| Summary: | Inversion of potential field geophysical data to generate physical property models is
becoming increasingly common in the exploration industry. This study aimed to develop
relationships between physical properties and mineralogy in ultramafic rock-hosted mineral
deposits, based on an analysis of the crater facies-dominated Anuri kimberlite (Canada) and the
intrusive magmatic sulfide deposit at Kabanga (Tanzania). Physical property distributions for
rock types and minerals that contribute to density and magnetic susceptibility were characterized
in both deposits.
Magnetic susceptibility is directly related to magnetite abundance, which is an igneous phase
and is produced by serpentinization of ultramafic rocks of both deposits. Magnetite in kimberlite
also occurs in crustal xenoliths, which dilute the diamond content. Consequently, susceptibility
in the Anuri kimberlite is inversely related to diamond grade. In the Kabanga magmatic sulfide
deposit, susceptibility is unrelated to ore content, but does indicate the degree of serpentinization.
Density is a function of dense minerals concentrated with ore during primary sorting and
settling processes in both deposits. As such, density is directly correlated with ore in both
volcaniclastic kimberlite breccia of the Anuri kimberlite and ultramafic rocks at Kabanga.
However, serpentinization decreases the density of ultramafic rocks significantly, masking any
density anomalies associated with sulfide minerals. Modeling demonstrates that a pervasively
serpentinized rock with up to 50% sulfide minerals can have a density equal to that of a barren
ultramafic rock.
A combination of susceptibility and density can be used to identify high-grade rocks in both
deposits. In the Anuri kimberlite, rocks with high diamond contents have susceptibilities less
than 10 x 10⁻³ SI and densities of 2.42 - 2.51 g/cm³. In magmatic sulfide deposits, susceptibility
and density can be used to accurately calculate ore mineral abundances.
Relationships developed between physical properties and mineralogy for these deposits can
not only be applied to other crater facies-dominated kimberlites and both intrusive and extrusive
magmatic sulfide deposits, but also to other ultramafic rock-hosted mineral deposits with
comparable geologic processes. Consequently, both magnetic and gravity surveys can be
interpreted in combination to give a powerful remote tool in predicting grade. === Science, Faculty of === Earth, Ocean and Atmospheric Sciences, Department of === Graduate
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