Earth and Space Sciences Regents, August 2025, question 30
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What the figure shows
The diagram Tectonic Locations Where Mineral and Metal Deposits Form shows seven tectonic settings with the metals and deposits found in each. Granitic plutons in continental crust: tin, tungsten, bismuth, copper; vein: contact metamorphic. Back-arc basin: copper, zinc, gold, chromium; volcanogenic massive sulfide, stratabound, evaporites. Magmatic arc: copper, gold, silver, tin, lead, mercury, molybdenum; porphyry copper: veins. Fore-arc basin: lead, zinc, copper; stratabound in sediments. Subduction zone: chromium; magmatic chromite. Oceanic crust: manganese, cobalt, nickel; manganese nodules. Mid-ocean ridge: copper, zinc; volcanogenic massive sulfide.
How to think about it
The stem gives two clues: a sulfide deposit (pyrite is an iron sulfide), and the metals zinc and copper. Check the Deposits row and the Metals row of each setting against both clues.
Based on the model above, identify the two tectonic settings in which pyrite, a sulfide-based deposit, forms in association with zinc and copper.
Choice 1 is right. Volcanogenic massive sulfide deposits appear in only two settings: the back-arc basin and the mid-ocean ridge. Both settings also list copper and zinc in the Metals row. At both, hot water heated by magma rises through the crust and leaves sulfide minerals on the sea floor.
The fore-arc basin lists zinc and copper, but its deposits are labeled stratabound in sediments, not volcanogenic massive sulfide. Stratabound deposits can also contain sulfides, but the model does not give this setting the volcanogenic massive sulfide label. The magmatic arc lists copper but not zinc, and its deposits are porphyry copper veins.
The mid-ocean ridge fits, but granitic plutons in continental crust list copper without zinc, and their deposits are labeled contact metamorphic veins, not volcanogenic massive sulfide. Contact metamorphic deposits can also contain sulfides, but the model does not give this setting the volcanogenic massive sulfide label.
The subduction zone lists only chromium, in magmatic chromite. The fore-arc basin has zinc and copper, but the model does not give it the volcanogenic massive sulfide label. This choice may come from matching the metals in one setting and not checking the deposit type.
