Guyana’s port city of Bartica sits where the Cuyuni, Essequibo and Mazaruni rivers meet. It has long served as a launching point for gold and diamond miners—known as pork-knockers—on their dangerous journey into the wilderness in search of fortune. Nicknamed after the pickled peccary, or wild hog, they often eat, the pork-knockers scatter throughout the dense jungle in small mining outfits of a dozen or so people. Countless pieces of jewelry gleaming in shop windows around the world have their origins here, in the back-breaking labor of the pork-knockers and…