HR: 0800h
AN: V31C-0638    [Abstracts]
TI: Residual Hydrochloride - Silicate Melt Associated With the Platinum-bearing Alaskan-type Galmoenan Intrusion (Koryak Highland, Russia)
AU: * Batanova, V
EM: batanova@mpch-mainz.mpg.de
AF: Max-Planck-Institut fur Chemie, Postfach 3060, Mainz, 55020 Germany
AU: * Batanova, V
EM: batanova@mpch-mainz.mpg.de
AF: Vernadskii Institute of Geochemistry, Kosigin str.19, Moscow, 117975 Russian Federation
AU: Kamenetsky, D
EM: Dima.Kamenetsky@utas.edu.au
AF: Centre for Ore Deposit Research, University of Tasmania, Private Bag 79, Hobart, Tasmania, 7001 Australia
AU: Pertsev, A
EM: alexein@igem.ru
AF: Institute of Ore Deposits Geology, Petrography, Mineralogy and Geochemistry, Staromonetnyi, 35, Moscow, 109017 Russian Federation
AU: Sobolev, A
EM: asobolev@mpch-mainz.mpg.de
AF: Max-Planck-Institut fur Chemie, Postfach 3060, Mainz, 55020 Germany
AU: Sobolev, A
EM: asobolev@mpch-mainz.mpg.de
AF: Vernadskii Institute of Geochemistry, Kosigin str.19, Moscow, 117975 Russian Federation
AB: Alaskan-type mafic-ultramafic complexes formed in subduction-related environments are considered to be a major source of platinum placer deposits [1]. A specific feature of these deposits is the dominant occurrence of Pt-Fe alloys (mainly isoferroplatinum) among PGE-bearing minerals [e.g. 2]. The PGE mineralization can be related to the high activity of chlorine in the parental magmas of Alaskan-type intrusions [3] and the potential of saline fluids to dissolve and transport Pt [4,5,6]. Fluxing of a refractory mantle wedge in a supra-subduction zone by chlorine-rich aqueous fluids was considered primarily responsible for the formation of PGE-enriched parental magmas [3]. Potential role of the saline magmatic fluids is further tackled by this study of melt/fluid inclusions in olivine from the Galmoenan pluton belonging to the Alaskan-type intrusive complex in the Kamchatka-Koryak province [7] and spatially associated with one of the most significant platinum placer deposits in Russia [8]. High-magnesian olivine (Fo 90.8) from the Galmoenan dunites hosts abundant hydrosaline chloride and hydrosaline chloride-silicate melt inclusions (5-30mkm). Inclusions trail fractures confined to individual olivine grains, and thus formed before re-crystallization completed. Heating stage experiments at 1 atm showed early melting within the inclusions at ~350C, however complete melting and homogenization was hampered by decrepitation at 650-750C. This suggests elevated pressures of trapping, at least 3-4 kb. The study of phase and chemical compositions of these inclusions by an electron probe, laser ablation ICP-MS and SIMS ion probe showed chlorides of Na, K, Ca, Fe and Ba, Fe-Cu-Ni sulfides and diopside among daughter phases; 2) high H2O abundances; 3) high abundances of alkali and alkali-earth elements (Na, K, Rb, Sr, Ba, Ca) and metals (Fe, Mn, Pb, Ni, Cu, Zn). Such compositions confirm the presence of metal-enriched hydrosaline melt at the latest stages of formation of the Pt-bearing Alaskan-type intrusion. We envisage that the hydrosaline melt owed its origin to prolonged fractionation of the parental ultramafic K- and Cl-rich melt [9,3], followed by saturation in the chloride components [10]. Our melt inclusion evidence suggests that the Galmoenan dunite was soaked in the residual chloride melt/fluid. The bearing of this melt/fluid on Pt mineralization is likely, but is yet to be established. [1] Taylor and Noble, Rep.21 IGC, pt 13, Copenhagen, 175-187, 1960; [2] Slansky et al, Miner.Petrol. 43, 161-180, 1991; [3] Batanova et al, JP. 46, 1345-1366, 2005; [4] Ballhaus and Stumpfl, CMP 94, 193-204, 1986; [5] Sassani and Shock, GCA 62, 2643-2671, 1998; [6] Hanley et al, GCA 69, 2593-2611, 2005; [7] Batanova and Astrakhantsev, Proc. 29 IGC, pt D, VSP, 129-143, 1994; [8] Tolstykh et al, Can.Miner.42, 619-630, 2004; [9] Kamenetsky et al, JP 37, 637-662, 1995; [10] Webster, Chem.Geol 210, 33-48, 2004
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
DE: 1043 Fluid and melt inclusion geochemistry
DE: 3618 Magma chamber processes (1036)
DE: 3640 Igneous petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005