Rocks pyroclastic

Some of the Kuroko deposits consist predominantly of pyrite containing a small amount of chalcopyrite. The ore deposits consisting predominantly of pyrite, either with an economical value of chalcopyrite or not, are called the Y sub-type deposits, which occur above dacite lava dome or lava flow, while copper-poor deposits occur mostly in pyroclastic rocks and are associated with a large amount of gypsum. The Matsumine deposit in the Hanaoka mine is typical of the Y sub-type. The Matsuki and Takadate deposits in the Matsuki mine are also classed as this sub-type (Kuroda, 1978). Many pyrite-rich ore bodies... 

Figure 1.12 shows the areal distribution of the B and C sub-type deposits in the Kosaka district. The Y sub-type deposits have not yet been found in the district. It appears that two zones characterized by the distribution of each sub-type deposit are distributed north-southernly in the Kosaka district as well as in the Hanaoka district (Fig. 1.13). Pyroclastic rocks in the Kosaka formation, in which all deposits occur, become thicker to the east, and probably moved from the eruptive centres to the east (Horikoshi, 1969). These types of evidence may indicate that the sea at that time became deeper to the east. Figure 1.12 shows also the top of the pre-Tertiary basements. Ore deposits, either B or C sub-type, occur above the crater-like depressions of basements. The Shinsawa deposit is the sole example of B sub-type in the midst of the Hanaoka-Kosaka district, so-called Hokuroku basin (Fig. 1.13). The Tsunokakezawa deposit in the Fukazawa mine and ore deposit in the Ezuri mine are also the B sub-type.

The Seigoshi and Toi deposits occur in the andesitic pyroclastic rocks of the upper horizon of the Yugashima Group and basic intrusive rocks. Distributions of the wallrock alteration minerals from underground in the Seigoshi mine and on the surface near the... 

The Hishikari Upper Andesites overlying the Hishikari Lower Andesites and the Shishimano Dacites consist of hypersthene-augite andesite lava flows and their pyroclastic rocks. 

The Okuaizu geothermal area is located in Northeast Japan (Fig. 2.18). Pyroclastic rocks are the oldest ones of early Miocene (18-16 Ma). These Miocene and Pliocene... 

Spieler O., Kennedy B., Kueppers U., Dingwell D.B., Scheu B., and Taddeucci J. (2004) The fragmentation threshold of pyroclastic rocks. Earth Planet. Sci. Lett. 226,... 

Fisher, R. V. Schmincke, H. U. 1984. Pyroclastic Rocks. Springer-Verlag, Berlin. 

Silicic volcanics occur as lavas at San Vincenzo, Roccastrada, Monte A-miata, Monti Cimini and Tolfa-Manziana-Cerite complex. Pyroclastic rocks are scarce or absent, and a few ignimbrites only occur at Monti Cimini and Cerite complex. Silicic intrusions crop out in the islands of Elba, Montecristo and Giglio, and at Campiglia and Gavorrano in southern Tuscany. Other granitoid bodies occur as seamounts in the northern Tyrrhenian Sea (e.g. Vercelli Barbieri et al. 1986) and as hidden intrusions in several places of southern Tuscany (e.g. Franceschini et al. 2000 Poli et al. 2003). 

Three monogenetic centres formed by olivine melilitite lava and pyroclastic rocks. 

Kalsilite melilitite lava flow overlying pyroclastic rocks, some of which contain abundant carbonates. 

Massive pyroclastic rocks containing kamafugitic juvenile material. 

The main questions concerning the volcanics of the IAP relate to the origin of the kamafugitic lavas at San Venanzo and Cupaello and the nature of carbonate-rich pyroclastic rocks present in several centres. Both issues have been much discussed in the literature, although the debate often has been based on preconceptions rather than on factual evidence. 

The core of the problem of carbonate-rich pyroclastic rocks form IAP relates to the question of whether they represent carbonatites or they are fragmented silicate rocks mixed with secondary calcite coming from the wall rocks. The main arguments that have been considered to be in favour... 

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. 

Like other Roman volcanoes, the Vico pyroclastic rocks contain xeno-liths of various origin, including bedrock fragments, intrusive equivalents of lavas, and cumulate rocks. These xenoliths often contain exotic minerals, such as Zr-Ti-Th-U-REE rich phases (e.g. britholite, baddelyite, and pyrochlore), which have been interpreted to be the result of deposition from late-magmatic fluids rich in incompatible elements (e.g. Della Ventura et al. 1999). 

Lava flows are more mafic (i.e. contain higher MgO) than pyroclastic rocks from the same eruptive phase, but ranges in silica and alkalies are similar (Trigila et al. 1995). 

Pyroclastic rocks include scoria and pumices, which show variably por-phyritic textures with dominant leucite phenociysts and minor clinopyrox-ene, some mica, and rare olivine, set in a microcrystalline to glassy matrix that has been generally affected by strong secondaiy processes, with abundant zeolites and clay minerals (Fomaseri et al. 1963 Trigila et al. 1995). Accessory phases include Fe-Ti oxides, apatite and rare garnet. 

Campi Flegrei About 0.2 Ma to 1538 AD. Buried volcanism 2 Ma old - Multicentre volcanic complex with two nested calderas and several monogenetic cones and maars, formed of prevailingly pyroclastic rocks with trachybasalt to trachyte-phonolite composition. 

Ischia island 150 ka to 1302 AD - Volcano-tectonic horst formed of prevailing pyroclastic rocks with trachybasaltic to dominant trachytic composition. 

The Island of Ventotene consists of a basal series of thin mafic lava flows cut by a caldera rim and covered by intermediate to felsic pyroclastic products. Santo Stefano is an eccentric lava dome covered by pyroclastic products. Pyroclastic rocks include fall, flow and surge magmatic and hy-drovolcanic products, and contain lava lithics, cumulate xenoliths and skams (Perrotta et al. 1996). Rock compositions range from basalt and trachybasalt to phonolite (Fig. 6.18). Basalts and trachybasalts have a por-phyritic texture with phenocrysts of olivine (about Fo85.65), diopside to... 

Lipari 220 ka to 580 AD - Multicenter volcano formed of calc-alkaline and high-K calc-alkaline basaltic andesite and andesite, followed by latite and abundant rhyolite lava flows, domes and pyroclastic rocks. 

Stromboli 200 ka to present - Stratovolcano with summit caldera and flank collapses, and a satellite neck (Strombolicchio) formed of mafic to intermediate lavas and pyroclastic rocks with calc-alkaline, shoshonitic and potassic alkaline petrochemical affinities. 

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