Alteration Of Ilmenite Research Articles

The continuous alteration of ilmenite through pseudorutile to leucoxene

Ore-microscopic examinations and microprobe analyses show the alteration of ilmenite by leaching to be a continuous process, proceeding from “leached ilmenite” through pseudorutile to leucoxene. In this process which takes place near the surface and requires the presence of water, a temperature of 50°C is not exceeded. Therefore, diffusion processes are of no importance. There are continuous phase transitions between ilmenite and its successive products. Pseudorutile, with its iron-poor members (=“leached pseudorutile”) in particular, is unstable and decomposes into leucoxene. As a result of this and also of leucoxenic changes brought about by recrystallization, there are sharp grain boundaries towards other alteration products, simulating discontinuous leaching processes. Ilmenite, leucoxene and their intermediate products are well distinguishable from each other by ore-microscopic and subordinate also by X-ray methods, with ore-microscopic studies enabling this distinction to be made faster and more easily. Water is the main agent in the leaching process which keeps going on as long as there is iron present that is able to migrate. The continuous alteration of ilmenite can be expressed in terms of two reactions: (a) 3Fe 2+TiO 3→Fe 3−x 2+ (Fe (2 3)x 3+ + □ (1 3)x ) Ti 3O 9 . In this equation x=0–3; x=0 corresponds to ilmenite, x=3, to pseudorutile. In the range of x=0–2.1 “leached ilmenite” occurs. Reaction (a) is established by oxidation and leaching of iron. (b) Fe 2 3+Ti 3O 9→Fe 2− y 3+Ti 3O 9−3y(OH) 3 y . In this equation y=0–2; y=0 corresponds to pseudorutile, y=2 to leucoxene. The range of y from 0.8–1.4 is identical with “leached pseudorutile”. Reaction (b) can be explained by hydrolization and leaching of iron. Whereas reaction (a) includes all phases representing oxides with different Fe 2+:Fe 3+ ratios, reaction (b) comprises all phases with iron occurring in its trivalent state and the O: (OH) ratio increasing as the Fe 3+ content is decreasing.

Fe-Ti-Oxide assemblages in the basal parts of the Central Alpine Brenner Mesozoic, Tyrol/Austria

Pseudorutile in the cores of strongly zoned ilmenite aggregates surrounded by titanhematite and rutile occurs in a metamorphic paleoweathering horizon locally covering the Austroalpine Oetztal-Stubai crystalline complex. Pseudorutile is believed to develop during early diagenetic alteration of ilmenite due to the incursion of marine groundwater. The accompanying Fe-Ti-oxide assemblages (magnetite, rutile, ilmenite, hematite) are subdivided into allothigenic, authigenic, diagenetic and metamorphic formations. The overlying clastic sediments (Upper Scythian) contain enrichments of magnetite which are interpreted as marine beach placers with reworked material of the paleoweathering horizon.

Alteration and mass transfer in cataclasites and mylonites in 6.6 km of granitic crust at the Siljan impact structure, central Sweden

