Tegist Chernet June, 2003 Research report M 19/2014/2003/2/41 Geological Survey of Finland, Research Laboratory, Espoo Applied mineralogical studies on Iso-Kisko ilmenite ore deposit with

the ore amenability to beneficiation, Kisko, Southern Finlan Tilaaja: ESA, GTK, Olli Sarapää Project no.: 2109000

RAPORTTITIEDOSTON:O 4761

respect to d

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1. General

Drill core samples (R462/69.0 m, R463/25.05 m, R463/67.55 m and R464/80.4 m) from Iso-

Kisko, Kisko ilmenite ore were submitted for mineralogical studies. The corresponding polished

thin sections were studied for ore and rock-forming minerals and their textural relationships by

reflected and transmitted light microscopy. Microphotographs of the ore minerals were taken to

illustrate observations on inclusions, alterations and other textural features. The aim was to

study ore and silicate minerals assemblages, mode of occurrences, effect of mineralogy and

texture on the amenability of the ore to processing and on the quality of the final product. The

sample, perhaps, hardly represents the ilmenite deposit at Kisko; however, it holds a great deal

of mineralogical information for the possibility of further investigation.

2. Observations and results

2.1 Microscopy for ore minerals

Based on the given samples, the ore mineral assemblage, in average, includes about 5-12%

ilmenite, 5-15% of magnetite, small amount of sulfides (pyrite, pyrrhotite, chalcopyrite) and

trace amount of hematite.

Ilmenite and magnetite occur as well developed crystals, but commonly filling the

interstices between the silicate minerals. As a result the shape of the grains are subhedral to

anhedral (Figs 1,2,4). The grain size varies between 0.1 - 1.5 mm occasionally exceeding 1.5

mm. Ilmenite also occurs as latticed oxyexsolution textures in magnetite (ilmeno-magnetite)

grains (Figs 2,3,4,7,8). Ilmenite grains are commonly free of exsolved materials.

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However, some ilmenite grains contain fine dusts of hematite particles and isolated rows of

hematite having their long dimensions parallel to each other (Figs 5,6). These needle like

exsolved particles range in length from 0.1 mm to the minimum limit of resolution. Commonly,

the dust like particles are evenly distributed throughout the ilmenite grains, though the

abundance of exsolutions varies from grain to grain. Ilmenite also rarely contains oriented, thin

needle like dark brown mineral, which is presumably spinel (Figs 3,4). The boundaries between

ilmenite and magnetite grains are occasionally delineated by a rim of spinel granules (Figs

3,4,7,8). Ilmenite lamellae in magnetite range from a few µm to about 50 µm in thickness and

reach up to several µm in length. Alteration and twinning of ilmenite is very rare. Magnetite

that can also be referred as ilmenomagnetite contains both ilmenite and spinel as exsolved

inclusions (Figs 3,4,7).

Commonly, fine blebs and needles of both magnetite and ilmenite micro crystals are

oriented along cleavage planes of the gangue minerals such as pyroxene and uralites (Figs

9,10). Magnetite also occurs as myrmikitic intergrowth with silicate minerals (Fig 11). Pyrite is

common as separate grains and veinlets across the silicates, ore minerals and mineral contacts

(Fig 12). According to the given sections, pyrite is more common at depth and pyrrhotite is

more abundant near the surface (Figs 13,14).

2.2 Microscopy for silicate minerals

The rock forming minerals are amphiboles (uralite), pyroxene, plagioclase, olivine, chlorite,

epidote (ziosite), fine-grained quartz, calcite, sphene and apatite. These silicate minerals

constitute 70-80% of the rock. Very common is uralitization of anhedral crystals pyroxene and

olivine to form uralites, which are secondary amphiboles like hornblende and actinolite (Fig a,

b, c). Chlorite is another abundant mineral probably derived from pyroxene and biotite due

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to metamorphism (Fig d,e). Biotite is practically absent, may be due to intense chloritization.

