Mineralization and deformation of the Malanjkhand terrane (2,490–2,440 Ma) along the southern margin of the Central Indian Tectonic Zone
- 171 Downloads
The Malanjkhand Cu–Mo–Au deposit, located near the northwest margin of the Malanjkhand batholith (terrane), is a strategic and significant porphyry-style deposit that experienced a protracted 50 m.y. deformational history shortly after its formation at 2,490±8 Ma (Stein et al. 2004). In a recent study, Panigrahi et al. (2004) averaged U–Pb SHRIMP zircon data from a pooled set of samples from the Malanjkhand batholith to advocate a meaningless intermediate age of ~2,476 Ma for the Malanjkhand granitoid and its Cu–Mo–Au deposit. In the northwest part of the Malanjkhand batholith, Re–Os dating of occurrence-specific molybdenite captures not only the age of porphyry-style mineralization and associated magmatism, but also elucidates a complex deformational history that extends to ~2,450 Ma. In the central part of the Malanjkhand batholith, Re–Os dating of delicate spindles of accessory molybdenite occurring with pristine muscovite in miarolitic cavities within the undeformed microgranitoid at the Devgaon Mo prospect unequivocally shows that deformation ceased at this location no later than 2,470–2,465 Ma. The deformational history recorded at the Malanjkhand deposit in the northwest most likely reflects prolonged transpressive convergence and docking of the Malanjkhand terrane with units in the poorly understood (proto) Central Indian Tectonic Zone (CITZ) along its southern margin, the Central Indian shear zone. The timing for this convergence is Late Archean–Early Paleoproterozoic.
KeywordsMalanjkhand Devgaon Re–Os dating Molybdenite Deformation Central Indian Tectonic Zone
A high level of interest in the Malanjkhand deposit prompted Mineralium Deposita editor Bernd Lehmann to invite us to expand our original discussion to include a few newly acquired age data and pictorial documentation of the Malanjkhand pit and granitoid-mineralization textures observed therein. We appreciate this opportunity. We thank M.K. Panigrahi for early sharing of information on the zircon ages at Malanjkhand through e-mail. We acknowledge the support of the US National Science Foundation (research grant EAR-0087483, planning visit INT-0431929) and Edward M. Warner. CSU graduate student Parham Gardner assisted with sampling and provided the new isotopic analyses reported here. We are indebted to our Indian colleagues (B.S. Jhala and G.L. Sindhupe, Hindustan Copper Ltd, and P.K. Raut, Geological Survey of India at Nagpur) with whom we spent a fruitful 3 weeks in January 2005 examining the Malanjkhand Cu–Mo–Au deposit and various prospects in the Malanjkhand batholith and surrounding terranes. The entire expedition would not have been possible without the expert guidance and oversight of M.K. Pandit (University of Rajasthan, Jaipur). For their welcome to us, their interest, their expert guidance, and their friendship we are most grateful.
- Ayers JC, DeLaCruz K, Miller C, Switzer O (2003) Experimental study of zircon coarsening in quartzite ± H2O at 1.0 GPa and 1,000°C, with implications for geochronological studies of high-grade metamorphism. Am Mineral 88:365–376Google Scholar
- Bhargava M, Pal AB (2000) Cu–Mo–Au metallogeny associated with Proterozoic tectono-magmatism in Malanjkhand porphyry copper district, Madhya Pradesh. J Geol Soc India 56:395–413Google Scholar
- Hannah JL, Stein HJ, Zimmerman A, Markey R, Sarkar SC, Pal AB (2002) Late Archean-Early Proterozoic formation and reworking of a porphyry Cu(Mo) deposit recorded in molybdenite: Re–Os dating at Malanjkhand, Central India. Geochim Cosmochim Acta 66(15):308Google Scholar
- Nemchin AA, Giannini LM, Bodorkos S, Oliver NHS (2001) Ostwald ripening as a possible mechanism for zircon overgrowth formation during anatexis: theoretical constraints, a numerical model, and its application to pelitic migmatites of the Tickalara metamorphics, northwestern Australia. Geochim Cosmochim Acta 65(16):2771–2788CrossRefGoogle Scholar
- Pal AB, Bhargava M (1998) Regional geology and petrochemistry of Proterozoic Cu-Mo mineralization in Malanjkhand granitoids, Madhya Pradesh. In: Paliwal BS (ed) The Indian Precambrian. Scientific Publishers (India), Jodhpur, pp 333–350Google Scholar
- Panigrahi MK, Misra KC, Bream B, Naik RK (2002) Genesis of the granitoid affiliated copper–molybdenum mineralization at Malanjkhand, Central India: facts and problems. In: 11th IAGOD symposium and GEOCONGRESS (ext. abstract) Windhoek, p 7Google Scholar
- Stein HJ (2005) Low-rhenium molybdenite by metamorphism in northern Sweden: recognition, genesis, and global implications. Lithos (in press)Google Scholar
- Stein HJ, Zimmerman A, Hannah JL, Markey RJ (2003) Late Archean–Early Proterozoic timing for an Andean-style porphyry Cu–Mo deposit at Malanjkhand, Central Indian Tectonic Zone: implications for a Late Archean supercontinent. Geophysical Res Abstr 5(07496)Google Scholar
- Zimmerman A, Stein HJ, Markey RJ, Hannah JL, Sarkar SC, Pal AB (2002) Re–Os dating of the Malanjkhand Cu (Mo) deposit in central India: tracking formation and deformation during the late Archean–early Proterozoic. Geol Soc Am Abstr Programs 34:187Google Scholar