Granitic rocks deformed by cataclasis and mylonitization on macro- (a few meters) and micro- (thin section) scales are found at depths down to 6.6km in the Siljan impact structure in central Sweden. Granites near fault planes exhibit: (1) fracturing, kinking, fragmentation, and recrystallization of feldspars into pure K and Na endmember varieties, (2) fragmentation, polygonization and development of undulose extinction in quartz, and (3) kinking, appearance of wavy extinction and alteration of biotite, chlorite, amphibole, and alteration of ilmenite and magnetite. Whole-rock chemical analyses of deformed and undeformed rocks show that deformed rocks are enriched in SiO2 (by about 5 wt.%) and depleted in other oxides by variable percentages. Apart from Rb and Co, the concentrations of other trace elements (including Ba, Sr, Zn, Zr, Pb, Cd, Cu, Cr, Ni, V, U, Th, La, and Li) are lower in deformed relative to undeformed rocks. Mass-balance calculations for a 1000 cm3 model granite which were based on modal mineralogy, whole-rock chemistry, and mineral analyses suggest that the break down of primary biotite, chlorite, and amphibole in deformed zones released elements to circulating fluids. These calculations also indicate liberation of water and a doubling of porosity (from ∼1 to 2%) during the deformation episodes. Later precipitation of minerals in shear and tension fractures reduced this porosity. Within the upper 2000 m of the Gravberg-1 well, the formation of fracture-filling minerals (smectite, calcite, hematite, chlorite, and albite) is impact-related, and was favored by active circulation of meteoric water. Fracture-filling minerals in the upper 2000 m of the borehole formed at temperatures of 70° to 200°C. Between depths of 2000 and 3500 m, fracture-filling mineral assemblages (dominated by Fe−Mg chlorite, sphene and epidote) suggest formation temperatures in the range of 150° to 300°C. Occurrence of pumpellyite and prehnite in some altered biotite and chlorite of the deformed zones between 3500 and 5500 m suggest preimpact metamorphism and formation temperature above 150°C. Below 5500 m, the mineral assemblages in the fractures are dominated by quartz, sphene, epidote, and some muscovite and chlorite, indicating a temperature range between 300° and 450°C. One of the possible origins for the CH4 and H2 gases detected in the Gravberg-1 well is a combination of hydrogen ions released by decomposition of hydrated silicates (biotite, chlorite, hornblende) with carbon. The presence of iron in the deformed granitic rocks prevented the resulting CH4 from being oxidized.

Alteration of detrital Fe-Ti oxides in sedimentary rocks

Scanning electron microscope study has revealed that in Proterozoic sandstones, shales, and carbonate rocks of the Visingso Group in southern Sweden, detrital Fe-Ti oxides have undergone alteration by dissolution and/or replacement mainly by titanium oxides, hematite (reddish rocks), or pyrite (greenish sandstones, shales, and carbonate rocks). The titanium oxides occur as either poorly crystalline masses, cryptocrystalline aggregates, or discrete, euhedral crystals of anatase, brookite, and rutile that attain a variety of crystal habits. Microprobe analyses have shown that the alteration of ilmenite occurs through several intermediate phases, each successively enriched in titanium and depleted in iron, to an almost pure form of TiO 2 . Some of the iron and titanium which is released during alteration of the Fe-Ti oxides is incorporated in associated clay minerals.

Uranium Mineralization in Singhbhum Shear Zone, Bihar II. Occurrence of 'Brannerite'

Abstract Composite grain-aggregates of titanium and uranium oxide phases resemble, both in texture and composition, those described as 'brannerite' grains occurring in quartz-pebble conglomerate-type uranium deposits such as those of Witwatersrand in South Africa and Blind River in Canada. The grain-aggregates contain variable amounts of quartz, rutile, anatase, uraninite, brannerite (s.s), pyrite, galena and hematite. Intimate inter-growths of uranium-rich and titanium-rich phases are observed. 'Brannerite' grains are secondary in origin, both detrital and metamorphic ilmenite being the antecedent mineral. They have been formed by the action of uranium-bearing solutions on ilmenite under conditions which favoured (i) alteration of ilmenite to titania by removal of iron (ii) simultaneous precipitation of uranium from solutions as uraninite and (iii) adsorption of uranium by titania. This can take place under both reducing and oxidizing conditions.

The dependence of alumina and silica contents on the extent of alteration of weathered ilmenites from Western Australia

AbstractThe distribution of the minor impurities, aluminium and silicon, between co-existing phases in altered ilmenite grains from three Western Australian localities has been investigated using SEM and electronmicroprobe analyses. A striking dependence of the impurity levels on the Ti/(Ti + Fe) fraction is observed. For compositions with Ti/(Ti + Fe) between 0.45 and 0.60, i.e. between ferrian-ilmenite and pseudorutile, the impurity content is virtually independent of Ti/(Ti + Fe), and is very low (0.2 wt. % Al2O3. 0.05 wt. % SiO2). For compositions between those of rutile and pseudorutile, there is a direct correlation between the impurity contents and the Ti content of the alteration phase. The impurity levels increase with increasing Ti/(Ti+Fe) to about 3 wt. % Al2O3and 1 wt. % SiO2for compositions close to TiO2. Thus during the latter stages of ilmenite alteration, alumina and silica are extracted from the ambient environment and are coprecipitated with, or adsorbed on to, the alteration products. The observed dependence of the alumina and silica contents on extent of alteration is consistent with a two-stage alteration mechanism earlier proposed (Grey and Reid, 1975).

