#epithermal

Source: PORPHYRY AND EPITHERMAL MINERAL DEPOSITS

Porphyry and epithermal deposits are two major types of hydrothermal ore deposits formed by magmatic fluids during the cooling and crystallization of magma bodies beneath the Earth's surface. Porphyry deposits are typically large, low-grade systems associated with copper and gold, while epithermal deposits are smaller, high-grade veins rich in gold and silver, forming at shallower crustal levels. The following explains a comparative geological cross-section illustrating the formation environments and characteristics of porphyry copper-gold (Cu-Au) and epithermal gold-silver (Au ± Ag) deposits:

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PORPHYRY AND EPITHERMAL MINERAL DEPOSITS Porphyry and epithermal deposits are two major types of hydrothermal ore deposits formed by magmatic fluids during the cooling and crystallization of magma bodies beneath the Earth's surface. Porphyry deposits are typically large, low-grade systems associated with copper and gold, while epithermal deposits are smaller, high-grade veins rich in gold and silver, forming at shallower crustal levels. The following explains a comparative geological cross-section illustrating the formation environments and characteristics of porphyry copper-gold (Cu-Au) and epithermal gold-silver (Au ± Ag) deposits: 1. Porphyry Cu-Au System (Left Side of Diagram) Location in Crust: Forms at greater depths and larger in size. Rock Alteration Zones: Potassic/Hornfels Zone: Closest to the magmatic source; high-temperature alteration. Phyllic/Argillic Zone: Intermediate alteration zone with quartz-sericite-pyrite minerals. Propylitic Zone: Outer alteration zone with chlorite, epidote, and calcite. Structures: Includes D-veins, breccia pipes, and stockworks within wallrock porphyry. Associated Deposits: Yanacocha and Veladero are key examples. 2. Epithermal Au ± Ag System (Right Side of Diagram) Location in Crust: Forms nearer to the surface in volcanic and sedimentary settings. Types: High Sulphidation: Associated with acidic fluids, advanced argillic alteration, and diatremes (e.g., Lepanto, La Arena). Low Sulphidation: Neutral-pH fluids forming in structurally controlled zones (e.g., Pajingo, Hishikari). Alteration Zones: Includes clay-rich zones, silica caps, and vuggy quartz structures. Host Rocks: Varies from tuffs, sandstones, andesites to metamorphic basement. 3. Geological Context Magmatic Source: Drives hydrothermal fluid flow leading to metal precipitation. Structural Controls: Faults, domes, and fracture zones guide mineralizing fluids. Rock Types: Include lapilli tuff, sandstone, andesite, welded tuff, and metamorphic rocks.