Who knows the title: B-movie, 1970s (?), set in South America, women abducted into the jungle

Hi folks,
here's what I remember of another movie which I once had in my collection but then lost somewhere:
Date of production - possibly the 1970s, maybe late 1960s; I saw some beautiful old cars on the streets of the city; not quite as old as those limousines from the 1950s which we can still see in Cuba, but definitely older than models like Volkswagen "Golf" or even Japanese types
Movie was filmed in Southern America - in some scenes we see the centre of a city (neither a metropole nor a small village), with a big market place, a beautiful big old church built in the colonial period.
In a modest little hotel (neither luxury class nor a shabby 3rd class kind of house) there was lodged a group of several young women (turists from various cuntries, mainly from the U.S., I think)... and one night, a number of them got abducted. In the city there were some canals similar to those in Venice; and I remember having seen a small "canoe-type" boat with some masked men rowind/paddling along one of these, taking away some of the women with them. These bad guys were clad like some sort of monks so that you couldn't see any details of their faces...
Later the group proceeded through dense forest and from that part I remember one scene: One of the women hat cut herself a small wound on a sharp stone or something, and then one of the abductors put some leaves of a plant on the wound which then mysteriously disappeared - now that these men no longer wore their "camouflage" but only loincloths, it was to see that they were muscle-packed; all of them had their heads shaved AND no one ever spoke a word (all through the movie)!
After some time of wandering through the jungle / rain forest they arrived at a secret place; it was a system of caves within a hill / mountain, either of natural origin or carved out, I don't know. There was a group of several dozens of women and it seems they all belonged to some sort of secret "order" or "sect", whatever; they had a female leader. And it turned out that there were other women who didn't belong to this group but hade been (I think) earlier abducted too and they were locked up in cages, small cells carved out of the rock... AND one single man who was NOT shaved bald and not mute either. This latter one was in a certain relationship with the female leader (I don't know whether they were a couple or he was just her servant, helphand, whatever). In any case, that guy wore a big amulet on a necklace...
So far, this is already pretty absurd, isn't it? An obscure B-movie, as I said. Sometimes I really love to waste time with that kind of stuff - AND I hope some of you moviebuffs out there has already yelled "Yeah!! I KNOW it!! This must be X, made by director Y in 19-... !!!")
All right, here's one more detail I found really interesting: At one point I think the guy with the amulet says something like "had I only left when I still could"... which made me think that he wasn't part of the "community" from the start but rather had been abducted, too... On the other hand, that means he must have won the "leading woman"'s confidence; how could he otherwise have obtained the amulet?
At one point late in the movie that guy ages very fast and is left alone in the jungle where he presumably dies...
If my recollection is correct, only one woman finally manages to escape from the "colony", with the aid of the aforementioned man; and she gets back to freedom.
What the true nature of the "colony" was I am at a loss to understand. A group of gone-mad people under a leading person who was also mad (Jones in Guayana, back in the 1970s?) - or maybe it had to do with some aliens ??
I think this is one of these movies where you are left in the end with more questions than solutions!!
Kind regards
Andreas (123all4me)