Assay Results

Assay results are one of the most important outputs in mineral exploration. They reveal the actual metal content of rock samples and determine whether a deposit is economically viable. Accurate assays guide drilling decisions, resource estimates, and mine planning.

What Are Assay Results?

Assay results are laboratory measurements that determine the concentration of metals or minerals in a sample. They are typically expressed as:

  • Grams per tonne (g/t) — for gold, silver, platinum
  • Percent (%) — for copper, lead, zinc, nickel
  • Parts per million (ppm) — for trace elements
  • Parts per billion (ppb) — for ultra‑low concentrations

Assays provide the quantitative data needed to evaluate ore grade.

Why Assay Results Matter in Mining

1. Determining Ore Grade

Assays reveal how much valuable metal is present.

2. Guiding Drilling Programs

High‑grade intervals help target follow‑up drilling.

3. Supporting Resource Estimates

Assay data is used to build 3D grade models.

4. Evaluating Economic Potential

Grade determines whether a deposit can be mined profitably.

5. Understanding Mineralization

Assays show metal zoning, alteration patterns, and deposit geometry.

How Samples Are Collected

1. Drill Core Samples

Core is cut lengthwise; half is sent to the lab.

2. RC (Reverse Circulation) Chips

Collected at regular intervals (usually 1–5 meters).

3. Grab or Channel Samples

Used in early exploration or underground mapping.

4. Soil and Stream Sediment Samples

Used for geochemical surveys.

Proper sampling ensures results are representative and reliable.

Assay Methods

1. Fire Assay

The gold standard for precious metals.

Used for:

  • Gold
  • Silver
  • Platinum group metals

Highly accurate for low‑grade samples.

2. Atomic Absorption Spectroscopy (AAS)

Measures metal concentrations after chemical digestion.

3. Inductively Coupled Plasma (ICP)

Used for multi‑element analysis.

Advantages:

  • Fast
  • Accurate
  • Detects trace elements

4. X‑Ray Fluorescence (XRF)

Portable or lab‑based.

Used for:

  • Base metals
  • Iron ore
  • Industrial minerals

Less accurate for precious metals.

5. Gravimetric and Wet Chemistry

Used for specific minerals or high‑grade samples.

Interpreting Assay Results

1. Grade

The concentration of metal in the sample.

Examples:

  • 1.5% Cu
  • 3.2 g/t Au
  • 45% Fe

2. Interval Length

Assays are reported over specific sample lengths.

Example:

  • 12 m @ 2.1 g/t Au

3. True Width vs. Drill Width

Drill width is the measured interval; true width accounts for the angle of the drill hole relative to the ore body.

4. Composite Grades

Multiple intervals may be averaged to show overall grade.

5. Cutoff Grades

Low‑grade values may be capped to avoid skewing results.

Common Reporting Formats

Example 1: Gold

  • 8.4 m @ 4.2 g/t Au
  • Including 1.2 m @ 12.5 g/t Au

Example 2: Copper

  • 22 m @ 0.85% Cu
  • Including 6 m @ 1.9% Cu

Example 3: Multi‑Element ICP

  • 150 ppm Mo
  • 0.12% Pb
  • 0.34% Zn

These formats help investors and geologists quickly interpret results.

Quality Control (QA/QC)

To ensure accuracy, labs and geologists use:

  • Blanks — samples with no metal
  • Standards — known metal concentrations
  • Duplicates — repeat samples
  • Check assays — sent to a second lab

Strong QA/QC builds confidence in the data.

Conclusion

Assay results are the backbone of mineral exploration. They quantify metal content, guide drilling, support resource estimates, and determine whether a deposit is economically viable. Accurate sampling, reliable laboratory methods, and strong QA/QC ensure that assay results provide a trustworthy foundation for mining decisions.