Ophiolitic chromitites of Timor Leste: their composition, platinum group element geochemistry, mineralogy, and evolution

Ultramafic rocks that crop-out as fault-bounded blocks within Hili Manu, ∼50 km east of the capital Dili on the north coast of Timor Leste, have been a topic of considerable debate regarding their ophiolitic affiliation with the Banda Arc or Australian subcontinental lithosphere. Two discrete ultramafic massifs separated by amphibolite of undefined origin, Be Heda Hill and Kerogeol Hill in the east and Subao Highway in the west, have been identified and host tabular and vein-like chromitite morphologies, respectively. The chromitite bodies at Hili Manu occur as small lenses a few meters in size. This paper presents the first detailed investigation of the chromitites from the two massifs at Hili Manu, including their mineralogy, textures, and chemistry. Chemically, the primary chromites from the Hili Manu chromitites comprise both high-Cr type (Cr2O3 40.24–56.95 wt.% and Cr# [Cr/(Cr + Al)] > 0.6) that occur at Kerogeol Hill and Subao Highway and high-Al type (Cr2O3 35.70–37.38 wt.% and #Cr < 0.56) that are restricted to Be Heda Hill. Similarly, the accessory spinels of the enclosing wall rocks also show high-Cr (#Cr = 0.60–0.82) and high-Al varieties (#Cr = 0.17–0.48). Platinum-group minerals (PGM) such as laurite and possible erlichmanite-series minerals, silicates, base metal sulfides (BMS), and arsenides are found as inclusions and within fractures in the chromite or the serpentinite matrix. The platinum-group element (PGE) concentration of the Hili Manu chromitites and its immediate host peridotite at the three localities varies, with total PGE (Os + Ir + Ru + Rh + Pt + Pd) in the ranges 73.1–1295 ppb and 28.5–364 ppb, respectively. The total PGE content is higher and the Pd/Ir ratio is lower in the Cr-rich chromitites compared to the Al-rich ones. Most of the PGM are 3–10 μm in size and occur as primary or composite inclusions in IPGE-bearing phases, particularly Os-rich laurite, within unaltered chromite grains. Host peridotite major- and trace-element geochemistry coupled with the chemistry of chrome-spinels for both the chromitites and host peridotites in this study show evidence of formation of the Hili Manu peridotite in an upper mantle in a supra-subduction zone setting, part of the young oceanic lithosphere from the Banda Arc.

[1]  W. Griffin,et al.  Genesis and Tectonic Implications of Podiform Chromitites in the Metamorphosed Ultramafic Massif of Dobromirtsi (Bulgaria) , 2015 .

[2]  H. Prichard,et al.  Platinum group element (PGE) mineralisation and chromite geochemistry in the Berit ophiolite (Elbistan/Kahramanmaraş), SE Turkey , 2014 .

[3]  W. Griffin,et al.  Chromitites in ophiolites: How, where, when, why? Part II. The crystallization of chromitites , 2014 .

[4]  R. M. Palomares,et al.  HYDROTHERMAL PALLADIUM ENRICHMENT IN PODIFORM CHROMITITES OF CALZADILLA DE LOS BARROS (SW IBERIAN PENINSULA) , 2013 .

[5]  C. Tassinari,et al.  Geochemistry and detrital geochronology of stream sediments from East Timor: implications for the origin of source units , 2013 .

[6]  J. Shulmeister,et al.  Rapid Pliocene uplift of Timor , 2013 .

[7]  M. Rajabzadeh,et al.  Mineralogy and distribution of Platinum-Group Minerals (PGM) and other solid inclusions in the Faryab ophiolitic chromitites, Southern Iran , 2013, Mineralogy and Petrology.

[8]  W. McDonough,et al.  Experimental constraints on the partitioning of Ru, Rh, Ir, Pt and Pd between chromite and silicate melt: The importance of ferric iron , 2012 .

[9]  S. Eggins,et al.  Enrichment of Rh, Ru, Ir and Os in Cr spinels from oxidized magmas: Evidence from the Ambae volcano, Vanuatu , 2012 .

[10]  John F. Lewis,et al.  Chromite and platinum group elements mineralization in the Santa Elena Ultramafic Nappe (Costa Rica): geodynamic implications , 2011 .

