Geology of The Area
Geology of The Area
Geology of The Area
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columnar stromatolites vary widely from isolated individual columns to branches froms. Columns show their growth perpendicular to the bedding planes. Excellent examples of columnar phosphatic stromatolites growing perpendicular to bedding planes can be observed west to the B-block mining area.
Mining methodology
It is an advanced stripping technique. Excavator, dumper and drilling machines are used to extract the ore and transport. Drilling machine is used to obtain sample of subsurface through coring. Core box were seen where number of samples are marked with arrows indicating the sequence of core according to depth. Diamond core drilling machine is used which are fitted with bit pipes to reach different depths (pic). For the purpose of mining operation, the deposit has been divided into several blocks. Deposit is being worked out with a system of benches. The mining of one by open cast is started from the outcrop of the deposit at the top of hills. The benches are between 8 to 10 meters vertical intervals. This makes removing of the overburden easier and also provides easy access to the deposits. Faces of benches are kept across the strike of the phosphorite and working at the face progress along the strike direction.
Grades of ore
There are three different grade of ore found in this mine: high grade ore with 34-36% avg P2O5, medium grade with 25-29% avg P2O5 and low grade ore. This difference in grade can be due to natural weathering of the host rock. In some places intense shearing had taken place and dolomite was crushed away and leaving some silica and iron which gets mixed with the phosphate reducing its grade a little. In the case of less deformed stromatolites, the grade variation is also dependent on the density of the column population. Where the column population is very dense, the P2O5 content could be as high as 30%. By contrast, the wider spacing of columns could reduce the grade to around 25%. Two different processes seem to have operated in upgrading of the phosphorite subsequent to its formation. These are weathering and tectonic reworking. In both the cases the upgradation of the one is due to removal of dolimitic carbonate, which occurs in the intercolumnar spaces and in between the phosphate lamellae within a column. Some amount of silica and iron oxides might have crept into the rock during this process. One common process of removal of dolomite is by
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brecciation resulting from caving of rock column during or subsequent to deagenesis. Silicification and deposition of iron might have reduced the grade at several localities. Crocodile skin weathering is observed which is mainly formed due to chemical weathering in which the dolomite is removed as solution or gets washed away.
Conclusion
We have been greatly beneficial by this field excursion.