Regional geology.
Areas are mostly covered by soil or laterite / bauxite capping. The low plateau consists of rocks of Achaean age. These include mica schist and quartzites, calc silicate rocks, amphibolites, granite and granite gneiss, pegmatite’s and quartz veins. Immediately overlying the Achaeans with an unconformity occur over rocks of Gondwana age consisting of coarse ferruginous sandstone and conglomerate. The Gondwana’s are overlain by Lameta with an unconformity. The Lameta starts with conglomerate at the base and other rock units include ferruginous grits, sometimes with shaly & clayey partings and calcareous grits. Overlying the Lameta occur almost horizontal Deccan Trap basalts which are massive, dark grey, hard and compact, finally overlying this trap rock occurs laterite with lithomarge clays and weathered basalts in between.

Local Geology.
The bauxite occurs in lensoid form within the laterite horizon which comprises various recognizable lithologic units.

The zone of lithomarge is quite distinctive and well defined and forms the lowest horizon of the laterite profile. It occurs just above the trap and thus separates it at few places in deep nalla beds and also along the scarps. The lithomarge is quite soft and plastic in nature. The average thickness of this zone is varies from 1.5 to 3.5 m.

The bauxite occurs in lensoid forms in laterite profile, generally below soil and pisolitic laterite. The bauxite can be put into two categories, i.e. pisolitic bauxite and massive bauxite. The pisolitic bauxite consists of closely packed pisolites ranging from few mm to 5 cm. It occurs mostly in upper horizon of the laterite above bauxite zone. The main mineral constituent is Gibbsite. These ore bodies persist up to maximum depth of 10 m. from the surface. The average thickness of bauxite deposit varies from 0.4 m. to 4.0 m. in the form of lenses. The intensity of bauxite is more in central part of the plateau and decreases towards the scraps. The upper contact of bauxite with overlying pisolitic laterite is quite sharp where as its lower contact is gradational.

All mining and transportation at the mine are undertaken by contractors.

The bauxite deposit of Mainpat Bauxite mines is situated over the plateau and the surface terrain is generally flat.

As the Bauxite deposit is found in shallow depth ranging from 0.40-10.0 meter, the method of mining of Bauxite is mechanized opencast mining, crushing, sizing, and sorting, by using excavator of 1- 5 Cum bucket size, dumper of 15-25 tons capacity, water sprinkler, blast hole drill machine, 100 mm dia, dozer, grader, crusher, screens and belt conveyor etc.

The over burden is top soil & soft laterite of 0 to 3.00 meters thickness after which there is a hard overburden of thickness varying from 0 to 5.70 meters. The thickness of ore zone is 0.40 m to 4 m. In general working is of shallow depth of avg. 4 to 5 m (maximum 10 m).

The general practice is to scrap the top soil separately by dozer or excavator dumper combination and use it for directly spreading over already backfilled compacted area. Drilling and blasting is practiced in hard OB benches and ore benches. Excavation is done by excavator dumper combination.

Since the deposits are strata-bound irregular and bouldery in nature, bauxite needs to be separated from laterite and murrum. It is proposed to mechanically crush and screen the ore so as to obtain desired grade bauxite with acceptable silica content. The backfilling is done in same sequence as it is found in the nature, i.e. hard OB in bottom, then soft OB above the hard OB, then top soil.

The height of OB benches is kept maximum of 6 meters and the ore benches are kept generally of 1 to 4 meters of height as per thickness of ore body.

The blast boreholes of 2 to 4 m depth are being drilled by DTH drills, which are required for blasting. Controlled blast technique is used for keeping the ground vibration, blast through and noise within permissible limit. The blast design and charge per delay are kept strictly as per the requirement of DGMS.

The bauxite extraction limit for Mainpat mine granted by MoEF is 750,000 tpa.

For getting the bauxite of desired grade and size, from blasted ore muck, it is subjected to mineral dressing, and this will be carried out by two ways.

* Where the deposits is homogeneous in quality, then the ROM will be processed, through mechanized way of mineral dressing by crusher and screening plant sets
* And, where deposit is of heterogeneous w.r.t. Quality, then the ROM will be subjected to manual method of sorting and sizing.
The sized and sorted bauxite found after crushing /screening or manual sorting is stored and analyzed for its quality before dispatch to plant by truck.