Drillhole Preferences for Evo Import

Drillhole Preferences for Evo Import is invoked from the Import from Seequent Evo dialog to view and customize various settings before initiating the import of drillhole data. Here, you can adjust options such as the conversion of negative values, the resurveying method, the survey data dip direction, and the default mask channel.

Drillhole preferences are global variables* that remain consistent across different data sets and Oasis montaj/Target projects. Any changes made in this dialog will be reflected in the Drillhole Preferences dialog available with the Drillhole Plotting extension and propagated to relevant processes (GXs) within the extension's workflows. Conversely, any changes made in the 'Drillhole Preferences' dialog will be reflected here.

Drillhole Preferences dialog options

Import Parameters
Auto-convert negatives on import?	Identify if assay negative values are automatically converted on import. If Yes is selected, all values in the assay channels will be scanned during import. Values less than zero are replaced by positive values that are half their original size (i.e., values are multiplied by –0.5). See the Application Notes below for further details on "negative" assay values and the conversion process. Script Parameter: DHPREFERENCES.CONVERT_NEGATIVES [0: No; 1: Yes]
Survey Parameters
Resurveying method	Resurveying is the mathematical process of converting a series of dip and azimuth measurements taken at various depths down a borehole into (X, Y, Z) coordinates. The collar is assumed to be at zero depth, and depth is the measured distance down the hole (even if it's horizontal). Select one of the available methods: Radius of curvature: The original resurveying method used in previous versions of Oasis montaj/Target. It synthesizes the trace as a collection of circular segments, each starting and ending at a single (dip, azimuth, depth) location. Polynomial fit: This method models the traces as a polynomial of a specified order that best fits the set of (dip, azimuth, depth) values. Higher orders provide better fits, with a trade-off in the overall smoothness of the hole trace. Straight segments: This method creates straight line segments between each survey depth reading, with no interpolation. It is primarily used for trenches or near-vertical holes. The (X, Y, Z) coordinates are stored in the 'DH_East', 'DH_North', and 'DH_RL' channels in the drillhole databases. For interval ('From-To') databases, these channels are calculated from the collar and survey data using the selected resurveying method and represent the midpoint of an interval. Script Parameter: DHPREFERENCES.RESURVEY [0: Radius of curvature; 1: Polynomial fit; 2: Straight segments]
Order for polynomial fit	This parameter is used in the polynomial fit resurveying method described above. The polynomial order is limited by the number of (dip, azimuth, depth) values, with a maximum of 20. A value of 5 is adequate for most smoothly curving holes. A higher order results in more accurate matching of dip and azimuth at each surveyed hole depth, while a lower order produces smoother final hole traces. Script Parameter: DHPREFERENCES.POLY_ORDER
Hole survey dip angle sign (downward)	Identify if the hole survey dips are negative downward or positive downward: Negative: Negative survey dips indicate holes pointing downward. Positive: Positive survey dips indicate holes pointing downward. Oasis montaj/Target has traditionally used the convention that dip is negative downward, meaning vertically downward is –90.0 degrees. Typically, vertically downward is +90 degrees, and selecting the 'positive' setting will cause Oasis montaj/Target to interpret all dip values in a drillhole database accordingly. This simplifies the import of data from other packages or formats where dips are positive downward. This convention is applied at plotting time, so if all your holes appear to go “up” instead of “down”, change this setting to correct the orientation. Script Parameter: DHPREFERENCES.DIP_SIGN [-1: Negative; 1: Positive]
Azimuth magnetic declination correction	Specify the magnetic declination correction angle to be applied to the X, Y, Z coordinates ('DH_East', 'DH_North', 'DH_RL' channels) for the survey, interval, and depth databases. Many downhole surveys use a Kodak-Eastman survey device, which records the azimuth in relation to a magnetic compass bearing. Consequently, the azimuth values recorded in the collar table and dip-azimuth survey databases do not reflect the "true" azimuth measured relative to north. This correction value will be added to the survey, interval, and depth data before resurveying. For instance, if magnetic north is 10 degrees west of true north, and the stored azimuth values are relative to magnetic north, enter the value "-10" as the correction. An azimuth of 10 degrees west will then be corrected to 0 degrees (true north) before resurveying the hole. Essentially, holes are rotated around the collar position by the correction angle. Script Parameter: DHPREFERENCES.AZIMUTHCOR
Plotting Parameters
Default mask channel	If a mask channel is specified, it will appear as the default mask channel in any GX within the Drillhole Plotting extension where the mask channel selection has not yet been made; it is subsequently used as the mask channel for any of these processes for masking. The mask channel will have its Class type set to MASK, and it is created within the interval and point databases. Only data values where the corresponding mask value is not a dummy, "", will be used for plotting or exporting data. When plotting, masked-out points or intervals will not appear, nor will depth ticks for these values. Although logically a "NO", '0' is treated as a non-dummy, so the data remains selected. Only the dummy "" can be used to mask out data. Values can be set to dummy by selecting them in the database and pressing the space bar. Script Parameter: DHPREFERENCES.MASK

Application Notes

*Global variables are stored in the geosettings file located in the user-specific folder '%USERPROFILE%\Documents\Geosoft\Desktop Applications\ini'.

"Negative" Assays

Assay values represent the measured geochemical concentrations of elemental abundance in geological samples (such as rock, soil, water, drill core, or rock samples). When assay values are measured in the lab, the concentration of an element can sometimes be very small, making it too low to be accurately detected by the method that is used to measure the concentration. This results in assay measurements reported using a "lower detection limit" value, often shown as a negative value or with a less than ('<') sign, such as '-0.01'. On import, you can choose to automatically convert these negative values or '<' signs to a value that is 1/2 of the numeric value used.

Resurveying Drillholes using Collar and Survey Data

The drillholes are always "resurveyed" on import in order to calculate the (X, Y, Z) coordinates on drillhole segments. This means a 3D spatial object (a drillhole "trace") is calculated for each drillhole. The output trace for any given hole can vary depending on what type of data is available during import (e.g., collars only, collar and survey data, etc.) and which method is selected to do the resurvey calculations. The various ways to calculate the traces, depending on which types of data are available, are described below:

With collar locations only, no survey data present:

If collar data includes dip and azimuth, these values are used to create straight segment traces for the entire hole, to the final depth.
If collar data does not include dip and azimuth, the holes are assumed to be vertical.

With collar locations and dip-azimuth survey data:

The survey data is "discretized" and a smooth curve is generated using the selected resurveying method.
The dip and azimuth values at the top-of-hole (depth = 0) in the survey data will be used, if present.
- Individual drillholes lacking survey data will be assigned default collar values: a dip of 90° and an azimuth of 0°.
- Individual drillholes that do not have a depth=0 start in their survey data will have the collar dip and azimuth values set to default values (90° and 0°, respectively) to ensure the X, Y, Z coordinates of intervals/depths are in the correct location.

A "resurvey" is triggered also when the Refresh tools, available with the Drillhole Plotting extension, are used. If any manual edits were made to collar location or survey measurement values (e.g., for incorrect X, Y, Z collar location or Dip/Azimuth/Depth survey values), a "resurvey" needs to be performed in order to recalculate the X, Y, Z collar and dip/depth/azimuth survey data.