  We present Lick line-index measurements of extragalactic globular clusters in
seven early-type galaxies (NGC 1380, 2434, 3115, 3379, 3585, 5846, and 7192)
with different morphological types (E-S0) located in field and group/cluster
environments. High-quality spectra were taken with the FORS2 instrument at
ESO's Very Large Telescope. About 50% of our data allow an age resolution dt/t
~ 0.3 and a metallicity resolution ~0.25-0.4 dex, depending on the absolute
metallicity. Globular cluster candidates are selected from deep B, V, R, I, K
FORS2/ISAAC photometry with 80-100% success rate inside one effective radius.
Using combined optical/near-infrared colour-colour diagrams we present a method
to efficiently reduce fore-/background contamination down to <10%. We find
clear signs for bi-modality in the globular cluster colour distributions of NGC
1380, 3115, and 3585. The colour distributions of globular clusters in NGC
2434, 3379, 5846, and 7192 are consistent with a broad single-peak
distribution. For the analysed globular cluster systems the slopes of projected
radial surface density profiles, of the form Sigma(R) ~ R^-Gamma, vary between
~0.8 and 2.6. Using globular clusters as a tracer population we determine total
dynamical masses of host galaxies out to large radii (~1.6 - 4.8 Reff). For the
sample we find masses in the range ~8.8*10^10 Msolar up to ~1.2*10^12 Msolar.
The line index data presented here will be used in accompanying papers of this
series to derive ages, metallicities and abundance ratios. A compilation of
currently available high-quality Lick index measurements for globular clusters
in elliptical, lenticular, and late-type galaxies is provided and will serve to
augment the current data set. [abridged]
