Procedure for Sampling and Estimation of Heavy Minerals in Mineral Sand Samples 1. Reconnaissance Survey: Undertake a reconnaissance-survey of the concession area and list out potential zones of concentration concentration of ‘Heavy Minerals’ (HM), which are indicated indicated by higher -dense higher -dense black or dark dark streaks streaks in sand. sand. (for this satellite satellite imageries imageries or or aerial surveys surveys may may be used) 2. Sampling: Sample the identified potential zones of HM sands by (a) removing top (~10 cm) surface layer, (b) digging (with a crowbar) to 10-15 cm and (c) collecting the sand obtained by digging, at every spot; dry the sample in the Sun and take a representative portion of the sample (1-2 (1-2 kg) by ‘Coning & Quartering’ method or a sample-splitter. sample -splitter. Dry the sample in the Sun. Record the number of sample-spot and depth on a cloth bag and also on a piece-paper to be placed along along with the sample in the bag. Sampling is also done done by auger-drilling auger-drilling till till bed-rock. bed-rock. 3. Preparing a ‘Composite Sample’: Sample’: Place the collected dry sand samples from 4-10 spots at one place, thoroughly mix it and take 1-2 kg composite sample, sample, by coning and quartering method or using a sample-splitter, and number the composite sample, both on the container-bag and on a piece paper paper to be placed along along with the sample. sample. Selection Selection of spots for composite-sampling composite-sampling should should be based on the existence existence of of same set of conditions conditions in the field such such that the concentration concentration of HM in the selected spots should be more or less same, e.g., samples from frontal or middle or rare dunes should be separately mixed and should not be mixed one from the other. 4. Determination of Bulk Density (BD): BD for each composite sample should be determined by (a) filling full (to the brim) of 100 cc glass beaker or any other measuring container, (b) removing excess sand by leveling the top-layer with a thick sheet of paper or glass slide and (c) weighing the sand in the container, on an electronic balance; then, BD (g/cc ) = Weight of sample in g/100 cc or volume of the container 5. Processing a representative portion of composite sample, as per the following steps in sequential order : (a) Take 100 g of a composite-sample by coning and quartering; (b) Wash the sample thoroughly 2-3 times with distilled water at low flow-rate and gentle slope to remove slimes (clay, etc.,), dry the sample and weigh the dried sample; record the difference (i.e.) 100 – 100 – this this weight is the loss in weight (in g) due to de-sliming of the sample (c) Treat the dried sample, after de-sliming, with dilute HCl (hydrochloric acid) to remove shell material and iron-stains; dry and weigh; the difference in weights is weight-loss due to acidtreatment (d) Magnetite should be removed from the sample by placing the dried sample as a thin-layer on a thick sheet of paper and moving close to the sample a low-powered hand-magnet with its ends covered by a watch-glass or a thick sheet of paper so that only highly magnetic mineral, viz., magnetite only is removed but not ilmenite; or by subjecting the sample for separation at 0.1 amp. of a bar-magnet; note the weight of magnetite that is separated (e) Sieve the dried and magnetite-free sample in a set of following sieves, preferably in an electrically-operated electrically-op erated sieve-shaker, by keeping the sample in the coarsest mesh, followed by next lower mesh-size, with lid at the top and collecting pan at the bottom: Lid → 35#(mesh) 60# 80# 100# +120# +140# +200 or 230# 230# → collecting-pan collecting -pan microns 500 250 177 149 125 105 74 62.5 (N.B. In case material materi al in any sieve is negligible, then that t hat sieve need not be used u sed in subsequent sieving-operations for samples drawn from that particular area)
(f) Collect carefully fractions of sand in each sieve in a plastic-cover or a thick paper, using an air- blower, if required to remove the grains struck in wire of sieve; weigh and note the weight (in g) of each fraction, and record the weight and mesh-size of respective fraction on plastic-cover (in g) Separate the magnetic-part from the non-magnetic part by subjecting each of the above fractions for separation at 0.25-0.35 amp. on a bar-magnet (g) Separation of heavy minerals from light minerals is to be carried by subjecting each of the non-magnetic fractions obtained above to heavy liquid separation, using either bromoform (sp. gr. 2.89) or tetrabromoethane (or acetylene tetrabromide, sp. gr. 2.967) when heavy minerals like rutile, zircon, monazite and sillimanite sink to the bottom and light minerals like quartz float; the heavy minerals of each fraction are to be carefully collected, dried and should be weighed, packed and weight of each is noted either on a plastic-cover or on thick paper, used to pack the fractions; light-fractions are rejected. (h) Microscopic grain-counting should be carried out by counting about 300 grains in each of the magnetic and non-magnetic heavy fractions, and noting number of grains of each heavy mineral counted in the total count to obtain volume % of respective heavy mineral; vol. % is then to be converted into wt. % by multiplying vol. % with sp. gr. of respective heavy mineral in each fraction and by summing up the wt. % of a particular heavy mineral in all the fractions, the wt. % of respective heavy mineral in 100 g raw-sand sample can be obtained. Generally, ilmenite and garnet occur in magnetic-heavy fractions and rutile, zircon, sillimanite, kyanite, andalusite, monazite, pyroxenes and amphiboles, besides quartz impurity, occur in non-magnetic heavy fractions. While counting, valuable HMs, viz., ilmenite, rutile and zircon need to be carefully counted and rest of the minerals can be grouped under ‘others’, except when minerals like sillimanite, kyanite, andalusite and monazite occur in notable contents, when they are also to be counted separately. Sequential separations of Magnetite-free Raw-Sand sample are given below: ↓ Electro-magnetic separation, using a bar-magnet at 0.2-0.4 amp. ↓ __________________________ ↓ ↓ Magneitics (Ilmenite & Garnet) Non-Magnetics (HM-separation, using bromoform or Tetrabromoethane) ← ← HMs ↓ ↓HMs (Rutile, zircon, monazite, sillimanite, etc.) Light minerals (reject) (microscopic grain-counting of each fraction of magnetic and non-magnetic HMs ↓ Calculation of vol. % & wt. % of constituent HM In each mesh-fraction & in total sample ↓ Computation of block volume & tonnage, and ore Reserves by summation of tonnage in different blocks (prepared by R. Dhana Raju)
