Earth’s Buried Treasures Earth Science Earth’s Buried Treasures An Introduction to Earth Materials: Minerals

The Importance of Minerals

Definition of a Mineral A Mineral is: Naturally Occurring Inorganic Solid Definite chemical composition Orderly internal arrangement of atom Gemstones Mineraloids lack an internal arrangement of atoms

Rocks vs. Minerals Minerals are the components of rocks. A thorough understanding of minerals provide a better understanding of the formation of rocks.

Elements of the Earth’s Crust An element is a substance that cannot be broken down into simpler, stable substances by chemical means. Each element has physical and chemical properties that can be used to identify it. The diagram above shows common elements in Earth’s crust. Approximately 90 elements occur naturally on Earth. Eight of these make up more than 98%of Earth’s crust.

Major Mineral Group: The Silicates Oxygen and Silicon are the most abundant elements in the Earth’s crust so… The Silicates are the most abundant group Made up of the Silicon-Oxygen Tetrahedron Identified by the SiO in the chemical formula Example: AlSiO2

Other Mineral Groups To determine the mineral group, look at the last part of the chemical formula

Other Mineral Groups

Mineral Resources Earth’s crust contains useful mineral resources. The processes that formed many of these resources took millions of years. Many of these mineral resources are mined for human use. Mineral resources can be either metals, such as gold, Au, silver, Ag, and aluminum, Al, or nonmetals, such as sulfur, S, and quartz, SiO2. If a volume of rock is enriched enough in an element or mineral to be potential valuable it is called a mineral deposit

Mineral Environments of Formation Mineral Environments refers to the "geologic environments" in which minerals occur – the types of rocks in which they are found.  While some minerals occur in two or more environments, others tend to be restricted to a single environment.  Example: If you think you have found the mineral kyanite in a sedimentary sandstone and see that it is a mineral formed by metamorphic processes you’ll know it can’t be kyanite.  Try celestite…  If you think you have found topaz in a cavity in basalt and read that it is largely restricted to pegmatite you’ll know it isn’t topaz.  And so on. Chapter18.9

Mineral Environments of Formation Ores form in a variety of ways, as shown below. Some ores, such as ores of chromium, Cr, nickel, Ni, and lead, Pb, form within cooling magma. As the magma cools, dense metallic minerals sink. As the minerals sink, layers of these minerals accumulate at the bottom of the magma chamber to form ore deposits. By knowing how specific minerals and the environments in which they form you can make an interpretation of paleo-environments as well as locate mineral resources. You can also use this to differentiate between similar appearing minerals

Mineral Environments of Formation The environments of mineral formation and growth are highly varied, ranging from slow crystallization at the high temperatures and pressures of igneous melts deep within the Earth's crust to the low temperature precipitation from a saline brine at the Earth's surface. Various possible methods of mineral formation include: - sublimation from volcanic gases - deposition from aqueous solutions and hydrothermal brines - crystallization from an igneous magma or lava - recrystallization due to metamorphic processes and metasomatism - crystallization during diagenesis of sediments - formation by oxidation and weathering of rocks exposed to the atmosphere or within the soil environment.

Mineral Environments of Formation 18.09.c Igneous crystallization Hydrothermal deposition EXPLANATION Igneous crystallization can concentrate minerals by crystal settling Hydrothermal deposition: from hot water along fracture (vein), hot springs, or vents on sea floor Hydrothermal replacement: fluids permeate rock and replace original minerals with ore minerals Metamorphism can allow new crystals to form, like these kyanite crystals used at one time for sparkplugs Volcanism can bring up precious minerals formed at depth, like these diamond pipes NOTES Igneous crystallization: magnetite layer over anorthosite, Bushveld, South Africa Hydrothermal deposition: gold vein, Oatman, Arizona Hydrothermal replacement: Rooiberg tin mine, South Africa Metamorphism: western Arizona Volcanism: Kimberly, South Africa Hydrothermal replacement Volcanism and volcanic pipes Metamorphism

Minerals Formed in Igneous Environments Mineral Environments of Formation Minerals Formed in Igneous Environments Quartz Na/Ca Feldspar K Feldspar Mica (Plagioclase) (Orthoclase) (Biotite) Mica Amphibole Pyroxene Olivine (Muscovite) 14

Minerals formed in Metamorphic Environments Mineral Environments of Formation Minerals formed in Metamorphic Environments Quartz Na/Ca Feldspar K Feldspar Mica Mica (Plagioclase) (Orthoclase) (Biotite) (Muscovite) Serpentine Chlorite Garnet Calcite 15

Important Base Metal Deposits Mineral Environments of Formation Important Base Metal Deposits Ores Hematite (Iron) Galena (Lead) Bauxite (Aluminum) Bornite (Copper) Sphalerite (Zinc) Apatite (Phosphorous Used in Fertilizers) 16

Where do Platinum deposits occur? Mineral Environments of Formation Where do Platinum deposits occur? Most Platinum deposits are associated with mafic or ultramafic igneou rocks that come from the mantle and rose into the crust. Pictured is the Bushveld Complex in South Africa. The dark layers are platinum and chromite and the light layers are anorthosite.

