THE AMERICAN MINERAI,OGIST, VOL. 41, JULY AUGUST, 1959 THE I\,IAGNETIC SEPARATION OF SOI'IE ALLUVIAL I,IINERALS IN I'IALAYA* B. H. FnNrant, Minerals Eramination Diaision, GeologicalSurttey D epartment, F'ederotion of M al,aya. Assrnlcr This paper presents the results of a seriesof magnetic separationswhich have been in- vestigated {or a number of minerals occurring in X{alayan alluvial concentrates.The pur- pose of the investigations was to establish,by the isolation of individual mineral species,a reproducible and reliable method for the identification and quantitative estimation of minerals in alluvial concentrates examined by the Geological Survey in Malaya In par- ticular was sought the isolation of columbite from ubiquitous ilmenite. All the separations were made on the small, highly sensitive Frantz Isodynamic Model L-1 laboratory separa- tor, The minerals which have been successfully separated include ailanite, anatase, andalu- site (and chiastolite), arsenopyrite, brookite, cassiterite,columbite, epidote, gahnite, garnet (pink), ilmenite, manganeseoxide (51.6/e Mn), monazite, pyrite, rutile, scheelite,siderite, staurolite, thorite, topaz, tourmaline, uranoan monazite, wolframite, xenotime, and zircon. PnocBpunp When using an inclined feed, the Frantz Isodynamic separator (see Figs. 1(A) & (B)) hasthree inherent variables. These are the field strengLh (current used),the sideslope, and the forward slope. 5;6s $lope wdrd 511)Pe (A) (B) Irc. 1. Diagrammatic representation of side slope and forward slope. The field strength is increasedby means of a rheostat which raises the current from zero in stagesof 0.05 amps. to 1.4 amps. Early in the investigationsit was decidedthat stepsof 0.1 amp. would be sufficiently gradual. The side slope can be varied continuously from 0 to 90o and can also be given a reverseslope, as much as 90", for the diamagneticseparation of minerals such as zircon. Results of a few separations made by my + Published by permission of the Director, Geological Survey, with the authority of the Minister of Natural Resources. Government copyright is reserved. 738 MAGNETICSEPARATION OF ALLUVIAL MINERALS 739 coileagueswhen the separator was firsl installed showed that, for the purpose of these investigations, side slopesvarying by lessthan 5o would produce no significant differentials, and further, that side slopesgreater than 15oshowed more promise, as regardsthe separationof columbite from ilmenite, than did slopesof less than 15o.Accordingly a seriesof tests was carried out at side slopesof 15o,20",25", and 30o. The forward slope and a fourth, independent, variable, the rate of feed, control the rate of flow of the sample.The steeperthe slope,the faster is the flow. The rate of flow of a sampleis not critical provided that it is slow enoughto allow the mineral to remain long enoughin the magnetic field for the magnetic pull exerted by the separator to be fully effective. A forward siopeof 15owas chosenfor, and maintained throughout, the investigation. Much more critical is the uniformity of grain size of the sample,as the larger grains tend to "suppress" the finer material. For the purpose of simple identification and the estimation of mineral percentagesin an alluvial concentrate a grain size of 0.4 mm. or 0.0166 inch (36 mesh B.S.S.)is considereda satisfactoryupper limit. With larger grainsdiffi- culty is experiencedin distinguishing amongst the opaque minerals and between the opaque minerals and the translucent minerals such as gahnite, cassiteriteand rutile. The grain sizeof 0.2 mm. or 0.0083inch (72 mesh B.S.S.) was selectedas a suitable lower limit. This gave uni- formity to the sample and provided finer material for a parallel seriesof tests to be conducted, thereby ascertaining whether a differencein grain size gives rise to any significant differencein results. For each mineral the same sample was used for all the separations, thus eliminating variations independent of the change in side slope. Each sample, averaging 2 to 3 gms., was dried before being passed through the separator. After separation the fractions were examined under the microscopeand the weight percentagesrecalculated to allow for any impurities, which were estimated visually. AssBsslmNr on RBsur,rs On the basisof the separationscarried out the mineralstested can be divided into two groups, the "magnetic" and the "non-magnetic." The "non-magnetic" minerals are those that are not attracted at a value of 1.4 amps. giving the maximum field strength of the separator.They are anatase,andalusite (and chiastolite),arsenopyrite, brookite, cassiterite, pyrite, rutile, scheelite, topaz, and zircon. The "magnetic" minerals are given in Tables 1 to 8. A study of these tables shows that, for the purpose for which the investigations were efiected, side slopesof 20' (Tables 3 and 4) and 30" B. H. FLINTER o r'i Fl a a z -m ! I :i< F N z& H< <' >a ei u) v f'l ff> tsN <N r .o' @ onN OI fl'o ir oNco F zfr O AZ ,.\OD ,H OOFO ^o iF:d i-; Ddfi .; <o &A 4.4 NrH<r .<i N cO.Oh ,n4 -oR3 F$H $ SF-S 13F \ia q: *rO\N O<1 fiFiro Zo N6 i4 "a@ t44 c) i & <1N. \oOD - cQ4 o . .! jor' FON FI 88: 14 <1dr. 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