iron ore Deposits in Australia
The iron ore deposits of India can be broadly divided in to the following six groups on the basis of mode of occurrence and origin:
1. Banded Iron Formations (BIF) of Pre-Cambrian Age
2. Sedimentary Iron Ore Deposits of Siderite and Limonitic Composition
3. Lateritic Ores derived from the Sub-Aerial Alternations
4. Apatite-Magnetite Rocks of Singhbhum Copper belt
5. Titanifereous and Vanadiferous Magnetites
6. Fault and Fissure Filling Deposits
Indian deposits of haematite belong to Pre-Cambrian Iron ore series and the ore is within Banded Iron Ore Formations (BIF) occurring as massive, laminated, friable and also in powdery form. Extensive outcrops of BIF are found in the States of Jharkhand, Bihar, Orissa, Madhya Pradesh, Chattisgarh, Maharastra, Karnataka, Goa and Tamil Nadu. The most common names used in India to designate BIF are Banded Haematite Quartzite (BHQ) and Banded Magnetite Quartzite (BMQ). In Jharkhand and Orissa, the names like Iron-Ore series and Iron-Ore group are used as stratigraphic names. Elsewhere in the world, names like taconite (Lake Superior), itabirite (Barzil), jaspilite (Western Australia) and Calico rock (South Africa) have been in use. In recent years, however, BIF has come to be generally acceptable both as a field term as well as stratigraphic term to designate iron-rich sedimentary rocks.
The BIF has given rise to vast accumulations of commercial grade iron ore deposits in India; more than 90% of the iron ore supplied to the industry comes from the BIF. The major ore minerals are haematite and magnetite. Important accumulations are in Singhbhum district (Jharkhand), Keonjhar (Orissa), Bellary (Karnataka), Bastar district (Chattisgarh) and Goa. Magnetite ore deposits are mainly confined to the Chikmagalur district in Karnataka and Salem and North Arcot districts in Tamil Nadu.
Different types of iron ore derived from banded haematite rocks met within the deposits of this group are (a) massive ore, (b) laminated ore and (c) blue dust. The massive ores occur as massive bodies in which no planar structures are seen. The laminated ores, though mineralogically and chemically similar to massive ores, have planar structures, which may be very closely spaced giving rise to biscuity ores. The blue dust is a form of very fine-grained powdery ore consisting of loose haematite and magnetite crystals. It often occurs as pockets in harder ores and forms the major constituent at depth. Major part of blue dusts is minus 10 mesh in size and generally these are from 10 to 50% of 100 mesh size, the proportion of minus 325 mesh to 100 mesh fraction being 80%. In addition, float ore accumulations on the slopes and foot of the hills as a result of disintegration of in situ ore bodies are commonly met with. The float ores are of different sizes and of different degrees of purity. In certain places, like deposits in the vicinity of Banspani in Keonjhar district, Bailadila range and Bellary-Hospet area, the float ore concentration is mostly free from any major impurities. The percentage recovery of ore from such horizons varies within very wide limits and is cent percent in some cases. Wherever such float ores are derived from massive or hard laminated ore bodies, the grade of the float ore is fairly rich. Thus, in the float ore workings in the vicinity of Banspani and in Bellary-Hospet sector, grade of the ore is about 64% or even more. The gangue minerals in case of float ores are usually shale, BHQ, dolerite and clay. Sometimes reconsolidated ores occurring as angular and sub-angular fragments cemented in the matrix of laterite is also noticed in float ore zones.
For example, in Jharkhand and Orissa area, this type of re-cemented ore is found, where it is locally called as “Canga”. The embedded high grade iron ore pieces cannot be easily dislodged from adhering material. Though angular pieces can be alone give 63 to 66% Fe, the overall material analyses only 55 to 60% Fe.