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And Chromium Deposits Hosted in Ultramafic Rocks in the Islamic Republic of Mauritania: Phase V, Deliverable 67

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And Chromium Deposits Hosted in Ultramafic Rocks in the Islamic Republic of Mauritania: Phase V, Deliverable 67 Prepared in cooperation with the Ministry of Petroleum, Energy and Mines, Islamic Republic of Mauritania Second Projet de Renforcement Institutionnel du Secteur Minier de la République Islamique de Mauritanie (PRISM-II) Mineral Potential for Nickel, Copper, Platinum Group Elements (PGE), and Chromium Deposits Hosted in Ultramafic Rocks in the Islamic Republic of Mauritania: Phase V, Deliverable 67 By Cliff D. Taylor, Erin E. Marsh, and Eric D. Anderson Open-File Report 2013‒1280 Chapter G U. S. Department of the Interior U. S. Geological Survey U. S. Department of the Interior SALLY JEWELL, Secretary U. S. Geological Survey Suzette M. Kimball, Acting Director U. S. Geological Survey, Reston, Virginia: 2015 For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment, visit http://www.usgs.gov or call 1–888–ASK–USGS. For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprod To order this and other USGS information products, visit http://store.usgs.gov Suggested citation: Taylor, C. D., Marsh, E. E., and Anderson, E. D., 2015, Mineral potential for nickel, copper, platinum group elements (PGE), and chromium deposits hosted in ultramafic rocks in the Islamic Republic of Mauritania (phase V, deliverable 67), chap. G of Taylor, C.D., ed., Second projet de renforcement institutionnel du secteur minier de la République Islamique de Mauritanie (PRISM-II): U. S. Geological Survey Open-File Report 2013‒1280-G, 85 p., http://dx.doi.org/10.3133/ofr20131280. [In English and French.] Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U. S. Government. Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner. Multiple spellings are used in various literatures, and may be reflected in the text. This report is preliminary and has not been reviewed for conformity with U. S. Geological Survey editorial standards or for stratigraphic nomenclature. The report is being released in both English and French. In both versions, we use the French-language names for formal stratigraphic units. ISSN 2331-1258 (online) ii Contents 1 Summary ............................................................................................................................................................. 1 2 Introduction ......................................................................................................................................................... 2 3 Potential for Ni, Cu, PGE, and Cr Deposits in Ultramafic Rocks of Mauritania .................................................... 8 3.1 Mesoarchean Greenstone Belts of the Tasiast-Tijirit Terrane ...................................................................... 8 3.2 Ultramafic Bodies in the Amsaga Complex ................................................................................................ 16 3.3 Mesoarchean and Neoproterozoic Greenstones of the Inchiri District ....................................................... 31 3.4 Mesoarchean and Paleoproterozoic Mafic-Ultramafic Rocks and Annular Ultramafic Complexes of the Northeastern Rgueïbat Shield ......................................................................................... 43 3.4.1 Mesoarchean Mafic-Ultramafic Rocks of the Zednes Suite and Temmimichate Tsabya Complex ........... 43 3.4.2 Paleoproterozoic Mafic-Ultramafic Complexes of the NW Rgueïbat Shield .............................................. 49 3.5 Ophiolite of the Gorgol Noir Complex in the Southern Mauritanides .......................................................... 57 The Diaguili Occurrence .................................................................................................................................... 62 The Oudelemguil Occurrence............................................................................................................................ 64 The Ndiéo Occurrence ...................................................................................................................................... 65 The Hassi Chaggar Occurrence ........................................................................................................................ 65 The Diagiuli Chromite Occurrence and Other Small Occurrences in the Southern Mauritanides ...................... 66 3.6 Mafic-Ultramafic Sills, Dikes, Laccoliths, and Chimneys of Mauritania ...................................................... 70 4 Permissive Tracts for Ni, Cu, PGE, and Cr Deposits in Mafic-Ultramafic Rocks in Mauritania .......................... 