Dredging operations in placer mining Background image : cutter head suction dredge MINE PORTAL TEAM www.MINEPORTAL.in CALL/WHATSAPP-8804777500 www.fb.com/mineportal.in

Placer deposits Loose, gravel and alluvial deposits Mineral nodule Gold, Titanium, rutile, zircon, garnet Sand and gravel Mineral noduls, heavy mineral, sand, gravel etc.

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,

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

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.

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

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

Bucket wheel dredge Cutting depth up to 35 m

Bucket line dredge Cutting depth up to 50 m

Clamshell dredges Cutting depth depends on the power of hoist rope

Backhoe dredges Up to 20 m

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

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

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

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.

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

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

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.

References: Hartman H.L., Introductory Mining Engineering 2nd ed., 2002 Mining Handbook, SME, 1992 Handbook of Dredging Engineering, John B. Herbich, 2000 www.ihcmerwede.com (retrieved on July 31 2011) www.dredging.org (retrieved on July 31 2011 ) www.dredge.com (retrieved on July 31 2011) www.dredgebrokers.com (retrieved on July 31 2011) www.imsdredge.com (retrieved on July 31 2011)

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