Geochemical sample preparation from drill core is a critical step in the laboratory process, ensuring that the resulting geochemical data are reliable and representative. Here, we outline the general process, considerations, and best practices for drill core sample preparation.

1. Assigning a Unique Sample Code

Each sample must be assigned a unique code for tracking and identification throughout the sampling and analytical process. This ensures that the data can be accurately linked back to the specific drill core interval from which the sample was taken. The sample code should follow a standardized naming convention that may include details such as drill hole ID and interval depth.

2. Splitting the Core

Drill core is typically split into two halves using a core saw or, in some cases, a core splitter. One half is retained for reference or future analysis, while the other half is used for geochemical sampling. This step requires precision to avoid contamination and to ensure an even split, both in terms of weight and estimated mineralization, e.g. try your best to avoid the nugget effect.

3. Determining Sample Intervals

Sampling intervals are generally around 2 meters in length, but adjustments may be necessary depending on the ore system and geological context:

• Ore System Considerations: For example, narrow high-grade veins may require shorter intervals to capture the variability in mineralization.
• Lithological Contacts: A new sample must always begin at a lithological contact to ensure that each sample represents a single geological unit. Sampling across lithological boundaries can introduce compositional variability that complicates interpretation.

4. Insertion of QA/QC Samples

To ensure data integrity and accuracy, quality assurance (QA) and quality control (QC) samples must be inserted into the sampling sequence. These include:

• Blanks: Materials with negligible concentrations of the target elements to check for contamination during preparation and analysis.
• Standards: Certified reference materials with known concentrations of target elements to assess analytical accuracy.
• Duplicates: A second split of the same sample to evaluate the precision of the sampling and analytical process.

QA/QC samples should be inserted at regular intervals, typically comprising about 10% of the total sample batch.

5. Laboratory Preparation

Once samples arrive at the laboratory, further preparation is conducted to ensure consistency and representativeness:

• Drying: Samples are dried to remove moisture, typically in an oven at low temperatures to prevent alteration of geochemical properties.
• *Splitting: *The dried sample is homogenized and split using a riffle splitter or similar equipment. This step reduces the sample to a manageable size for analysis while preserving representativeness.

Best Practices for Drill Core Sampling

• Documentation: Maintain detailed records of sample intervals, lithological descriptions, and QA/QC sample insertion points.
• Cleanliness: Use clean equipment and workspaces to prevent contamination.
• Training: Ensure all personnel involved in sample preparation are trained in proper techniques and QA/QC protocols.

Proper preparation of drill core samples is essential for obtaining high-quality geochemical data. By following standardized procedures and incorporating robust QA/QC measures, exploration teams can ensure the reliability of their results, facilitating accurate geological interpretations and decision-making.

By prioritizing these steps, geochemists and exploration teams can confidently advance their projects with data they trust.