Geology - Earth Resources We Depend On - Quick Guides | Geology

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Study GuideGeology–Earth Resources We Depend On1. Metallic DepositsWhat Are Metallic Ore Deposits?Metals are found in almost all rocks, but usually in very small amounts. These amounts are often toolow to be worth mining.Metallic oredepositsare different. They areunusual concentrations of metal-rich minerals,usually sulfides, that contain enough metal to be mined for profit.Whether mining is profitable depends on many factors, such as metal prices, mining costs, andtechnology.Some of the most important metals we rely on include:•Iron, copper, and aluminum•Lead, zinc, silver, and gold•Chromium, nickel, cobalt, and manganese•Molybdenum, tungsten, vanadium, tin, and mercury•Magnesium, platinum, and titanium1.1Mineral ExploraƟon: Finding New Ore DepositsMineral explorationis the search for new ore deposits. In the past, many deposits were easy to findbecause they were exposed at Earth’s surface. Today, most surface deposits have already beendiscovered and mined.As a result, modern exploration is more challenging. Scientists now focus on developing new methodsto locate ore deposits that liehundreds or even thousands of feet below the surface, where theycannot be seen directly.

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Study Guide1.2 How Metallic Ores Become ConcentratedMetallic minerals occur in all types of rocks and even in some soils. However, they only become oredeposits when natural processesconcentrate them into rich masses. These processes include:•Igneous processes•Hydrothermal processes•Weathering and erosion1.3 Igneous (MagmaƟc) Ore DepositsSome metals, such as chromium, platinum, nickel, copper, and iron, can formsulfide mineralsasmagma cools.As the magma cools:•Heavy mineral crystals settle to the bottom of the magma chamber.•These minerals formthin but very high-grade layers.These are calledmagmatic deposits, and they often form inside intrusive igneous bodies.1.4 Hydrothermal Ore DepositsMany important metal deposits form fromhot, metal-rich fluidscalled hydrothermal solutions.1.4.1 Where Do These Fluids Come From?•They may originate from nearby magma intrusions.•They can also bemeteoric water(rainwater) that moves deep underground, heats up, andrises again.As these hot fluids move through cracks in surrounding rock, they:•Dissolve metalsfrom the rocks they pass through.•Deposit metals when pressure and temperature change.This process often happens repeatedly until the heat source cools or the cracks become filled.

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Study Guide1.4.2Metals Commonly Found in Hydrothermal DepositsCopper, lead, zinc, gold, silver, molybdenum, tin, mercury, and cobalt.1.5 Main Types of Hydrothermal Deposits1. Contact Metamorphic DepositsThese form when hot fluids move outward from a cooling intrusion and deposit minerals in cracks innearby rocks.2. Hydrothermal VeinsThese are mineral-filled cracks and faults thatmay not be directly linked to magma.Some of the richest gold and silver deposits in the world are hydrothermal veins.3.Disseminated DepositsIn these deposits, metal isspread evenlyin low concentrations through a large volume of rock.•A major example is theporphyry copper deposit, which contains copper and molybdenum.•Large, low-grade gold deposits in Nevada are also disseminated deposits.4. Hot Springs DepositsThese form at Earth’s surface due to hot spring activity.They may contain gold, silver, antimony, arsenic, and mercury.

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Study Guide1.6 Ore Deposits Formed at Earth’s Surface1.6.1 Mississippi Valley–Type DepositsThese deposits contain lead and zinc and form in porous limestone and sandstone.•They are created bylow-temperature waterpushed out of deeper sediments duringcompaction.•These deposits are common in the central United States.•Unlike most ore deposits, they may not be linked to igneous heat.1.6.2 Marine Chemical DepositsMuch of the world’s iron and manganese formed when metals werechemically precipitated inancient oceansand settled on the sea floor.1.6.3 Placer DepositsPlacerdepositsform when heavy minerals are concentrated by moving water or waves.Examples include:•Gold•Diamonds•Iron and titanium mineralsEven if the original source rock contained only small amounts of metal, weathering, erosion, transport,and deposition can create rich concentrations in rivers or beaches.1.6.4 LateriƟc and Supergene DepositsIn tropical climates, intense chemical weathering removes many elements from rock, leaving certainmetals behind.•Nickel and aluminumcan form rich lateritic deposits.•Gold and copper can also become concentrated downward, formingsupergene deposits.

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Study GuideA rusty, iron-rich surface layer called agossanmay be the only visible sign of a buried ore deposit.Finding a gossan often suggests valuable minerals exist below.1.7 Plate Tectonics and Metallic Ore FormaƟonMost metallic ore deposits are linked toplate tectonic activity.1.7.1 Divergent Plate BoundariesAt mid-ocean ridges:•Hot, metal-rich fluids erupt asblack smokers.•These fluids deposit iron, copper, zinc, lead, gold, and silver on the sea floor.•Dense metal-rich fluids can collect in ocean basins and form rich deposits.1.7.2 Convergent Plate BoundariesAt subduction zones and island arcs:•Massive sulfidedeposits rich in base metals form.•Gold-silver deposits develop near volcanic activity.•Porphyry copper depositsform from magma generated by partial melting of the crust.Some metals in these magmas may come from sea-floor deposits that were subducted and recycledinto new magma.1.7.3 Ultramafic IntrusionsChromite deposits can form in ultramafic rocks within new oceanic crust at divergent boundaries.2. Energy Resources: An OverviewEnergy resources are materials we use to produce power forelectricity, transportation, heating, andindustry. The main energy resources include:

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