Have to wonder if the rock chips were / were not subjected to much weathering as it sounds like this is important.
If the rock chips with the high grade were not as exposed to weathering/Leaching this would IMO be encouraging, particularly if the lower grade chips were likely subject to leaching.
Complex field this geology - no wonder ye olde traditional drill rig separates the wheat from the chaff.
Looking forward to the drilling program.
The impact of weathering on rock chip samples, particularly concerning lead (Pb) concentrations, can vary depending on several factors such as the mineralogy of the rock, the local climate, and the duration of exposure to weathering processes.
Weathering Processes and Lead Concentration
Chemical Weathering:
- Oxidation and Hydrolysis: Lead-bearing minerals such as galena (PbS) can undergo chemical weathering processes. When exposed to oxygen and water, galena can oxidize to form secondary minerals like cerussite (PbCO3) and anglesite (PbSO4). These secondary minerals can remain in the rock, potentially increasing the apparent lead concentration in the weathered rock chip samples.
- Leaching: In areas with significant rainfall or acidic conditions, lead can leach out of the rock. This leaching process can reduce the lead concentration in surface rock chips over time. The extent of lead leaching depends on factors such as pH, temperature, and the presence of organic acids.
Physical Weathering:
- Physical weathering processes, like freeze-thaw cycles, do not significantly alter the chemical composition of the rock but can break it into smaller pieces, exposing fresh surfaces to chemical weathering processes.
Influence of Local Climate
- Arid Climates: In dry, arid climates, the rate of chemical weathering is generally slower, and lead is less likely to leach out. Thus, lead concentration might remain relatively stable in surface rock chips.
- Humid Climates: In contrast, humid climates with higher rainfall can enhance chemical weathering and leaching processes, potentially decreasing the lead concentration in surface samples over time.
Impact on Lead Concentration in Rock Chips
- Retention of Lead: In many cases, secondary lead minerals formed during weathering are not highly soluble in water, which means that lead may stay within the rock or be redeposited nearby, thus maintaining or even increasing the lead concentration in surface rock chips.
- Leaching of Lead: In environments with intense weathering and high leaching potential, lead can be removed from the rock chips, reducing their concentration.
Conclusion
The impact of weathering on lead concentration in rock chip samples is complex and site-specific. While chemical weathering can lead to the formation of secondary lead minerals that may stay in the samples, leaching under certain conditions can decrease lead concentration. Therefore, to accurately assess the lead content and its mobility, it is crucial to consider the specific environmental conditions and the nature of the lead-bearing minerals in the rock.
For a more detailed understanding, examining local geological surveys and weathering studies specific to the region of interest, such as those conducted by geological institutions or mining companies, would provide more precise insights.
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