The official Facebook page for the R&B group -- comprised of three Hutchinson sisters -- made the announcement Sunday, saying Pam passed away Friday ... going on to explain she succumbed to health issues she'd been battling for years.

They add, "Now our beautiful sister will sing amongst the angels in heaven in perfect peace. During this time, the family kindly asks for fans and friends to respect our privacy. We appreciate all kind words, photos, and videos you may want to post for our beloved Pamela and of course your loving prayers."

Of Pam, the group also says ... "A life so beautifully lived deserves to be beautifully remembered. We love you, Pamela!"

Pam was the youngest of the famous trio -- her older sister, Wanda and Sheila are a good 5 to 7 years older than her ... which might have to do with the fact that Pam actually replaced the other original sister, Jeanette. Despite their age differences, The Emotions left their mark in music history ... of course, with a major contribution of Pamela as one their key singers.

The group got its start in the '60s, but skyrocketed to mainstream fame in the 1970s with a string of hits that landed on the Billboard charts. They're perhaps best known for their single "Best of My Love," but they also have a legendary collab with Earth, Wind and Fire.

The girls served as the backup singers for "Boogie Wonderland" -- a gig that landed them a Grammy nomination in 1979 ... this after they'd already won one a couple years prior. Over the span of their multi-decade career, they cranked out 9 albums ... 2 of which achieved were certified gold, and one platinum. The Emotions pumped out countless singles too.