Search Ellipsoid Parameters

Axis 1 Factor 

The length of the first or main ellipsoid axis, multiplied by the Radius to establish the final axis length. The Main Axis Factor is generally the longest dimension; in geological terms it represents the down-plunge length of the ellipsoid.

Axis 1 Azimuth

The azimuth (in degrees) of the long axis of the search ellipsoid measured clockwise from north, between 0 and 360. In geological terms, it represents the trend of linear features within a plunging orebody, such as fold axes or main structural lineations.

If you use either Geological orientation mode, the application will automatically calculate the Axis 1 azimuth. You must enter it for Geostatistical and Rotation modes. In Rotation mode and Geostatistical mode, the permissible range is between -360 and +360.

Axis 1 azimuth corresponds to strike whenever the Axis 1 plunge is zero (see below).

Axis 1 Plunge

The downward inclination of the main ellipsoid axis from horizontal (in degrees), between 0 and 90. Geologically, it represents the plunge of linear features within the orebody.

If you use Geological (pitch) orientation mode, the application will automatically calculate the Axis 1 plunge. You must enter it for all other modes. In Rotation mode and Geostatistical mode, the permissible range is between -90 and +90.

Axis 2 Factor

The length of the second ellipsoid axis, multiplied by the Radius to establish the final axis length. The Second Axis Factor usually falls between the Main Axis Factor and the Third Axis Factor; in geological terms it is similar to the down-dip length of the ellipsoid, but is measured in a plane perpendicular to Axis 1 instead of vertically.

Axis 2 Azimuth

The azimuth (in degrees) of the second ellipsoid axis measured clockwise from north, between 0 and 360. In Rotation mode and Geostatistical mode, the permissible range is between -360 and +360.

If you use Geostatistical orientations mode, you must enter the Axis 2 azimuth. The application will automatically calculate it for all other modes.

Axis 2 Plunge

The plunge of the second ellipsoid axis from horizontal, between 0 and 90°. In Geostatistical mode, the permissible range is between -90 and +90.

If you use Geostatistical orientations mode you must enter the Axis 2 plunge. The application will automatically calculate it for all other modes.

Axis 2 has no direct geological equivalent; however it equates to the down-dip direction of the plane containing the ellipsoid whenever the Axis 1 plunge is zero.

Axis 2 Rotation

If you use Rotation mode, specify the Axis 2 Rotation, measured in degrees from -90 to 90, in a plane perpendicular to Axis 1. The sign represents the orientation relative to Axis 1: when looking in the direction of Axis 1, a positive value represents an anti-clockwise rotation and a negative value a clockwise rotation.

Axis 2 rotation is equivalent to dip whenever the Axis 1 plunge is zero, although it can be either positive or negative. Rotation does not equate to dip if the Axis 1 plunge is anything other than zero.

Axis 3 Factor

The length of the third axis of the search ellipsoid, always perpendicular to the first and second axes. This value is multiplied by the Radius to establish the final axis length. The Third Axis Factor is usually the shortest dimension; in geological terms it represents the thickness of the search ellipsoid.

Where there is a significant directional variation in the continuity of the modelled mineralisation (in a folded structure for example) a Variable search option allows the rotation angles for the search ellipsoid to be defined (in the Blocks from file form (Block Model | Estimation | Inverse Distance Weighting ONLY). The search ellipsoid orientation can be controlled on a block-by-block basis, reflecting the directional trends in the mineralisation.