Uranium mineralization by ground water in sedimentary rocks, Japan

Abstract

To solve the mechanism of uranium concentration in stratabound uranium deposits occurring in the basal part of Neogene sediments overlying granite basement, attention has been paid to uranium leaching from weathered granite by circulating carbonated fissure waters, to effective adsorbents for fixing uranium from uraniferous ground waters, to structural features controlling the ground-water circulation, and other relevant factors. The evidence for uranium transportation by hydothermal solutions, including hot spring waters, is hard to observe. Conclusions are summarized as follows:(1) Uranium in the deposits is supplied from surrounding source rocks, mostly from granite.(2) Uranium is transported by circulating ground-water solutions.(3) The uranium dissolved in ground water is fixed in minerals in various ways, the most important being adsorption by carbonaceous matter.(4) Ore-grade uranium concentrated from very dilute solutions occurs by multiple repetition of a leaching-and-fixation cycle between minerals or adsorbents and circulating uraniferous ground water.(5) Important factors for uranium mineralization are sufficient uranium, supplied mostly from granite, the existence of effective adsorbents such as carbonaceous matter in the host rocks, and favorable geological, geochemical, and geophysical environments.The last seem to require not only physical and chemical conditions but also correct flow and volume of ground water. Geological settingDistribution of important uranium deposits in Neogene sediments in Japan is shown in Figure 1 and their general features are summarized in Table 1.The deposits occur exclusively in basal coarsegrained sediments of Neogene age unconformably overlying granites which are mainly of pre-Tertiary age. The deposits are generally flat, lenticular in shape, and concordant. Most important deposits are located in sediments rich in carbonaceous matter and cover depressions or troughs in basement rocks. In some deposits, such as Tono, Ningyotoge, and others, ore shoots occur along shear zones, faults, or dikes cutting the host sediments. Generally speaking, however, the uranium mineralization occurs in a definite horizon in each district.Uranium content and thickness of the orebodies vary considerably.Effects on the uranium mineralization due to volcanism or hydrothermal activity are hard to observe. MineralogyCoffinite and uraninite are the most common primary ore minerals of the deposits, but ningyoite (Muto, 1962(Muto, , 1965 is found as a primary constituent in the Ningyotoge and Okushiri deposits. In many cases, the uranium present is adsorbed on carbonaceous matter and zeolites, and in some deposits uranian apatite occurs as the major uraniumbearing mineral. The most common ore mineral in the oxidized zone is autunite. Other secondary uranium-bearing minerals occur in accordance with the geochemical environments of the deposits. Pyrite 628 URANIUM IN SEDIMENTARY ROCKS 629 is the most common accompanying mineral and is widely distributed in ore-bearing horizons associated with ca...

Smectite‐Zeolite Envelope Surrounding the Tsukiyoshi Uranium Deposit, Central Japan: A Natural Analogue Study

“…The mode of occurrence of uranium in the Tsukiyoshi uranium deposit was well documented in many papers (Yamamoto et al, 1974;Doi et al, 1975;Yoshida et al, 1991;PNC, 1994). Identified uranium-bearing minerals are uraninite, coffinite, autunite, uranocircite, phosphouranylite, torbernite, tyuyamunite, b-uranophane, zippeite, uranopilite and andersonite (PNC, 1994).…”

Unsaturated Zone and Saturated Zone Transport Properties (U0100)

“…Ames et al (1983) report that clinoptilolite has a low affinity for trace levels of uranium in the plH range from 8 to 9 in 0.01 M NaHC03. Doi et al (1975) found that uranium at concentrations of lo4 g per g of 0 ANL-NBS-HS-000019, Rev 00, ICN 1 solution was strongly sorbed onto clinoptilolite from perchlorate solutions in the pH range from 4 to 8.5.…”

Overview of the National Uranium Resource Evaluation Hydrogeochemical and Stream Sediment Reconnaissance Program

“…The SRL also requires a photograph of the site and directions for reaching the site. weather -Seasonal climatic conditions may drastically affect uranium concentrations in surface waters and, to a much lesser extent, in sediments (Fix, 1956;Germanov et al, 1958;Doi et al, 1975;Rose et al, 1976). Consequently, hydrogeochemical surveys should be completed as rapidly as possible.…”

“…Sediments from acidic igneous rocks generally have greater uranium concentration than sediments from other rock types (Rogers and Adams, 1970). Also, ground waters that circulate along fractures and faults may contribute significant amounts of uranium as well as other trace metals (Doi et al, 1975;Dyck, 1975). Consequently, the local geology may be the most help in the interpretation of the data.…”