Localized uniform conditioning (LUC): method and application case studies
MZ Abzalov
A new method, localized uniform conditioning (LUC), was proposed in 2006
for modelling grades of small blocks of ore when data spacing is too broad
for their accurate modelling by the linear regression based techniques, such
as kriging (Abzalov, 2006). It represents a modified uniform conditioning
(UC) technique that calculates the grade distribution functions for the large
panels. LUC uses partitioning of the panels onto the small blocks and then
ranks them in increasing order of grade. Based on the block ranks, a single
grade value can be deduced for each block from the UC model of the gradetonnage
relationships of the corresponding panel.
After being first presented in 2006, the LUC method has been
implemented in ISATIS© (commercial software) and became one of the
common approaches for grade estimation when data spacing is broad in
comparison with the estimated block size. Several years of study on the
LUC method and its application to different geological environments, have
allowed identification of the strengths and weaknesses of the method,
which are as follows:
* The method produces accurate grade-tonnage functions, which
are in a good accordance with a volume-variance relationship
principles
* An initial ranking of the selective mining unit (SMU) blocks can
be made by direct kriging from the sparse data grid. Therefore, the
LUC method can be particularly useful at the early stages of
exploration and mining project evaluations when sparsely
distributed data is often the only available information
* Accuracy of the local estimation depends on the SMU ranking
techniques. When ranking performed by direct kriging of the SMU
blocks their spatial distribution is approximate. When the
variogram of the studied variable is characterized by a large
nugget effect, the block ranks produced by kriging can significantly
differ from their ‘true’ distribution
* Block ranking can be improved using auxiliary data, either
geophysical or geochemical. This allows use of the LUC method
for integrating different data sets. In particular, LUC can be used
for grade control in open pits by integrating resource definition
data (e.g. drill-hole assays) and blast-hole assays. The latter are
used for the block ranking.
Keywords: geostatistics, localized uniform conditioning, LUC, resource modelling.