A rock magnetic study of the lower massive sandstone, Moenkopi Formation (Triassic), Gray Mountain Area, Arizona

This paper describes the results of rock magnetic and petrographic studies of the Lower Massive sandstone of the Moenkopi Formation, north central Arizona, which heretofore has been considered to be a reliable magnetostratigraphic unit. The rock‐magnetic studies included stepwise thermal demagnetization of samples of intraformational mudstone clasts and a deformed shale lens, both of which occur within the lower part of the sandstone, and stepwise thermal and selective destructive demagnetization (SDD) of samples of the sandstone containing black sand laminae composed largely of opaque grains. In samples both from the claystone clasts and deformed shale lens two secondary components, one of modern normal polarity and one of Triassic normal polarity, were unambiguously identified, and a third CRM component of Triassic reversed polarity was tentatively identified. There is no evidence in samples of either the claystone clasts or deformed shale lens of a remanence acquired prior to deposition or to deformation, respectively. SDD, by means of which the small‐scale homogeneity of remanence within samples of the Lower Massive sandstone containing black sand laminae could be assessed, shows that each sample primarily contains a heterogeneous three‐dimensional mixture of Triassic normal and reversed components. The Triassic normal direction that is characteristic of the Lower Massive sandstone is a vector resultant of almost balanced proportions of the two nearly antiparallel components, averaging about 55 to 60% normal and 45 to 40% reversed. The local variability in both direction and intensity of remanence within and between individual black sand laminae confirms that acquisition of the remanence took place over a geologic time interval that spanned at least two and probably several polarity intervals and that, on a small scale, the remanence was sporadically acquired more or less randomly, probably in response to local conditions in the interstitial physicochemical environment that affected the growth of authigenic hematite. No primary component of remanence acquired at or soon after deposition could be identified. The remanence in the black sand‐bearing Lower Massive sandstone is largely carried by the black sand grains which, as determined from reflected‐light petrographic studies, are primarily martite (67%) and altered ilmenite grains (20%) composed of complex intergrowths of hematite and iron‐titanium minerals. These data strongly suggest that these grains, deposited initially as unaltered to only moderately altered magnetite and ilmenite, subsequently underwent oxidation during which they acquired their remanence.

Alteration of Beach Sand Ilmenite from Manavalakurichi, Tamil Nadu, India

Abstract The study shows that the alteration of ilmenite has taken place according to the two stage model proposed by Grey and Reid (1975). Identification of the intermediate altered compound, pseudorutile, was found difficult in earlier studies by optical and X-ray diffraction methods, because of the occurrence of this phase in altered ilmenite in very fine grain size (30 Å), its poor crystallinity and coincidence of many of the diffraction lines with those of other phases. The present study has shown that the Mossbauer technique is more suitable in the identification and estimation of this phase. The relative amount of pseudorutile increases progressively in the magnetic fractions in the following order: 0.30 - 0.35 amps (5%), 0.25 - 0.30 amps (40%), 0-0.25 amps (75%) and 0.35 - 0.50amps (95%), indicating that the magnetic susceptibility of the grains is increasing initially with progressive pseudorutile formation, and decreasing in the later stages of alteration. Reflectivity and hardness are also increasing up to the stage of pseudorutile formation and decreasing in the later stages.

X-ray diffraction and magnetic studies of altered ilmenite and pseudorutile

SynopsisIT was not until 1966 that pseudorutile was first defined. Earlier, its X-ray diffraction spectrum had been confused with that of futile and, to a lesser degree, with those of hematite and ilmenite. Subsequent work has shown that pseudorutile has a world-wide distribution in detrital ilmenite-bearing heavy mineral deposits. The present work has confirmed its magnetic susceptibility and density. In addition pseudorutile is shown to be a magnetic spin glass with a peak susceptibility at 23 °K.Altered ilmenites, in which pseudorutile occurs as a secondary alteration product, display a range of chemical composition and magnetic susceptibility. The most highly magnetic fractions are not necessarily those containing the least-altered ilmenite, and in material from Capel, Western Australia, the most highly magnetic fractions were those containing grains of ferrimagnetic ferrian ilmenite.Quantitative X-ray diffraction has shown that West Australian altered ilmenite contains significant amounts of amorphous ilmenite, pseudorutile, and rutile. The magnetic susceptibility of paramagnetic fractions of altered ilmenite from Capel, Western Australia, can be calculated from normative compositions based on chemical analyses.

