PLACER DEPOSITS

PRESENTED BY :- ROHIT ANAND (063/13) ABHISHEK KUMAR (064/13) ABHISHEK NAYAN (065/13)

CONTENT

1. Introduction2. Types3. Alluvial or stream placer4. Eluvial placer5. Beach placer6. Eolian placer7. Paleo placer8. Role of human being9. Bibliography

INTRODUCTION

Placer deposit is a natural concentration of heavy mineral caused by the effect of gravity on moving particles.When heavy stable minerals are freed from their matrix by weathering processes,they are slowly washed down slope into the stream that quickly winnow the lighter matrix.Thus the heavy minerals concentrated in stream,beach and lag(residual) gravels and constitute workable ore deposits.mineral that forms placer deposits have high specific gravity and chemically resistant to weathering and are durable.such deposits include gold,platinum,magnetite,chromite and various gemstone.

TYPES OF PLACER DEPOSITS

Stream or alluvial placerEluvial placerBeach placerEolian placerPaleo placer

Stream or alluvial placer

Alluvial placer are those form in river or stream sediments.It is formed by the deposition of dense particle at a site

where water velocity remains below that required to transport them further.

Typical location for alluvial gold placer deposit are on the bends of river and creeks; in natural hollow at the break of slope on stream.

To form a placer deposit the particle desired must show a marked density contrast with the gangue material which is able to be traspoted away from the trap site.

Most of the concentration of heavy mineral occurred during flooding when current velocity and winnowing are at maximum.Each time if flood occurs heavy mineral which were once randomaly scatterd within the sediments endup resting on new stream bed created by the scouring action of the flood due to which deposition and accumulation of heavy mineral take place in bed rock this is why placer deposits of gold and other heavy mineral take place near the bed rock.

ELUVIAL PLACER: It forms on hillslopes from weathered deposits.they are not acted on by stream but by rainfall and wind,which carry away the light material;thus they may be considered intermediate in the formation of stream placer.ex includes the earlier worked gold deposits of Australia and the cassiterite.

BEACH PLACER: It forms on seashore where wave action and shore current shift material,the lighter more rapidly than the heavier,thus concentrating them ex. Gold deposits of nome,Alaska

EOLIAN PLACER: It form in arid areas where wind ,not water,acts as the concentrating agent,removing fine particles of the lighter dross ex. Gold deposits of some parts of Australian desert .

PALEO PLACER: It is afossilized placer deposit. In other words, the uncon soldiated deposit originally formed at the surface by running water was buried to sufficient depth to lithify the sediments into solid sedimentary rock.

CONCLUSION

The erosion of weathered rock and minerals results in the mechanical concentration of the more resistant higher specific gravity or in lay man’s term the tougher heavier material stay behind as the less resistant material moves away.When the condition are right ,valuable mineral can concentrate to form placer deposit.Mechanical concentration starts where the rocks and mineral are exposed to the element at the surface.

REFERENCES

1. www.Wikipedia.org2. www.geology.gov.yk.ca3. www.Britannica.gov.org4. www.ranjit.rds.net.in/