What is core logging: drill hole and field mapping glossary

Exploration geology terms that come up when logging drill holes and mapping at surface. Each entry gives the technical definition and, below it, how that data is recorded in Field Manager, with the manual chapter that explains it.

Core logging and drill holes

Core logging

Core logging is the systematic, interval-by-interval geological description of the material recovered by drilling: core from diamond drill holes, or chips from reverse circulation (RC) drilling. For each depth interval (From/To) the geologist records lithology, alteration, mineralisation and structures and, in geotechnical logging, recovery and RQD. The logs of every hole in a project are the basis for geological sections, the geological model and the resource estimate.

In Field Manager: logging is done on the tablet, interval by interval, over the hole's strip log, with one table per subject (lithology, alteration, mineralisation, structure, sampling, geotechnics) and no internet connection. See Core logging.

Drill hole

An exploration borehole drilled to recover core or chips and see the geology below surface. It is identified by its Hole ID and defined by its collar, its path (survey) and its final depth. By method it can be diamond (recovers core) or reverse circulation (recovers chips).

In Field Manager: each hole is picked in the hole selector, which can be searched by name, and the whole logging screen is filtered by it. See Core logging.

Core

The rock cylinder recovered by diamond drilling, in standard diameters (BQ, NQ, HQ, PQ). It is laid out in core trays by depth, described at the logging table and, for assaying, usually cut in half: one half goes to the lab and the other is kept as a record.

In Field Manager: core photos are stored in the Photos table, linked to the depth interval they show. See Logging tables and QA/QC.

Collar

The point where the hole enters the ground. Its record holds the coordinates and elevation of the hole mouth, the starting azimuth and dip, and the final depth, and it is the origin every depth in the hole is measured from.

In Field Manager: the collar lives in the Downhole Data table, which can also be filled by importing an Excel, CSV, TAB or shapefile with a Hole ID column. See Import drill hole data.

Downhole survey

Azimuth and dip readings taken at successive depths inside the hole with a magnetic or gyroscopic instrument. They show how far the hole drifts from its planned path and place each logged interval in space.

In Field Manager: deviation surveys are stored in the Downhole Data table, together with the collar. See Logging tables and QA/QC.

From / To (interval)

The pair of depths that bounds each described run: where an observation starts and where it ends. They are measured along the hole axis from the collar, not vertically, so in an inclined hole they are not the depth below surface.

In Field Manager: together with the Hole ID they are required fields in every logging table. When a new interval is entered, From defaults to the To of the last interval of that hole, and overlapping intervals are rejected unless the table is set up to allow them. See Logging tables and QA/QC.

Hole ID

The unique identifier of the drill hole (for example, DDH-001). It is the field that ties together the lithology, alteration, mineralisation, structures, sampling, geotechnics and photos of one hole.

In Field Manager: when a drill hole table is imported, you choose which column of the file holds the Hole ID, and the hole selector lists every loaded identifier. See Import drill hole data.

Strip log

A vertical graphic view of the hole against depth, with one column per variable: lithology as colours or patterns, alteration, mineralisation, and grades or RQD as a curve. It is the graphic version of the logging sheet.

In Field Manager: each visible table with a style set up becomes a column, drawn as colour intervals, symbols, or a bar, line or area chart, with a depth ruler and vertical zoom. See Core logging.

Describing the core

Lithology

The rock type of each interval and the lithological unit it belongs to, with its description: texture, grain size, colour, composition. It is the base logging table and usually sets the main colours of the strip log.

In Field Manager: the Lithology table records rock type, unit and description per interval. See Logging tables and QA/QC.

Alteration

The mineralogical and textural changes the rock underwent through hydrothermal fluids (for example potassic, phyllic (sericitic), argillic or propylitic alteration) or supergene weathering. It is described per interval with its type, intensity and defining minerals.

In Field Manager: the Alteration table records type and intensity per interval, alongside the lithology of the same run. See Logging tables and QA/QC.

Mineralisation

The ore minerals present in the interval, their style (disseminated, veinlet, breccia, massive), their textures, and the visual estimate of their abundance or grade, which is later checked against the assay results.

In Field Manager: the Mineralization table records ore minerals, textures and visual grade estimates per interval. See Logging tables and QA/QC.

Structural measurement

The orientation of a plane (bedding, fault, vein, foliation, joint) or of a lineation. Planes are given as dip and dip direction, or strike and dip; lineations as plunge and trend. In core, each structure's angle to the core axis (alpha) is measured and, if the core is oriented, the beta angle as well.

In Field Manager: at surface, the measurement is taken by laying the tablet on the plane, using the device's compass and rotation sensor; values can also be typed in. In drill holes, the Structure table records type, angle and description per interval. See Geocoders.

Magnetic declination

The angle between magnetic north, where the compass points, and true north. It changes with place and over time, and without correcting it, compass directions end up rotated against the map.

In Field Manager: when measuring a structure, the app gets the declination at the current position and applies it to the compass reading if the corresponding checkbox is ticked. See Geocoders.

RQD

Rock Quality Designation: an index of rock mass quality. It is the percentage of a run's length made up of sound core pieces 10 cm or longer, measured along the axis; breaks caused by drilling or handling do not count.

