Sampling passes & composites
Sampling passes & composites
Open a hole and you may find two samples over the same depths — say a 0–5 ft bag and a 0–10 ft one that covers it. Nothing is wrong. They are two sampling passes: the hole was sampled twice, on purpose.
Why a hole gets sampled twice
The usual design is cost control. Gold is nuggety, so you assay Au on every 5-ft bag. The pathfinder and lithogeochemistry suite (a 48-element ICP package) varies slowly downhole, so you run it on 10-ft composites made from the pulps of two bags — half the bill for a signal that does not need the resolution. The composite goes to the lab as its own sample: its own sample ID, its own certificate, often a different lab a week later.
So a composite is a real physical sample, not a duplicate and not QC. It is also not something geoDB could calculate for you — averaging two gold values does not give you an ICP result — and deleting it to "clean up the overlap" throws away every value on its certificate. One project we work with holds 4,260 of them.
The one rule
Within one pass, in one hole, sample intervals must not overlap. Across passes, anything goes. Sample names stay unique across the whole project regardless — a lab ID names one physical bag, whichever pass it belongs to.
Every drill sample belongs to exactly one pass. A project starts with a
default pass and every existing sample sits in it; a pass carries a kind
(primary, composite, metallurgical / bulk, re-split, historic, other) so its
label is honest.
Who reads which pass
Some surfaces need one clean downhole sequence — an interval table cannot carry overlaps. Others just list rows. geoDB keeps the two apart on purpose:
| Needs ONE sequence → reads ONE pass | Lists rows → shows EVERY pass |
|---|---|
| Leapfrog / the ODBC interval table · the 3D viewer and grade shells · map drill traces · compositing and intercept tables · Quick Log start-depth auto-fill | the Drill Samples grid (a Pass column) · CSV / XLSX exports (a sample_set column) · the Quick Log roster (each row badged) · the API list · strip-log sample tracks (with a pass filter) |
The one-sequence surfaces read the project's export pass — set it under Project settings → Data Export & ODBC → Drill Sample Set; left blank, they read the default pass. Passes are never merged. A 3D or map drill layer can pick a different pass of its own. This is why an ODBC table can have fewer rows than the grid: the table serves one pass, the grid lists them all.
Importing a second pass
Import a composite file over a hole that already has its 5-ft bags and the importer stops and asks before writing anything: how many rows overlap the target pass, in which holes, with sample pairs. Three ways through:
- Name a new pass for the file (with its kind) — created when you confirm.
- Pick an existing pass that is not the default.
- Fix the file, if the overlap really is a mistake.
Rows that re-use an existing interval under a new sample name ask the same
question — a re-split is a pass too. A drill_sample_set column in the file
names the pass row by row; an unknown name is refused rather than created
silently. In Petra, the same question arrives as a card; answer it by
telling Petra what the pass is and it re-lands the file into it.
Managing passes
- Create, rename or archive a pass: the Drill Sample Sets page.
- Which pass exports: Project settings → Data Export & ODBC.
- Which pass new Quick Log samples land in: the Pass: picker on the Quick Log's Samples tab — it also decides where start-depth auto-fill continues from. It never hides rows; every pass stays listed.
- Per-layer: the 3D drill-hole setup and the map's drilling configuration each carry a pass picker.
Composites that are already in your project
If your composites were imported before passes existed, they sit in the default pass and the validator counts every one as an overlap (on one real project: 8,652 pairs). Moving them out is a reviewed proposal, not an automatic fix: support runs a dry run that finds rows containing two or more others in the same hole, reports which naming convention each matched, and writes a CSV for a person to read before anything is applied — with a snapshot and a revert. Rows with no naming signal are left alone: on one real project a single "composite" spans 740 m over 36 samples, which is a logging error, not a composite. Ask Petra, or support, to start that review.