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

[Fran Manns]

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 ----- From: Isobel Clark To: Stephen Henley Cc: AI Geostats mailing list 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! 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Version: 7.1.375 / Virus Database: 267.15.2/253 - Release Date: 07/02/2006 * 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 * 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

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