In Field Manager: it is recorded in the Geotechnics table, together with recovery, fracture count and RMR classification, and it can be plotted as a curve on the strip log. See Logging tables and QA/QC.

Core recovery

The percentage of core length recovered against the length drilled in each run. Low recovery points to broken rock, fault zones or lost material, and limits confidence in the grades of that run.

In Field Manager: it is recorded in the Geotechnics table, per interval. See Logging tables and QA/QC.

Sampling and quality control

Sampling

Taking representative material for laboratory analysis: half core or chips per interval in drill holes; rock, soil or sediment at surface. Each sample carries a unique code that ties it to its interval or its position.

In Field Manager: in drill holes, the Sampling table records each sample with its interval, and the code can be checked for duplicates when entered; if the layer has Positioned GPS sampling active, the sample also stores the GPS coordinate, taken only once it meets the configured minimum accuracy. At surface, each sample is a point on the map. See Logging tables and QA/QC.

QA/QC

Quality assurance and quality control: the control samples inserted into the sample stream to check the lab's precision and accuracy and to rule out contamination. They are standards (reference materials of known grade), blanks (barren material) and duplicates of the same sample.

In Field Manager: control samples are recorded in the Sampling table, together with regular samples, and data entry can require fields that only apply to standards, blanks or duplicates. See Logging tables and QA/QC.

Surface mapping and GIS

Geological mapping

The plan-view record of geological units, their contacts, measured structures, outcrops and sample points, over a topographic base or an image.

In Field Manager: the map works with no signal over layers downloaded before going to the field; contacts and structures are drawn with the pen or by taking points with the GPS. See Offline geological mapping.

DEM (digital elevation model)

A raster whose pixel value is terrain elevation. It is used for hillshades, topographic profiles and projecting structures onto the topography.

In Field Manager: with a DEM in the project, the Intersect DEM tool draws the line where a plane of given dip and azimuth cuts the terrain: the expected trace of a contact or vein from a single measurement. See Draw and edit geometries.

Raster

A georeferenced image layer on a pixel grid: drone orthophoto, satellite image, scanned map or DEM.

In Field Manager: GeoTIFF, JPEG2000, ECW, PNG, JPG, BMP, PDF and GRD are imported; the app detects the georeferencing on its own (embedded, world file, .prj and others) and adds the image as a map layer. See Vector, raster and WMS layers.

GeoTIFF

A TIFF image format that carries its georeferencing (coordinate system and location) inside the file itself. It is the most common format for drone orthophotos and DEMs.

In Field Manager: it is imported as a raster layer, BigTIFF files included. For very large images it is preferable to JPEG2000 or ECW, which have a 1-gigapixel limit. See Vector, raster and WMS layers.

WMS layer (WMS, WMTS, XYZ)

A basemap served over the internet: satellite imagery, topography or geological maps. WMS is the OGC standard that returns an image of the requested area; WMTS and XYZ deliver the map as pre-cut tiles per zoom level.

In Field Manager: the project comes with ready-made basemaps (OpenStreetMap, Esri Satellite, Esri Relief, among others) and accepts your own WMTS or XYZ servers. Tiles you have viewed stay in memory for 30 days, and an area can be downloaded by zoom range for use with no signal. See Offline maps.

Shapefile (SHP)

Esri's vector format, made of several files (.shp, .shx, .dbf, .prj), with a single geometry type per file and field names of up to 10 characters. It is the most widespread interchange format between GIS programs.

In Field Manager: it is imported and exported, as are TAB, Excel, CSV, KML, Geodatabase and GeoPackage; each table can have an export filter that limits which rows go out. See Export and import data.

GeoPackage (GPKG)

An open OGC standard that stores several vector layers, with their attributes and coordinate system, in a single SQLite file, without the shapefile's field-name length limit.

In Field Manager: it is imported and exported from the Resource Manager, like the other table formats. See Export and import data.

Projection (SRID, EPSG)

The coordinate system positions are expressed in, for example WGS 84 geographic or UTM WGS 84 zone 19S. The EPSG registry gives each one a numeric code (SRID): EPSG:4326 for WGS 84 geographic, EPSG:32719 for UTM zone 19S.

In Field Manager: the map projection is searched by SRID, name or Proj4 definition, and custom projections can be created. Each layer can be in a different system from the map. See Preferences.

Positioning

NMEA (external GPS)

The standard protocol a GNSS receiver uses to stream its position, as text sentences such as GGA or RMC. It is what lets you use a GPS more accurate than the tablet's built-in one.

In Field Manager: any Bluetooth-paired receiver that streams NMEA can be chosen as the project's GPS source instead of the built-in GPS. See Preferences.

RTK and NTRIP

RTK (real-time kinematic) is the technique that takes a GNSS receiver from metre-level to centimetre-level accuracy by applying differential corrections from a reference station. NTRIP is the protocol for receiving those corrections over the internet from a server (caster), chosen by its mount point.

In Field Manager: the app pulls the corrections from the NTRIP caster and passes them over Bluetooth to an external receiver that accepts them; the receiver computes the corrected position and the status bar shows RTK or FRTK. See Preferences.