Gold assay explained: ppm, g/t and how to read a gold assay before you buy land
26 Oct 2026 · Aurelot
If you are buying a gold plot from abroad, the gold assay result is the closest thing you have to walking the ground. It is also the easiest number to misread. This guide explains what the figures mean and which ones deserve your trust.
ppm and g/t are the same thing
Gold grade is the amount of gold in a given mass of rock.
- 1 ppm (part per million) of gold means 1 gram of gold in every million grams of rock.
- A million grams is one tonne, so 1 ppm is exactly 1 gram per tonne (1 g/t).
Soil and stream samples often report in ppb (parts per billion). Divide by 1,000 to get ppm: 250 ppb is 0.25 ppm.
Older North American reports use troy ounces per short ton (oz/t or "opt"). One troy ounce is 31.1 grams and a short ton is 0.907 tonnes, so:
| Reported | In g/t (ppm) |
|---|---|
| 0.01 oz/short ton | 0.34 |
| 0.1 oz/short ton | 3.43 |
| 1 oz/short ton | 34.3 |
| 1 oz/tonne | 31.1 |
On Aurelot every result is converted to ppm automatically, and the original figure is shown next to it so you can check the conversion yourself.
What counts as a good grade?
There is no single cut-off, because the economics depend on the size of the deposit, how deep it is, and how the gold is recovered. As a rough guide:
| Average grade | What it usually supports |
|---|---|
| Below 0.5 ppm | Rarely economic on its own |
| 0.5 to 1.5 ppm | Large open-pit operations with heap leach or bulk processing |
| 1.5 to 4 ppm | Open-pit and well-run small-scale mining |
| 4 to 10 ppm | Underground and artisanal shaft mining |
| Above 10 ppm | Rich veins, often narrow; confirm with more samples |
A small plot with a single 20 ppm sample is not necessarily better than a larger plot averaging 2 ppm across dozens of samples. Consistency matters more than one spectacular number.
The method matters as much as the number
Two samples can report the same grade and deserve very different levels of trust.
Fire assay is the industry standard for gold in rock. A measured portion of crushed sample is fused at high temperature, the gold is collected and then measured. Results from an accredited lab using fire assay are what serious investors and banks rely on.
Aqua regia digestion dissolves the sample in acid. It is widely used for soil geochemistry and can under-report gold locked inside resistant minerals, so treat it as a strong indicator rather than a final grade.
Cyanide leach tests measure how much gold dissolves in cyanide, which says something useful about recovery, not only grade.
Handheld XRF readings are fast and cheap, but these instruments struggle at the low gold levels most deposits contain. A handheld reading of tens of ppm on a single rock is a reason to send samples to a lab, not a reason to buy.
Panning estimates show that free gold is present. They cannot give a reliable grade.
This is why Aurelot calculates the headline grade from lab assays first, and from lab assays we have verified against the certificate before anything else. A field reading can never inflate the number at the top of a listing.
Sample type: where did the rock come from?
- Grab samples are hand-picked pieces of rock. Sellers naturally pick the best-looking ones, so grab results tend to overstate the grade.
- Channel and chip samples are cut across a vein or rock face in a line. They represent the true width of mineralisation far better.
- Soil samples show where gold is in the ground nearby. They are reported in ppb and are used to find targets, not to estimate grade.
- Drill core is the most reliable sample type and the basis for any formal resource estimate.
Averages are not a resource estimate
An average of sample results tells you whether a plot is worth a closer look. It does not tell you how many ounces are in the ground. A formal mineral resource needs systematic drilling, density measurements and a qualified person's report under a recognised reporting code such as JORC or NI 43-101. Treat any seller who quotes "ounces in the ground" from a handful of grab samples with caution.
Eight questions to ask before you trust an assay
- Can I see the original lab certificate, not a retyped table?
- Which lab issued it, and is that lab accredited (for example to ISO/IEC 17025)?
- Which method was used: fire assay, aqua regia or something else?
- What type of sample was it, and how wide was the vein or channel?
- Who collected the sample, and who carried it to the lab?
- Where exactly was it taken? Ask for GPS coordinates and photos.
- Were blanks, standards and duplicates included to check the lab's accuracy?
- Can my own geologist resample the same spots before I pay?
If a seller cannot answer most of these, the grade is a claim, not evidence.
How Aurelot handles grades
Every plot on Aurelot lists all of its samples, not just the best ones. Each sample shows its type, method, depth, lab and certificate. Samples our team has matched to the original certificate carry a green seal, and the headline grade is calculated from verified lab assays whenever they exist. Before you pay, you can ask for an independent geologist to resample the ground, and your deposit stays in escrow until the transfer is registered.