1. Dredging operations in placer mining
Background image : cutter head suction dredge
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2. Placer deposits Loose, gravel and alluvial deposits Mineral nodule
Gold, Titanium, rutile, zircon, garnet
Sand and gravel
Mineral noduls, heavy mineral, sand, gravel etc.

3. Placer mining
It is defined as extraction of sand, gravel and loose unconsolidated deposits with the help of water . This ore is generally processed with water by using gravity separation method .
Includes hydraulicking and dredging, water helps in excavation of the deposits,

4. Technology : placer mining
Hydraulicking
Dredging
In hydraulicking the excavation is done with the aid of water jet and and material is transported in the slurry form with the help of sluice nad natural gradient of the ground, in dredging the excavation action is done with the aid of mechanical cutting force as well as the water also helps in the excavation by loosening the deposits

5. Dredging
Dredging is basically extraction of material/ore from the bed of water body; this water body is some time natural and some time human made for the purpose of extraction of the deposits.

6. Cutter head suction dredge
Dredges: types
Suction dredges
Plain suction dredge
Cutter head suction dredge
Bucket wheel dredge
Mechanical dredges
Bucket line dredge
Clamshell dredge
Backhoe dredge
Based on the mode of material transport from the place of excavation to the barge or dredge this classification has been made , hand book of derdging engineering john h herbich 2000
Source : Hnadbook of Dredging technology, John B Herbich, 2000

7. Cutter head suction dredge
Cutting depth up to 18 m, can cut hard deposits

8. Bucket wheel dredge
Cutting depth up to 35 m

9. Bucket line dredge
Cutting depth up to 50 m

10. Clamshell dredges
Cutting depth depends on the power of hoist rope

11. Backhoe dredges
Up to 20 m

12. Cycle of operation Excavation of material
Transportation of material from water bed to the vessel/barge and then to the place of processing
Processing of ore
Disposal of waste

13. Advancement in dredging technology
Positioning system, underwater mapping
Improvement of hydraulics
High horse power wheel and cutter head for higher cutting force
Prevention of choking of slurry pump/pipes in suction dredges, provision of flushing

14. Current practices of dredging
Placer mining
Deepening of port, harbor,
Fishing
Marine mining
Reclamation
Maintenance of navigational channels

15. Applications of dredging
Mining of minerals like gold, tin, titanium, diamond; found in placer deposits
Sand and gravel mining
Beach nourishment
Reclamation of island
Maintenance of harbor, ports.

16. Advantages of dredging
High production rate (max. of 7 million m3 a year)
Lowest mining cost
Low labor requirements, fully mechanized
Good recovery (up to 90%)
Continuous operation

17. Disadvantages of dredging
It may result in severe environmental damage
Limited to unconsolidated deposits
High capital investment for large dredges
Inflexible and unselective, limited to placer type deposit only

18. Case Study : Sand Mining, Millville, New Jersey, USA
Location: Millville, New Jersey, USA
Geological condition: sand – up,to 40 m depth, water table at 20 m depth
900 hp diesel operated, hydraulic cutter head dredges (14’’ dia.)
14’’ floating pipe line for transportation to the processing plant (removal of clay. gravel, and stones)
Pump with 12’’ impeller diam.was used for tranporting to 300’, silica sand is used for glass making industry.

19. References:
Hartman H.L., Introductory Mining Engineering 2nd ed., 2002
Mining Handbook, SME, 1992
Handbook of Dredging Engineering, John B. Herbich, 2000
(retrieved on July )
(retrieved on July )
(retrieved on July )
(retrieved on July )
(retrieved on July )

20. Thank you