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Nov 2017 - High Grade Thrusts

Some Orebodies may have two High Grade Plunge Directions

The following comments are based purely on observation, but to some degree what started this was my observation that an old black & white section by Dominion through Meekatharra closely resembled that of its section through the Westralia pit of Mt Morgans.

Some orebodies may have two high grade plunge directions
The following comments are based purely on observation, but to some degree what started this was my observation that an old black & white section by Dominion through Meekatharra closely resembled that of its section through the Westralia pit of Mt Morgans.

Dacian discovered multiple shallow angled (~20 to 30 degrees) north dipping thrusts controlling the high grades compared to the steep south dipping ore shoots that have been historically mined in the Westralia pit as per ERAs 2016 Dacian report (see : www.eagleres.com.au /images/pdfs/reports/2016/dcn25jul16v2.pdf). The north dipping thrusts can in fact now (2017) be seen in the sidewall of the dewatered Westralia pit, plus the steep angles in the opposite direction.

Meekatharra's ore shoots also dipped steeply north, and hence the sections appeared similar, so when I saw Westgold (WGX) as part of writing a report on them, I remarked as to whether they had considered the possibilty of shallow dipping thrusts in the opposite direction, ie south. Westgold remarked that they had in fact discovered them about one month ago in the underground development of the Prohibition (Vivan-Consols) orebody on 3 levels at Paddy's Flat, encountering higher grades where they were not expected.

Subsequent drilling identified the thrusts and consequently WGX made the announcement of intercepts up to 438g/t on 16 October 2017, being the day I walked into their new Perth offices. WGX are in fact mining those thrusts by air-leg, which are subtle and it can be seen how they were historically missed.

As shown in the figure, the geos could not find the visible gold (grading ~ 200g/t to 400g/t). Even viewing the drillcore we initially thought "have we got the right piece". That is until the sun glinted on the drillcore, and it appeared that someone had somehow sprinkled gold dust down the drillcore and it had sunk into the quartz and hence had a grade of ~1200g/t. Being in the lamination, when viewed side on, it was not obviously visible either in core or underground, despite its grade.

However, the two opposing angles on strike appeared to be an incredible coincidence, and thinking back to the Macphersons four page report I/ERA wrote in August 2017 (www.eagleres.com.au /reports/item/aug-2017-macphersons-res) that has multiple north dipping shallow thrusts compared to the steeper south dipping ore zones (in Boorara South).

So armed with such knowledge, I began to look for two opposing angles of possibly higher grade mineralisation in open-cuts, and the same can be seen in the old Caledonian pit at Nannine (south of Meekatharra), ie steep north and shallow south.

Interestingly subsequently visiting HBJ (the old New Celebration/Jubilee) pit of Westgold's SKO operation, it was remarked that there appeared to be two opposing steeply dipping directions there - and that had been encountered in underground development on two levels.

Examining Figure 4a of our/ERA's report on Draig's Bellevue (www.eagleres.com.au /reports/item/oct-2017-draig-resources-limited) it is not too hard to infer low angled high grade parallel thrusts dipping south, and possibly higher grade shoots also dipping steeply north.

Having just completed an IPO summary (late November 2017) for BC8 (the Black Cat Syndicate) currently expected to IPO in early December 2017, it was interesting to read that the Main Lode in the Queen Margaret (QM) Mines at Bulong plunged south while the adjacent East Lode plunged north (the lodes are separated by albite alteration).

More detail on the IPO should be available on the BC8 website (www.blackcatsyndicate.com.au) and my/ERA summary should become available on the eagleres.com.au website. The QM Mines area is one of those unloved, forgotten areas near Kalgoorlie that has remained dormant for over 100 years, while explorers have gallavanted the world searching for orebodies.

Quite amazingly, QM Mines in its day was renowned for discovering 100oz to 400oz "slugs" of pure gold and occasionally grades of 70oz/t were mined. Even as recently as 2001, Anglogold walked away from BC8's Bulong Project area, describing it as potentially a narrow-vein high-grade Kundana look-alike which failed to meet Anglogold's (then) expectations, along with intersections of 3m @ 31.4g/t, 2m @ 38.4g/t, 9m @ 9.3g/t & 10m @ 7g/t at the Anomaly 38 prospect.

However, returning to the high grade plunge directions, speaking recently to a colleague, they remarked that the two opposing high grade dip angles can also be seen at Northern Star's Jundee.

Which begs the question as to whether the two opposite high grade angled ore shoots on strike is just an Australian "thing", as in just peculiar to Australia ?

However, even if it is just Australia, the common practice of forcing orebodies to wireframe in one direction, should perhaps instead consider the possibility that the higher grades in their orebodies can plunge in two opposing directions at the same time.

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 (AFSL 247083).

Figure. Figure. The Super High Grade Thrusts at Paddy's Flat (Meekatharra October 2017)
Reading Old Workings

  • Written by: Keith Goode
  • Friday, 15 December 2017

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