Blank types

Blanks answer where contamination happens, and the two kinds answer different halves:

• A coarse (field) blank — barren, unpulverised rock — goes in before prep. It tests the crusher and pulveriser, where most contamination actually occurs.
• A pulp (fine) blank — already pulverised — tests the assay step and instrument carry-over.

Placement is the whole point. A blank after barren samples tests nothing; insert blanks after mineralised samples. Simón's ordering refinement: after a high-grade interval, fine blank first, then coarse — that way the fine one is assayed right after the high-grade sample and the coarse one is prepared right after it. A blank at position 1 of a batch is equipment cleaning, not QC. (Caveat worth knowing: some labs alternate two pulverisers, which can defeat placement logic entirely — Bloom's fix is submitting high-grade samples as a separate batch.)

Material pitfalls

• "Bricks are not an acceptable barren material!" (Bloom)
• Wrong matrix defeats the assay silently — limestone in a fire assay flux designed for volcanics may under-recover gold, so the blank reads clean when it isn't.
• Too fine (won't test prep) or too small (100 g won't clean a 1 kg pulveriser bowl).
• Not verified barren — Rainy River's local-intrusive blank read >3× DL in ~15% of results; marble garden stone brought that to 0.7%.

In geoDB

geoDB's QC types distinguish field-inserted blanks from lab blanks, and coarse from pulp where you record it — so log the blank kind correctly when inserting. geoDB does not evaluate placement or material; those are field-protocol decisions this topic exists to inform.

What geoDB does do with a blank once the lab reports it is judge it against a threshold ladder — see Blank thresholds. Worth knowing here: a blank whose element has no resolvable threshold reads "unknown", not "pass". A page full of "unknown" blanks is a configuration gap, not a clean result — and it is not evidence the blank material or its placement worked.