Carbonate siderite

Key indicators of alteration and proximity to ore are increased K2O (particularly in the shale component) near complete loss of Na20 increased FeO (particularly in the siltstone-sandstone component) and increased CO2 in shale. These changes reflect the development of iron carbonate (siderite and ankerite) by carbonate introduction and some alteration of existing calcic carbonate in siltstone-sandstone samples. Destruction of albite, absence of chlorite and increased abundance of muscovite due to potassic alteration, are the other major mineral alteration effects in the altered host rocks. Trace elements enriched in the primary dispersion zone are Zn, Pb, Ag, Sb, As, Rb, and TI. Antimony provides the most consistent and extensive trace element dispersion halo around the deposit and is also preserved in most of... 

Carbonates — Siderite-ankerite concentrations, dolomite, calcite, ankerite Ankerite, calcite, dolomite —... 

Thus it is to be expected that in the case of sedimentary or diagenetic formation of magnetite and hematite of iron-formations the oxygen isotopic ratios of these two minerals will be similar and will correspond approximately to the 5 0 of the water of the sea basin. Iron carbonates (siderite, sideroplesite) formed in the same way would be substantially enriched in the heavy isotope (up to 15-20%o). 

On the basis of the isotopic data obtained, the hypothesis of chemogenic deposition of cherty iron sediments of complex composition in sea basins seems to be most applicable. Only by such a process was it possible for compounds to form which already differed sharply in oxygen isotopic composition—oxides (goethite or hematite, magnetite) and carbonates (siderite, sideroplesite)—in the original iron sediment. 

The chief ores of iron are its oxides hematite, Fe Os, and magnetite, Fea04, and its carbonate siderite, FeCOg. The hydrated ferric oxides such as limonite are also important. The sulfide pyrite, FeS2, is used as a source... 

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