Compositing downhole with geologic breaks--adding hanging short intervals within a tolerance

donald 7 years ago in Resource Estimation updated by anonymous 5 years ago 4

Is there a way to reduce short-length composites produced by a downhole compositing to geology breaks that don't make the minimum length screen by adding them to the previous composite within a tolerance? This allows use of more data while still maintaining the nominal composite support and is an option used by others to eliminate systematic rejection of short composites at contacts. I have not noticed an option to do this or been able to think of a workaround.

Hi Donald, MM 2018 can now do this:

The final intervals are inserted into the last interval. The way Micromine does this, is it will attach the final interval regardless of your composite interval specified. In the screen shot above I have specified 2 m composite length and 0.5 minimum composite length. This in turn will generate a maximum composite length less than 2.5 m. Depending on your tolerances, you can adjust the minimum allowable composite length.

Hi Trevor,

Yes, the development team worked on this and I did some testing with them to make sure it works.  Note the other option to Redistribute intervals to avoid residual as well.There are cases when that is desirable, especially where you have a lot of compositing breaks.  The options are really useful in any kind of narrow deposit.

Have you used the redistribution of intervals? Let me know if you are encountering the same issues:

Their are two main issues that I've noticed with my very limited use:

1. If a minimum is not entered, the redistributed lengths will not exceed the specified composite interval. Ideally, with this tool, we would have some intervals longer and some shorter. Instead, the compositing with residual redistribution over represents the shorter intervals. Ultimately, the adjustment should go both ways within the user's specified tolerance.

2. If a minimum composite length is entered, there is tolerance within Micromine to allow for composite lengths greater than the specified composite length interval, however, the smaller intervals are still way over represented. 

I'm not sure why I would select redistribution if I didn't also select a minimum.  The idea is to maintain equal support for the composites.  If I select 10m for my comps and no minimum and select redistribute residuals, there are no residuals by definition. When I run a test file with a fixed length and no minimum, redistributing residuals, I get almost the same result as running with fixed length, no minimum and None (discard residual).  11 records of 20,999 are eliminated somehow by choosing this option, but the overall means are the same to 3 decimal places.  I have a few issues with blank intervals in the assay file so it's not an ideal test case.  If we run with a 5m minimum and redistribute, the composite variance drops 40%.  If you change the minimum, the number of composites greater than the nominal length and the range will vary according to the characteristics of the input file.  You may have steps in the composite lengths; e.g., some assays at 2m and others at 1m, that will generated a lot of residuals depending on the minimum threshold picked.  I think one can be satisfied if the resulting composite support is tightly distributed around the nominal value and the number of short-length composites is minimized.  If you have step-wise distribution of assay-lengths in the file from different campaigns the distribution will not be perfect.  In the general case, choosing 50% of the nominal composite length as the minimum will give good results.

Your question does bring up an interesting test condition.  I ran a file just now with no minimum and add residual (which shouldn't exist in this case) to last interval.  The output file returned several NEGATIVE intervals and others >>specified composite length.  It looks like the utility has a bug under this condition.