75 5 Conclusions ....................................................................................................................................................... 79 6 References ........................................................................................................................................................ 79 Figures Figure 1. Generalized Ni-Co laterite profile: Idealized cross-section through a Ni-Co laterite weathered profile illustrating all the possible horizons.Natural profiles tend to be much more complex, containing variable sequences of any or all of the layers shown.Modified from Samama (1986) .................. 3 Figure 2. Simplified geologic map of the northwestern Rgueïbat Shield showing the Choum-Rag el Abiod and Tasiast-Tijirit terranes. The principal greenstone belts and mineral occurrences discussed in the text are shown (from Gunn and others, 2004). ...................................................................................... 11 Figure 3. A cross section of a weathered laterite profile from the Tasiast-Tijirit region showing the progressive weathering of the serpentinized peridotite host rock.Modified from Freyssinet (1994) ............. 14 Figure 4. Profile at Inkebden showing a geologic cross section of the sampling transect and the Ni (in green), Co (in blue), and Cu (in orange) geochemistry across the transect (modified from Dumas, 1971) ........................................................................................................................................................... 15 Figure 5. Generalized geology, reduced-to-pole (RTP), and analytic signal maps from the Tasiast-Tijirit region.The Khnefissat and Inkebden Ni-laterite occurrence are shown. A, The geology in the region consists of granodiorite, gneiss, mafic metavolcanic, metagabbro, and BIF. Dikes trending mostly north-northeast are also mapped in the region (black lines). B, The RTP map shows through-going, linear magnetic anomaly highs associated with the mapped dikes. Broader magnetic anomaly highs are associated with granodiorite and gneiss units. The linear north-northwest magnetic anomaly highs correlate with BIFs. Magnetic highs and lows are shown as warm and cool colors, respectively. C, The analytic signal map highlights the greenstone belt between the BIFs. Also shown are several, more isolated analytic signal highs that correlate with mafic metavolcanic, actinolite schist, and metagabbro units which are considered favorable parent rock for Ni-laterite deposits. Analytic signal highs and lows are shown as warm and cool colors, respectively ........................ 16 iii Figure 6. View along the margin of the Iguilid metagabbro massif ........................................................................... 20 Figure 7. View looking north at the Guelb el Foulet chromite occurrence ................................................................ 20 Figure 8. Thin section photomicrograph of sample CT07RIM-19-1 under 5x (left image) and 10x (right image) objectives in plane polarized light. Numbered red spots indicate EMPA sites. Both images show large black chromite grains with interstitial pyroxene and plagioclase.Circled area shows lath- shaped pyroxenes interstitial to chromite ..................................................................................................... 26 Figure 9. Thin section photomicrograph of sample CT07RIM-19-1 under 5x (left image) and 10x (right image) objectives in reflected light. Numbered red spots indicate EMPA sites. Both images show relatively unaltered light gray chromite grains with interstitial dark gray pyroxene and plagioclase. Minor small opaque grains are bright whitish-gray ...................................................................................... 27 Figure 10. Thin section photomicrograph of sample CT07RIM-21-1 under 10x objective in reflected light.Numbers indicate EMPA sites. Both images show relatively unaltered gray chromite grains with interstitial dark gray pyroxene and plagioclase. Distinctive light gray ferrit-chromite alteration rims are present around all grains and along cracks within grains............................................................... 28 Figure 11. Tectonic discriminant analysis based on electron microprobe data from chromites from the Guelb El Foulet occurrence. A. (Cr×100)/(Cr+Al) vs (Mg×100)/(Mg+Fe2+) plot. B. Ternary plot of Fe3+, Al, and Cr. C. TiO2 vs (100×Cr)/(Cr+Al) plot. Compositional fields and tectonic settings after Jan and Windley (1990), Arai (1992), and Arif and Jan (2006) .................................................................... 29 Figure 12. Generalized geology,
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