Test-Pit Bulk Sampling: The Six-Hole Program That Turns Alluvial Hints into a Defensible Gold Grade

Procedure Description – Exploration Stage (Resource Evaluation)

1. Excavation
   Six test pits are opened.

2. Dimensional Survey
   Width, length and depth of every pit are measured to compute in-situ volume.

3. Density Measurement
   The dry bulk density of the in-situ material is determined for each pit.

4. Gold Recovery & Weighing
   Alluvial gold from each pit is collected, dried and weighed.

5. Grade Calculation
   Using the above data, the gold grade (mass of gold per unit volume or mass of material) is calculated for every pit; the six individual grades are averaged to obtain a representative grade for the tested volume.

Mining Development Category: Exploration – Resource Evaluation / Bulk-Sampling (Grade Verification)

This procedure is a classic example of exploration-stage bulk sampling (also called test pitting or pilot-scale testing) within the prospecting / early-exploration category of mining development. By excavating small, controlled volumes of surficial material, measuring their exact dimensions and in-situ density, and physically recovering and weighing the contained gold, the operator is not yet engaged in full-scale mining but is instead gathering quantitative data to verify the presence, grade, and continuity of an alluvial gold resource. The six-pit campaign is designed to convert anecdotal indications of gold into a defensible grade estimate that can support a decision to advance toward larger-scale trenching, drilling, or even a small trial mining operation.

In the mining-industry lexicon, the work described falls squarely under exploration-stage bulk sampling, a sub-set of the broader prospecting / early-exploration category. The objective is not to generate immediate cash flow, but to obtain a statistically meaningful sample of the near-surface material so that the average gold grade can be estimated with enough confidence to justify further expenditure. Each test pit functions as a miniature, controlled “sample chamber”: its volume is precisely quantified so that the dry mass of the in-situ soil can be calculated from the measured density; the contained gold is then recovered—usually by gravity concentration followed by panning or laboratory tabling—and weighed on a high-precision balance. By repeating the exercise in six discrete pits, the explorer can compute both the arithmetic mean and the variance of the gold grade, two parameters that are critical for determining whether the alluvial deposit is erratic nuggety gravel or a relatively continuous sheet with economic potential. If the average grade exceeds the conceptual cut-off (commonly 0.1–0.3 g/m³ for simple gravity operations in remote areas), the next step is typically to expand the test-pit grid or move to small-scale trenching or reverse-circulation drilling to delineate a maiden resource.

Terms

Bulk Sampling

Bulk sampling is the process of taking a representative portion from a larger, non-uniform quantity of material—such as soil, ore, grain, or waste—for analysis or testing. The goal is to ensure that the sample accurately reflects the average characteristics of the entire batch, despite potential variations in composition.

Early Exploration

In the context of gold exploration, early-exploration refers to the initial phase of investigating a prospective area where gold mineralization is suspected but not yet confirmed. This stage typically involves:

• Regional targeting using geological maps, satellite imagery, and geophysical data
• Stream sediment or soil sampling to detect anomalous gold concentrations
• Prospecting and mapping to identify quartz veins, alteration zones, or other surface indicators
• Initial trenching or shallow drilling to test near-surface gold potential

The goal is to identify and prioritize targets for more detailed follow-up work, not yet to define a resource.

Test Pitting

Test pitting is the process of digging small, exploratory holes (typically 1–2 m deep) to examine subsurface soil, rock, or groundwater conditions. It’s a basic form of site investigation used in geotechnical, environmental, and archaeological work to assess material types, stratification, contamination, or artifacts before larger-scale excavation or construction.

In-Situ

in-situ (adverb & adjective)
In its original place; positioned where it naturally occurs or was first installed—without having been moved, extracted, or disturbed.

Laboratory Tabling

Laboratory tabling is a small-scale mineral separation technique that uses a shaking table—a sloped deck with a rifled surface—to separate heavy minerals from lighter gangue based on differences in density, size, and shape. Water flows across the deck while it vibrates, causing heavier particles to migrate upslope into concentrate launders, while lighter particles wash downslope into tailings.

Defensible Grade Estimate

A “defensible grade estimate” is a resource grade (grams of gold per cubic metre, in this case) that has been calculated with enough rigor, documentation, and reproducibility that a third party (investor, regulator, lender, or joint-venture partner) can examine the data and be convinced the number is reasonable and not just a hopeful guess.

In the context of the six-test-pit programme it means:

• Each pit’s volume was accurately measured and the in-situ bulk density was determined, so tonnes (or cubic metres) are known.
• All of the material was screened and the gold was physically collected and weighed, so contained metal is known.
• Sample weights, screen sizes, loss factors, moisture, and any spillage were recorded, so a check-reader can re-calculate the numbers.
• The six pits are spread far enough apart to show whether the grade is continuous or just a local “nugget effect.”
• The resulting arithmetic (gold grams ÷ cubic metres) gives a grade number that can be quoted in a report, listed in a simple resource statement, or used to compare economic upside versus the cost of the next exploration phase.

Because these steps are transparent and can be audited, the grade estimate is “defensible.”