Two Other Types of Metal Deposits Mineral Environments of Formation Two Other Types of Metal Deposits Mississippi Valley lead-zinc deposits Sudbury nickel deposits EXPLANATION Mississippi Valley deposits have lead and zinc and formed by saline waters flowing through sedimentary rocks Sudbury nickel deposits formed with layered intrusion, perhaps triggered by a meteorite impact that left behind joints called shatter cones NOTES Mississippi Valley photograph: fluorite, galena, and calcite from central U.S. Shatter cones (from impact) 18.11.d

How do precious metal deposits form? Mineral Environments of Formation How do precious metal deposits form? Veins from hot water Veins in metamorphic rocks Gold in gravel EXPLANATION Hydrothermal fluids deposit gold and silver in veins, commonly near volcanic centers or plutons Veins can form during metamorphism and redistribute gold, or gold veins can be introduced later Gold is dense and accumulates at bottom of river gravels Some gold-bearing gravels have been buried, like in South Africa Gold is so expensive that large volumes of rocks that are only a little bit rich in gold are mined Gold is produced from large copper mines, adding more value to the copper ore Gold-bearing conglomerates (placer deposits) By-product gold Low-grade gold deposits 18.10.a

Mineral Environments of Formation Quartz Vein with Gold Deposits

Mineral Environments of Formation Diamond Formation Kimberlite is the type of rock typically associated diamonds Diamonds do not originate from the metamorphism of coal but rather form in the mantle and are brought to the surface by geologic features called kimberlite pipes

Mineral Environments of Formation Other sources of diamond formation: Kimberlite Pipe (most common) Subduction Zones Asteroid Impact Sites Meteorites (brought by meteorites)

Mineral Environments of Formation Rubies are a form of corundum, a rare mineral made up of densely packed aluminum and oxygen atoms, which are normally colorless. When other atoms are substituted for a few of the aluminum ones, bright hues emerge. Small amounts of chromium impart the deep red color of ruby, traces of titanium and iron produce the stunning blue of sapphire, and chromium and ferric iron create the delicate orange shades of the extremely rare and costly padparadscha.

Mineral Environments of Formation Where do Copper Deposits form? Porphyry copper deposits Massive sulfide deposits Sedimentary copper deposits EXPLANATION Porphyry copper deposits form near plutons below composite volcanoes Massive sulfide deposits are formed by black smokers Sedimentary copper deposits form in several ways, from groundwater NOTES Ore and porphyry: Boulder Mountains, Montana Massive sulfide: Ansil deposit, Quebec, Canada Copper: central Arizona 18.11.a

Mineral Environments of Formation 18.09.c Formation by weathering Weathering enrichment EXPLANATION Extreme weathering can leach away most material, concentrating less mobile elements such as nickel or aluminum (such as at this bauxite mine) Elements can be leached from rocks by weathering, carried by groundwater, and deposited elsewhere (copper) Transport in rivers or wave action on beaches can concentrate valuable minerals, such as diamond in these river gravels Salt, gypsum, and other commodities can be precipitated in lakes and seas NOTES Formation by weathering: bauxite mine, eastern India Weathering enrichment: Silverbell, Arizona Mechanical concentration: Kimberly, South Africa Low-Temp precipitation: Gypsum, Colorado Mechanical concentration Low-temperature precipitation

Minerals formed From Weathering Mineral Environments of Formation Important Minerals Minerals formed From Weathering Quartz Kaolinite Hematite Bauxite 26

Mineral Environments of Formation Gold that has been liberated by weathering and erosion get carried away by streams and deposit within placer deposits

Where do base metal deposits form? Minerals as Indicators of Ancient Environments Where do base metal deposits form? Most of our iron ores are mined from formations called banded iron formations (BIF’s) . These iron and quartz rich layers are an indication of the Great Oxygenating event that occurred during the Precambrian 2 billion years ago Other iron ore deposits form as magma intrudes into the crust and releases metal rich fluids

Evaporites and Precipitants Mineral Environments of Formation Evaporites and Precipitants Gypsum and Halite are examples of evaporites. These minerals from in low temperature aqueous environments. Calcite and Travertine are examples of precipitants. These minerals precipitate out of water under the correct environmental conditions.

Marine evaporite deposits in the United States Minerals as Indicators of Ancient Environments Gypsum and Halite are evaporites that form by the evaporation of ocean water. Thus these deposits indicate the location of ancient seas

Minerals as Indicators of Ancient Environments This image, taken by the Mars Exploration Rover Opportunity's panoramic camera, is an approximate true-color rendering of the "Berry Bowl," a rock in the "Eagle Crater" outcrop that contains pebble-like hematite spherules Marble-like hematite concretions litter the Navajo Sandstone surface in southern Utah's Grand Staircase-Escalante National Monument.

Minerals as Indicators of Ancient Environments

Earth’s Buried Treasures Conclusion Earth’s Buried Treasures An Introduction to Earth Materials: Minerals