Diamonds from Wellington, NSW: insights into the origin of eastern Australian diamonds

Abstract Diamonds from alluvial deposits near Wellington, New South Wales, have been characterized on the basis of morphological features, mineral inclusions, C isotope signatures, N content and aggregation state and internal structure. The diamonds are of two types. The larger group (Group A) is indistinguishable from diamonds found worldwide from kimberlitic and lamproitic host rocks. This group is inferred to have formed in a peridotitic mantle source in Pre-Cambrian subcratonic lithosphere. The second group (Group B) is unique in its internal structures (which show evidence of growth in a stress field and non-planar facets), has unusually heavy C isotopic compositions and contains Ca-rich eclogitic inclusions. This group is inferred to have formed in a subducting slab. Diamonds of both groups have external features (corrosion structures and polish) indicating transport to the surface by lamproitic-like magmas. The diamonds show evidence of long residence at the earth's surface and significant alluvial reworking: they are not accompanied by typical diamond indicator minerals.

[1]  E. Eide,et al.  Microdiamond in high-grade metamorphic rocks of the Western Gneiss region, Norway , 1995 .

[2]  小松 啓.  Structure in diamonds as revealed by etching, M. Seal, Amer. Mineral. 50, 105-123(1965) : ダイヤモンドのマクロ・マイクロモルフォロジー , 1976 .

[3]  A. R. Lang,et al.  Orientation-dependent nitrogen incorporation on vicinals on synthetic diamond cube growth surfaces , 1990 .

[4]  P. Cartigny,et al.  Nitrogen isotopes in peridotitic diamonds from Fuxian, China: the mantle signature , 1997 .

[5]  M. Otter,et al.  The application of C isotope measurements to the identification of the sources of C in diamonds: a review , 1991 .

[6]  Barron B.J,et al.  Subduction model for the origin of some diamonds in the Phanerozoic of eastern New South Wales , 1996 .

[7]  W. Eppler.  Inclusions in Diamond , 1961 .

[8]  W. Griffin,et al.  Subduction-related diamond deposits? Constraints, possibilities, and new data from eastern Australia , 2000 .

[9]  N. Sobolev,et al.  Diamond inclusions in garnets from metamorphic rocks: a new environment for diamond formation , 1990, Nature.

[10]  S. O’Reilly,et al.  MULTIPLE SOURCES FOR BASALTIC ROCKS FROM DUBBO, EASTERN AUSTRALIA : GEOCHEMICAL EVIDENCE FOR PLUME-LITHOSPHERIC MANTLE INTERACTION , 1997 .

[11]  W. Collins,et al.  Palaeozoic arc growth, deformation and migration across the Lachlan Fold Belt, southeastern Australia , 1992 .

[12]  W. Griffin,et al.  Trace-element partitioning between garnet and clinopyroxene in mantle-derived pyroxenites and eclogites: P-T-X controls , 1995 .

[13]  P. Ortoleva.  Role of attachment kinetic feedback in the oscillatory zoning of crystals grown from melts , 1990 .

[14]  P. Robinson,et al.  Possibly diamond-bearing mantle peridotites and podiform chromitites in the Luobusa and Donqiao ophiolites, Tibet , 1993 .

[15]  B. Jamtveit,et al.  Morphological instabilities during rapid growth of metamorphic garnets , 1992 .

[16]  W. Tiller,et al.  Discussion of interface stability of large facets on solution grown crystals , 1968 .

[17]  H. Meyer,et al.  Unusual diamonds and unique inclusions from New South Wales, Australia , 1995 .

[18]  P. Meakin,et al.  Statistical characteristics and origin of oscillatory zoning in crystals , 1997 .

[19]  J. Hoefs.  Stable Isotope Geochemistry , 1973 .

[20]  W. Griffin,et al.  A xenolith-derived geotherm for southeastern australia and its geophysical implications , 1985 .

[21]  T. Evans,et al.  Aggregation of nitrogen in diamond, including platelet formation , 1981, Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences.

[22]  D. Robinson.  Surface textures and other features of diamonds , 1979 .

[23]  W. Griffin,et al.  Trace elements in sulfide inclusions from Yakutian diamonds , 1996 .

[24]  J. Veevers.  Case for the Gamburtsev Subglacial Mountains of East Antarctica originating by mid-Carboniferous shortening of an intracratonic basin , 1994 .

[25]  G. Bulanova.  The formation of diamond , 1995 .

[26]  M. Otter,et al.  Morphological, Resorption and Etch Feature Trends of Diamonds from Kimberlites within the Colorado-Wyoming State Line District, USA , 1991 .

[27]  E. Vance,et al.  Possible origins of α-damage in diamonds from kimberlite and alluvial sources , 1973, Mineralogical Magazine.

[28]  Iu L Orlov.  The mineralogy of the diamond , 1977 .

[29]  P. H. Nixon,et al.  Ultrahigh Pressure Metamorphism: Orogenic ultramafic rocks of UHP (diamond facies) origin , 1995 .

[30]  P. H. Nixon,et al.  Geochemical constraints on the petrogenesis of diamond facies pyroxenites from the Beni Bousera Peridotite Massif, North Morocco , 1993 .

[31]  W. Griffin,et al.  Nucleation environment of diamonds from Yakutian kimberlites , 1998, Mineralogical Magazine.

[32]  E. Leitch,et al.  The nature and origin of eclogite blocks in serpentinite from the Tamworth Belt, New England Fold Belt, eastern Australia , 1992 .

[33]  W. L. Bond,et al.  Nitrogen, a major impurity in common type I diamond , 1959 .

[34]  A. Provost,et al.  Oscillatory zoning: a pathological case of crystal growth , 1981, Nature.

[35]  W. Collins,et al.  A rift-drift-delamination model of continental evolution: Palaeozoic tectonic development of eastern Australia , 1994 .

[36]  H. Milledge,et al.  Geologically Significant Information from Routine Analysis of the Mid-Infrared Spectra of Diamonds , 1995 .

[37]  B. A. Engel,et al.  Depositional and tectonic history of the southern New England Orogen , 1987 .

[38]  W. J. Meyers,et al.  Oscillatory zoning of Mn in solution-grown calcite crystals , 1990 .

[39]  P. Deines,et al.  The carbon isotopic composition of harzburgitic, lherzolitic, websteritic and eclogitic paragenesis diamonds from Southern Africa; a comparison of genetic models , 1995 .

[40]  V. Bennett,et al.  The persistence of off-cratonic lithospheric mantle: Os isotopic systematics of variably metasomatised southeast Australian xenoliths , 1997 .