Crushing and grinding are essential steps when preparing drillcore samples for geochemical analysis. These processes break down the sample into smaller particles or fine powders, making it appropriate to analyze. However, contamination can creep in during these stages, potentially skewing your results. Understanding these risks and knowing what checks to perform can help you maintain the integrity of your data.

Crushing vs. Grinding: What’s the Difference?

Crushing is the first step where large pieces of drillcore are broken into smaller chunks. Equipment like jaw crushers or gyratory crushers are commonly used. This stage focuses on reducing size to a fraction suitable for grinding, typically below 10 mm.

Grinding comes next, where those chunks are ground into fine powders, often with a particle size below 75 microns. This step is crucial for techniques requiring a uniform, fine sample, such as XRF or ICP-MS analysis.

Why Contamination Matters

Contamination during crushing and grinding can lead to incorrect results, misinterpreted geochemical signatures, and ultimately, wasted time and resources. Here are the main ways contamination can sneak in:

1. Residue from previous samples can stick to the equipment, mixing with your sample.
2. Metals from the grinding plates or crushers can wear off and contaminate your sample with elements like Fe, Ni, or Cr.
3. Dust and debris from nearby operations can settle on your sample during processing.
4. Simple mistakes like mislabeling or poor cleaning practices can result in cross-contamination.

How to Avoid Contamination

Even if you are not doing the crushing and grinding yourself, knowing how contamination is managed can help you ask the right questions. Here are some steps to minimize risks:

1. Equipment must be cleaned between samples using brushes, compressed air, or non-contaminating cleaning agents. Some labs run blank samples (like quartz sand) through the equipment to flush out residues. Understanding where your high-grade samples are and asking the lab to insert extra quartz sand is best practice.
2. Laboratories should be using equipment with tungsten carbide or ceramic components instead of softer metals to reduce the risk of introducing foreign elements.
3. Processing should take place in a clean, well-ventilated area to minimize dust contamination.
4. Your own blank materials should be run through the system periodically to check for contamination as part of your QA/QC design.

Checks You Can Expect (or Ask For)

To ensure contamination has not compromised your samples, labs often perform quality control checks. Here’s what that might include:

1. Blanks are processed through the system to detect any contamination from the equipment.
2. Duplicate samples are tested to ensure results are consistent and reliable.
3. Certified Reference Materials (CRMs) are analyzed to ensure the process aligns with expected values.
4. The lab will periodically analyze residues from cleaning and equipment wear to detect any potential contamination early.
5. Labs keep detailed documentation of cleaning, sample handling, and equipment use to trace any issues that arise. Constant communication with your lab is key!

Where Does This Leave You?

If you’re sending drillcore samples for analysis, understanding the above sources of contamination can help you communicate with labs and ensure you’re getting reliable results. LKI Consulting regularly conducts lab audits and assists clients in identifying contamination risks in their workflows. If you’re curious about optimizing your lab practices, let’s connect!