MINERALOGICAL MAGAZINE, JUNE r980, VOL. 43, PP. 775-7

The telluride melonite from the Jaduguda uranium deposit, Singhbhum Shear Zone, Bihar, India

N. KRISHNA RAO, D. NARASIMHAN, AND G. V. U. RAO Ore Dressing Section, Bhabha Atomic Research Centre, Chandralok, I i x, Sarojini Devi Road, Hyderabad 5oo oo3, (A.P.), India

SUMMARY. The rare nickel telluride mineral melonite Occurrence. The mineral which was later identi- is identified from Jaduguda uranium ore, Singhbhum fied as melonite has been observed in a few samples Shear Zone, Bihar, India. Its physical, optical, chemical, of an apatite-magnetite vein from the o-metre level and paragenetic characteristics are described. The com- as well as in a millerite-rich sample from 165-metre position as obtained by EPMA is NiTel.66Bi0.06 or level in the Jaduguda uranium mine. In the former approximately Ni3(Te,Bi)5. The association of melonite with molybenite in this ore deposit is unusual, since it is closely associated with molybdenite and occurs melonite is generally associated with tellurides of gold and as fillings in the form of coarse xenomor- silver. This is the first reported occurrence of melonite phic grains and flakes in a matrix of apatite, mag- from India. netite, chlorite, and quartz (figs. I and 2). Veinlets traversing cracks and cleavages in molybdenite are DURING the course of an intensive mineralogi- also common (fig. 2). In the I65-metre level sample cal study of uranium prospects from parts of Singh- it occurs as skeletal particles in chalcopyrite bhum Shear Zone, Bihar (Rao, i977) , the rare associated with molybdenite, gersdorffite, and nickel telluride mineral melonite was identified in millerite. a few samples from the Jaduguda uranium mine. Physical and optical properties. The mineral has Though several telluride have been re- perfect (ooo~) , is very soft, and takes a ported from different parts of the Singhbhum Shear scratch-free polish with difficulty. The Vickers Zone, melonite has not previously been reported. microindentation hardness varies between 67 and This occurrence is also new to India. 76 kg/mm 2 with an average of 73 kg/mm2.

FIGS. I and 2. FIG. I (left). Xenomorphic grain of melonite (me) showing (000I) cleavage. Flaky chlorite (ch) euhedral quartz (q) are the other associated minerals. Secondary electron image taken in ETEC SEM. FIG. 2 (right). Association of melonite (me) with flaky molybdenite (mo) and granular magnetite (mt) are the other associated minerals. Veinlets of melonite occupy cleavage in molybdenite. (~) Copyright the Mineralogical Society 776 N. KRISHNA RAO ET AL.

