Digby, at last a real question!
> Is use of estimation variance for classification of
> resource confidence e.g the AusIMM's resource
> categories of Measured, Indicated and Inferred
> common and is this good practice.
Depends on how you use it, whether your estimates and
errors have Normal distributions, how many samples you
can find within your search radius plus a whole can of
There are as many different ways of using the kriging
variance as there are major mining houses and
consultancy groups. If you want to classify on a
block-by-block basis, the following seems to work
pretty well. As professional engineers with 30 years
of experience specialising in resource and reserve
estimation, we have found this acceptable to most
Measured resource: kriging variance less than ordinary
statistical sample variance (or total sill if you have
Indicated resource: not measured but within the range
of influence of at least 4 samples (not sure how you
would apply that if you have no sill!)
Inferred resource: anything that a competent geologist
can justify on the grounds of physical continuity.
In plain words: measured is something that you can
have some confidence in; indicated is within range but
the local average is a better estimator than the
kriging; inferred is a can of worms.
> Also how is this
> effected by block size in that should a reasonable
> block size be chosen e.g. 1/4 drillhole spacing.
The 'sample variance' referred to in the measured
category should be reduced by the within block
variance to be meaningful. This means the bigger the
block the better the estimate must be to be measured.
Drillhole spacing is not the issue in classification
or confidence measurements -- the range of influence
or distance scaling parameters are.
Hope this helps
Do You Yahoo!?
Get your free @... address at http://mail.yahoo.co.uk
or your free @... address at http://mail.yahoo.ie
* To post a message to the list, send it to ai-geostats@...
* As a general service to the users, please remember to post a summary of any useful responses to your questions.
* To unsubscribe, send an email to majordomo@...
with no subject and "unsubscribe ai-geostats" followed by "end" on the next line in the message body. DO NOT SEND Subscribe/Unsubscribe requests to the list
* Support to the list is provided at http://www.ai-geostats.org