Ferruginous chert

Positive Eu anomaly is observed for barite, Kuroko ores, ferruginous chert (tet-susekiei), and hydrothermally altered basaltic and dacitic rocks overlying the Kuroko ores. 

Figure 1.46. REE patterns of the altered volcanogenic rocks and Kuroko ores. Data sources Shikazono (1999a). (A) Hydrothermally altered dacite and anhydrite underlying the Kuroko ores. (B) Barite, Kuroko ore and ferruginous chert. (C) Hydrothermally altered basalt overlying the Kuroko ores (Shikazono, 1999a).

Light rare earth enrichment is distinct and REE contents are relatively high for the ferruginous chert. 

Heavy Rare Earth Element). Therefore, it is considered that negative Ce and positive Eu anomalies in hydrothermally altered volcanic rocks, Kuroko ores, and ferruginous chert and LREE enrichment in the Kuroko ores have been caused by hydrothermal alteration and precipitations of minerals from hydrothermal solution responsible for sulfides-sulfate (barite) mineralization. 

Positive Eu anomaly is observed for hydrothermal solution issuing from the hydrothermal vent on the seawater at East Pacific Rise (Bence, 1983 Michard et al., 1983 Michard and AlbarMe, 1986). Guichard et al. (1979) have shown that the continental hydrothermal barites have a positive Eu anomaly, indicating a relatively reduced environment. Graf (1977) has shown that massive sulfide deposits and associated rocks from the Bathurst-Newcastle district. New Brunswick have positive Eu anomalies. These data are compatible with positive Eu anomaly of altered basaltic rocks, ferruginous chert and Kuroko ores in Kuroko mine area having positive Eu anomaly and strongly support that Eu is present as divalent state in hydrothermal solution responsible for the hydrothermal alteration and Kuroko mineralization. 

As noted already, Kuroko deposits are characterized by the following zonal arrangement in ascending stratigraphic order siliceous ore (quartz, chalcopyrite, pyrite), yellow ore (chalcopyrite, pyrite), black ore (sphalerite, galena, barite), barite ore (barite and quartz) and ferruginous chert ore (microcrystalline quartz, hematite). 

Barite is common in the black ore and abundant in barite ore. Barite is also found in ferruginous chert ore (Kalogeropoulos and Scott, 1983). 

Ferruginous chert in which abundant silica occurs formed below the seafloor by the mixing of ferruginous sediments and hydrothermal components (Kalogeropourous and Scott, 1983). 

Barite-silica chimney found in back-arc basin formed in the conditions similar to that of ferruginous chert and barite bed in the Kuroko deposits temperature is relatively low (ca. 150-100°C), and flow rate of fluids may be slow. 

Barite is abundant in the massive strata-bound ore bodies (black and barite ores) in Kuroko deposits and occurs in the ferruginous chert ore in Kuroko deposits, and chimneys in active deposits at back-arc basins. 

Simonson B. M. and Goode A. D. T. (1989) First discovery of ferruginous chert arenites in the Early Precambrian Hamersley Group of Western Australia. Geology 17, 269-272. 

Tetsusekiei (ferruginous chert) zone hematite, quartz Fe, Si... 

Main opaque minerals are chalcopyrite, pyrite, pyrrhotite, sphalerite and bornite (Table 2.22). These minerals commonly occur in massive, banded and disseminated ores and are usually metamorphosed. Hematite occurs in red chert which is composed of fine grained hematite and aluminosilicates (chlorite, stilpnomelane, amphibole, quartz) and carbonates. The massive sulfide ore bodies are overlain by a thin layer of red ferruginous rock in the Okuki (Watanabe et al., 1970). Minor opaque minerals are cobalt minerals (cobaltite, cobalt pentlandite, cobalt mackinawite, carrollite), tetrahedrite-tennantite, native gold, native silver, chalcocite, acanthite, hessite, silver-rich electrum, cubanite, valleriite , and mawsonite or stannoidite (Table 2.22). 

Belevtsev, Ya.N. and Goroshnikov, B.I., 1969. On the rationality of the terms iron chert", ja.spilite , and ferruginous quartzite . In Problemy obrazovaniya zhelezistykh porod dokembriya (Problems of the Formation of the Prccambrian Iron Formations). Izd. Naukova Dumka, Kiev, pp. 299-303 (in Russian). 

Melnik (1973, 1982) and Ewer (1983), but the environment of iron-formation deposition is perhaps too poorly constrained to adequately interpret what is known about iron-silica colloids. Furthermore, the simultaneous precipitation of iron-free chert and ferruginous iron formation demonstrates that an iron-rich colloid is not necessary for chert precipitation. 

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