K-Ar ages

Dymond, J. 1975. K-Ar ages of Tahiti and Moorea, Society Islands, and implications for the hot-spot model. Geology 3 236-240. 

Figure 1.6. Di.stribution and temporal and spatial relationship of late Cenozoic gold deposits in the Japanese Islands. 1 Quartz vein-type gold deposits with little to no base metals. 2 Gold-silver deposits with abundant base metals. 3 Distribution boundary of gold deposits formed during the Miocene. 4 Location of Plio-Pleistocene gold deposits at the actual island arc junctions. 5 Location of Plio-Pleistocene gold deposits in front of the actual island arc junctions. Numbers in the figure are K-Ar ages of epithermal Au-Ag veins (Kubota, 1994).

The age of Kuroko mineralization can be estimated from (1) K-Ar ages of igneous rocks associated with Kuroko deposits and (2) foraminiferal assemblages in mudstone directly overlying Kuroko deposits. 

Ma. Considering uncertainty of foraminiferal and K-Ar ages it seems reasonable that the Kuroko deposits in Hokuroku district formed in 14-12 Ma (more likely 13.6-... 

The age of formation of epithermal vein-type deposits can be estimated from K-Ar ages of K-bearing minerals (adularia, sericite) in veins and in hydrothermal alteration zones nearby the veins. A large number of K-Ar age data have been accumulated since the work by Yamaoka and Ueda (1974) who reported K-Ar age data on adularia from Seigoshi Au-Ag (3.7 Ma) and Takadama Au-Ag deposits (8.4 Ma). Before their publication on the K-Ar ages of these deposits it was generally accepted that epithermal... 

The K-Ar age data are summarized in Figs. 1.64 and 1.65. It is obvious in these figures that (1) ages of formation of epithermal vein-type deposits vary widely from 15 to 1 Ma, but are mostly 6-1 Ma, (2) epithermal vein-type deposits have been formed... 

Figure 1.64. Ages of formation of Neogenie ba,se-metal vein-type, Au-Ag vein-type and Kuroko deposits, estimated from K-Ar age and paleontologic data (Shikazono, 1987b).

Figure 1.65. Histogram of K-Ar ages of hydrothermal ore deposits in the Shakotan-Shikotsu district, Hokkaido (Sawai and Itaya, 1996).

Tonnages of gold, silver and the other associated metal, silver/gold ratio, K-Ar ages and host rocks for the Te-type and Se-type epithermal gold deposits (Shikazono et al., 1990)... 

Deposit Au Ag Ag/Au Other Year of K-Ar ages Host and country rocks... 

K-Ar ages data on adularia and sericite in the veins and altered host rocks indicate that ages of mineralization vary widely, ranging from 1 Ma to 68 Ma and from 1 Ma to 24 Ma for the Se-type and Te-type, respectively (Tables 1.17 and 1.18). 

K-Ar age data on the vein-type and Kuroko-type deposits in southern Hokkaido (Shikazono and Shimizu, 1993)... 

It seems clear by comparing Fig. 1.159 with Table 1.26 that the ages of hydrothermal mineralization and alterations determined by K-Ar age dating are consistent with those of sedimentary rocks affected by hydrothermal activity in the Oga. Hydrothermal activities were intense at ca. 14-13 Ma, 12.6 Ma, 10.5 Ma, and 8.2 Ma. 

The Kishu deposit, located at middle Honshu, is associated with Kumano acidic rocks intruded into the Shimanto and Kumano formations. K-Ar age determination indicates that the activity of Kumano acidic rocks occurred at middle Miocene (14 1... 

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). 

Izawa, E., Kurihara, M. and Itaya, T. (1993) K-Ar ages and the initial Ar isotopic ratio of adularia-quartz veins from the Hishikari gold deposit, Japan. Resource Geology Special Issue, 14, 63-69. 

Maeda, H. (1997) K-Ar age of mercury mineralization and related volcanic activity in Kitami metallogenic province, Hokkaido, Japan Specimens from Asahino disseminated and Tokoro vein-type mercury deposits. Resource Geology, 47, 11-20. 

Sawai, O. and Itaya, T. (1996) K-Ar ages of vein-type deposits in the Otaru-Shikotsu district, southwest Hokkaido, Japan. Resource Geology, 46, 33-42 (in Japanese). 

Sawai, O., Yoneda, T, and Itaya, T. (1992c) K-Ar ages of Chitose, Todoroki and Teine Au-Ag vein-type deposits. Mining Geology, 42, 323-330. 

Shikazono, N. (1985e) K-Ar ages for the Yatani Pb-Zn-Au-Ag vein-type deposits and Otoge kaolin-pyrophyllite deposits, Yamagata Prefecture, northeastern part of Japan. Mining Geology, 35, 205-209 (in Japanese with English abst.). 

Togashi, Y. and Shibata, K. (1984) K-Ar age for alumite-bearing rock from the Iwato gold deposit, Kagoshima Prefecture, southern Japan. Mining Geology, 34, 281-286 (in Japanese). 

Yamaoka, K. and Ueda, Y. (1974) K-Ar ages of some ore deposits in Japan. Mining Geology, 24, 291-296 (in Japanese). 

The basement rock of the area is composed of the Mesozoic (limestone, chert, and late Tertiary volcanic formation. Osorezan is a composite volcano with caldera structure and post caldera domes. The K-Ar age of strata volcano in the earliest stage and the latest domes are 1 Ma and 0.2 Ma, respectively (Aoki, 1991). 

Kamata, H. and Watanabe, K. (1985) Comparison and examination of K-Ar age and fission track age of the volcanic rocks in central-north Kyushu, Japan. The age when the volcano-tectonic depression was initially formed. Assoc. Mineral Petrol Econ. Geologists, 80, 263-271 (in Japanese with English abst.). 

Fig. 4.7. K-Ar ages of vein-type deposits in Japan (Shikazono, 1988).

The K-Ar age and foraminiferal age of epithermal vein-type and Kuroko deposits clearly demonstrate that epithermal precious and base metal vein-type deposits formed... 

If the samples are irradiated by fast neutrons, 39Ar is produced from K by the reaction 39K (n, p) 39Ar. The K can be determined by neutron activation on the identical sample for which the 40Ar is determined, resulting in a K-Ar age. 

Schwarzmiiller, J. Stettler, A. (1970). Trapped solar wind noble gases, exposure age and K/Ar-age in Apollo 11 lunar fine material. Proc. Apollo 11 Lunar Sci. Conf, 2,1037-70. 

Figure 11.18 Apparent K-Ar ages of minerals from Idaho Springs Formation (Front Range, Colorado, 1350-1400 Ma) in zone subjected to contact metamorphism by intrusion of a quartz monzonite (Eldora stock, 55 Ma). Reprinted from S. R. Hart, Journal of Geology, (1964), 72, 493-525, copyright 1964 by The University of Chicago, with permission of The University of Chicago Press.

Harrison T. M. and McDougall I. (1982). The thermal significance of potassium feldspar K-Ar ages inferred from " °Ar/ Ar age spectrum results. Geochim. Cosmochim. Acta, 46 1811-1820. 

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