3D Modeling of the Epembe (Namibia) Nb-Ta-P-(LREE) Carbonatite Deposit: New Insights into Geometry Related to Rare Metal Enrichment

Geological 3D modeling delivers essential information on the distribution of enrichment zones and structures in (complex) mineral deposits and fosters a better guidance to subsequent exploration stages. The Paleoproterozoic Epembe carbonatite complex showcases the close relation between enrichment of specific elements (Nb, Ta, P, Total Rare Earth Element (TREE) + Y) and shear zones by structural modeling combined with geochemical interpolation. Three-dimensional fault surfaces based on structural field observations, geological maps, cross-sections, and drillhole data are visualized. The model shows a complex, dextral transpressive fault system. Three-dimensional interpolation of geochemical data demonstrates enrichment of Nb, Ta, P, and TREE + Y in small, isolated, lens-shaped, high-grade zones in close spatial distance to faults. Based on various indicators (e.g., oscillating variograms, monazite rims around the apatite) and field evidence, we see evidence for enrichment during hydrothermal (re-)mobilization rather than due to magmatic differentiation related to the formation of the alkaline system. This is further supported by geostatistical analysis of the three-dimensional distribution of Nb, Ta, P, and Light Rare Earth Elements (LREE) with respect to discrete shear zones.

[1]  B. Bühn.  The role of the volatile phase for REE and Y fractionation in low-silica carbonate magmas: implications from natural carbonatites, Namibia , 2008 .

[2]  D. Bird,et al.  KARRAT ISFJORD: A NEWLY DISCOVERED PALEOPROTEROZOIC CARBONATITE-SOURCED REE DEPOSIT, CENTRAL WEST GREENLAND , 2013 .

[3]  Adrian P. Jones,et al.  Carbonate Melts and Carbonatites , 2012 .

[5]  Jean-Laurent Mallet,et al.  Discrete smooth interpolation , 1989, TOGS.

[6]  M. Andersson,et al.  Magma transport in sheet intrusions of the Alnö carbonatite complex, central Sweden , 2016, Scientific Reports.

[7]  G. Caumon,et al.  Surface-Based 3D Modeling of Geological Structures , 2009 .

[8]  L. Diamond,et al.  Hydrothermal formation of heavy rare earth element (HREE)–xenotime deposits at 100 °C in a sedimentary basin , 2018 .

[9]  J. Kynický,et al.  Diversity of Rare Earth Deposits: The Key Example of China , 2012 .

[10]  L. Feltrin,et al.  Modelling the giant, Zn-Pb-Ag Century deposit, Queensland, Australia , 2009, Comput. Geosci..

[11]  Katherine R. Royse,et al.  Combining numerical and cognitive 3D modelling approaches in order to determine the structure of the Chalk in the London Basin , 2010, Comput. Geosci..

[12]  Richard Gloaguen,et al.  Remote Sensing Exploration of Nb-Ta-LREE-Enriched Carbonatite (Epembe/Namibia) , 2016, Remote. Sens..

[13]  A. Williams-Jones,et al.  Carbonate–silicate melt immiscibility, REE mineralising fluids, and the evolution of the Lofdal Intrusive Suite, Namibia , 2017 .

[14]  E. Laine,et al.  Structure of the Outokumpu ore district and ophiolite-hosted Cu–Co–Zn–Ni–Ag–Au sulfide deposits revealed from 3D modeling and 2D high-resolution seismic reflection data , 2014 .

[15]  I. Fletcher,et al.  The Kunene anorthosite complex, Namibia, and its satellite intrusions: Geochemistry, geochronology, and economic potential , 2013 .

[16]  B. Lévy,et al.  Stochastic simulations of fault networks in 3D structural modeling. , 2010 .

[17]  Philippe Renard,et al.  Three-dimensional geometric modeling of a faulted domain: the Soultz Horst example (Alsace, France) , 1994 .

[18]  L. Kogarko,et al.  Alkaline rocks and carbonatites of the world , 1995 .

[19]  Simone Sterlacchini,et al.  3D reconstruction of complex geological bodies: Examples from the Alps , 2009, Comput. Geosci..

[20]  Jean-Laurent Mallet,et al.  Discrete smooth interpolation in geometric modelling , 1992, Comput. Aided Des..

[21]  Teresa E. Jeffries,et al.  XENOTIME-(Y) FROM CARBONATITE DYKES AT LOFDAL, NAMIBIA: UNUSUALLY LOW LREE:HREE RATIO IN CARBONATITE, AND THE FIRST DATING OF XENOTIME OVERGROWTHS ON ZIRCON , 2008 .

[22]  R. Klemd,et al.  Magmatic loading in the proterozoic Epupa Complex, NW Namibia, as evidenced by ultrahigh-temperature sapphirine-bearing orthopyroxene–sillimanite–quartz granulites , 2007 .

[23]  N. Cook,et al.  Mineral chemistry of Rare Earth Element (REE) mineralization, Browns Ranges, Western Australia , 2013 .

[24]  David J. Sanderson,et al.  A new 3D geological model and interpretation of structural evolution of the world-class Rio Tinto VMS deposit, Iberian Pyrite Belt (Spain) , 2015 .

[25]  M. Andersson,et al.  Unravelling the internal architecture of the Alnö alkaline and carbonatite complex (central Sweden) using 3D models of gravity and magnetic data , 2017 .

[26]  J. Mallet.  GOCAD: A Computer Aided Design Program for Geological Applications , 1992 .

[27]  G. Calas.  Mineral Resources and Sustainable Development , 2017 .

[28]  Guillaume Caumon,et al.  Three-Dimensional Implicit Stratigraphic Model Building From Remote Sensing Data on Tetrahedral Meshes: Theory and Application to a Regional Model of La Popa Basin, NE Mexico , 2013, IEEE Transactions on Geoscience and Remote Sensing.

[29]  A. Williams-Jones,et al.  Hydrothermal Mobilisation of the Rare Earth Elements – a Tale of “Ceria” and “Yttria” , 2012 .

[30]  Matteo Massironi,et al.  3D fold and fault reconstruction with an uncertainty model: An example from an Alpine tunnel case study , 2008, Comput. Geosci..

[31]  George J. Simandl,et al.  Carbonatites: Related ore deposits, resources, footprint, and exploration methods , 2018, Applied Earth Science.

[32]  C. Passchier,et al.  Brittle reactivation of ductile shear zones in NW Namibia in relation to South Atlantic rifting , 2015 .

[33]  E. Schetselaar.  Mapping the 3D lithofacies architecture of a VMS ore system on a curvilinear-faulted grid: A case study from the Flin Flon mining camp, Canada , 2013 .

[34]  D. Nel,et al.  3D implicit modeling of the Sishen Mine: new resolution of the geometry and origin of Fe mineralization , 2018, Mineralium Deposita.

[35]  Pär Weihed.  3D, 4D and Predictive Modelling of Major Mineral Belts in Europe , 2015 .

[36]  D. Green,et al.  An experimental determination of primary carbonatite magma composition , 1988, Nature.

[37]  Olivier Kaufmann,et al.  3D geological modelling from boreholes, cross-sections and geological maps, application over former natural gas storages in coal mines , 2008, Comput. Geosci..

[38]  KaufmannOlivier,et al.  3D geological modelling from boreholes, cross-sections and geological maps, application over former natural gas storages in coal mines , 2008 .

[39]  Gus Gunn,et al.  Evidence for dissolution-reprecipitation of apatite and preferential LREE mobility in carbonatite-derived late-stage hydrothermal processes , 2016 .