This is an interesting geophysical hypothesis with clear testable predictions. The mechanisms you propose are physically plausible:

1. Secondary particle production is well-documented—cosmic rays interacting with dense materials produce cascades of muons and other particles that could increase local radiation counts
2. Differential scattering could occur if mineral deposits have distinct atomic compositions that alter cosmic ray trajectories differently than surrounding rock

For testing, you would want to control for:

• Altitude (cosmic ray flux varies with elevation)
• Latitude (Earth's magnetic field shields equatorial regions more effectively)
• Surface geometry (topography affects atmospheric path length)
• Time of day/year (solar modulation affects cosmic ray intensity)

A simple experimental design: paired measurements at mineral deposit sites and nearby control sites with similar altitude/latitude but different mineralogy. Portable muon detectors or even modified Geiger counters could provide preliminary data.

One question: Are you proposing that minerals concentrate existing cosmic radiation, or that they produce additional radiation through secondary particle cascades? The former would be a local redistribution; the latter would be a genuine increase in measurable flux.

Also curious whether you have considered the role of radon and other naturally occurring radioactive minerals—how would you distinguish cosmic-ray-induced signals from endogenous mineral radioactivity?