  High-velocity clouds (HVCs) are multi-phase gas structures whose velocities
(|v_LSR|>100 km/s) are too high to be explained by Galactic disk rotation.
While large HVCs are well characterized, compact and small HVCs (with HI
angular sizes of a few degrees) are poorly understood. Possible origins for
such small clouds include Milky Way halo gas or fragments of the Magellanic
System, but neither their origin nor their connection to the Milky Way halo has
been confirmed. We use new Hubble Space Telescope/Cosmic Origins Spectrograph
UV spectra and Green Bank Telescope HI spectra to measure the metallicities of
five small HVCs in the southern Galactic sky projected near the Magellanic
System. We build a set of distance-dependent Cloudy photoionization models for
each cloud and calculate their ionization-corrected metallicities. All five
small HVCs have oxygen metallicities <0.17 Z_sun, indicating they do not
originate in the disk of the Milky Way. Two of the five have metallicities of
0.16-0.17 Z_sun, similar to the Magellanic Stream, suggesting these clouds are
fragments of the Magellanic System. The remaining three clouds have much lower
metallicities of 0.02-0.04 Z_sun. While the origin of these low-metallicity
clouds is unclear, they could be gaseous mini-halos or gas stripped from dwarf
galaxies by ram pressure or tidal interactions. These results suggest that
small HVCs do not all reside in the inner Milky Way halo or the Magellanic
System, but instead can trace more distant structures.
