We present BVI photometry of the globular cluster NGC 6642 using the SOI imager at the SOAR Telescope .
The Colour Magnitude Diagrams ( CMD ) reach \approx 1.5 mag in V below the main sequence turn-off .
A comparison of the overall sequences , and in particular the Red Giant Branch slope of NGC 6642 with that of M 5 indicates that the two clusters must have a similar metallicity of [ Fe / H ] \approx - 1.3 .
We also obtain for NGC 6642 a reddening E ( B-V ) =0.42 \pm 0.03 , and a distance from the Sun of d _ { \odot } =7.2 \pm 0.5 kpc .
Therefore NGC 6642 is a moderately metal-poor globular cluster , spatially located in the bulge , at a galactocentric distance of R _ { GC } \approx 1.7 kpc .
The comparison of CMDs of NGC 6642 with those of M 5 shows that there is a very good match of magnitude difference between turn-off and horizontal branch , suggesting comparable ages .
M 5 has an age typical of the halo globulars , and consequently NGC 6642 is coeval with the halo .
NGC 6642 is a good candidate to be one of the few genuine metal-poor and old bulge clusters , and might be one of the most ancient fossils in the Galaxy .