Veinlets of chlorite are also common (Fig e). Recrystallization of quartz and quartz veinlets are

also observed (Fig f). Prismatic to granular plagioclase is one of the major rock-forming

minerals with the composition of mainly labradorite (Fig g, h). In the polished sections, it is

subhedral with subparallel arrangement reaches up to 2 mm in length (Fig h). Calcite and

epidote (ziosite) are also common replacing mainly plagioclase (Fig i). Sphene is observed

often rimming ilmenite grains and as veinlets dissecting ilmenite grains and other ore and rock

forming minerals (Fig j).

Inclusions/exsolution of ilmenite and magnetite in silicate minerals, mainly in uralites

are very common (Fig k, l). Pyroxenes and amphiboles are chocked by fine dust-like particles of

ilmenite and magnetite.

2.3 Electron probe microanalysis

The chemical compositions of the ore minerals were determined with a Cameca SX50 electron

microprobe at the GTK. Analyses were carried out to determine composition of magnetite and

ilmenite, and trace elements content in ilmenite. The analytical parameters were 20kV-

accelerating voltage, 20nA probe current and 1 µm beam diameter. Analyses results are given in

Table 1 and Table 2.

The total iron is analysed in the form of ferrous iron oxide. In average, ilmenite is

composed of 46.7% of FeO(t) and 49.8% TiO2, the ilmenite lamellae contain 46.4% FeO and

50.1% TiO2. The TiO2 content (49-50%) is the same as Kälviä ilmenite composition (49.3%-

50.6%) (Chernet, et al 1995, Chernet, 1999). Interestingly, the Cr2O3 content of ilmenite grains

and lamellae is negligible. Magnetite also shows very low content of Cr2O3.

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Table 1. Electron probe microanalyses of ilmenite grains and ilmenite lamellae in magnetite from drill core samples R462/69.0 m and R463/25.05 m. Operator: Lassi Pakkanen

The V2O3 content of ilmenite grains ranges from 0.1-0.4% (0.21% in average) and the lamellae contains nearly the same value, 0.0-0.4% (in average 0.17%). The V2O3 content of magnetite, on the other hand, ranges from 1.1-2.8% (in average 1.71%). The MgO both in ilmenite grains and lamellae is insignificant, 0.07 and 0.02 % respectively. Ilmenite contains considerable

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amount of MnO (0.9-1.5%) with nearly the same concentration both in the grains and lamellae.

Both MgO and MnO are nearly absent in magnetite.

Table 2. Electron probe microanalyses of magnetite from drill core samples R462/69.0 m and R463/25.05 m. Operator: Lassi Pakkanen

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Mineralogical and textural aspects affecting processing and the quality of ilmenite

The evaluation of Iso-Kisko ilmenite deposit and the design of procedures for mineral

processing require knowledge of the distribution and amount of the minerals, their chemical

composition, textural relationships, and grain size distributions.

The relative proportion and content of minerals vary substantially from one sample to

another even within a single drill hole. Chemical analyses, for e.g, from R461 show these

variations (See Appendix I). The recoverable ilmenite, according to the submitted samples

however, is about 5-12vol%, which is lower than Koivusaarenneva, Kalviä ilmenite deposit.

The average ilmenite content of Otanmäki, Kälviä and Tellnes ores are 28%, 15%, 35%, and the

content of the gangue minerals is about 35%, 72%, 62% respectively (Chernet, 1999). The Iso-

kisko ilmenite ore is medium to fine-grained, and both ilmenite and magnetite grains rarely

exceed 1.5 mm in diameter. The ore should, therefore, be finely ground to achieve liberation,

and should then be concentrated mainly by flotation. If ilmenite processing is considered for

Iso-kisko ilmenite ore, high intensity magnetic separation has to be applied for gangue mass

reduction before any attempt by flotation.

