Geochemistry of aluminum and titanium in volcanic areas of island arcs |
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| Abstract: | The relation between aluminum and titanium in the course of bauxite formation is one of the key problems in deciphering the genesis of bauxitic rocks, particularly those occurring in geosynclinal areas. The source of aluminum and titanium in marine geosynclinal bauxites is related directly to the effects of volcanism. Ultra-acidic thermal waters may extensively leach volcanic rocks, resulting in the removal and migration of large amounts of aluminum in solution. These solutions are extremely stable, even when diluted by surface waters, and move to the sea without losing aluminum by precipitation. Primary titanium minerals are also decomposed and displaced in hydrothermally-altered rocks. Titanium is removed primarily as colloidal titanium hydroxide. Aluminum in solution and titanium in the form of colloidal titanium hydroxide films are carried to the sea in acid streams. As the acid streams are neutralized upon mixing with sea water, aluminum forms an amorphous colloidal hydroxide that coagulates and crystallizes. Titanium is extracted by its co-precipitation with aluminum hydroxide by a sorption mechanism. The migration and co-precipitation of these elements in the manner outlined is believed to be responsible for the formation of geosynclinal bauxite deposits in volcanic areas of island arcs. — R.D. DeRudder. |
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