Aenigmatite, sodic pyroxene, arfvedsonite and associated minerals in syenites from Morotu, Sakhalin

Aenigmatite, sodic pyroxene and arfvedsonite occur as interstitial minerals in metaluminous to weakly peralkaline syenite patches in alkali dolerite, Morotu, Sakhalin. Aenigmatite is zoned from Ca, Al, Fe3+-rich cores to Ti, Na, Mn, Si-rich rims reflecting the main substitutions Fe2+Ti4+⇌Fe3+, NaSi⇌CaAl and Mn2+⇌Fe2+. Aenigmatite replaces aegirine and ilmenite supporting the existence of a ‘no-oxide’ field in $$f_{{\text{O}}_{\text{2}} }$$ — T space. In one case aenigmatite has apparently formed by reaction between ilmenite and arfvedsonite. Titanian aegirine (up to 3.0 wt% TiO2) and Fe-chlorite may replace aenigmatite. Sodic pyroxene occurs as zoned crystals with cores of aegirine-augite rimmed by aegirine and in turn by pale green aegirine containing 93 mol% NaFe3+Si2O6. Additional substitution of the type NaAl⇌CaFe2+ is indicated by significant amounts (up to 6 mol%) of NaAlSi2O6. Arfvedsonite is zoned with rims enriched in Na, Fe and depleted in Ca which parallels the variation of these elements in the sodic pyroxenes. The high peralkalinity of the residual liquid from which the mafic phases formed resulted from the early crystallization of microperthite (which makes up the bulk of the syenites) leading to an increase in the Na2O/(Na2O+K2O) and (Na2O+K2O)/Al2O3 ratios of the remaining interstitial liquid which is also enriched in Ti, Fe, and Mn. Bulk composition of the melt, $$f_{{\text{O}}_{\text{2}} }$$ , temperature and volatile content were all important variables in determining the composition and stability of the peralkaline silicates. $$f_{{\text{O}}_{\text{2}} }$$ in the residual liquid appears to have been buffered by arfvedsonite-aegirine and later by the arfvedsonite-aenigmatite and aenigmatite-aegirine equilibria under $$f_{{\text{O}}_{\text{2}} }$$ conditions of a ‘no-oxide’ field. An increase in $$f_{{\text{O}}_{\text{2}} }$$ , above that of the alkali buffer reactions, is inferred by an increase of Ti and Mn in aenigmatite rims. The latest postmagmatic vapour crystallization stage of the syenites is marked by extremely low $$f_{{\text{O}}_{\text{2}} }$$ which may have been facilitated by exsolution of a gas phase. Low $$f_{{\text{O}}_{\text{2}} }$$ is supported by the replacement of aenigmatite by titanian aegirine, and the formation of rare Ti-rich garnet with a very low (ΣTi4++Fe3+)/(ΣTi+ΣFe) ratio of 0.51, associated with leucoxene alteration of ilmenite.

Distribution of niobium in stream sediments related to heavy-mineral sand dunes, near pemberton, Western Australia

Abstract After the completion of a programme of regional stream sediment sampling to observe base metal distributions in drainage systems in the southwest of Western Australia, it was noted that above background Pb and Sn contents in minus 80-mesh fractions of samples from the Warren River area, were related to unusually high Nb contents in the same samples. Further investigations revealed that the anomalous samples were from streams draining eroded sand dunes containing heavy mineral sands, related to a former shore line. Assays of heavy mineral differentiates from these dune sands gave values up to 0.12% Nb in samples of altered ilmenite.

