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Exploration, Discovery, and Geology of the Ntaka Hill Nickel Sulfide Deposits: A Potential New Proterozoic Nickel District in the Nachingwea Area, Mozambique Belt, Tanzania

By
P. A. Tirschmann
P. A. Tirschmann
Continental Nickel Limited, 114 Lakeshore Road East, Suite 202, Oakville, Ontario, Canada L6J 6N2 ptirschmann@continentalnickel.com
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C. S. MacDougall
C. S. MacDougall
Continental Nickel Limited, 114 Lakeshore Road East, Suite 202, Oakville, Ontario, Canada L6J 6N2 ptirschmann@continentalnickel.com
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G. R. Katchen
G. R. Katchen
Continental Nickel Limited, 114 Lakeshore Road East, Suite 202, Oakville, Ontario, Canada L6J 6N2 ptirschmann@continentalnickel.com
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Published:
January 01, 2010

Abstract

The Ntaka Hill nickel sulfide deposits are hosted in the peridotitic to pyroxenitic Ntaka ultramafic intrusion located in the Nachingwea area and are the first significant occurrence of nickel sulfides in the Tanzania portion of the Late Proterozoic Mozambique belt. High-grade nickel sulfide mineralization was first discovered at Ntaka Hill in 2006. Six near-surface sulfide deposits have since been delineated containing a measured and indicated mineral resource of 1.8 million tonnes (Mt) @ 1.82 percent Ni and 0.31 percent Cu. The recent discovery history can be traced back to the presence of a historic surface copper oxide malachite showing. Subsequent soil sampling defined a large coincident Ni-Cu anomaly that provided the impetus for airborne and ground geophysical surveys and ultimately diamond drilling leading to the initial discovery. Further ground electromagnetic surveys were successful in defining additional moderate to high conductance anomalies resulting, upon drill testing, in the discovery of five additional nickel sulfide zones.

The Ntaka intrusion is postulated to have formed from a relatively primitive, high MgO magma, dominated by the crystallization and accumulation of olivine and pyroxene. The intrusion is characterized by high MgO contents, low CaO, Al2O3, Cu, PGE, and incompatible element contents, and relatively flat chondrite-normalized REE profiles lacking Eu anomalies. The geologic setting is similar to that of the Early Proterozoic Thompson Nickel belt in Canada. There supracrustal rocks formed on a continental margin platform and were intruded by ultramafic sills that interacted with the sulfidic metasedimentary rocks to produce the resulting nickel deposits.

The Ntaka Hill sulfide zones occur in separate south-plunging lenses but may represent remnants of a dismembered original basal sulfide zone. The zones consist of magmatic, remobilized, and graphite-bearing mineralization with variable nickel grades of as much as 17 percent. Mineralization consists of disseminated, net-textured, and massive magmatic sulfides, as well as remobilized semimassive and massive sulfide veins and stringers composed of pyrrhotite, pentlandite, pyrite, chalcopyrite, and violarite. Pentlandite is the main nickel-bearing sulfide mineral occurring as coarse grains and eyes that are as large as 5 cm in diameter. Pyrrhotite-rich, nickel-poor, graphite-bearing, disseminated to massive sulfide mineralization occurs at several locations within the Ntaka intrusion and is thought to have formed by assimilation of graphitic metasedimentary rocks.

The Ntaka intrusion possesses a number of elements critical to the formation of nickel sulfide deposits and good potential exists to discover additional nickel sulfide deposits, both in the Ntaka Hill area and regionally. Exploration challenges in this underexplored belt include a complex deformation history, an abundance of graphitic metasedimentary rocks, and a paucity of outcrop.

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Contents

Special Publications of the Society of Economic Geologists

The Challenge of Finding New Mineral Resources: Global Metallogeny, Innovative Exploration, and New Discoveries

Richard J. Goldfarb
Richard J. Goldfarb
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Erin E. Marsh
Erin E. Marsh
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Thomas Monecke
Thomas Monecke
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Society of Economic Geologists
Volume
15
ISBN electronic:
9781629490403
Publication date:
January 01, 2010

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