Igneous activity

In spite of low copper contents, massive horizontal development renders porphyry deposits amenable to large-scale production methods. Porphyry deposits are associated with igneous activity and intmsion of molten rocks into cooler parts of the earth s cmst, often in connection with the formation of mountains. Erosion of mountainous areas exposes these deposits to weathering, and, under the right conditions, enables the formation of oxidized or secondary copper deposits. Copper mines in the United States are Usted in Table 2. 

Hg deposits are distributed along the MTL (Median-Tectonic Line) in Southwest Japan and in Northeast Hokkaido (Fig. 1.184). The deposits are vein or disseminated in form. The deposits are hosted by sedimentary and igneous rocks. No K-Ar age data on the deposits are available. However, from the age of host rocks, the age of igneous activities along MTL and the studies on the movement of MTL and K-Ar ages of Au-veins associated with Hg mineralization in Northeast Hokkaido (e.g., Khonomai), it is likely that these deposits formed at middle Miocene age. However, mercury mineralization in Kitami Province (north Hokkaido) occurred at approximately the same age as the epithermal gold-silver mineralization in the same district (4.5-5.3 Ma) (Maeda, 1997). 

Horikoshi (1995) showed areal extension of volcanic belts since middle Miocene in the Japanese Islands. He suggested that Hg and Sb mineralization in outer zone of Southwest Japan and north Hokkaido (Kitami district) related to forearc igneous activities in trench side. 8 S values become heavier across the Northeast Japan arc from the trench to the back-arc side. He thought that the changes in tectonic character from forearc to arc environment controlled the 8 S values. 

Kanehira, K. (1991) Ore deposits in relation to igneous activities. In Hashimoto, M. (ed.). Geology of Japan. Terra Sci. Publ. and Kluwer Acad. Publ., pp. 201-216. 

Ozawa, A. (1963) Neogene orogenesis igneous activity and mineralization in the central part of northeast Japan. I. On the Neogene igneous activity. Japan. Assoc. Mineral. Petrol. Econ. GeoL, 50, 167-184 (in Japanese). 

Shikazono, N., Shimizu, M., Inoue, A. and Utada, M. (eds.) (1999) The Japanese Island Arc Its Hydrothermal and Igneous Activity. Resource Geology Special Issue, 20. 

Tsukada, Y. and Uno, T. (1980) On the hydrothermal alteration halo associated with the Ohe Mn-Pb-Zn mineralization, west Hokkaido. Mining Geology, 30, 63-72 (in Japanese with English abst.). Tsunakawa, H. (1986) Neogene stress field of the Japanese Arcs and its relation to igneous activity. Tectonophysics, 124, 1-22. 

Tsunakawa, H. and Takeuchi, A. (1986) Paleo-stress field and igneous activity of Japanese Island. In Taira, A. 

Utada, M. (1980) Hydrothermal alterations related to igneous activities in Cretaceous and Neogene formations of Japan. Mining Geology Special Issue, 8, 67-83. 

Tsunakawa, H. and Takeuchi, A. (1986) Paleo-stress field and igneous activity of Japanese Island. In Taira, A. and Nakamura, K. (eds.). Formation of the Japanese Island. Iwanamishoten, pp. 201-208 (in Japanese). 

Igneous activity that occurred between Late Cretaceous and Early Tertiary time shows a strong northeast-southwest trend, which is also evident in the regional aeromagnetic data. The aeromagnetic... 

Possible heat sources for melting in meteorite parent bodies are discussed in Chapter 11. Differentiated meteorites generally have old radiometric ages (Chapter 9), which indicate igneous activity began and ended soon after their parent bodies accreted. 

Figure 7.4. A sedimentation diagram for a hypothetical Devonian-age carbonate sequence. The curve for the sequence gives its inferred position relative to sea level and land surface elevation since the time of its sedimentation. Schematic subsurface isotherms are also presented based on estimates of crustal thickness and hypothetical heat flow values related to plate movements and igneous activity. [Adapted from Siever s (1979) representation of the Esopus Formation.]...

LA-ICP-MS using a multi-collector instrument for Pb-Pb dating via ° Pb/ °" Pb and ° Pb/ ° Pb isotope ratio measurements of natural rutile crystals has been utilized to study geological temperature-time histories. The significance of Devonian-Carboniferous igneous activity in Tasmania on the basis of U-Pb dating has been measured by sensitive high resolution ion microprobe (SHRIMP). ... 

Wadhwa M., Shukolyukov A., and Lugmair G. W. (1998) Mn- Cr systematics in Brachina a record of one of the earliest phases of igneous activity on an asteroid. In Lunar Planet. Sci. XXIX, 1480. The Lunar and Planetary Institute, Houston (CD-ROM). 

Wellman P. and McDougall I. (1974) Cainozoic igneous activity in eastern Australia. Tectonophysics 23, 49- 65. Wetherill G. W. (1954) Variations in the isotopic abundance of neon and argon extracted from radioactive minerals. Phys. Rev. 96, 679-683. 

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