Have a look at the following reference whihc outlines the protocols used at the Geological Survey of Canada for the processing of glacial sediments for the recovery and identification of indicator minerals. Most of these indicator minerals are in the heavy fraction (s.g. >2.8 or >3.2). You might be able to identify key minerals associated to the REE.

Plouffe, A., McClenaghan, M.B., Paulen, R.C., McMartin, I., Campbell, J.E., and Spirito, W.A., 2013. Processing of glacial sediments for the recovery of indicator minerals: protocols used at the Geological Survey of Canada; Geochemistry: Exploration, Environment, Analysis, v. 13, p. 303-316.

Dear Mr. Kumar,

First and foremost it is important to know which part of the alluvial-fluvial drainage system you are considering for stream sediment analysis. Taking samples from the estuaries of the Gulf of Bengal or from the promontory of the Lesser Himalayas makes a difference, I know both.

6000 ppm is high to expect monazite or xenotime as a heavy mineral. If LREE are high monazite is more likely, if Y and HREE are high it is more likely to have to deal with xenotime.

For a review I took the particle size between 63 µm and 630 µm.

After separation with Na-polytungstate, I apply a simple flow sheet -controlled analysis starting with the petrographic microscope (63-300 µm), SEM-EDX/WDX accompanied by XRF. You should carry out a mineralogical and chemical analysis. At an advanced level EMPA and ICP-MS are an option.

Please take a look at some of the paper below and consult for techniques and interpretation:

DILL, H.G., KAUFHOLD, S., LINDENMAIER, F., DOHRMANN, R., LUDWIG, R. and BOTZ, R. (2012) Joint clay-heavy-light mineral analysis: A tool to investigate the hydrographic-hydraulic regime of the Late Cenozoic deltaic inland fans under changing climatic conditions (Cuvelai-Etosha Basin, Namibia).- International Journal of Earth Sciences, 102: 265-304

DILL, H.G., WEBER, B. and KLOSA, D. (2012) Crystal morphology and mineral chemistry of monazite–zircon mineral assemblages in continental placer deposits (SE Germany):Ore guide and provenance marker.- Journal of Geochemical Exploration, 112: 322-346.

DILL, H.G. and KLOSA, D. (2011) Heavy-mineral-based provenance analysis of Mesozoic continental-marine sediments at the western edge of the Bohemian Massif, SE Germany: With special reference to Fe-Ti minerals and the crystal morphology of heavy minerals. - International Journal of Earth Sciences, 100: 1497-1513.

DILL, H.G. (2008) Geogene and anthropogenic controls on the mineralogy and geochemistry of modern alluvial-(fluvial) gold placer deposits in man-made landscapes in France, Switzerland and Germany.- Journal of Geochemical Exploration, 99: 29-60.

DILL, H.G. and LUDWIG, R.-R. (2008) Geomorphological-sedimentological studies of landform types and modern placer deposits in the savanna (Southern Malawi).-Ore Geology Review , 33: 411-434.

DILL, H.G. (2007) Grain morphology of heavy minerals from marine and continental placer deposits, with special reference to Fe -Ti oxides.- Sedimentary Geology, 198: 1-27.

If you cannot download the papers, I can send you privately a copy upon request.

Please let me know the positioning of the sampling sites within the drainage system and the REE variation. Going any further would be a bit of speculation at the moment.

Best regards

Harald G. Dill

Thanks Plouffe for answer .... I have downloaded your paper and will go through it!

Thanks Prof. Dill for answer and suggesting related publications.... I will try to find out these papers and if unable to find then request for personal copy. The further details of the topic are as: 

The sampling sites are first and second order nalas from a metamorphic and granitic terrain with some mafic dykes rich in biotite. Yes, LREE is high in general with Y upto 700ppm in few samples.

In addition, I would like to know that after bromoform separation, can non-magnetic heavy minerals be identified by XRD instead of SEM ?

Dear Mr. Kumar,

XRD powder analysis requires rather high quantities . If you are able to do single-crystal analysis you can pick out grains and investigate them (Weissenberg method). It is not an easy task and I recommend studies using either SEM /WDX or /EDX or EMPA, Yttrium is not a member of the REE group. However, if its values are high you may expect Y(PO4) which used to concentrate HREE such as Dy, Gd, Tb and Lu. So I expect xenotime to be part of your heavy mineral suite. Keep me posted please.

Harald G. Dill

Dear Ravi!

If you want to consider all minerals use MLA-Analysis or QUEMSCAN (also for quantitative Information), identify Mineralphases which can contain high amounts of REE and analyze them with LA-ICP-MS or EPMA.

For sampling and preparation you may consider the following paper:

Stocker, K. & Raith, J.G. (2014): Optimization of Niobium-Tantalum Prospecting in Austria - Routines for Sampling, Peparation and Analysis. Mitt. Österr. Miner. Ges. 160, 43 - 47.

Regards,

Kristina