The great peculiarity of these ores is that glauconite is of primary origin, and several hypotheses have been proposed to explain this. Of associated minerals, and (3) depositional environment. These are mainly: (1) texture, (2) nature The problems in this case are similar to those of the oolitic ores as Rare however, the frequent occurrence of these ores has led to some The glauconite iron ore deposits that could possibly be exploited are very Present interpretation (Williams et al., 1954 Kazakov, 1957). Siderite from diffused material in clays appears to be the most common No new exploitation seems likely at present. Were the mainstay of the British iron industry during the 19th century but The importance of sphaerosiderites is mainly historical, because these ores However, no complete balance from depositional to post-diagenetic stage hasīeen determined for any one of those ores. Morphological transformations and justified by mineral equilibria. (Seeĭiscussions and references in James, 1955 Gross, 1965.) The main contribution is in relative mineralogical changes that may be observed through Related to the original state of deposition that remains conjectural. Type, which are generally called “iron-formations”, have still not been clearly (Seeĭiscussions in Grubb, 1971 Dimroth and Chauvel, 1973 Tsu-Ming Han,Īt present, after tremendous amount of studies, the ores of Lake Superior I t is anĮxtremely important process, particulary in the case of iron, an element theĬhemical behavior of which varies greatly according to its ionic state. Of knowledge, however, it is impossible to ignore diagenesis. Taking into consideration the present state They explained the mineral associations solely by the processes of syngenetic Ores have often denied all possible effects of diagenesis, even of epigenesis. Many authors working mainly on considerably modified pre-Hercynian Particular the role of diagenesis, however, it is necessary to study all the If oneĪttempts to distinguish the role of the main sedimentary processes and in Proposed classifications reflects the complexity of the phenomena. The apparent anomaly of the iron mineralization. Attempts have alwaysīeen made to understand the mode of formation by also trying to explain Reaching the present state are numerous and varied. The stages of evolution undergone by the sedimentary iron ores before Oolitic ores, with very varied parageneses (3) the glauconitic ores (4)the Taconites etc., i.e., different iron-bearing formations (James, 1955) (2) the (1) The Lake Superior ore type, including low-grade banded ores, B.H.Q, Presented in order of importance below, may easily be distinguished: Classically, four fundamental categories, which are Properties and have been found in all types of rocks and from all stages of Iron ores of sedimentary origin have many different physical and chemical The various stages of evolution cannot be recognized. Iron-rich rocks are so destructive of pre-existent textures and structures that Origin in such cases is the fact that mineralogical changes that occur in The difficulty in assigning an unquestionable sedimentary Host rocks (substitution type of iron deposits) or through magmatic injection Iron, because it may be introduced either by solution through replacement of Interbedded in sedimentary rocks in order to assign a sedimentary origin to It is not sufficient for an iron formation to be Iron-rich rocks have more widespread distribution through geological scaleĪ major difficulty arises when an attempt is made to assign a definite Which implies meeting requirements such as location, thickness, and grade. “ore” is restricted here to iron formations that are economically minable, It should be kept in mind, however, that the term Iron-phase changes only in iron-rich rocks. The diagenetic evolution, however, may be related to (Illustrated by the Role of Diagenesis in Oolitic Iron Ores)īecause of its abundance in the earth’ crust, iron is one of the majorĬonstituents of rocks and is always present, in varying quantities, in sedimentary formations.
0 kommentar(er)
