D. F. Hewett
1966
<p><span>Compared with the </span>stratified<span> </span>deposits<span> of iron minerals, those of </span>manganese<span> minerals have received little attention until recent years. Before 1930, students of the </span>stratified<span> </span>deposits<span> of </span>manganese<span> minerals have generally concluded that the contained </span>manganese<span> was derived from the decomposition of the rocks that formed the borders of the basins. Only in a few places have geologists recognized that if these rocks were the principal source of the contained </span>manganese<span> the basins should contain also enormous quantities of iron minerals, whereas most of the large </span>deposits<span> of </span>manganese<span> contain little iron. Even though more than 100 years ago some geologists proposed that the iron contained in some </span>deposits<span> of </span>stratified<span> iron minerals was probably derived from hydrothermal waters related to centers of volcanism, not until about 1930 was this source of </span>manganese<span> in similar </span>deposits<span> seriously proposed. This mode of origin was given the name "volcanogene sedimentaire" by French geologists working in Morocco. Since then, other names, such as "exhalative sedimentaire," have been used by geologists working in several European districts. Because of the development of new techniques for the study of the chemical and physical features of the minerals, and because close attention to the lithologic environments of the beds is being given more and more during recent years, it has seemed advisable to review the features of </span>stratified<span> </span>deposits<span> of the </span>manganese<span> minerals in many parts of the world and over a wide range in age. This study indicates that at least three sources may have contributed the </span>manganese<span> in the large </span>deposits<span> of iron-free </span>oxides<span> and </span>carbonates<span>: (1) the rocks that form the borders of the basins, either marine or continental; (2) the nearby underlying sediments, largely of igneous origin, decomposed by warm waters largely derived from depth; and (3) waters of hydrothermal origin derived from great depths during epochs of volcanism from which iron minerals with little </span>manganese<span> are deposited in deep zones, then minerals with much iron and more </span>manganese<span> at intermediate depths, and, finally, </span>manganese<span> minerals with little iron near the surface. As the hot waters of many thermal springs contain more </span>manganese<span> than iron, such waters could yield the pure </span>manganese<span> </span>oxides<span> and </span>carbonates<span> found in </span>stratified<span> </span>deposits<span>. Several kinds of evidence indicate that most of the </span>manganese<span> in the large </span>stratified<span> </span>deposits<span> of the </span>oxides<span> and </span>carbonates<span> of </span>manganese<span> in many parts of the world has been derived from hydrothermal waters from depth related to centers of volcanism. Obviously, </span>manganese<span> derived from decay of the rocks on the lands adjacent to large basins-marine and continental -may have been added to that derived from centers of volcanism to form the sedimentary </span>deposits<span> found in the basins. </span></p>
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10.2113/gsecongeo.61.3.431
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Society of Economic Geologists
Stratified deposits of the oxides and carbonates of manganese
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