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Two Se‐bearing Ag–Bi Sulphosalts, Benjaminite and Matildite from the Ikuno Deposits, Hyogo Prefecture, Japan –Au–Ag Mineralization in Polymetallic Zone
Author(s) -
SHIMIZU Masaaki,
KATO Akira,
MATSUYAMA Fumihiko
Publication year - 1998
Publication title -
resource geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.597
H-Index - 43
eISSN - 1751-3928
pISSN - 1344-1698
DOI - 10.1111/j.1751-3928.1998.tb00011.x
Subject(s) - mineralization (soil science) , geology , cassiterite , geochemistry , mineralogy , tin , metallurgy , materials science , soil science , soil water
Se‐bearing benjaminite and matildite are described from the polymetallic zone of the Ikuno deposits, Japan. The former is the first occurrence in Japan, and is from two separate veins, the Nanten and Daimaru, while the locality of the latter could not be specified. The empirical formulae of two benjaminites based on 22 atoms are (Ag 2. 74 Cu 0. 24 ) Σ2. 98 (Bi 7. 00 Sb 0. 01 ) Σ7. 01 (S 10. 89 Se 1. 12 ) Σ12. 01 (Nanten) and (Ag 2. 90 Cu 0. 10 ) Σ3. 00 (Bi 6. 74 Pb 0. 18 Sb 0. 07 ) Σ6. 99 (S 11. 68 Se 0.33)Σ12. 01 (Daimaru), leading to the validation of the formula Ag 3 Bi 7 S 12 as the ideal one for benjaminite, and that of matildite based on 4 atoms is Ag 1. 00 Bi 1. 00 (S 1. 78 Se 0. 22 )Σ 2. 00 . These designate the substitution of Se for S in all of them, where Se is preferentially incorporated into these Ag‐Bi sulphosalts. The unit‐cell parameters of them and matildite are: a 13. 272, b 4. 037, c 20. 185 Å, and β 103. 16° (Daimaru), a 13. 270, b 4. 040, c 20. 273 Å, and β103. 17° (Nanten); and a 4. 0670, c 18. 996 Å, respectively. The products of Au‐Ag mineralization in the Ikuno polymetallic vein‐type deposits also occur as such Ag‐Bi sulfosalts as benjaminite and matildite, in addition to pavonite, “treasurite derivative” and “electrum” with cassiterite in the polymetallic zone, and also do as “electrum”, acanthite, and pyrargyrite‐proustite in the Au‐Ag zone. The significant quantity of the Ag‐Bi sulfosalts does not violate the zoning occupying the outermost part of the zonal distribution of ores in the deposits.