[11]  W. Griffin,et al.  High-Cr and high-Al chromitites from the Sagua de Tánamo district, Mayarí-Cristal ophiolitic massif (eastern Cuba): Constraints on their origin from mineralogy and geochemistry of chromian spinel and platinum-group elements , 2011 .

[12]  H. Furnes,et al.  Ophiolite genesis and global tectonics: Geochemical and tectonic fingerprinting of ancient oceanic lithosphere , 2011 .

[13]  T. Meisel,et al.  Comparison between Nickel‐Sulfur Fire Assay Te Co‐precipitation and Isotope Dilution with High‐Pressure Asher Acid Digestion for the Determination of Platinum‐Group Elements, Rhenium and Gold , 2010 .

[14]  D. Haig,et al.  Deformation and exhumation in Timor: Distinct stages of a young orogeny , 2010 .

[15]  Ryan D. Taylor,et al.  Stratiform chromite deposit model , 2010 .

[16]  S. Arai,et al.  Platinum-group elements distribution and spinel composition in podiform chromitites and associated rocks from the upper mantle section of the Neoproterozoic Bou Azzer ophiolite, Anti-Atlas, Morocco , 2009 .

[17]  T. Meisel,et al.  Petrology of Al- and Cr-rich ophiolitic chromitites from the Muğla, SW Turkey: implications from composition of chromite, solid inclusions of platinum-group mineral, silicate, and base-metal mineral, and Os-isotope geochemistry , 2009 .

[18]  L. Bailly,et al.  Zoning of laurite (RuS2)–erlichmanite (OsS2): implications for the origin of PGM in ophiolite chromitites , 2009 .

[19]  R. Hall.  The Eurasian SE Asian margin as a modern example of an accretionary orogen , 2009 .

[20]  J. Proenza,et al.  Composition and textures of chromite and platinum-group minerals in chromitites of the western ophiolitic belt from Pampean Ranges of Córdoba, Argentina , 2008 .

[21]  M. Economou-Eliopoulos,et al.  Diversity of platinum-group minerals in podiform chromitites of the late Proterozoic ophiolite, Eastern Desert, Egypt: Genetic implications , 2007 .

[22]  I. Uysal,et al.  PLATINUM-GROUP-ELEMENT GEOCHEMISTRY AND MINERALOGY OF OPHIOLITIC CHROMITITES FROM THE KOP MOUNTAINS, NORTHEASTERN TURKEY , 2007 .

[23]  J. Korenaga,et al.  Chemical composition of Earth's primitive mantle and its variance: 1. Method and results , 2007 .

[24]  A. Tamura,et al.  Harzburgite-dunite-orthopyroxenite suite as a record of supra-subduction zone setting for the Oman ophiolite mantle , 2006 .

[25]  R. Berry,et al.  Whole-rock geochemistry of the Hili Manu peridotite, East Timor: implications for the origin of Timor ophiolites , 2006 .

[26]  J. Royer,et al.  Late Cenozoic geodynamic evolution of eastern Indonesia , 2005 .

[27]  H. Keppler,et al.  Solubility of rutile in subduction zone fluids, as determined by experiments in the hydrothermal diamond anvil cell , 2005 .

[28]  I. Uysal,et al.  Mineralogy and composition of the chromitites and their platinum-group minerals from Ortaca (Muğla-SW Turkey): evidence for ophiolitic chromitite genesis , 2005 .

[29]  J. Malpas,et al.  REE and PGE Geochemical Constraints on the Formation of Dunites in the Luobusa Ophiolite, Southern Tibet , 2004 .

[30]  L. Beccaluva,et al.  Tethyan vs. Cordilleran ophiolites: a reappraisal of distinctive tectono-magmatic features of supra-subduction complexes in relation to the subduction mode , 2004 .

[31]  M. Audley-Charles.  Ocean trench blocked and obliterated by Banda forearc collision with Australian proximal continental slope , 2004 .

[32]  Conny Bockrath,et al.  Fractionation of the Platinum-Group Elements During Mantle Melting , 2004, Science.

