Mode of Occurrence of Minerals
Minerals are generally found in "ores", which is actually an accumulation of any mineral mixed with other elements. To obtain a pure mineral, the it has to be separated from its ore.
This process of separating the mineral from its ore is called smelting
Smelting of iron ore
Minerals generally occur in many forms, they are:
1. Veins and Lodes
Minerals generally occur in the cracks, crevices, faults and joints of the igneous and metamorphic rocks. Smaller occurrence of such type is called a vein and a larger occurrence is called a lode.
Gold being extracted from a vein
Minerals like tin, copper, zinc, and lead etc. are found in veins and lodes
2. Beds or Layers
The minerals which are formed as a result of deposition, accumulation and concentration generally occur in horizontal layers.
Mineral deposits in layersCoal deposits
Minerals such as coal, gypsum, potash salt and sodium salts are formed in such modes.
3. Residual mass of weathered particles
When the decomposed rocks are washed away by water, the soluble constituents are removed leaving a mass containing ores. Such occurrences are called residual mass. Bauxite occurs in such a mode.
Bauxite deposits left out after being washed out
4. Alluvial deposits or Placer deposits
These are the deposits found in the sands of valley floor and at the foot hill. These deposits consist of the minerals which cannot be corroded by water.
Mining in placer deposits
Gold, silver,tin,platinum are some of the minerals found in such deposits.
Gold in placer deposits
Ocean waters contain large quantities of of minerals such as common salt, magnesium and bromine.
However they are not of economic significance as they are widely diffused.
Distribution of Minerals : India is fortunate in having fairly rich and varied mineral resources, but the minerals in India are unevenly distributed. Minerals like coal, mica an many non-metallic minerals are found in the peninsular rocks
Petroleum deposits are found in Assam and Gujarat.
Many non-ferrous minerals are found in rocks of Rajasthan.
There are no mineral deposits in the Northern plains of India.
Reasons for uneven distribution of minerals in India
- Differences in geological structure
- Different processes involved in the formation of minerals
- Time involved in formation
- Concentration of the mineral in the ore
- Mining is done only when the percentage if the mineral in the ore is high
- Ease of extraction
- Should be easy for mining without any physical or climatic barrier
- Closeness to the market
The mine should be close to the market or else the transportation cost involved is high which increases the cost of the mineral.
When all the above factors are favorable, a mineral deposit or a reserve turns into a mine.