Alteration and Exsolution Characteristics of Ilmenites of Moheskhali Island, Chittagong, Bangladesh

Mineralogical analysis of Moheskhali beach sands revealed the presence of high amount of ilmenite. About 50% of these ilmenites are unaltered which are characterized by the presence of exsolution of ilmenite with hematite, ilmenite with magnetite, and ilmenite with rutile. Others (50%) are unexsolved where 30-50% grains partially or fully altered. These altered and unaltered phases of ilmenite are confirmed by X-Ray diffraction study. Ilmenite-hematite exsolution comprising 70-80% of the total exsolution. The widely banded exsolved phases were formed by continuous exsolution mechanism while the second generation thinner bands were formed discontinuously. Seriate texture dominates (about 75%) over emulsion, granular, quadrangular, sub graphic, veined and special types. Optical study suggests that the alteration of ilmenite is seen to proceed along grain boundaries and/or fractures resulting in an amorphous to microcrystalline mass resembling leucoxene. The chemical composition of the alteration products of ilmenite frequently fluctuates within definite ranges (pseudoilmenite and pseudorutile ranges) of a nonstoichiometric composition and thus deviates from their ideal composition. Key words: Ilmenite; Rutile; Opaque; Exsolution; Alteration. DOI: 10.3329/bjsir.v45i1.5173 Bangladesh J. Sci. Ind. Res. 45(1), 17-26, 2010

Electron-probe investigation of some intergrowths in iron-titanium minerals from Rosetta black sands

The nature of exsolution of ilmenite in titanomagnetite and of the alteration of ilmenite in Rosetta black sands was investigated by the electron micro-probe analyzer. The mode of formation of such micro-intergrowths has been explained and mainly attributed to oxidation processes.

Pseudorutile—a New Mineral Intermediate between Ilmenite and Rutile in the N Alteration of Ilmenite

ALTERATION of the mineral ilmenite, FeO·TiO2 in nature involves the processes of oxidation and leaching whereby iron is progressively removed to give a residual product, essentially TiO2. Several investigations have been reported of the alteration products of ilmenite, but apart from composites of known oxides of iron and titanium, no distinct intermediate phase has been discovered. As a result of an investigation of several altered ilmenite concentrates by X-ray techniques hitherto not applied to this problem, a new crystalline phase has been identified as a major constituent of altered ilmenite. The new phase crystallizes in a disordered structure of hexagonal symmetry and has the theoretical composition Fe2O3·3TiO2. We propose the name ‘pseudorutile’ for this new mineral.

Alteration of ilmenite

Ilmenite and its alteration products in commercial heavy-mineral concentrates were studied by means of chemical analysis, optical microscopy, electron microscopy, electron microprobe, and X-ray diffraction. Breakdown of ilmenite involves oxidation and ultimate removal of iron. Alteration starts on surface of grains and on cleavages and fractures. Phases present in the altered material are ilmenite, rutile, and a new iron-titanium oxide named pseudorutile. Final removal of iron from altered ilmenite occurs only in or above the zone of water-table fluctuation.

Leucoxene terminology and genesis; Discussion of Alteration of ilmenite by L. E. Lynd (l960)

In connection with recent discussion of the nomenclature of ilmenite alteration products, and particularly with reference to the proposal for a unified system of terminology, cites examples from observations of the titaniferous constituents of beach sands and other sediments of southeast Australia which illustrate some of the unresolved problems regarding the processes of leucoxenization.

Postdepositional alteration of sandstone minerals under acidic reducing conditions; a factor in the interpretation of sandstone texture

Notes that development of secondary clay minerals from potash feldspar and other detrital minerals in the Carboniferous (Namurian) subgraywacke sandstones of southwest Derbyshire, England, may have occurred in a highly acid reducing environment such as has been postulated for postdepositional alteration of ilmenite in unconsolidated sediments.

Ilmenite, magnetite, and feldspar alteration under reducing conditions

Discussion of GeoScience Abstracts 2-2320. It is reaffirmed that acid reducing conditions favor alteration of ilmenite to titania. Post-depositional processes involving reducing conditions are as effective as weathering in altering ilmenite and perhaps magnetite and other Fe-Ti-bearing minerals as well as possibly feldspar. Thus the maturity of a sediment as indexed by the disappearance of these minerals can be produced by several processes.

Malayan ilmenite vs. arizonite

Replies to criticism regarding the use of the term arizonite to designate the product of the final stage of ilmenite alteration, and rejects the term leucoxene in this connection.

Alteration of ilmenite and "arizonite

Criticizes the proposed use of the term arizonite to designate the end-product of alteration of ilmenite, as suggested in a paper by Flinter.