what is placer deposit?

                              

Placer deposit generally defines the deposition of minerals at place to place or at various places.

                                                              OR

It is the accumulation of valuable minerals by the means of various sources like river, glacier etc. generally by the help of the natural separation processes like gravity separation.   

In gravity separation process minerals are separated from the impurities due to their respective specific weights. Similar to this, placer deposit is also due to the relative weight of the minerals that they are separated from other particles (depending upon means of transport).

The basic property that the mineral should possess to be deposited as placer deposit is that they must be dense and resistant to weathering.  For example: During transportation, the minerals might be carried as suspended load by water then the  carried mineral must be dense and resistant than other particles present in water. So which it can be deposited somewhere depending upon the nature of the river flow without being weathered.

Gold, diamond etc. are very precious and deposited as placer deposit. Diamond being the most precious one, formed at maximum depth with both maximum pressure and temperature. But sometimes they are found on the earth surface as they are mostly embedded with igneous rock called kimberlite. When these rocks are acted by the action of water or other medium, the minerals present moves with the flow of the medium during its transportation and as by their physical property they are deposited as placer deposits. In this case too, gold and diamond are more dense than the particles present in water mostly quartz.

 

Placer deposits are of different types depending upon their mode of deposition:

1)    Alluvial:

         This is the process of deposition of minerals which is dominated by the running water. Precious minerals are sometimes found on the earth surface or sometimes associated with rocks like (Kimberlite). Then the mineral on the surface is acted by the flow of water and starts to move with the flow. When the velocity of the water becomes low the carried load of mineral starts to deposit at place to place slowly depending upon the flow of water.

 

2)    Eluvial:

             This process is dominated by the physical process like weathering and erosion. Minerals are sometimes associated with the host on the surface depending upon the nature of mineral. But due to weathering, mineral present in the rocks gradually starts to detach and further it is acted by the action of gravity. This leads to the deposition of mineral at another place after the continuous action of weathering and mass wasting (under the action of gravity).

 

3)    Diluvial :

           This process is dominated by the rapid flow of the water. Sometimes the water velocity of the river increases with increase with rainfall and mostly results to the flood. The rapid water current carries the mineral present on its path and deposits at different place far from the initial deposition.

 

4)    Proluvial:

            This depositional process is due to the sudden rapid flow of the stream at the high elevation which gradually takes away the minerals present on its path and mostly deposits on the foot of the hills at the lower elevation. And this deposition is foot- step deposition.

 

5)    Aeolian:

            This depositional process is dominated by the action of wind. The high wind current not only carries away the sediments like sand particles but also the minerals associated with it. Hence the minerals found on the surface are carried away by the action of strong wind and deposits on different place depending upon the nature of the wind.

These are major depositional process which helps to deposit minerals from one place to another and known as placer deposits.