FW: [ai-geostats] Re: Geostats Scam?

Thu, 09 Feb 2006 05:02:06 -0800

Title: Message
4 times !
 
I guess my forwarded mail should be read by the rest of the list as well to avoid similar situations in the future.
 
Thanks
 
Gregoire
 
 
 From: Gregoire Dubois [mailto:[EMAIL PROTECTED]
Sent: 09 February 2006 13:32
To: 'Fran Manns'
Subject: RE: [ai-geostats] Re: Geostats Scam?

Fran,
 
I have received your message 3 times!
 
The ai-geostats mail server needs to redistribute your mail to more than 1000 people and it is not the only mailing list the server is hosting.
So please wait at least a few hours before sending your message again or contact me if you think there are problems with your postings.
 
Thank you for your cooperation
 
Gregoire (moderator of ai-geostats)
 
 

__________________________________________
Gregoire Dubois (Ph.D.)

European Commission (EC)
Joint Research Centre (JRC)
WWW: http://www.ai-geostats.org

"The views expressed are purely those of the writer and may not in any circumstances be regarded as stating an official position of the European Commission."

-----Original Message-----
From: Fran Manns [mailto:[EMAIL PROTECTED]
Sent: 09 February 2006 12:42
To: AI Geostats mailing list; Isobel Clark
Cc: J. E. Tilsley
Subject: Re: [ai-geostats] Re: Geostats Scam?

Isobel,
 
I keep in mind at all times that wonderful sentence in Clark (1979), "Systematic errors, be they sampling , analytical, or whatever, will not be picked up by geostatistics and will be transferred to any estimates produced." (p. 119) 
 
Isobel, this wisdom should be included in the disclaimer of any geostatistical report.  If one looks at the lead paper of the Australian Best Practices Volume (proper citation not available because I have misplaced the book).  More than 50% of gold deposits fail to achieve nameplate output in the first year of production due to grade shortfall (David Harquail, Graham Clow and and Australian masters thesis).  Then things improve, not from statistics, but using fudge factors(mine call factor, cutting, whatever). 
 
Mike Armitage, Managing Director of SRK, is on record in the SRK newsletter stating that the predictability of geostatistics is no better today than at any time in the past.  I took issue with Danie Krige in the SAJG for saying, in 2001, the framework of geostatistics included all the necessary elements and no further discoveries need be made. 
 
In my experience, the issue is sampling, splitting, analysis, and execution.  By the time a geological sample gets to a 30 gram aliquot, the likelihood of that 30 grams representing 1,000,000 grams of rock is probably compromised about 50% of the time.  So we respond, in ignorance, by taking thousands of samples.  In my opinion, 33 samples will suffice in am stope, giving two extra sample for more confidence. ... Need to take large enough samples to be representative though.  Got to avoid the systematic error of not having a representative sample for the region, deposit, stope, etc. 
 
I cringe when I see geostatistics applied to ground water projects or remediation projects, or astrophysics.  Ask yourself whether asteroid size distribution as sampled might suffer a 'nugget effect'.
 
Francis T. Manns, Ph.D., P.Geo. (Ont)
Artesian Geological Research
Toronto, Ontario
 
 
And the following sense from Jim Tilsley also need to be integrated....
Fran,
 
Questioning geo-stats is an advancement in understanding.  This is good for everyone and everything involved.
 
The point most overlooked in the 'equation' is the first half of the term. GEO!
 
I, as you know, have always objected to statistics being the main focus.  FIRST do the geology.  Then we may find that some sort of statistical treatment can be applied rationally.
 
As we have discussed before on many occasions, Kreiging works wonderfully on mature gold placers of the Wits.  The trouble comes in when attempts are made to apply it to another type of mineralized zone, one that has not been deposited under the same energy regime as the Wits.
 
There can be a relationship between grade - a parameter fraught with difficulties in the details - and relative position in respect to another grade, only when there is some sort of energy gradient that ties the two together - as in the paleo-placers for which the approach was developed.  Since the energy budget correlates with the distance from the centre of the channel, decreasing toward the limits of flow - (Hydraulics 101) detrital heavy mineral concentration can be expected to reflect the mechanical energy applied, and some sort of distance/grade relationship is plausible.
(The Carbon Leader gold mineralization is another matter, but if the algae mats acted as chemical traps and there was some difference in total flow (volume) from a 'channel' axis across the mats, one could expect to see a similar distribution  of values, but the geological controls and the difference in depositional environment must be considered.)
 
