  We study ultra-high-energy particle collisions and optical effects in the
extraordinary class of mining braneworld Kerr-Newman (KN) naked singularity
spacetimes, predicting extremely high efficiency of Keplerian accretion, and
compare the results to those related to the other classes of the KN naked
singularity and black hole spacetimes. We demonstrate that in the mining KN
spacetimes the ultra-high centre-of-mass energy occurs for collisions of
particles following the extremely-low-energy stable circular geodesics of the
\uvozovky{mining regime}, colliding with large family of incoming particles,
e.g., those infalling from the marginally stable counter-rotating circular
geodesics. This is qualitatively different situation in comparison to the
standard KN naked singularity or black hole spacetimes where the collisional
ultra-high centre-of-mass energy can be obtained only in the near-extreme
spacetimes. We also show that observers following the stable circular geodesics
of the mining regime can register extremely blue-shifted radiation incoming
from the Universe, and see strongly deformed sky due to highly relativistic
motion along such stable orbits. The strongly blue-shifted radiation could be
thus a significant source of energy for such orbiting observers.
