Tutorial: Practicing "safe geology" in the field.

Introduction

In the field of geochemistry, stream sediment analysis plays a crucial role in understanding the mineralization of various elements. By concentrating heavy minerals found in stream sediments, we can obtain valuable information about the composition and concentration of minerals present in the area. In this tutorial, we will discuss the process of stream sediment analysis and how to effectively concentrate heavy minerals for accurate results.

Concentrating Heavy Minerals

When analyzing stream sediments, it is important to note that a significant portion of the material collected is waste and does not contain any useful information. Therefore, any technique that can be used to concentrate the heavy minerals, which are typically associated with mineralization, will greatly improve the results obtained from the analysis. By enriching the sample intentionally, we can obtain a more representative and informative sample for further laboratory analysis.

The Panning Technique

The panning technique is commonly used to concentrate heavy minerals in stream sediments. Instead of using a small cup, a larger bucket is used for this technique. The process involves the following steps:

1. Start by measuring the volume of the material collected in the stream sediment sample.
2. Weigh the sample to determine the weight by volume.
3. Repeat the process for multiple samples to ensure consistency and accuracy.
4. By doing this in a systematic manner, it becomes easier to identify if there are any significant findings or anomalies present in the sample.

Sample Collection

When collecting stream sediment samples, it is important to consider the location and characteristics of the sample site. To maximize the chances of finding valuable minerals, it is recommended to collect samples from areas where the water flow is moderately fast, allowing for the washing away of lighter materials while retaining the heavier minerals.

Look for areas with obstructions in the river, such as fallen trees, as they tend to accumulate heavy minerals. Collect the sample from the upstream side of the obstruction, ensuring that the water flow has had the opportunity to wash away any lighter material.

Another factor to consider is the meandering patterns of rivers. Meanders create areas where the flow of water is concentrated, resulting in the accumulation of heavy minerals. Look for areas where rocks are exposed along the riverbank, as these are usually good indicators of mineral concentration.

Homogenization of Samples

To ensure that the collected sample is representative of the entire sediment layer, it is crucial to homogenize the sample. This involves mixing the sample thoroughly to distribute the heavy minerals evenly.

An easy and effective way to homogenize the sample is by using a condom filled with water from the river. The condom acts as a barrier between the sample and any external contaminants. Simply fill the condom with water, ensuring that there is no oil present. Then, mix the sample by gently squeezing and releasing the condom for a few seconds.

Concentrating the Sample

Once the sample has been homogenized, it is time to concentrate the heavy minerals. This process involves the following steps:

1. Hold the condom containing the sample with one hand.
2. With a vertical motion, gently shake the condom for approximately 10-15 seconds.
3. After shaking, you will notice that the heavy fraction of minerals has concentrated at the tip of the condom, while the lighter material remains dispersed throughout the rest of the sample.
4. If you are specifically interested in the heaviest minerals, you can selectively collect them from the concentrated tip of the condom. Otherwise, you can discard the lighter material and retain the concentrated heavy fraction for further analysis.

Conclusion

Stream sediment analysis provides valuable insights into the mineralization of a particular area. By concentrating heavy minerals present in stream sediments, we can obtain accurate and representative samples for laboratory analysis. The panning technique, combined with careful sample collection and homogenization, allows us to concentrate the heavy minerals and ensure accurate results. By following these steps, you can effectively analyze stream sediments and gather valuable information about the geochemistry of a given area.

P. Geo. Ricardo A Valls, M. Sc.

Valls Geoconsultant

ORCID ID- https://orcid.org/0000-0002-5421-0914

Scopus Author ID: 7003369619/35335510700

ResearcherID: S-6604-2018

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