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Sep 2015 - Focusing Alteration

Exploration Focusing on Alteration

This month's Paydirt GMJ column has been based purely on observation as so far this year of the companies ERA has visited I have noticed an increasing trend focusing on alteration compared to conventional gold mineralisation in quartz or other host rocks.

At Dacian's Jupiter complex in WA, the historical interpretation appeared to have been distracted by the patterns of the syenite lacing across the rock, whereas Dacian instead identified that the controlling factor on grade appears to be alteration in the syenite (from darker mafic to lighter/whiter albite), and whether sulphides (eg pyrite) are present. The alteration of basalt to light brownish coloured albite surrounding cross-cutting veins is shown in the Figure from the sidewall between Joanne and Jenny (since renamed Doublejay). The veins cross through (ie are post) the syenite as shown in the Figure.

The influence of albite on grades is clearly shown at 28.3g/t and 16.6g/t in drillhole 13JUDD019, while alteration at 22.1g/t in the syenite can also be seen in drillhole 15JUDD047  (in Figures 20 and 21 on page 11 of ERA's 30 July 2015 Dacian report available on www.eagleres.com.au). The identification of the alteration has resulted in the current model at Heffernans as shown in the Figure (similar to Wallaby style mineralisation), together with the delineation of the Cornwall Shear Zone.

The 738koz resource at Heffernans as at the time of the report in July 2015 (like Jupiter before it), consisted of a high grade component (expected to be treated by CIL) of 9.8mt @ 1.74g/t (0.9g/t COG) for 548koz, and a low grade component (expected to be treated by heap leach) of 11.6mt @ 0.51g/t (0.3g/t to 0.9g/t) for 190koz. 

Just before Diggers in August 2015 we revisited Gold Road's Gruyere orebody.  Gruyere has now been interpreted as a porphyry. It does not resemble PXG's Castle Hill/Kintore tonalite or Gryphon's Nogbele granodiorite/tonalite, and instead appears to be an albite-altered monzonite porphyry with quartz-carbonate veining and sulphide mineralisation.

Gruyere can have higher values than the ~1.2g/t resource grade (of ~14.5g/t & 4.4g/t, or even visible gold as in Figure 2b on the front page of ERAs update visit report of 10 Sept 2015 available on www.eagleres.com.au. The higher grades appear to be associated with the degree of albite alteration.

Visiting Phoenix's prospects after Diggers one could not now help but notice some rocks / boulders in an old bund wall with veins showing alteration, that may have been overlooked.

The above are just 3 examples that I have so far seen this year, that possibly highlight alteration as an overlooked indicator of mineralisation.

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 a Financial Services Representative with Taylor Collison Ltd.

Figure 1: Alteration at Dacian's Jupiter and Gold Road's Gruyere Projects

fig1-sep15-altern

  • Written by: Keith Goode
  • Tuesday, 01 September 2015

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