The colour in polished sections is creamy white, the reported analyses also correspond to the NiTe2 tarnishing to brown on long exposure. It shows composition (Vlasov, t966, p. 691; Strand, i975; faint bireflectance. The reflectivity is high, slightly Ebner, I978). greater than that of pyrite. The spectral reflectivity The composition of Jaduguda melonite is values measured with a photoelectric device Ni3Te5 ignoring Bi. Thus it is a member of the developed in the Ore Dressing Section, BARC, are NiTe-NiTe2 solid solution series, and the composi- illustrated in fig. 3. The reflectivity spectrum is tion falls at the point NiTez = 80 ~ in the NiTe- characterized by a sharp increase in reflectivity with NiTe2 join. The presence of bismuth reflects the wavelength between 5oo-6oo rim. common occurrence of several bismuth teUuride minerals in other parts of the Singhbhum Shear 70 Zone. Melonite from Jaduguda shows more intense anisotropism and vivid polarization colours com- pared with melonites from elsewhere (Uyten- bogaardt and Burke, I97 t, p. 252 ). The relatively 60 higher content of nickel may explain these non- typical optical properties. Paragenesis. Melonite commonly occurs in (i) gold and silver ores of vein associations, (ii) meta- somatic aureoles associated with other tellurides and (iii) high-temp, copper-nickel deposits of non- 50 volcanic origin (Ramdohr, i969, p. 419; Ebner, I978). Chalcopyrite is a common associate of all I I I I I I known occurrences of melonite whereas pyrite is 450 500 550 600 650 700 generally conspicuous by its absence. The occur- WAVE LENGTH nm rence in Jaduguda is unique in that it is not asso- FIG. 3, Spectral reflectivity curve of melonite. ciated with any gold and silver tellurides, but with molybdenite. Several telluride minerals have been reported Under crossed polars it shows vivid polarization from copper deposits of parts of Singhbhum Shear colours dominated by a violet tinge, which is dearly Zone; these are wehrlite, tetradymite (Sarkar and seen with nearly crossed polars. Larger grains show Deb, i969), volynskite (Narasimhan and Rao, spindle-shaped twin lamellae, perhaps resulting 1976), and suspected krennerite and (Rao from deformation during polishing. No internal et al., i967). In all these occurrences molybdenite reflections are observed. is also a common associate of telluride minerals. Identification. The physical and optical proper- Further, melonite has been observed only in the ties resemble those of the nickel telluride mineral Jaduguda area where no other telluride mineral has melonite (Vlasov, I966, p. 691 ; Uytenbogaardt and so far been reported. This is perhaps related to the Burke, 197i , p. 252; Ramdohr, ~969, p. 42o). The fact that nickel mineralization is more intense in the identification is confirmed by the wavelength dis- Jaduguda area than in other parts of the Singh- persive X-ray fluorescence spectrum of one grain bhum Shear Zone. taken in a ETEC Scanning Electron Microscope, which showed that nickel and are the Acknowledgements. The authors are grateful to Dr V. K. essential constituents of this mineral. Moorthy, Head, Metallurgy Group, for his sustained Chemical composition. The composition of the interest in these investigations and to Professor N. K. Jaduguda melonite obtained in a Geoscan EPMA, Mukerjee, Banaras Hindu University for his critical com- after corrections for atomic number, absorption ments. Thanks are also due to Shri S. K. Khera for help and fluorescence factors is Te 75.o2 ~, Ni 2o.78, in EPMA and to Dr R. Krishnan for help in SEM study. Bi 4.zo. It recalculates to NiTel.66Bi0.o6 or ap- proximately Ni3(Te, Bi)s. REFERENCES According to Ramdohr (i 969, P. 419) melonite is a member of the NiTe-NiTe2 solid solution series Ebner (F. S.), I978. Econ. Geol. 73, 447-9. and is often close to NiTe. At 45o ~ a continuous Narasimhan (D.) and Rao (G. V. U.), I976. Indian Geo- logical Congress, First Session, 5 (Abstracts). solid solution series is known to exist between Peacock (M. A.) and Thompson (R. M.), I946. Univ. NiTe2 join. The presence of bismuth reflects the Toronto Studies, Geol. Set. no. 5o, 63-73. studies by Peacock and Thompson (I946) have Ramdohr (P.), 1969. Ore minerals and their intergrowths shown the composition ofmelonite to be NiTe2 and (Pergamon Press), 1I74 pp. MELONITE FROM BIHAR, INDIA 777 Rao (N. K.), i977. Unpublished Ph.D. Thesis, Banaras microscopic identification of ore minerals (Elsevier Hindu University. Publishing Co.), 43 ~ pp. -- Rambabu (Ch.), and Rao (G. V. U.), I967. B.A.R.C. Vlasov (K. A.) (Ed.), 1966. Geochemistry and mineralogy Internal Report Met./Io, pp. 3t-9 . of rare elements and genetic types of their deposits. Sarkar (S. C.) and Deb (M.), I969. Mineral. Mag. 37, Vol. II. (Israel Programme for Scientific Translation, 423-5 . Jerusalem.) 945 PP- Strand (G. S.), I975. Norsk Geol. Tidsskr. 55, 299-3o 3. Uytenbogaardt (W.) and Burke (E. A. J.), 197 I. Tables for [Manuscript received 3I April I979]