Abstract
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.
Highlights
Rutile is a common metamorphic rock forming mineral that crystallizes in wide range of temperature and pressure, significant for petrogenetic studies (Myron, 2003; Zack et al, 2004a; Xiong et al, 2005; Meinhold et al, 2008; Luvizotto & Zack, 2009)
Given the important role played by rutile, we present in this paper, the geochemical feature of greyish-black rutile megaclasts from this ore minerals deposition in other to contribute to its characterization and determine its origin
A total of nineteen greyish-black rutile megaclasts from the Nsanaragati gem placer deposit were morphologically examined at the laboratory of Applied Geology-Metallogeny, Department of Earth Sciences, University of Yaoundé I, Cameroon
Summary
Rutile is a common metamorphic rock forming mineral that crystallizes in wide range of temperature and pressure, significant for petrogenetic studies (Myron, 2003; Zack et al, 2004a; Xiong et al, 2005; Meinhold et al, 2008; Luvizotto & Zack, 2009) This mineral crystallizes mostly in high grade metamorphic rocks: eclogites (Zack et al, 2002; Miller et al, 2007), some granulites and gneisses (Stendal et al, 2006; Meinhold, 2010); but can be found in some low grade metamorphic rocks: blueschist and greenschist (Meinhold, 2010). Given the important role played by rutile, we present in this paper, the geochemical feature of greyish-black rutile megaclasts from this ore minerals deposition in other to contribute to its characterization and determine its origin
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