What is the origin of this particular conspiracy theory? It seemed to crop up in the 1980s in Posse Comitatus circles and ramped up in the first Clinton administration along with the black helicopters and the Red Chinese armies massing in Mexico theories. But the other two conspiracy theories can be explained.There were actually "black" (really dark olive) helicopters used by the Army in the 1990s. Foreign invaders infiltrating into Mexico is an old scare story, perhaps left over from the Civil War, when the French under Napoleon III took advantage the turmoil in the U.S. to conquer our southern neighbor. During World War I, rumors abounded that the Kaiser was massing the Wehrmacht in Sonora and Chihuahua.
However, the origins of the "gold fringe" conspiracy theory are unknown to me.