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Jul 2007 - Nickel Lava Channels

Divergent Nickel Lava Channels

Sally Malay’s recent discovery of the Deacon orebody (probably >60,000t Ni @ at Lanfranchi @ 2.6%Ni, being still open at depth with intersections of 93m @ 2.24%Ni & 72m @ 2.95%Ni), appears to be another diverging nickel lava channel, raising the question as to whether they are more common than envisaged.

Please note that this column has been drawn purely from observations and has applied some generalisations that may not conform to the accepted nickel geological theory at Kambalda.

The komatiite nickel deposits of the Kambalda and Widgiemooltha nickel fields can be described as being analogous to flowing rivers of nickel-rich lava. There appears to have been a number of these almost parallel north-south (actually more NNE/SSW) flowing rivers of lava through the Kambalda and Widgiemooltha regions.

The uplift of 3 domes resulted in the main deposits of Kambalda (now mainly owned by Independence (IGO), Mincor (MCR) and Consmin (CSM) from a dome with a north-south axis), Widgiemooltha (now mainly owned by MCR and CSM also from a dome with a north-south axis), and Tramways or Lanfranchi (now owned by Sally Malay (SMY) in a 75%/25% JV with the TSX listed Brilliant Mining from a dome with an east-west axis).

The Kambalda and Widgiemooltha N/S striking domes caused the lava rivers or channels to be disrupted and wrap around them with rivers that flowed over the central axis becoming generally almost vertical at each end. While at Lanfranchi, they wrap over the lateral east-west dome (or domes) and may be on the northern underside of the dome too.

Looking at the figure, the resulting nickel orebodies do uncannily resemble frozen rivers flowing down mountain sides of yellow basalt, which opens for debate the timing of when in the formation/solidification of the lava channels, that the domes uplifted.

The first diverging nickel lava channel that we (ERA) saw was at Consmin’s Beta-Hunt mine between the 20 and 40 surfaces (shown inset in the figure), where the 40 surface appears to have been diverted around an object and later link with the 20 surface deeper (or lower) down. It can be seen that there appears to be an oblique initial link between the 20 and 40 surfaces and hence drilling on the line of strike of the channel could interpret that the channel was truncated whereas instead it probably obliquely links to another nickel orebody (or lava channel). The lower link between the channels is the one that has been mapped and intersected as shown.

Similarly at Lanfranchi, drilling to define the limit of the Helmut South orebody, instead found a link with the intersections in October 2007 of 91m @ 2.3%Ni and 111m @ 2.9%Ni (from 67m to 178m downhole, including 11m @ 4.3%Ni [132 to 143m] and 6m @ 7.6%Ni [169 to 175m]), which are unheard of intersections in the Kambalda nickel fields. Examining the drillhole values and core show steady continuous lengths of matrix nickel mineralisation grading ~2% to 4%Ni with massive nickel mineralisation up to ~10%Ni.

The upper link from Deacon has yet to be delineated but it could obliquely link to Helmut South. At this stage Deacon/Helmut South does remain open at depth with intersections such as 93m @ 2.24%Ni & 72m @ 2.95%Ni near the resource boundary, and some even more spectacular ones such as 33m@ 4.7%Ni higher up.

Before Deacon had been discovered the often made comment was that “all we need to find is another Skinner”. Skinner was a small high grade orebody that was discovered by accident by WMC developing around the Schmitz orebody and was responsible for the bulk of Lanfranchi’s 13,700tNi @ 5.3%Ni that was produced in 2000. Generally believed to be simply “there”, and truncated both north and south, it could in fact obliquely link to the Schmitz orebody at its upper and lower extremities.

The perceived faulted lower block at Winner may also hence not be faulted at all, and instead it may be part of a divergent channel. (In fact as a general observation aside from the major lateral east-west fault at Beta-Hunt we (ERA) have seen little east-west fault displacements in the Kambalda/Widgiemooltha nickel mines; instead the faulting mainly appears to be north-south drop down faults).

On an even grander scale for divergent lava channels may be even Schmitz and Deacon/Helmut South link at depth. Looking at plans and 3d modelling it does appear to be possible.

Also interesting is that all these divergences have been on the western side of the perceived main lava channel. Whether that is coincidentally due to the river analogy on the side of a hill and hence for orebodies such as IGO’s Long/Victor and MCR’s Miitel infer that any possibly divergent channels they have would be east of their orebodies, or whether Lanfranchi consists of two separate domes is a matter for geological debate.

The discovery of two instances of diverging lava channels at two different nickel fields (being Lanfranchi and Kambalda), raises the question as to whether there are more and whether they are more common than previously envisaged. It also raises the question as to whether they should be considered as part of an exploration programme wherever there are nickel lava channels, possibly following from detailed 3d reconstruction of the basalt/ultramafic interface.

Disclosure and Disclaimer : This article has been written by Keith Goode, the Managing Director of Eagle Research Advisory Pty Ltd, (ERA, an independent research company) who is an Authorised Representative with Taylor Collison Ltd, and with his associates, may hold interests in some of the stocks mentioned in this article. The opinions expressed in this article should not be taken as investment advice, but are based on observations by the author. The author does not warrant the accuracy or completeness of any information and is not liable for any loss or damage suffered through any reliance on its contents.

Figure 1. Diverging Nickel Lava Channels at Lanfranchi, and inset at Beta-HuntGDNjul07

  • Written by: Keith Goode
  • Sunday, 01 July 2007

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