[33]  R. Cabella,et al.  Chromite composition and platinum-group mineral assemblage in the Uktus Uralian-Alaskan-type complex (Central Urals, Russia) , 2003 .

[34]  J. Brenan,et al.  PHASE-EQUILIBRIUM CONSTRAINTS ON THE MAGMATIC ORIGIN OF LAURITE + Ru–Os–Ir ALLOY , 2002 .

[35]  T. Charlton.  The structural setting and tectonic significance of the Lolotoi, Laclubar and Aileu metamorphic massifs, East Timor , 2002 .

[36]  A. H. Ahmed,et al.  Unexpectedly high-PGE chromitite from the deeper mantle section of the northern Oman ophiolite and its tectonic implications , 2002 .

[37]  J. Dyment,et al.  Magnetic lineations constraints for the back-arc opening of the Late Neogene South Banda Basin (eastern Indonesia) , 2001 .

[38]  A. Crawford,et al.  Factors Controlling Chemistry of Magmatic Spinel: an Empirical Study of Associated Olivine, Cr-spinel and Melt Inclusions from Primitive Rocks , 2001 .

[39]  J. Brenan,et al.  HIGH-TEMPERATURE STABILITY OF LAURITE AND Ru–Os–Ir ALLOY AND THEIR ROLE IN PGE FRACTIONATION IN MAFIC MAGMAS , 2001 .

[40]  J. Shervais.  Birth, death, and resurrection: The life cycle of suprasubduction zone ophiolites , 2001 .

[41]  R. Wirth,et al.  Spinel inclusions in olivine of peridotite xenoliths from TUBAF seamount (Bismarck Archipelago/Papua New Guinea): evidence for the thermal and tectonic evolution of the oceanic lithosphere , 2000 .

[42]  A. Crawford,et al.  Melt inclusions in detrital spinel from the SE Alps (Italy–Slovenia): a new approach to provenance studies of sedimentary basins , 2000 .

[43]  N. Shimizu,et al.  Whole rock compositional variations in an upper mantle peridotite (Horoman, Hokkaido, Japan): Are they consistent with a partial melting process? , 2000 .

[44]  R. Harris,et al.  The Timor Ophiolite, Indonesia: Model or myth? , 2000 .

[45]  J. Melgarejo,et al.  Al- and Cr-rich chromitites from the Mayari-Baracoa ophiolitic belt (eastern Cuba); consequence of interaction between volatile-rich melts and peridotites in suprasubduction mantle , 1999 .

[46]  Mei-Fu Zhou,et al.  Controls on platinum-group elemental distributions of podiform chromitites : A case study of high-Cr and high-Al chromitites from Chinese orogenic belts , 1998 .

[47]  W. McDonough,et al.  The composition of peridotites and their minerals: a laser-ablation ICP–MS study , 1998 .

[48]  H. Helmers,et al.  Late Miocene obduction and microplate migration around the southern Banda Sea and the closure of the Indonesian Seaway , 1997 .

[49]  P. Robinson,et al.  Origin and tectonic environment of podiform chromite deposits , 1997 .

[50]  B. Franklin,et al.  Chemistry and mineralogy of podiform chromitite deposits, southern NSW, Australia: a guide to their origin and evolution , 1996 .

[51]  A. Hofmann,et al.  Fluid- and melt-related enrichment in the subarc mantle: Evidence from Nb/Ta variations in island-arc basalts , 1996 .

[52]  D. Blundell,et al.  Continental collision in the Banda arc , 1996, Geological Society, London, Special Publications.

[53]  P. Robinson,et al.  High-Cr and High-Al Podiform Chromitites, Western China: Relationship to Partial Melting and Melt/Rock Reaction in the Upper Mantle , 1994 .

[54]  M. D. Smet,et al.  A geometrically consistent plate-tectonic model for eastern Indonesia , 1989 .

[55]  A. Crawford,et al.  Classification, petrogenesis and tectonic setting of boninites. , 1989 .

[56]  G. Garuti,et al.  Platinum-Group Minerals in Chromite-rich Horizons of the Niquelandia Complex (Central Goias, Brazil) , 1988 .

