ultrapotassic (Appleton 1972 Giannetti and Ellam 1994). The volcanic activity took place in a zone of NW-SE trending extensional faults cut by younger N-S faulting (Chiesa et al. 1995 Fig. 5.1). 

The volcanic sequence consists of dominant pyroclastic deposits and minor lava flows, which cover an area of about 150 km2. Activity took place between about 0.8 and 0.1 Ma (La Volpe et al. 1984 Guest et al. 1988 La Volpe and Principe 1991). The oldest activity (0.8-0.7 Ma) was characterised by phonolitic to trachytic ignimbritic eruptions and emplacement of some lava domes. The following activity was dominated by... 

The cherty iron-keratophyre formation (CIK) is characterized by the para-genetic association of acid dacite-rhyolite lavas, tuff-keratophyres, and cherty iron deposits. The formation is more uniform in facies. It is believed that the cherty iron sediments were formed near volcanic centers at times when volcanism was dying out. Semenenko assigns the deposits of the Upper suite of the Upper Konka group in the Konka syncline, and also the rocks of the Upper Bazavluk group in the Teplovka belt in the Verkhovtsevo syncline, to the CIK. 

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