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Oct 2004 - Fluorescent Minerals

Using fluorescent minerals to identify ore mineralisation

The use of fluorescent minerals to identify fluorspar and scheelite is known by those mining it. However, it is the first time that I have encountered it being used as an industry standard technique to identify gold and other ore mineralisation in drill-core and underground, which is what I encountered when recently visiting Dragon Mining’s gold mine operations in Finland.

The ability of minerals to fluoresce or emit light when under ultra-violet (uv) light was first observed in fluorspar which gave rise to the name. It relates to the uv light (usually short-wave, though long-wave is also used) causing certain electrons in a mineral to jump to a higher energy level and release a usually vivid colour particular to that mineral when the electrons jump back down again.

The subject of fluorescent minerals was not covered when I was at uni over 30 years’ ago, and tended later to be more something that could be seen as a feature in the geological section of a museum. However, the study and collection of fluorescent minerals has grown, especially in North America, in the past 5 or 6 years and there is a whole suite of minerals that are capable of fluorescing as can be seen in the following web reference (//minerals.galleries.com/minerals/fluotabl.htm).

On a visit to Dragon’s operations in Finland in mid-September 2004, I saw it being used underground at Pampalo in south-eastern Finland to identify the host rock boundaries for the gold mineralisation by using light blue-grey fluorescing scheelite (scheelite and gold apparently have a good correlation).

It is also being used at their Vammala operation in south-western Finland using blue fluorescing scheelite at their Jokisivu prospect, and yellow fluorescing andalusite in drill core (viewing the core in a windowless room) at their new Sarvisuo orebody at Orivesi. It was also used to identify each of the original 5 pipes of mineralisation at Orivesi all with their own fluorescent minerals such as blue fluorescing lazulite in one of the pipes as shown in Figure 1.

The gold mineralisation at Orivesi is in a 1.9bn year-old east-west trending greenstone belt called the Tampere schist belt, while Jokisivu is in a migmatite (caused when one rock is squeezed into another rock) south of the Tampere schist belt. Pampalo’s gold mineralisation is in an Archaean mafic/ultramafic greenstone belt called the Hattu schist belt with felsic porphyrys. The use of fluorescence was regarded as a standard industry technique to identify mineralisation in Finland.

The cost of uv torches has apparently dropped significantly to only $50 to $60 or so, and care has be taken not to look directly at short-wave as it can apparently cause blindness, hence for that reason some prefer to use long-wave.

Perhaps there are other applications of using fluorescent minerals and it could become a recognised technique to identify ore mineralisation in Australia too.

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 Authorised Representative with Taylor Collison Ltd, and with his associates, holds interests in 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. Fluorescent Minerals from the Vammala Region of FinlandGDNoct04

  • Written by: Keith Goode
  • Friday, 01 October 2004