Statistics, in my experience, may be applicable in ore reserve estimation, (and will solve many problems if properly applied) providing they are used with due reference to the geological controls on deposition.  And this applies to mechanical and chemical mineralization systems equally.  The chemical systems are usually the more difficult to deal with.
 
Jim
----- Original Message -----
Sent: Wednesday, February 08, 2006 10:07 AM
Subject: [ai-geostats] Re: Geostats Scam?

And don't forget the 27 page article by Philip & Watson "Matheronian geostatistics - Quo Vadis?" in Mathematical Geology, vol 18, pp 93-117. 24 pages on what a confidence trick geostatistics is.
 
There are response letters in that volume and later volumes from members of the geostatistical community. A wonderful example of neither side listening. Bear in mind when you read this article that it was not refereed before publication.
 
In fact, this is a very good paper to illustrate the enormous difference which can occur when you approach a problem from a completely different direction.
 
What baffled me for a long time is that their argument is that where you have more data, you have more variability and therefore less confidence in your estimates. This seemed to me, set in my ways as a classical statistician as counter-intuitive. Some years later I was discussing a possible geostatistics study with a colleague who was a land surveyor when the penny dropped! P&W are geographers. They can SEE the surface they are trying to map. So they MAKE more observations where the land surface is more variable. Completely logical. Where they have fewer observations, it is because the surface is flat and they are confident in their estimates. And vice versa.
 
Matheron developed geostatistics, just as econometricians and statisticians developed time series analysis -- for surfaces and series which cannot be seen. More data does not mean less confidence in local variability, it just means more data.
 
As you said, Steve, if geostatistics does not make sense for your application or the results don't make sense in the context of you data, there are lots of other things you can do. And, if you are happy with using geostatistics, keep it simple!
 
Isobel
http://www.kriging.com/courses

Stephen Henley <[EMAIL PROTECTED]> wrote:
Hi Mach -

Jan Merks isn't the only one who has questioned the fundamentals of
geostatistics. You might also like to look at the work of Robert F. Shurtz.
Perhaps the most interesting is a slim volume published by the Mining &
Metallurgical Society of America, "A Geostatistical Monograph" (in 1997, I
believe, though the book isn't dated). This is in the form of a debate
between Robert Shurtz (criticising geostats) and Harry Parker (defending
geostats).

If you want alternatives to geostats, there are plenty on offer. Problem is,
of course, that after thirty-something years geostatistics has become the
'accepted wisdom' in the mining community, and you have an uphill struggle
to justify using any other method. Unfortunately, also, any geostatistical
practitioner who uses a fancy new nonlinear kriging method has much less of
a struggle even if that new method is little better than alchemy. Linear
kriging does actually have some nice mathematical properties if its
assumptions are satisfied and when used properly ('best linear unbiased
estimator' and all that) but what many users seem to forget is that, as soon
as they tweak the method, they lose some or all of these properties. In my
opinion many of the more exotic variants of kriging are worse than using
non-geostatistical methods because they encourage - wrongly - a belief that
they are in some ways superior simply because they are known as "xxxxx
kriging".

- Steve Henley

================================
Dr Stephen Henley
Resources Computing International Ltd
185 Starkholmes Road
Matlock, Derbyshire DE4 5JA, UK
+44(0)1629 581454
Skype: silicondale
[EMAIL PROTECTED]
================================


----- Original Message -----
From: "Mach Nife" <[EMAIL PROTECTED]>
To:
Sent: Tuesday, February 07, 2006 6:58 PM
Subject: [ai-geostats] Geostats Scam?


> Hi,
>
> This guy (Jan W Merks) seems to devote his life trying
> to prove that Geostatistics is a scam... If it's true
> I'm gonna start looking for alternatives.
>
> http://www.geostatscam.com
>
> Anyone has a point of vue on this?
>
> machnife
>
> __________________________________________________
> Do You Yahoo!?
> Tired of spam? Yahoo! Mail has the best spam protection around
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>


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