Isobel et al,
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 -----
*From:* Isobel Clark <mailto:[EMAIL PROTECTED]>
*To:* Stephen Henley <mailto:[EMAIL PROTECTED]>
*Cc:* AI Geostats mailing list <mailto:[email protected]>
*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"
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
> http://mail.yahoo.com
>
>
--------------------------------------------------------------------------------
>* By using the ai-geostats mailing list you agree to follow
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>
> * To unsubscribe to ai-geostats, send the following in the
subject or in
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[EMAIL PROTECTED]
>
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--------------------------------------------------------------------------------
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----- Original Message -----
*From:* Isobel Clark <mailto:[EMAIL PROTECTED]>
*To:* Stephen Henley <mailto:[EMAIL PROTECTED]>
*Cc:* AI Geostats mailing list <mailto:[email protected]>
*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"
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
> http://mail.yahoo.com
>
>
--------------------------------------------------------------------------------
>* By using the ai-geostats mailing list you agree to follow
its rules
> ( see http://www.ai-geostats.org/help_ai-geostats.htm )
>
> * To unsubscribe to ai-geostats, send the following in the
subject or in
> the body (plain text format) of an email message to
[EMAIL PROTECTED]
>
> Signoff ai-geostats
--------------------------------------------------------------------------------
No virus found in this incoming message.
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Version: 7.1.375 / Virus Database: 267.15.2/253 - Release
Date: 07/02/2006
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