Greyish-Black Rutile Megaclasts from the Nsanaragati Gem Placer, SW Cameroon: Geochemical Features and Genesis

  •  Nguo Sylvestre Kanouo    
  •  Rose Fouateu Yongue    
  •  Shouyu Chen    
  •  Emmanuel Njonfang    
  •  Changqian Ma    
  •  Tanwi Richard Ghogomu    
  •  Jiangnan Zhao    
  •  Elise Sababa    


Greyish-black rutile megaclasts from the Nsanaragati gem placer in south western Cameroon display a wide range of lithophile and siderophile elements in LA-ICP-MS analyses. TiO2 abundances exceed 94 wt.%, with FeO (up to 4.2 wt.%), SiO2 (up to 1.5 wt.%) and Al2O3 (up to 1.8 wt.%) forming noticeable contents. Minor and trace elements with significant to moderate values (ppm) include Nb (965-4814), V (729-1846), Cr (495-756), Ta (44-180), and Zr (43-210). Nb/Ta ratios range between 10.0-44.9 and place the Nsanaragati rutile grains within the Niobium rutile. The measured contents for other elements including total REE are < 150 ppm, mostly falling below detection limits. Al2O3-MgO plots (wt.%) indicate that most rutile grains fall within a crust-derived rutile field, with rare plots in the mantle-derived field. Cr-Nb plots suggest the grains are related to rutile from metapelitic rocks, rather than metamafic rocks. Temperatures calculated from Zr in rutile thermometry range from 470 to 675°C, compatible with a likely crustal metapelitic source.

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  • ISSN(Print): 1916-9779
  • ISSN(Online): 1916-9787
  • Started: 2009
  • Frequency: semiannual

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