![]() □ Some minerals are found in sands of valley floors and at the base of hills. □ Alluvial deposits or Placer deposite :. Bauxite is formed by the decomposition of surface rocks. ![]() □ When decomposition of surface rocks and the removal of soluble constituents takes place, it leaves a residual mass of weathered material containing mineral ores. They have been formed as a result of deposition, accumulation and concentration in horizontal strata. □ In sedimentary rocks a number of minerals occur in beds or layers. □ Through the layers of Sedimentary rocks :. Major metallic minerals like tin, copper, zinc and lead etc. ![]() □ In most cases they are formed when minerals in liquid / molten and gaseous forms are forced upward through cavities towards the earth’s surface. The smaller occurences are called veins and the larger are called lodes. □ In igneous and metamorphic rocks minerals may occur in the cracks, crvices, faults and joints. □ Through Igneous and Metamorphic rocks :.
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