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We present JWST/NIRSpec R~2700 spectra of four high-redshift quasars: VDESJ0020-3653 (z = 6.860), DELS J0411-0907 (z = 6.825), UHS J0439+1634 (z = 6.519)and ULAS J1342+0928 (z = 7.535). The exquisite data quality, signal-to-noiseratio of 50-200, and large $0.86\!~\mu{\rm m}\le \lambda \le 5.5\!~\mu{\rm m}$spectral coverage allows us to identify between 13 and 17 intervening andproximate metal absorption line systems in each quasar spectrum, with a totalnumber of 61 absorption-line systems detected at 2.42<z<7.48 including thehighest redshift intervening OI 1302 and MgII systems at z=7.37 and z=7.44. Weinvestigate the evolution of the metal enrichment in the epoch of reionizationat z>6 and find: i) A continued increase of the low-ionization OI, CII, andSiII incidence, ii) Decreasing high-ionization CIV and SiIV incidence with atransition from predominantly high- to low-ionization at $z\approx6.0$, andiii) a constant MgII incidence across all redshifts. The observations support achange in the ionization state of the intergalactic medium in the EoR ratherthan a change in metallicity. The abundance ratio of [Si/O] in five z>6absorption systems show enrichment signatures produced by low-mass Pop III pairinstability supernovae, and possibly Pop III hypernovae. In the Gunn-Petersontroughs we detect transmission spikes where Ly$\alpha$ photons can escape. From22 absorption systems at z>5.7, only a single low-ionization system out of 13lies within 2000 km/s from a spike, while four high-ionization systems out ofnine lie within ~2000 km/s from a spike. This confirms that galaxiesresponsible for the heavy elements that are transported into the circumgalacticmedium lie in predominantly in high-density, neutral environments, while lowerdensity environments are ionized without being polluted by metals at $z\approx$6-7. [abridged]

Metal enrichment and evolution in four z > 6.5 quasar sightlines observed with JWST/NIRSpec