Controlling Quality Sample Data Allocation to a Seam in GEOVIA Minex

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If you’re wondering why your seam reports or models do not show quality even though your boreholes sample has data for that depth, it may be because your quality data sample intervals do not match roof or floor of seams.

For example:

  • There may be several sample intervals in the seam interval (one sample per ply in the seam).
  • Stone bands may not have been sampled
  • The sample may cover an interval that is great than or less than the correlated seam interval. For example, a full working section may have been sampled, but the current working section is over a shorter or longer length
  • Sometimes due to core recovery issues, the seam needs to be corrected with geophysics, causing mismatch of seam depths and sample depths

Weighted averages

Minex calculates the weighted average to composite the analyzed data over the seam interval.

When calculating the weighted average to composite the sample data over the seam interval, Minex uses the analyzed value (a) and the thickness of the interval sampled (b).

So, for plies 1, 2, 3, and 4, the formula is as follows:

You can also use density and yield compositing.

When you work with sample data composited over the seam interval (for example, reporting, plotting), you may consider the following:

  • Does the analyzed data accurately reflect the quality of the seam?
  • Will grids created from the borehole data accurately represent the quality of the seam?

Controlling Quality over seam intervals

The following borehole database properties control how sample data is allocated to a seam interval.

Below are explanations of key borehole database properties.

  • Percentage of seam to be sampled: The amount of each seam interval that must be covered by sample data intervals for the sample data to be allocated to that seam interval. A value of 100means that the whole seam interval (from seam roof to seam floor) must be covered by the sample data intervals. If any of the seam interval (for example, a stone band) was not sampled, then Minex does not composite the sample data. As a result, no sample data is allocated to the seam.

    If you set the Percentage of seam to be sampled to 95, then sample intervals must represent 95% of the seam interval. If < 95% of the seam is covered by the sample intervals the sample data is not composited for that seam, and it has a Null value for the variable(s).

  • Seam Sampling Tolerance: The distance (in metres or feet) that is used to determine if the sample data intervals match the seam interval. By default it is false. You need to make it true and enter value. If you set the Seam Sampling Tolerance to 10, then the roof of the shallowest sample must be within 10 cm of the roof depth of the seam, and the floor of the shallowest sample must be within 10 cm of the floor depth of the seam. If the difference for either roof or floor is greater than 10 cm, then the seam is assigned a Null value for the variable(s).

These two properties work together to decide the outcome.

Next, you need to cross check the seam and sample boundaries in boreholes. Minex’s Quality Validation tool helps in this analysis. It reports any quality samples are within the seam intervals or whether a part of any sample is outside a seam interval as shown below.

It is a good idea to carry out tolerance analysis to study suitable settings for your borehole database or seams by reporting and plotting sections.

 

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Ajay Reddy

Ajay Reddy

Senior Industry Process Consultant, Mining at Dassault Systèmes
Ajay Reddy is a qualified Geologist with over 24 years of experience in coal exploration, mining and resources estimation. He has previously worked for one of the largest Indian coal exploration and mining companies, Singareni Collieries, and TATA Steel. Based in Brisbane, Australia, Ajay specializes in GEOVIA Minex and Surpac.