Metamorphism and Petrogenesis of the Dalli-Rajhara and Ari Dongri Iron Formations, Madhya Pradesh

The minerals present in the iron formations are divided into oxides, silicates and sulphides. Hematite occurs in all the three stratigraphic members and magnetite is present mainly in Ari Dongri. Sulphides are present only in the Ari Dongri Iron Formation. The amphibole group is predominant amongst the silicates. Stilpnomelane and minnesotaite are also present.

The rock types are phyllites, schists, talcose and ferruginous shales, iron-formation, amphibolites, traps, granites and gneisses. The iron-formation consists of banded hematite-quartzites, shales and banded magnetite-quartzites, The unaltered banded hematite-quartzites are of two types-granular and non-granular or slaty. The latter is more common than the former. The rocks which are associated with the ore deposits are ferruginous shales and banded hematite-quartzites. The amphibolites are considered to be metabasites. The basic intrusives are predominant at Ari Dongri.

The silicates are secondary derived by diagenetic or low grade metamorphic effects. Metamorphism increased the grain size in case of hematite and magnetite. There is no coincidence of the metamorphic zones with the boundaries of the stratigraphic units. The cross-cutting relations of the acidic and mafic rocks are thought to be probably related to the last stages of metamorphism.