Shigen-Chishitsu
Online ISSN : 2185-4033
Print ISSN : 0918-2454
ISSN-L : 0918-2454
Volume 60, Issue 3
Displaying 1-8 of 8 articles from this issue
Original Articles
  • Ryoichi YAMADA, Takeyoshi YOSHIDA
    2010 Volume 60 Issue 3 Pages 143-152
    Published: 2010
    Released on J-STAGE: July 18, 2013
    JOURNAL FREE ACCESS
    We examined the distribution of the 17 rare metals accompanied by various types of base-metal deposits in order to delineate the relationship between the concentrations, and the geologic and tectonic developments of the northern Honshu arc in the late Cenozoic age. We selected 54 probably representative samples among previously collected from 56 mines on the basis of the descriptions in the operating period, and investigated them by means of statistical studies of the analytical results. The correlation coefficients among the 17 rare metals together with 4 base metals (Cu, Pb, Zn and Fe) and 2 precious metals (Au, Ag) are as follows: Sr-Ba(0.87), In-Sn(0.83), Sn-Bi(0.74), Se-Te(0.74), In-Bi(0.66), V-Ag(0.58), Fe-Bi(0.58), Tl-Ge(0.53), Fe-In(0.52), V-Ga(0.51), Zn-Ga(0.48), Pb-Se(0.47), Fe-Sn(0.46), Ge-Te(0.41), Ge-Te(0.41) in descending order. The normative compositions of ore minerals, which were calculated from the base metal grades including Ba, have correlation coefficients against rare metals as follows: the norm barite with Sr, 0.87; Tl, 0.37; Ag, 0.32, and Sb, 0.27; norm galena with Se, 0.47; Te, 0.28; Ag, 0.24, and Ge, 0.21; norm sphalerite with Ga, 0.48; Ge, 0.40; Cd, 0.39, and Mo, 0.21; norm chalcopyrite with Bi, 0.17, and norm pyrite with Bi, 0.58; Sn, 0.48; In, 0.48, and Co, 0.27. The other silicate gangues are correlated with Ti, Au and Be with correlation coefficients of 0.54, 0.27 and 0.26, respectively.
    We classified the ore deposits type into the following 6 categories on the basis of the previous studies (MITI, 2000; 2001) and recently-compiled data-base (Tsuchiya, 2008);
    1) typical Kuroko deposits (T-type), 2) massive sulfide ore regarded as Kuroko analogue (A-type), 3) stringer ore similar to the Kuroko footwall mineralization (S-type), 4) stockwork to veinlets deposits with sulfate minerals (N-type), 5) fissure-filling veins (V-type) and 6) xenothermal deposits around granitoid intrusions (X-type). The variation of rare metal contents, equivalent to the sulfide+sulfate=100% basis, indicates that the concentration of the In-Sn-Co-Bi segment associated with norm pyrite is gradually increasing from the above 1) to 6), that of the Te-Se segment associated with norm galena is remarkably concentrated in 4) (N-type), and that of the Tl-Sb segment associated with norm barite is gradually decreasing from 1) to 6).
    The tectonic settings in the northern Honshu arc are divided from west to east into a) Hachimori rise, b) Babame rift, c) Ani rise, d) Kuroko rift and e) fore-arc region based on our previous studies (Yoshida et al, 2005; Yamada and Yoshida, 2005). The In-Sn-Co-Bi segment has high concentration in the Ani rise (zone c) and the fore-arc region (zone e). On the contrary, the Tl-Sb segment is rich in the Kuroko rift (zone d). Te-Se is remarkably concentrated within the fore-arc region.
    These statistical analyses suggest that many rare metals are strongly associated with both deposit types and tectonic settings. Indium, economically most significant, is rich in xenothermal and polymetallic deposits of the types N and V, and it exists mainly in the pyrite-rich ore with Sn, Co and Bi in the intra-rift rise and the fore-arc region.
    Download PDF (595K)
  • Ryoichi YAMADA, Takeyoshi YOSHIDA, Takeshi KAKEGAWA, Fumiko NARA, Yasu ...
    2010 Volume 60 Issue 3 Pages 153-164
    Published: 2010
    Released on J-STAGE: July 18, 2013
    JOURNAL FREE ACCESS
    High-indium ore deposits are associated within the rise tectonic zones of progressive rift-rise structures resulted from the late Cenozoic back-arc spreading of the northern Honshu arc. We examined the indium concentration mechanism around the Hokuroku district, which constitutes one of the typical rift-rise settings. The Tatsumata mine area in the SE wing of the Hokuroku rift comprises three segments of base-metal vein system which is thought to be xenothermal type related to gabbroic to dioritic stocks emplaced at ca. 17 Ma. Almost all the specimens taken from stock piles of the ores have high indium contents ranged from several tens to 400ppm, correlated with tin, bismuth and cobalt contents.
    The vein system is composed of two different mineralization stages; chalcopyrite-pyrite veins with subordinate pyrrhotite, magnetite and rare sphalerite, and the following sphalerite-dominant veins with subordinate galena and a few manganese minerals. Indium is contained in the both stage mineralizations. It is concentrated only in the marginal part of the sphalerite crystal with chalcopyrite exsolution blebs, although it has no obvious correlation with Zn and Cu contents.
    Sulfur isotopes indicate two different series of the hydrothermal activity. The first is characterized by relatively low δ34S values which exists in the gabbroic stocks, the lower unit silicified rocks and the early stage veins. This series was suggested to be formed dominantly from a magmatic hydrothermal solution with relatively reducing condition. Another series has relatively heavy δ34S values and occurs in the diorite porphyry stocks, the upper unit silicified zones and the later stage veins. This series was suggested to be formed by a relatively oxidized hydrothermal solution originated by mixing with sea water. Indium may have been released in the early stage hydrothermal fluid with tin, bismuth and cobalt and was involved in sphalerite crystal, probably replaced to iron, of the late stage mineralization.
    In consideration of the stratigraphic position and the mineralization timing in the tectonic history of the northern Honshu arc, it was suggested that the mineralization environment changed from a terrestrial rise setting in which magmatic emanation was predominant from a deep seated magma chamber to a rift wing setting in which brine water was circulating along a fracture system formed by rapid rifting of the adjacent area. The drastic redox condition change of the ore-forming solution in conjunction with the rapid tectonic change should be important for the indium concentration.
    Download PDF (4776K)
Review Articles
Resource News
feedback
Top