Nickel Prospect Research Articles

Tokapal Tuff-facies Kimberlite, Bastar Craton, Central India: A Nickel Prospect?

Abstract We report the occurrence of garnierite (a general term referring to Ni-Mg bearing hydrous silicates in laterites) from the crater-facies Tokapal kimberlite of the Bastar craton, Central India. Garnierite occurs as discrete ovoid or amoeboid segregations (up to 200 mm) or as veinlets with up to 18.1 wt% NiO and high iron contents (up to 36.2 wt% FeOT). Chemical composition of the garnierite implies its derivation from a magnesium-rich protolith. Extensive lateritisation of the large crater-facies (∼2.5 km diameter) saucer-shaped kimberlite under tropical weathering conditions, aided by suitable topography, drainage and favourable structural set-up, are the factors inferred to be responsible for the formation of garnierite in the Tokapal system. As lateritic nickel ores constitute significant resources for nickel exploration, the perspective of the Tokapal kimberlite as a nickel prospect needs to be investigated.

Sulfides and Sulfarsenides from the Rosie Nickel Prospect, Duketon Greenstone Belt, Western Australia

Recent exploration in the Duketon greenstone belt, Yilgarn craton, Western Australia, led to the discovery of a new occurrence of high-grade Ni-PGE (platinum group element) sulfide mineralization associated with komatiite; this is referred to as the Rosie Ni Prospect. The mineralization consists predominantly of disseminated and brecciated semimassive to massive base metal sulfide with 0.5 to 5 cm thick sulfarsenide-bearing lenses. This pilot study focuses on the petrology, mineralogy, and trace element mineral chemistry of sulfides and sulfarsenides, and the mineralogy of minor PGE-rich minerals (sperrylite, melonite, and bismuthotel-lurides) in selected samples representing different parts of the orebody, with a particular emphasis on the sulfarsenide-rich lenses. Our mineral chemistry and mineralogical studies indicate that As-rich phases (either as a melt or as primary minerals) played a critical role in collecting and concentrating PGEs from the komatiitic magma. The concentrations of trace elements within the sulfarsenides and sulfides from the different mineralization types reflect the interaction between the silicate and sulfide liquids. The concentration of PGEs in the As-rich minerals is a function of the volume of sulfide melt with which they have interacted. The smaller the proportion of the sulfarsenide relative to sulfide in the rock is, the higher the PGE concentration in the sulfarsenide will be. In situ Se analysis of the base metal sulfides from the different ore types indicates that Se concentrations in pentlandite and pyrrhotite from sulfarsenide-rich lenses are an order of magnitude higher than those of sulfides found in As-poor samples. This correlation between the Se concentrations in the sulfide minerals and the As concentration in the whole rock indicates that the processes which led to As enrichment at Rosie also contributed to Se enrichment. The particular As-Se enrichment is inferred to have been triggered by the erosion and assimilation of sulfidic sediments enriched in organic matter (now observed as shales and/or black shales) by the komatiitic magma flows, leading to the formation of immiscible S-As-rich melt, where PGEs partition preferentially into the As-rich phases.

Horses for (conductive) courses: DHEM and DHMMR

A test drillhole magnetometric resistivity (DHMMR) survey has recently been carried out at a nickel prospect in Western Australia to compare the effectiveness of this relatively new method with that of drillhole electromagnetics (DHEM), which is routinely used for nickel sulphide exploration.The DHMMR clearly defined a zone of shallower matrix sulphides which were only weakly detected by some of the earlier DHEM surveys (and then only in hindsight). In contrast, the DHMMR only weakly responded to the massive sulphides that had been well defined by the DHEM. Thus, these two methods can be considered, at least for this type of target, as complementary methods, with the DHMMR responding well to bodies with a relatively large cross-sectional area and DHEM to bodies of much larger long-sectional area. Although usually of lower grade, the matrix sulphides at this prospect, with their larger cross-sectional area and hence bigger tonnage, may make a more attractive economic proposition.

Variability of magmatic sulphide compositions at the Kabanga nickel prospect, Tanzania

Magmatic NiCu sulphide deposits are often geometrically and compositionally complex, and it is important to understand this complexity at an early stage of their economic evaluation. The Kabanga Ni prospect in Tanzania consists of two deposits associated with cumulate-textured ultramafic intrusions. The Ni occurs in a typical magmatic sulphide assemblage of pyrrhotite-pentlanite-chalcopyrite-pyrite and magnetite, with net-textured, disseminated and massive textures. The sulphides occur as layers within, and at the lower boundary of small, elongate transgressive olivine-pyroxene cumulate bodies, which were derived from a high Mg basaltic magma. Different layers within the intrusions have distinct sulphide geochemistry, with Ni tenor varying from 0.5 to over 20% in 100% sulphide. Generally, the lowermost layers have higher metal tenors, higher Ni Cu , and lower S Se ratios than the upper ones, suggesting a temporal evolution of sulphide chemistry. These trends suggest that the earliest sulphide melts separated from a primitive basaltic melt with a relatively high ratio of silicate to sulphide melt ( R factor). Later sulphides separated from a more fractionated silicate melt with a lower R factor, implying an increasing contribution of sedimentary sulphide by wall rock assimilation during fractionation in a lower magma chamber.

Geochronological constraints on the age of komatiites and nickel mineralisation in the Lake Johnston greenstone belt, Yilgarn Craton, Western Australia

SHRIMP U‐Pb zircon geochronology has been carried out on two volcanic units from the Maggie Hays nickel prospect. A sample from the footwall to the komatiites that host the nickel mineralisation gives an age of 2921 ± 4 Ma, whereas a sample from the hangingwall gives an age of 2903 ± 5 Ma. These results constrain the age of the primary nickel mineralisation and the host komatiites.

Geology and ore deposits of the Dillon nickel prospect, southwestern Montana

The Dillon Nickel Prospect is 23 miles southeast of Dillon, Montana, where a pre-Cambrian ultramafic complex about four and one-half miles long and one mile wide has intruded pre-Cambrian gneiss and schist of the Cherry Creek series. The complex is composed of saxonite, peridotite, nickeliferous serpentine, and related rocks. The chief nickel-bearing mineral is annabergite, found only as incrustations restricted to one intermediate phase of the saxonite. No sulphides were found other than a small amount of pyrrhotite and pentlandite, in a small body of gabbro on one claim. The gabbro assays 0.003 to 0.09 per cent nickel and the ultramafic complex proper 0.15 to 1.25 per cent.There is large amount of low-grade nickel silicate ore, but the economic possibilities of the annabergite outcrops can only be determined by further prospecting. The area is within easy access to the railroad at Dillon and from the writer's study merits further prospecting.

The Hodges nickel prospect, Torrington, Connecticut

The Hodges nickel prospect, Torrington, Connecticut