Re: [ai-geostats] variogram analysis

[DWMCCARN]

Dear Rajive:   I cannot conclude with only 328 pairs that the feature is "wavy" because I do not know how those pairs are distributed for each point in the variogram.  Try different lag spacings, or create an "equal-n" lag variogram where each lag has the same number of pairs.  If that shows the same feature, then perhaps there is a repeating feature (faults, fractures, ore controls, etc.) occurring at regular intervals throughout the sampling domain.  I take it that you have 26 or so sample locations.   Using "equal-distance" lags usually gives a large number of pairs to the first couple of lags, and then the n drops off rapidly, and the variogram is harder to interpret than with an "equal-n" type variogram.   I wrote my variography codes to work both ways...   Dan ii   Dan W. McCarn, AIPG CPG #10245, Wyoming PG #3031, EurGeol #462 10228 A Admiral Halsey NE; Albuquerque, NM 87111 USA Home: +1-505-822-1323; Cell: +1-505-710-3600 The College of Santa Fe 4501 Indian School NE Ste. 100; Albuquerque, NM 87110 (505) 884-2732 fax (505) 262-5595 [EMAIL PROTECTED] Institut f�r Geowissenschaften; Montanuniversit�t Leoben Peter-Tunner-Strasse 5; A8700 Leoben, AUSTRIA Cell: +43-676/725-6622; Fax; +43-3842-402-4902; Office: +43-3842-402-4903 In a message dated 12/7/2004 3:27:31 PM Mountain Standard Time, [EMAIL PROTECTED] writes: Usually when I've seen a "wavy" semivariogram, it's because of a local feature superimposed over an existing field function - for instance, a release of mercury in a field  of soil with very low "natural" mercury content. The period of the waviness is related to the distance across the feature (the width of the spill, in this case).  Of course, this is nothing particularly earth-shattering, but useful none the less. I've used semivariograms like this in the past to "guestimate" the approximate size of a plume based on sparse data.  Not all geostatistics ends up in gridding and estimating at every point!  Sometimes just looking at the semivariogram is very useful.   Tim Glover Senior Environmental Scientist - Geochemistry Geoenvironmental Department MACTEC Engineering and Consulting, Inc. Kennesaw, Georgia, USA Office 770-421-3310 Fax 770-421-3486 Email [EMAIL PROTECTED] Web www.mactec.com -----Original Message----- From: Rajive Ganguli [mailto:[EMAIL PROTECTED] Sent: Tuesday, December 07, 2004 4:50 PM To: [EMAIL PROTECTED] Subject: [ai-geostats] variogram analysis My question is general.  What do you conclude if your variogram is wavy? Cyclic patterns?  I have what appears to be high nugget, followed by a wavy pattern. If you wish, here is more info: an offshore placer platinum deposit, not too many boreholes - just 29 from decades ago spanning several square kilometers.  The variogram (from GEOEAS) of the grade (ln) is given in: http://www.faculty.uaf.edu/ffrg/Variogram.zip The variogram is cyclic. Goes up and down.  I tried various lags/directions.  I will try to dig up the geological information and see what it says. -- Rajive   CONFIDENTIALITY NOTICE: The materials in this e-mail transmission (including all attachments) are private and confidential, and the property of the sender. The information contained in the materials is privileged and intended only for the use of the named addressee(s). If you are not the intended addressee, be advised that any unauthorized disclosure, copying, or distribution, or the taking of any action in reliance on the contents of this material is strictly prohibited. If you have received this e-mail transmission in error, please immediately notify the sender by sending an e-mail message, and thereafter destroy the e-mail you received and all copies thereof.

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