Ilmenite-magnetite

Anorthositic deposits - nearly all of the known commercially important rock deposits of titanium minerals are associated with anorthositic or gabbroic rocks. There are three main types (a) ilmenite-magnetite (titanoferous magnetite), (b) ilmenite-haematite, and (c) ilmenite-rutile. 

The ilmenite-magnetite deposits usually contain ilmenite and magnetite as granular intergrowths, which can be separated readily to yield ilmenite and magnetite concentrates. 

Minerals. Iron-bearing minerals are numerous and are present in most soils and rocks. However only a few minerals are important sources of iron and thus called ores. Table 2 shows the principle iron-bearing minerals. Hematite is the most plentiful iron mineral mined, followed by magnetite, goethite, siderite, ilmenite, and pyrite. Siderite is unimportant in the United States, but is an important source of iron in Europe. Tlmenite is normally mined for titania with iron as a by-product. Pyrite is roasted to recover sulfur in the form of sulfur dioxide, leaving iron oxide as a by-product. 

Parameter Hematite Magnetite Goethite Siderite Ilmenite Pyrite... 

According to Ishihara (1977), these granitic rocks are ilmenite-series while granitic rocks in Green tuff region are magnetite-series. ... 

Ilmenite-series and magnetite-series granitic rocks are defined as follows (Ishihara, 1977) the magnetite-series and ilmenite-series granitic rocks are distinguished by the presence or absence, respectively, of magnetite in polished sections. 

Figure 1.166. Distribution or initial Sr/ Sr (r, ) for the Cretaceous-Paleogene plutonic rocks. Open squares gabbros open circles granites. Numbers indicate the last two or three digits of r, values. Solid squares and solid circles imply the magnetite-series open squares and open circles the ilmenite-series. (Shibata and Ishihara, 1979).

Ishihara, S. (1977) The magnetite-series and ilmenite-series granitic rocks. Mining Geology, 27, 293-305. 

Ilmenite. There are currently no experimentally-determined ilmenite-melt partition coefficients. We must rely instead on phenocryst-groundmass data analyzed by PIXE (Stimac and Hickmott 1994 Ewart and Griffin 1994). Like magnetite, ilmenite is characterised by two relatively small sites, and is therefore unlikely to take up appreciable amounts of lanthanides or large alkaline earths. We will confine ourselves again to U, Th and Pa. 

The most abundant titanium sand deposits are black sands in streams and on beaches of volcanic regions. The principal black minerals are magnetite, titanoferous magnetite and black silicates, chiefly angite and homblend. It is quite difficult to produce an ilmenite suitable for pigment product from black sand, but other sand deposits that contain rutile, ilmenite and often monazite are found in Australia, USA, India and Africa. These deposits are either alluvial or marine in origin. 

This is one of the oldest operations in the world. The mine and plant are located in the southern part of Norway. This ore can be classified as an ilmenorutile, with ilmenite and magnetite as the valuable minerals. The gangue consists mainly of feldspar, hypersthene and biotite. The secondary minerals present in this ore include pyrite, olivine and pyrrhotite. 

The Otanmaki ore contains about 35% magnetite, 28% ilmenite, 1% pyrite and 35% silicate minerals. This ore contains an appreciable amount of fine ilmenite, most of which reports to the slime fraction. About 10-12% of the total ilmenite in this ore reports to the slime fraction. 

Runolima, U., How Otammaki Floats Ilmenite from Fnland Titaniferous Magnetite, Mining World San Francisco, pp. 49-55, 1957. 

One pecuhar oxygen buffer reaction is the well-known thermobarometric equation of Buddington and Lindsley (1964), which furnishes information on both T and the activity of molecular oxygen. The reaction uses the equilibrium among titanomagnetite (or ulvospinel ), magnetite, hematite, and ilmenite components in the hemo-ilmenite and spinel phases ... 

Figure 5,73 Isopleths of titaniferous components ilnenite (FeTi03) and ulvospinel (Fe2Ti04) in spinel and hemo-ilmenite coexisting at equilibrium in various Uq -T conditions. Position of hematite-magnetite buffer (HM) is also shown. From Spencer and Lind-sley (1981). Reprinted with permission of The Mineralogical Society of America.

Several minerals have been identified in polished thin sections of various rock types including massive sulphide, gossan, intermediate crystal-lapilli tuff, and felsic ash tuff (Fig. 2). These minerals include apatite, monazite, zircon, allanite, titanite, xenotime, magnetite, cassiterite, cobaltite-gersdorffite, rutile, ilmenite, goethite, sphalerite, galena, arsenopyrite, chalcopyrite, pyrite, and pyrrhotite. These minerals range in size from 20 pm to 250 pm and represent potential Indicator minerals. 

Biotite and magnetite are also usually present and visible in hand specimen, muscovite may be present, and more rarely other oxides may be seen. Field estimates of modes ranged from 20-35 vol.% quartz, 15-35 vol.% plagioclase, 30-50 vol.% potassium feldspar, and 1-10 vol.% biotite. Accessory minerals include magnetite, muscovite, monazite, xenotime, zircon, apatite, epidote, ilmenite, titanite, allanite, molybdenite, and galena. The major U and Th minerals are uraninite and uranothorite. 

There are structural analogues of a number of iron oxides in the Fe-H-O system. Under certain conditions, continuous solid solutions exist between the two members of a pair. The magnetite-ulvospinel and the hematite-ilmenite pairs are well-known examples. The principle in going from the Fe oxide to the Ti-containing phase is to replace two Fe by one Fe" and one Ti , thereby increasing the unit cell size. 

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