LiInSe(2) is one of the few (only 5) non-oxide nonlinear optical crystals whose band-gap (2.86 eV) and transparency allowed in the past nanosecond optical parametric oscillation in the mid-IR without two-photon absorption for a pump wavelength of 1064 nm. However, the first such demonstration was limited to the 3.3-3.78 microm range for the idler and the average idler power did not exceed 2.5 mW. Here we report broadly tunable operation, from 4.7 to 8.7 microm, of an OPO based on LiInSe(2), achieving maximum idler pulse energy of 282 microJ at approximately 6.5 microm, at a repetition rate of 100 Hz (approximately 28 mW of average power).