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Jul 2009 - Dykes & Faults

Dykes and Faults can be an Opportunity

We all know the theory, a dyke gets injected in a weakness in the earth, sometimes there are dyke swarms. Occasionally a dyke and/or mineralisation is injected along a fault – and in general they are regarded as a nuisance.

However, in the last three reports ERA has written so far this year to June 2009 (Apex, Silver Lake and Panoramic), the presence of dykes and/or faults has had a significant influence on their adjacent mineralisation. At Apex, the almost north/south main east and west faults contain most of the mineralisation, with successive ore shoots (reminiscent of Gympie’s Inglewood structure) or patterns of mineralisation that appear to replicate or shadow across the fault structures.

Keeping within gold, something happens with that major dyke at Daisy- Milano, remobilising the gold such that south of the barren 30m wide almost vertical dyke (that occurs ~1bn years later than the main gold mineralisation) on the 21 and 23 Levels (that we have seen) are those 6kg/t intervals.

To dub it as gold remobilisation with a bit of heat, seems to be an oversimplification. However, nickel sulphide can be just as fluid as we saw once at Independence’s Lightning (Long) nickel mine where it had flowed around angular blocks of basalt. The old Long mine was renowned for the difficulties caused by the ~7 phases of cross-cutting porphyry dykes, although it was also often remarked that the nickel grades often improved in the region of a number of the porphyries.

Previously when a horizontal dyke was encountered in a gold or nickel orebody, it was perceived as truncating the orebody, whereas often now, the orebody continues on the other side of the dyke or intrusion – as has also been seen at Western Areas.

At Panoramic’s Savannah nickel mine in northern WA, there is a smear of nickel sulphide just where you would expect it to be (on the edge of the dyke) if it was remobilised, as shown in Figure 1. The continuation of the drillhole (KUD810), intersected the main orebody about 20m further down hole with the ~3.3m of massive nickel within a ~10m thick mineralised interval.

The presence of the horizontal dyke is significant because the Savannah orebody appears to have rotated slightly and moved horizontally fault-wise back towards the east, as identified by the position of the northern ore zones (NOZ) ’s “spine” (that juts out northwards from the east-west striking main ore zone (MOZ)).

The behaviour of nickel mineralisation at Savannah also changes according to the major faults, with the higher grade (~2% to 3%) nickel, (compared to the average 1.2% to 1.4%Ni) apparently moving out of the MOZ above the 500 fault and into the NOZ below the 500 fault with the “T-bone” formation where the two ore zones meet/intersect, becoming stronger at depth.

Possibly it is due partly to Savannah being horizontally domained or the sub-horizontal injection of its nickel mineralisation, but another significant change to the nickel mineralisation appears to be that above the coincidental dyke/fault the massive nickel tended to have waste inclusions, whereas now (below the dyke) it appears to more closely resemble Kambalda-looking massive.

While at Panoramic’s Lanfranchi Nickel mines’ Deacon, the shear size of Deacon and its infill drilling has identified more faulting than was originally perceived at Lanfranchi, being both north/south striking and east-west striking. The north-south striking faults actually appear to control most of Deacon’s embayment formation, and as Helmut South in fact appears to lie on a fault on the eastern side of Deacon, there is now an exploration targeted “West Wing” or western side of Deacon’s embayment that may have been mainly formed due to a fault.

However, Deacon is also east-west major step faulted, sometimes with downthrows up to 50m (based on the base plane/keel of the orebody), which then raises the question as to just what lateral extent these step faults have, and whether some of the truncated downward extensions of Lanfranchi’s orebodies such as Skinner etc, actually terminated in downthrown faults. And of course there are those relatively high grade Helmut footwalls being mined using air-legs in the faulted “gap” area between Helmut and Helmut South.

There is in fact some major east-west step faulting throughout the Kambalda- Widgiemooltha region as has been seen at the original Silver Lake nickel mine at Kambalda and at Mincor’s Miitel mine at Widgiemooltha.

So instead of perceiving faults and dykes as a nuisance, it appears that they should instead be viewed as a possible opportunity.

Disclosure and Disclaimer: This article has been written by Keith Goode, the Managing Director of Eagle Research Advisory Pty Ltd, (an independent research company) who is an a Financial Services 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. One of Panoramic’s Savannah Mines’ June 2009 Deep / Lower Zone drillholes (KUD810)GDNjul09

  • Written by: Keith Goode
  • Wednesday, 01 July 2009

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