The Seta low sulfidation epithermal gold deposit is the most recently discovered gold deposit in Japan. The deposit is characterized by well preserved near surface hydrothermal activity features such as the presence of in-situ silica sinter, kaolin deposit, mercury deposit and hydrothermal breccias. These features were the clues for discovery of the deposit. The main mineralization zone is located at approximately 250 m below the present land surface, and a very shallow depth of gold mineralization is proposed.
Mineralization occurs in two stages, (i) white crustiform quartz veins and (ii) black sulfide-rich breccia. Both types are hosted predominantly by tuff breccia and andesite lavas. The former at maximum reaches 19 m in core length and locally they may grade up to 50g/t. They formed from an ascending near neutral hydrothermal fluid. The veins in the north of the area are steep and has a NW-SE succession but at the south to southwest area, the veins become narrower and irregular and at the southernmost of the area, the veins become to be horizontal. This suggests that the hydrothermal fluids were restricted by the hydrostatic gradient when flowing from north to south. The latter exists in four parts and are oriented in a NW-SE trend forming an en-echelon pattern. Width reaches 25 m in core length but gold grade is generally low. It is proposed that it formed by mixing of following upwelling neutral hydrothermal fluid and low pH water percolating downwards from the aerated ground which were developed by condensation and oxidation of H₂S rich steam accompanied by reduction of the watertable.
BROWNE, P. R. L. and ELLIS, A. J. (1970): The Ohaki-Broadlands hydrothermal area, New Zealand: Mineralogy and related geochemistry: American Journal of Science, 269, 97-131.
FOURNIER, R. O. (1984): Carbonate transport and deposition in the epithermal environment; In Geology and Geochemistry of Epithermal Systems, (BERGER, B. R. and BETHKE, P. M., eds.), Society of Economic Geologists, Society of Economic Geologists. Reviews in Economic Geology. Vol. 2, 63-72.
GOTO, Y., NAKAGAWA, M. and WADA, K. (1995): Tectonic setting of the Miocene volcanism in northern Hokkaido, Japan: Speculation from their K-Ar ages and major element chemistry. Jour. Min. Petrol. Econ. Geol., 90, 109-123 (in Japanese with English abstract).
Hokkaido Development Bureau (1991): Survey report on zeolite deposit in Kamishihoro. 37p (in Japanese).
Hokkaido Development Bureau (1991): Survey report on a hot spring type gold deposit in Kamishihoro. 10p (in Japanese).
KATAOKA, T.(1994): A study on the epithermal gold mineralization at the Seta area, Kamishihoro-cho, Hokkaido, B.Sc. Thesis, Hokkaido Univ., 74p (in Japanese).
KATAOKA, T. (1996): A study on the characteristic features and the formation condition of epithermal gold mineralization at the Seta area, Kamishihoro-cho, Hokkaido, M. Sc. Thesis, Hokkaido Univ., 79p(in Japanese).
KOSHIMIZU, S. and KIM, C. W. (1986): Fission-track dating of the Cenozoic formations in Central-Eastern Hokkaido, Japan (part II)-"Green tuff" in the Western-Central zone-. Jour. Geol. Soc. Japan, 92, 559-568 (in Japanese with English abstract).
KIMURA, G., MIYASHITA, S. and MIYASAKA, S. (1983): Collision tectonics in Hokkaido and Sakhalin. In Accretion Tecton-ics in the Circum-Pacific Region (M. HASHIMOTO and S.Uyeda eds.), 123-134. Terra Sci. Pub., Tokyo.
MAEDA, H. (1990): Mineralization ages of some epithermal gold-silver vein type deposits in the central Kitami mining district of the Kitami metallogenic province, Hokkaido, Japan. Mining Geol., 40, 17-22.

View full abstract

Egg-shaped uraninite nodules were discovered near Yambla creek in central Australia during work carried out on the Arunta uranium exploration project by Power Reactor and Nuclear Fuel Development Corporation.
The Yambla area is geologically situated in the eastern part of the Arunta Inlier which consists of several lower Prot-erozoic metamorphic sequences. The distribution and mode of occurrence of the uraninite nodules has been investigated by detailed surface mapping, intensive mapping and sampling in trenches. It was found that the uraninite nodules are distributed over a 1 km north-south trend on the surface and in the trenches are intimately associated with plagioclase-scapolite phase (white phase) and amphibole-rich phase (dark phase) in an amphibolite host rock. The surface trend parallels the strike of the host sequence.
From chondrite-normalized REE pattern, radiometric age dating and high thorium content, the uraninite is estimated to be produced by high temperature mineralizing fluids at some 360 million years age which corresponds to the Carboniferous Alice Springs Orogeny. The white and dark phases originated by metasomatic replacement during injection of a high temperature (above 400°C) fluid along fractures and metamorphic foliation planes.

View full abstract

This paper introduces our recent trials on geophysical surveys used in exploration for uranium deposits in the Athabasca basin, northern Saskatchewan, Canada. The uranium deposits are associated with the unconformity between the Helikian (Middle Proterozoic) Athabasca sandstone and an older crystalline basement.
The current standard geophysical exploration flow in this area consists of a series of geophysical methods with electromagnetic methods as its core. That is, in view of the association between non-magnetic basement graphitic metasediments and the uranium deposits, air-borne magnetic and electromagnetic methods are the primary reconnaissance tools, and they are followed by ground electromagnetic methods to delineate the graphitic horizons prior to exploratory drilling.
Here, I show that three-component time domain electromagnetic measurements can provide a more accurate estimation of the locations of the conductor axes (intersections between the graphitic horizons and the unconformity) than conventional two-component measurements, and that direct current resistivity mapping is effective for picking shallow alteration zones.

View full abstract

It is indispensable for mineral exploration program that alteration zone which is closely related to the mineralization is clarified on its characteristics and is delineated from an investigation area. In this paper, Fazenda Brasileiro mine as a lode type of gold ore deposits pregnated in the greenstone was selected as a study area, aiming at extracting alteration zone, which is considered to be associated with primary alteration, around the ore body, by the use of remote sensing techniques.
As the results, spectral analysis using field spectroradiometer against surface soils might be important tool for further exploration program in the preliminary stage. Through this spectral analysis, kaolinite, which is produced by weathering process, was focused as one of the indices showing wall rock alteration in this study area.

View full abstract