Mineralium Deposita

, Volume 45, Issue 5, pp 443–460 | Cite as

The Kabanga Ni sulfide deposits, Tanzania: II. Chalcophile and siderophile element geochemistry

Article

Abstract

The Kabanga deposit constitutes one of the most significant Ni sulfide discoveries of the last two decades (indicated mineral resource 23 Mt of ore at 2.64% Ni, inferred resource 28.5 Mt at 2.7% Ni, November 2008). The sulfides are hosted by predominantly harzburgitic and orthopyroxenitic intrusions that crystallized from magnesian basaltic and picritic magmas. However, compared with other sulfide ores that segregated from such magmas (e.g., Jinchuan, Pechenga, Raglan), most Kabanga sulfides have low Ni (<1–3%), Cu (∼0.1–0.4%), and PGE contents (≪1 ppm), high Ni/Cu (5–15), and low Ni/Co (10–15) and Pd/Ir (2–20). Sulfides with higher metal contents (up to ∼5% Ni, 0.8% Cu, 10 ppm PGE) are found in only one unit from Kabanga North. The observed metal contents are consistent with segregation of magmatic sulfides from fertile to strongly metal-depleted magmas, at intermediate to very low mass ratios of silicate to sulfide liquid (R factors) of approximately 10–400. Sulfide saturation was triggered prior to final emplacement, by assimilation of up to 50% of the total sulfur in the intrusions from sulfide-bearing metasedimentary country rocks. Immiscible sulfide liquid was entrained by the magma and ultimately precipitated in dynamic magma conduits that formed tubular and sill-like mafic–ultramafic bodies characterized by abundant magmatic breccias, highly irregular layering, and frequent compositional reversals. The unusually large degree of crustal contamination and the low R factors render Kabanga an end-member in the spectrum of magmatic Ni sulfide ores.

Supplementary material

126_2010_283_MOESM1_ESM.pdf (20 kb)
Fig. 1S contents plotted vs. height in the MNB and Kabanga North intrusions. Note that both intrusions show a broad trend of progressive decrease in S with height. (PDF 20 kb)
126_2010_283_MOESM2_ESM.xls (137 kb)
Table 1Concentrations of S and chalcophile elements in Kabanga and Luhuma rocks (XLS 137 kb)
126_2010_283_MOESM3_ESM.xls (34 kb)
Table 2Results for in-house and international reference materials (XLS 34 kb)

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Copyright information

© Springer-Verlag 2010

Authors and Affiliations

  1. 1.Department of GeologyUniversity of OuluOuluFinland
  2. 2.Sciences de la TerreUniversité du Québec à ChicoutimiChicoutimiCanada

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