Himalayan Geology, Vol. 38 (1), 2017, pp. 78-85, Printed in India 78 Petrography and Oxygen, Carbon isotopic signatures of the Magnesite from Bageshwar district, Kumaun Himalaya focusing on genesis and depositional environment of Magnesite PRABHAJOSHI*, P.D. PANT Department of Geology, Centre of Advanced Study, Kumaun University, Nainital, India *Present Address: Anjuman-I-Islam's Kalsekar Technical Campus, School of Engineering & Technology, Civil Engineering Department, New Panvel, Navi Mumbai-410206, India Email (Corresponding author): prabha_geo@rediffmail.com, pjoshiaiktc@gmail.com Abstract: Keywords The Deoban Formation of the Calc Zone of Tejam in the Kumaun inner Lesser Himalaya consists of coarsely crystalline magnesite deposits along with talc mineralization. These deposits, hosted within Precambrian marine dolomite have been investigated for petrography and isotopic composition to infer genesis and environment of deposition. Microscopic features represent a tidal flat environment wherein different phases of replacement of dolomite by magnesite are observed. O for dolomite varies from -10.9‰ to - 21.2‰ PDB with a mean -16.05‰ PDB, and for the magnesite it varies from -14.9‰ to -22.4‰ with a mean value of -17.2‰ PDB. The obtained C for dolomite varies from 0.1‰ to 5.4‰ PDB, with a mean value of 3.7‰ PDB. For magnesite C ranges from 1.1‰ to 5.4‰ PDB, with a mean of 3.4‰ PDB. The near similar O values, C representing a marine water source, combined with petrography and field evidences suggest that the studied magnesite resulted from the replacement of early formed dolomite during diagenesis in a restricted tidal flat environment. The intimate association of these deposits with stromatolites indicate that the algal activity might had stimulated the favourable environment through increased Mg concentration in the basin fluid. : Magnesite, Stable Isotope, Lesser Himalaya, Diagenesis. δ δ δ δ δ 18 13 13 18 13 INTRODUCTION The carbonate rocks of the Kumaun inner Lesser Himalaya host - magnesite and talc deposits at a number of places. These deposits of exploitable size and grade are confined within the Deoban Formation, which constitute an important sedimentary formation in the Kumaun region. The present work aims to understand the genesis of magnesite by studying petrography and stable isotopic composition of magnesite and eSXuslkbV fu{ksiksa dh mRifRr rFkk fu{ksi.k okrkoj.k ij /;ku dsafnzr djrs gq, ckxs'oj ftyk] dqekÅa fgeky; ds eSXuslkbV dh 'kSyo.kZuk rFkk vkWDlhtu] dkcZu leLFkkfud Lo:i izHkk tks'kh ] ih Mh iar * * - - -- HkwfoKku foHkkx] mPp v/;;u dsUnz] dqekÅ fo'ofo|ky;] uSuhrky] Hkkjr orZeku irk% flfoy bathfu;fjax foHkkx] U;w iuosy 410206] Hkkjr ¡ vatqe&b&bLyke dylsdj VsfDudy dSEil] Ldwy vkWQ bathfu;fjax ,.M VsDuksykWth] ] uoh eqacbZ& lkjka'k ladsr 'kCn vkarfjd dqekÅa y?kq fgeky; esa rste ds dSYd tksu esa nsocu lewg esa VSYd rFkk nh?kZfØLVyh eSXuslkbV fu{ksi ik;s tkrs gSA dSfEcz;u iwoZ leqnzh MksyksekbV esa fLFkr bu fu{ksiksa dh 'kSy o.kZuk rFkk muds leLFkkfud Lo:i dk v/;;u mudh mRifRr rFkk fu{ksi.k okrkoj.k dks tkuus ds fy;s fd;k x;kA mudk xBu Tokjh; ryh; okrkoj.k dk izfrfuf/kRo djrk gS tgka eSXuslkbV }kjk MksyksekbV ds izfrLFkkiu ds vusd Lrj ifjyf{kr gksrs gSaA MksyksekbV ds fy;s ih Mh ch e/;eku ds lkFk ls rd feykA MksyksekbV esa e/;eku ds lkFk ls rd eSXuslkbV esa 3-4 e/;eku ds lkFk ls rd ik;k x;kA ds MksyksekbV rFkk eSXuslkbV esa yxHkx leku vkadMs rFkk vkadM+ksa dk leqnzh tyh; lzksr iznf'kZr djuk rFkk 'kSyo.kZuk ,oa {ks= izek.k fl) djrs gSa fd bl {ks= ds v/;;u fd;s x;s eSXuslkbV fu{ksi 'kSoky fØ;kvksa ls cus vojks/kh Tokjh; ryh; okrkoj.k esa igys cus MksyksekbV ds izla?kuu ds nkSjku gq, izfrLFkkiu ls fufeZr gq, gSA % eSXuslkbV] fLFkj leLFkkfud] y?kq fgeky;] izla?kuuA % ls ih Mh ch rd rFkk eSXuslkbV esa ih Mh ch e/;eku ds lkFk ih Mh ch ih Mh ch feykA ih Mh ch LVªksesVksykbV ds lkFk bu fu{ksikas dk fudV laidZ ladsr djrk gS fd “kSokyh; xfrfof/k us csflu rjy inkFkZ esa eSXuhf”k;e lkUnz.k ls vuqdwy okrkoj.k dks çsfjr fd;kA δ O -16.05 -14.9‰ 22.4 C 3.7 0.1 5.4 1.1 5.4 18 13 ‰ -10.9‰ 21.2‰ 17.2‰ ‰ δ ‰ ‰ ‰ C ‰ ‰ ‰ O C δ δ δ 13 18 13