This is not without error I am sure (I am a grad student in medieval literature with some experience translating Latin), but it reads roughly as follows:
Negros, having exhaused the veins of metal, had to give labor to make sugar.
Initially then, the Spanish used the work of the Negroes to boil up the metallic veins, but after those were exhausted, the government began to use these at the mills which processed sugar cane, to gather up and cook the sugar: in that service they are still for the most part occupied. In fact, with the Island so humid and hot, sugar canes and reeds grow(?) with little trouble; the [stuff] is crushed [out] and thrown in pots, and boiled, and after being cleaned and dried into sugar, a great profit is typically made. Besides this, the work of these Negroes is used in the care of the herds, and the remaining administrative matters which are necessary to their use.
Thanks so much for this!