Grade Control Grade Calculation

The next stage of GRADE CONTROL is to attempt to delineate the boundary between ore and waste. The distinction between ore and waste is often based on a grade cutoff. This is the case especially in orebodies where there is no distinct change in geology between "ore" and "waste" making a visual delineation very difficult. In this circumstance a combination of local knowledge and grade estimation provides the solution. The Grade Control module provides three different grade estimation techniques.

Two of these will typically be used in Open pit bench mining operations:

• Arithmetic Mean

Estimates the grade inside a closed segment by finding the mean sample value of all the sample points inside a closed segment.

• Sichel Mean

Uses a Sichels t estimator on the sample values of all the sample points which are inside a closed segment. The Sichel t estimator is a good estimate of lognormal distributions and overcomes the tendency of the arithmetic mean to overestimate the average.

The third technique for estimating grades will more commonly be used in underground mining operations or in situations where large numbers of channel samples and drill holes are used at regular spacings, e.g. sectional drilling. This method uses length weighted averaging of all samples, and fractions of samples which are inside a closed segment.

In preparation for this stage of the grade control task a number of prior steps need to have been completed.

• The drill hole and channel sample survey data must have been loaded into the drill hole database.
• The sample assays must have been loaded and merged with the survey data by using the unique sample ID as a key.
• Elevation composites for the mining bench of interest, or Sections for grade calculations must have been extracted from the drill hole database. See the functions, Composite By Elevation and Extract Sections For Calculation.

After these preparatory steps have been completed you are ready to use the Grade Control grade estimation functions.