Hematite Inclusions Research Articles

On the source of the iron in the Lahn ore deposits

A brief summary on the geology and the iron ore deposits of the Devonian Lahn Geosyncline (West Germany) is followed by the examination of the iron variation in the eruptive rocks in this area and in analogous magmatic associations elsewhere. A major strong point is the sporadic appearance of xenolithic inclusions of hematite in some keratophyres of the Lahn area. As a result, analytical, mineralogical and textural evidence is against dependence of the iron in the ore deposits on the contemporaneous femic rocks, whereas, in the keratophyre, another source of that iron is indicated. Thus two periods of magmatic events are derived. Special attention is called to the effects and conditions in the earlier period, and it may be suggested that three magmatic units corresponding to keratophyre, weilburgite and iron ore, owe their origin to the specific hydromagmatic conditions of a spilitic differentiation process in that early period.

Inclusions in muscovite of iron oxides and hydroxides

Muscovites from Rajasthan often contain numerous inclusions of magnetite, maghemite, hematite, lepudocrocite and geothite. Magnetite shows polygonization structure which is often preserved in its transformation products, maghemite and hematite. Optical, chemical and X-ray studies of single crystal of green muscovite showing zones of inclusions indicate that magnetite was exsolved from initial Fe rich muscovite. Subsequent oxidation of magnetite gave rise to maghemite and hematite. Lepidocrocite and goethite are formed by the hydration of hematite. The exsolution of magnetite took place below 500°C and the oxidation to maghemite and hematite at about 375°C.

Einige geochemische Untersuchungen an Sandsteinen aus Perm und Trias

In about 100 samples of “Buntsandstein” (Lower Triassic) and “Rotliegendes” (Lower Permian) iron, manganese, vanadium, copper, and lead have been determined. TiO 2 and Zr have been analysed semi-quantitativly. The Fe 2O 3, Mn, TiO 2, Zr, and higher Cu data are results of X-ray fluorescence-the V, Pb, and lower Cu data are from optical emission spectroscopie methods. Ferrous iron has been chemically determined in several samples. Reduction in natural environment was simulated by treatment of sample material by dithionite. The relation between the iron-, manganese-, and vanadium-contents and the mineral composition (from optical and X-ray investigations) is demonstrated as the following examples show: The dissolving of hematite in several sandstones (change of red and green layers, local bleaching) is caused by the reduction of ferric iron and subsequent removal of ferrous iron. The inclusion of hematite as red zones in those quartzes of red sandstones which still grew after deposition, show that the hematite must have been dissolved in the early diagenetic stage. This observation agrees with the absence of hematite in quartzes of colourless sandstones. The reduction probably is caused by syngenetically deposited organic matter. Spherical haloes of discolourization often occur in rocks with a higher content of clay. They result from the limited transportation of solutions in sediments with a small interconnected pore volume. Beside its occurrence in the detrital material from weathered rocks, manganese is found in several oxides of different valency and together with calcium in carbonates. Related to Calcite as much as 1 per cent MnCO 3 contents occur. The formation of the dark brown manganese oxides is indirectly influenced by the contact with carbonates. Calcite in equilibrium with solution causes a pH-environment which facilitates the formation of higher manganese oxides with low solubility. The contents of vanadium and iron show a distinct proportionality. This occurs as well in the residues of weathered rocks as in the hematite. This is probably the result of the formation of slightly soluble iron-vanadates. The high concentration of vanadium in the dark cores of spherical haloes in the “Rotliegendes”-sandstone can easily be derived from normal vanadium contents of the surrounding rocks. There the vanadium may be mobilized when the hematite is dissloved by reduction. In the strong reducing environment of the core V 5+ is reduced to the much less soluble V 3+ (or V 4+) and precipitated. Precipitation occurs mainly around residues of organic material (carbon analysis). The contents of lead and copper of the investigated samples can easily be explained by the trace amounts in silicates. Few samples with higher contents are probably influenced from primary enrichment of heavy metal-sulfides. Although these investigations have been made on sandstones of a limited area, the results may be applied to many other sandstone deposits formed under climatic conditions similar to those of the “Rotliegendes” and “Buntsandstein”-time (sandstones of the Colorado Pateau (USA), etc.