RASKASMINERAALIEN SEPAROINTIKOKEET HYDROSEPAROINTILAITTEELLA PIETARISSA: MENETEL~N SOVELTUVUUS ISOTOOPPIGEOLOGISIIN NAYTTEISIIN

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1 Geologian tutkimuskeskus Arkistoraportti M4 1.1/2003/1 RASKASMINERAALIEN SEPAROINTIKOKEET HYDROSEPAROINTILAITTEELLA PIETARISSA: MENETEL~N SOVELTUVUUS ISOTOOPPIGEOLOGISIIN NAYTTEISIIN Irmeli Mantt2ri ja Jukka Karhunen Espoon yksikko Tutkimuslaboratorio

RASKASMINERAALIEN SEPAROINTIKOKEET HYDROSEPAROINTILAITTEELLA PIETARISSA: MENETELMAN SOVELTUVUUS ISOTOOPPIGEOLOGISIIN NAYTTEISIIN Irmeli Manttliri ja Jukka Karhunen Tutkimuslaboratorio Geologian

2 RASKASMINERAALIEN SEPAROINTIKOKEET HYDROSEPAROINTILAITTEELLA PIETARISSA: MENETELMAN SOVELTUVUUS ISOTOOPPIGEOLOGISIIN NAYTTEISIIN Irmeli Manttliri ja Jukka Karhunen Tutkimuslaboratorio Geologian tutkimuskeskus PL 96,02151 Espoo Raskasmineraalien separointi Clerici-liuoksella pyritak lopettamaan GTK:ssa sen myrkyllisyydesta johtuen. Tutkirnrne halvan, yksinkertaisen ja kontaminaatiovapaan hydroseparointilaitteen soveltuvuutta lahinna isotooppigeologisten naytteiden raskasmineraaliseparointiin. Laitetta on kaytetty enirnrnaseen PGE-mineraalien rikastamiseen seka mineraalien erotteluun Re-0s-menetelmaa varten. Testinaytteena olleen graniitin hydroseparoinnin mineraalirikasteet koostuivat paaasiassa kevyista, felsisista mineraaleista. Toisaalta graniitin parhaissa rikasteissa zirkonin ja titaniitin osuus oli noin puolet koko rikasteen maiirastii. Tassa tapauksessa mineraalien kasin erottaminen rikasteista ikbaiirityksia varten olisi viela suhteellisen jiirkevaa. Graniitin toisessa osanaytteessa hydroseparoinnin raskasmineraalien havikki oli huomattavan suuri. Vahan zirkonia sisaltavk vulkaniittinaytteen harvalukuiset zirkoni- ja titaniittirakeet melkein havisivat rikasteisiin, jotka koostuivat lahes yksinomaan muista mineraaleista. Puhtaimpiin, tai ainakin yhta puhtaisiin raskasmineraalirikasteisiin psstsn melko nopeasti metyleenidijodidiseparoinnilla (3.3 g ja magneettisella erottelulla magneettikenth voimakkuuksia, naytteen syottonopeutta, kaadetta ja kulmaa vaihtelemalla. Rikasteiden seulonta separoinnin lopuksi saattaa myos parantaa joidenkin raekokofraktioiden puhtautta. Hydroseparoinnissa kevyet, rikasteeseen jaavat felsiset mineraalit ovat jatkopuhdistuksen kannalta ongelmallisia, koska nha eivat erotu hyvin magneettisesti. Talloin, varsinkin vahk ikamaiiritettavia mineraaleja sisaltavat naytteet saattavat aiheuttaa kohtuuttomasti pikkaustyota. Toisaalta, menetelmalla voitaisiin mahdollisesti paasta parempaankin erottelutulokseen, jos veden pulssitaajuutta ja -voimakkuutta pienennett2isiin. Hydroseparointitekniikan huonona puolena voidaan myos mainita tassa testissa havaittu merkittiiva raskasmineraalihavikki. Lisasi tama menetelma ei kilpaile tehokkuudessaan ylivoimaisesti perinteisten raskasmineraalien separointimenetelmien kanssa.

11 Kuva 4. Hydroseparoinnin rikaste naytteestii GR-BI; c75 pm - raekokofraktio. Kuva 5. Hydroseparoinnin rikaste nayi3eesti-i GR-BI; pm - raekokofraktio.

$Optimal grain liberation was achieved by grinding the sample in small portions for short periods (15-20 s), sieving to remove the fine fraction and regrinding the residual coarse fraction.$

21 Liite vibration grinder (Pulverizette-9) with a 100-ml steel mill. The chemical composition of the mill is known and contaminant particles can easily be recognized. Optimal grain liberation was achieved by grinding the sample in small portions for short periods (15-20 s), sieving to remove the fine fraction and regrinding the residual coarse fraction. This process was repeated until the entire sample reached the desired maximum grain size. In this way overgrinding (and consequent loss) of small accessory particles is minimized. After complete grinding the sample powder was passed through standard sieves on a Retsch classifier: -45, 45-75, and pm. This minimized grain-size effects during the hydroseparation. After the hydroseparation the concentrate was examined in polished thin sections and mineral grains were analysed qualitatively and quantitatively with an electron microprobe (Camscan. Microspec-4DV, Link AN , Microspec). The concentrates were compared with polished thin sections of the rock sample to establish the mineral paragenetic relations. Principles of hydroseparation The hydroseparation technique relies on the separation of particles by density in a carefully controlled water flow. Air bubbles should be evacuated before the separation as they may interfere with the process. To avoid clustering of grains, an antiflocculant can be added, but for most materials it is sufficient to suspend the particles in water in an ultrasonic bath. The heavy-mineral concentrates are produced by the settling of particles in an upward fluid flow, but in contrast to previous techniques that follow Stokes' law 1,2,9 exclusively the hydroseparator HS-01 uses a pulsating water flow to simulate the swash action of waves on natural beach placers.12 Natural placers usually contain relatively pure, well-sorted heavy-mineral concentrates that are well separated from larger, less dense particles that would have similar Stokes' settling velocities. The preferential concentration is believed to depend on the combined effects of suspension, entrainment and shear sorting. l2,13 The swash action limits the settling of large, less dense particles, but still allows small, dense particles to settle unhindered. It has, additionally, the effect of repeatedly reworking the settled particles, which greatly enhances the efficiency of separation (the surface shear would preferentially pick up large, light particles from the sediment 12 ). The hydroseparator (HS-01) is covered by international patents on the separation technique, design and method, which give a full description.23 It consists of two main components-a water flow regulator and a glass separation tube. The regulator controls the water flow, pulse intensity and pulse rate, which are adjusted to yield the maximum separation of the desired particles. The unit is connected to a pressurized water supply (ca 3 atm is recommended) and normal mains power. The separation tube is positioned vertically with its lower end connected to the water outlet of the regulator. Sample material is introduced as a particle suspension at the upper end of the tube. After separation the heavy-mineral concentrate is washed from the tube by the water flow on to a filter paper for drying. Applications For most materials the heavy-mineral separates are produced from the fine size fractions of the primary sample. For studies of PGE usually all the PGM grains

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