A significant proportion of REE minerals reside in accessory minerals in common rocks. Praseodymium (Pr),  is a LREE which is commonly concentrated in accessory minerals of the rocks. Praseodymium is found in the rare earth minerals monazite and bastnäsite, typically comprising about 5% of the lanthanides contained therein.

as i have observed in literature pertaining to chondrite normalized patterns of some of  these common accessory minerals, it is found that mineral zircon shows negative Pr anomaly, i.e., your sample might be having a zircon concentration there by giving negative Pr anomaly or it could be depletion of Pr bearing monazite/ bastnasite in the sample Hope it is useful to some extent.

you may refer the following paper for further details.

Reference: Geochemistry of the Lanthanide Elements

Fernando Bea

Department of Mineralogy and Petrology. University of Granada

Hi Dilip,

If you are confident your bulk-rock analytical results are robust, look if possible at the REE pattern of your accessory minerals, particularly any apatite, allanite, sphene or zircon you may have. Also Cerium enrichment, (for example in zircons), might be worth checking for, as well as Pr depletion.

Puchelt & Emmerman (1976) suggested that a late-crystallizing apatite deficient in Ce & Pr might result from earlier crystallization of accessory phases which have an affinity for these species (e.g. allanite, monazite). Whether this process could affect bulk rock concentrations in granites is unclear, however.

Examples of distinct –ve Pr anomalies in granites and felsic volcanics (either whole-rock or in accessory minerals) are incredibly rare in the literature. Some examples are given below.

Hope this helps,

Regards Graham

Exley, R. A. "Microprobe studies of REE-rich accessory minerals: implications for Skye granite petrogenesis and REE mobility in hydrothermal systems." Earth and Planetary Science Letters 48.1 (1980): 97-110.

Puchelt, Harald, and Rolf Emmermann. "Bearing of rare earth patterns of apatites from igneous and metamorphic rocks." Earth and Planetary Science Letters 31.2 (1976): 279-286.

Jefferies, N. L. "The distribution of the rare earth elements within the Carnmenellis Pluton, Cornwall." Mineralogical Magazine 49.353 (1985): 495-504.

Buda GY, Nagy GÉ. Some REE-bearing accessory minerals in two types of Variscan granitoids, Hungary. Geologica Carpathica. 1995 Apr;46(2):67-78.

Thanks for your reply. 

In my sample zircon, monazite are present in good quantities but not bastnaesite. 

Thanks Prof. Howes for your observations.