[57]  R. Pedersen,et al.  The Use of Mantle Normalization and Metal Ratios in Discriminating between the Effects of Partial Melting, Crystal Fractionation and Sulphide Segregation on Platinum-Group Elements, Gold, Nickel and Copper: Examples from Norway , 1988 .

[58]  B. A. Wills,et al.  Chromite- mineralogy and processing , 1988 .

[59]  A. J. Naldrett,et al.  The origin of the fractionation of platinum-group elements in terrestrial magmas , 1985 .

[60]  J. Hawkins,et al.  Petrology of Mariana Trough and Lau Basin basalts , 1985 .

[61]  T. Augé.  Platinum-group-mineral inclusions in ophiolitic chromitite from the Vourinos Complex, Greece , 1985 .

[62]  Z. Ahmed.  Stratigraphic and textural variations in the chromite composition of the ophiolitic Sakhakot-Qila Complex, Pakistan , 1984 .

[63]  H. Stockman,et al.  Platinum-group minerals in alpine chromitites from southwestern Oregon , 1984 .

[64]  H. Dick,et al.  Chromian spinel as a petrogenetic indicator in abyssal and alpine-type peridotites and spatially associated lavas , 1984 .

[65]  M. Leblanc,et al.  Distribution of aluminum-rich and chromium-rich chromite pods in ophiolite peridotites , 1983 .

[66]  Peter C. Jones,et al.  Platinum-group minerals and other solid inclusions in chromite of ophiolitic complexes: Occurrence and petrological significance , 1983 .

[67]  J. Tarney,et al.  Petrologic Evolution of the Mariana Arc and Back-Arc Basin SystemA Synthesis of Drilling Results in the South Philippine Sea , 1982 .

[68]  M. Rabinowicz,et al.  Podiform Chromite Ore Bodies: a Genetic Model , 1982 .

[69]  Z. Ahmed.  Porphyritic-nodular, nodular, and orbicular chrome ores from the Sakhakot-Qila complex Pakistan, and their chemical variations , 1982, Mineralogical Magazine.

[70]  R. Berry.  Petrology of the Hili Manu lherzolite, East Timor , 1981 .

[71]  M. Leblanc,et al.  Structural classification of chromite pods in southern New Caledonia , 1981 .

[72]  R. Berry,et al.  Deformation and metamorphism of the Aileu Formation, north coast, East Timor and its tectonic significance , 1981 .

[73]  M. Leblanc.  Chromite growth, dissolution and deformation from a morphological view point: SEM investigations , 1980 .

[74]  A. J. Naldrett,et al.  The composition of Ni-sulfide ores, with particular reference to their content of PGE and Au , 1979 .

[75]  H. Prichard.  A petrographie study of the process of serpentinisation in ophiolites and the ocean crust , 1979 .

[76]  D. Greenbaum.  The chromitiferous rocks of the Troodos ophiolite complex, Cyprus , 1977 .

[77]  R. Berry,et al.  Some Palaeozoic‐Mesozoic stratigraphic‐structural relationships in east timor and their significance in the tectonics of timor , 1977 .

[78]  A. Barber,et al.  Thrust tectonics in Timor , 1977 .

[79]  A. J. Naldrett,et al.  Ultramafic and related mafic rocks; their classification and genesis with special reference to the concentration of nickel sulfides and platinum-group elements , 1976 .

[80]  A. Streckeisen.  To each plutonic rock its proper name , 1976 .

[81]  F. Chamalaun,et al.  The Bouguer gravity field and crustal structure of eastern Timor , 1976 .

[82]  J. S. Dickey.  A hypothesis of origin for podiform chromite deposits , 1975 .

[83]  H. T. Millard,et al.  Osmium, ruthenium, iridium and uranium in silicates and chromite from the eastern Bushveld Complex, South Africa , 1974 .

[84]  L. Cabri,et al.  Mooihoekite and haycockite, two new copper-iron sulfides, and their relationship to chalcopyrite and talnakhite , 1972 .

[85]  M. Audley-Charles.  The Geology of Portuguese Timor , 1968, Geological Society, London, Memoirs.

[86]  T. P. Thayer.  Principal features and origin of podiform chromite deposits, and some observations on the Guelman-Soridag District, Turkey , 1964 .