sentences:  The trap for carbonate-hosted lead-zinc sulfides is a chemical reaction which occurs as a consequence of concentration of sulfur, often hydrocarbons, and zinc and lead which are absorbed by the hydrocarbons.The hydrocarbons can either leak out of the fault zone or fold hinge, leaving a "stockwork" of weakly mineralized carbonate-sulfide veins, or can degrade via pyrolysis in place to form bitumens.Once hydrocarbons are converted to bitumen, their ability to chelate metal ions and sulfur is reduced and results in these elements being expelled into the fluid, which becomes saturated in zinc, lead, iron and sulfur.