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Geology - Earth Resources We Depend On

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    Study Guide Geology – Earth Resources We Depend On 1. Metallic Deposits What Are Metallic Ore Deposits? Metals are found in almost all rocks, but usually in very small amounts. These amounts are often too low to be worth mining. Metallic ore deposits are different. They are unusual 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, and technology. 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 titanium 1.1 Mineral Explora Ɵ on: Finding New Ore Deposits Mineral exploration is the search for new ore deposits. In the past, many deposits were easy to find because they were exposed at Earth’s surface. Today, most surface deposits have already been discovered and mined. As a result, modern exploration is more challenging. Scientists now focus on developing new methods to locate ore deposits that lie hundreds or even thousands of feet below the surface , where they cannot be seen directly.

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    Study Guide 1.2 How Metallic Ores Become Concentrated Metallic minerals occur in all types of rocks and even in some soils. However, they only become ore deposits when natural processes concentrate them into rich masses . These processes include: • Igneous processes • Hydrothermal processes • Weathering and erosion 1.3 Igneous (Magma Ɵ c) Ore Deposits Some metals, such as chromium, platinum, nickel, copper, and iron, can form sulfide minerals as magma cools. As the magma cools: • Heavy mineral crystals settle to the bottom of the magma chamber. • These minerals form thin but very high - grade layers . These are called magmatic deposits , and they often form inside intrusive igneous bodies. 1.4 Hydrothermal Ore Deposits Many important metal deposits form from hot, metal - rich fluids called hydrothermal solutions. 1.4.1 Where Do These Fluids Come From? • They may originate from nearby magma intrusions. • They can also be meteoric water (rainwater) that moves deep underground, heats up, and rises again. As these hot fluids move through cracks in surrounding rock, they: • Dissolve metals from 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 Guide 1.4.2 Metals Commonly Found in Hydrothermal Deposits Copper, lead, zinc, gold, silver, molybdenum, tin, mercury, and cobalt. 1.5 Main Types of Hydrothermal Deposits 1. Contact Metamorphic Deposits These form when hot fluids move outward from a cooling intrusion and deposit minerals in cracks in nearby rocks. 2. Hydrothermal Veins These are mineral - filled cracks and faults that may not be directly linked to magma . Some of the richest gold and silver deposits in the world are hydrothermal veins. 3. Disseminated Deposits In these deposits, metal is spread evenly in low concentrations through a large volume of rock. • A major example is the porphyry copper deposit , which contains copper and molybdenum. • Large, low - grade gold deposits in Nevada are also disseminated deposits. 4. Hot Springs Deposits These form at Earth’s surface due to hot spring activity. They may contain gold, silver, antimony, arsenic, and mercury.

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    Study Guide 1.6 Ore Deposits Formed at Earth’s Surface 1.6.1 Mississippi Valley – Type Deposits These deposits contain lead and zinc and form in porous limestone and sandstone. • They are created by low - temperature water pushed out of deeper sediments during compaction. • 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 Deposits Much of the world’s iron and manganese formed when metals were chemically precipitated in ancient oceans and settled on the sea floor. 1.6.3 Placer Deposits Placer deposits form when heavy minerals are concentrated by moving water or waves. Examples include: • Gold • Diamonds • Iron and titanium minerals Even 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 Lateri Ɵ c and Supergene Deposits In tropical climates, intense chemical weathering removes many elements from rock, leaving certain metals behind. • Nickel and aluminum can form rich lateritic deposits. • Gold and copper can also become concentrated downward, forming supergene deposits .

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    Study Guide A rusty, iron - rich surface layer called a gossan may 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 Forma Ɵ on Most metallic ore deposits are linked to plate tectonic activity . 1.7.1 Divergent Plate Boundaries At mid - ocean ridges: • Hot, metal - rich fluids erupt as black 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 Boundaries At subduction zones and island arcs: • Massive sulfide deposits rich in base metals form. • Gold - silver deposits develop near volcanic activity. • Porphyry copper deposits form from magma generated by partial melting of the crust. Some metals in these magmas may come from sea - floor deposits that were subducted and recycled into new magma. 1.7.3 Ultrama fi c Intrusions Chromite deposits can form in ultramafic rocks within new oceanic crust at divergent boundaries. 2. Energy Resources: An Overview Energy resources are materials we use to produce power for electricity, transportation, heating, and industry. The main energy resources include:

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