The boundaries between the ore and the gangue minerals are normally simple, and

minerals can be separated easily by crushing and grinding. Sometimes, however, the grain

boundaries are complex on a micro-scale and interpenetrating (e.g., microintergrowths of

ilmenite with magnetite and finely oriented grains of ilmenite and magnetite in the silicates);

complete unlocking cannot be obtaining. Thus, ilmenite as exsolutions and inclusions or

titanium in the lattice of magnetite and silicate minerals is not recoverable. Silicate minerals like

sphene and uralites rim some of the ilmenite grains. Occasionally the replacing mineral shows

an irregular extension in to the ilmenite grain. Apart from the induced decrease of the titanium

content of ilmenite, the partially or completely rimmed ilmenite affects both on the consecutive

processing stages and the quality of the final products.

In spite of exsolutions and unfavourable textural features, the recoverable ilmenite

content of the rock is not exceeding 15vol%, which implies only about 2 - 8% of TiO2. The

deposit seems to be low grade and the TiO2 content of the ore, for e.g., as chemical analysis

usually determines it, is not totally recoverable. The mineralogical source of TiO2 is not only

the free crystals of ilmenite but also the exsolved ilmenite particles in magnetite, ilmenite

inclusions in silicates, titanium in mineral lattices and other titanium bearing minerals.

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Furthermore, the quality of ilmenite grains can be affected by the abundance of trace

elements and their provenance in the ilmenite lattice. Cr, V and Nb are colourizers, and their

presence may reduce the value of a concentrate as pigment plant feed (Stanaway, 1994).

Magnesium decreases the rate of precipitation of hydrous titanium dioxide in the sulphate

process (Jalava, 1993). MgO and Cr2O3 contents are negligible (Table 1). According to the

microprobe analysis, the vanadium content (about 0.17-0.2% V2O3 in average) is a bit lower

than in Kälviä ilmenite concentrate (av. 0.23%), and very similar to that of the Tellnes

commercial ilmenite concentrates (av. 0.2). Considering the negligible content of MgO and the

given amount of MnO, the ilmenite has more of pyrophanite component.

5. Summary

In terms of oxide mineral association, textural relationships and nature of the host rock, the Iso-

Kisko ilmenite deposit can be classified as disseminated ilmenite-titaniferous magnetite

occurrence composed mainly of ilmenite, ilmenomagnetite, spinel and sulphides. The ore

minerals usually occur filling the interstices between silicate minerals with simple and

occasionally irregular boundaries. The host rock had been subjected to a retrograde

metamorphism, and, as a result, the primary silicate minerals are intensively replaced by

uralites, chlorite, epidote and calcite. Alteration of ore minerals is practically absent.

With a maximum of 15% ilmenite content, the ore is low grade. Considering the

abundance of ilmenite lamellae in magnetite and inclusions of ilmenite in uralites, the

recoverable TiO2 content is lower than what the whole rock chemical analyses may indicate. In

spite of the economic consideration, the ore could be tested to concentrate ilmenite. Good grade

may be expected in the expenses of recovery. From experiences, magnetic separation stages are

necessary to improve ilmenite recovery.

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6. References

Chernet, T., Kärkkiäinen N. (1995): Geology and mineralogy of the Koivusaarenneva ilmenite

deposit, Kälviä, western Finland. Geol. Survey of Finland, Special Paper 20, pp. 17-22.

Chernet, T. (1999): applied mineralogical studies of Koivusaarenneva ilmenite deposit, Kälviä,

Western Finland, with special emphasis on the altered part of the ore. Chronicle of

Mineral Research and Exploration, 535, 19-28.

Jalava J. (1993): Precipitation and Properties of TiO2 Pigments in the Sulfate Process. 2. Effects

of Trace Elements, Kemira Pigments Oy, unpublished results.

Stanaway K.J. (1994): Overview of titanium dioxide feedstocks. Mining eng., 46(12), 1367-

1370.