Pyroclastics

Chemogenic Volcanogenic Polygenic <10 >50 <10 Iron-manganese nodules, glauconite, phosphorite, nodules, phUlipsite, palagonite, celestobarite, and evaporites Pyroclastic material 38 Red clay... 

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 Izu Peninsula is mainly composed of pyroclastic and volcanic rocks of Tertiary-Quaternary age. The general geology of the peninsula has been well studied (Tayama and Niino, 1931), and thus, it is briefly described below. 

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... 

The area consists of Quaternary late Pliocene pyroclastics and sedimentary rocks. Marine mudstone and sandstone of Mesozoic-lower Tertiary Shimanto Supergroup are overlain by these rocks. Thick (more than 1,000 m) dacitic tuffs interbedded with marine sedimentary rocks of late Pliocene-early Pleistocene age occur. These rocks overlie altered andesite lava and dacitic pyroclastics of Miocene-late Pliocene (Yoshimura et al., 1988). 

Dudas M. I, Schmitt R. A., and Harward M. E. (1971). Trace element partitioning between volcanic plagioclases and dacitic pyroclastic matrix. Earth Planet. Set Letters, 11 440-446. 

Cambro-Ordovician altered meta-rhyolitic pyroclastics are host to the Thalanga Zn, Pb and Cu massive sulfide deposit in Queensland (Govett Atherden 1987). Beyond the sub-outcrop gossan zone mineralization is covered by up to 70 m of Tertiary horizontal terrestrial sandstones, conglomerates and siltstones (Campaspe beds). 

Because of their proximity ( 770 km) and similar Class 2 kimberlite designation, some discussion of the similarities and dissimilarities between the Buffalo Head Hills and Fort a la Come fields is warranted. Both fields are dominated by primary pyroclastic, volcaniclastic and resedimented volcaniclastic kimberlite, and have large, multi-aged bodies. Hence, a favourable consequence to diamond explorers is that the inter- and extra-crater morphologies of Class 2 kimberlite in the WCSB could cover vast areas. 

In the preceding paragraphs we have mentioned some of the researches that are necessary on the chemical substances of the earth s surface. We come next to aggregates, including the igneous rocks, the pyroclastic and sedimentary rocks, the oceans and other bodies of water, and the atmosphere. 

Sato H., Eujii T., and Nakada S. (1992) Crumbling of dacite dome lava and generation of pyroclastic flows at Unzen volcano. Nature 360, 664-666. 

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,... 

Wallace P.J., Dufek J., Anderson A.T., and Zhang Y. (2003) Cooling rates of Plinian-fall and pyroclastic-flow deposits in the Bishop Tuff inferences from water speciation in quartz-hosted glass inclusions. Bull. Volcanol. 65, 105-123. 

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

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. 

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