Rajive, Cyclic variograms indicate that your attribute of interest also fluctuates. I encountered this when working with time-series of water levels, in which case the fluctuations were related to seasonality. I am not sure what it would mean in the case of platinum deposits. Such variograms can be modeled using the hole effect model, but 2-dimensional semivraiogram modeling when you have anisotropy to account for, can be tricky with a hole effect because you cannot apply a hole effect model in more than one direction. It may be better to work with a residual, i.e. to find a correlated cyclic variable, remove the cyclicity for semivariogram and kriging purposes and add the kriged residual back in at the end. If you do want to model such a variogram, e.g. if you only encounter the cyclicity in one direction, and you are working with GSLib, then you may have to modify the kriging code, as the dampening factor (if the cyclicity diminishes with lag)is not specified in the parameter file. I don't know what other programs allow you to do with the hole effect model, though ...
Noémi -----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
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