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Which type of ore deposit is formed from the crystallization of magmas?
Which type of ore deposit is formed from the crystallization of magmas?
What are the examples of hydrothermal ore deposits?
What are the examples of hydrothermal ore deposits?
Which type of ore deposit is associated with fluid movement during metamorphism?
Which type of ore deposit is associated with fluid movement during metamorphism?
Which of the following is NOT a type of metamorphic ore deposit?
Which of the following is NOT a type of metamorphic ore deposit?
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What type of ore deposits are formed by chemical precipitation or sedimentary processes?
What type of ore deposits are formed by chemical precipitation or sedimentary processes?
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Which of the following is a subtype of hydrothermal ore deposits?
Which of the following is a subtype of hydrothermal ore deposits?
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Supergene ore deposits form primarily due to which process?
Supergene ore deposits form primarily due to which process?
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Which of the following is an example of sediment-hosted copper deposits?
Which of the following is an example of sediment-hosted copper deposits?
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Which mineral is NOT typically found in mineralized pegmatites?
Which mineral is NOT typically found in mineralized pegmatites?
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What is a key feature of mineralized pegmatites that distinguishes them from other igneous rocks?
What is a key feature of mineralized pegmatites that distinguishes them from other igneous rocks?
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Which component significantly lowers the crystallization temperature and increases the mobility of ions in pegmatite formation?
Which component significantly lowers the crystallization temperature and increases the mobility of ions in pegmatite formation?
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Hydrothermal ore deposits are primarily formed from which of the following sources of fluids?
Hydrothermal ore deposits are primarily formed from which of the following sources of fluids?
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What kind of textures do granites that contain high concentrations of rare metals typically exhibit?
What kind of textures do granites that contain high concentrations of rare metals typically exhibit?
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Which of these rare metals is NOT mentioned as commonly found in mineralized pegmatites?
Which of these rare metals is NOT mentioned as commonly found in mineralized pegmatites?
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What geological settings are mineralized pegmatites typically associated with?
What geological settings are mineralized pegmatites typically associated with?
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What mineral is an example of a gemstone that could be found within pegmatites?
What mineral is an example of a gemstone that could be found within pegmatites?
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What primarily composes the iron-rich layers in Banded Iron Formations (BIFs)?
What primarily composes the iron-rich layers in Banded Iron Formations (BIFs)?
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In which tectonic setting are Banded Iron Formations most likely to form?
In which tectonic setting are Banded Iron Formations most likely to form?
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Which model of BIF formation involves hydrothermal fluids at tectonically active regions?
Which model of BIF formation involves hydrothermal fluids at tectonically active regions?
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What is the role of the Great Oxidation Event in the formation of Banded Iron Formations?
What is the role of the Great Oxidation Event in the formation of Banded Iron Formations?
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Which type of layers alternate with the iron oxides in BIFs?
Which type of layers alternate with the iron oxides in BIFs?
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Which mineral is a secondary iron mineral that can form through the weathering of hematite and magnetite?
Which mineral is a secondary iron mineral that can form through the weathering of hematite and magnetite?
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What feature characterizes the layering found in Banded Iron Formations?
What feature characterizes the layering found in Banded Iron Formations?
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In which model does the formation of BIFs occur at the boundary between oxygenated surface waters and anoxic deep waters?
In which model does the formation of BIFs occur at the boundary between oxygenated surface waters and anoxic deep waters?
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What type of minerals are commonly found in Banded Iron Formations (BIFs)?
What type of minerals are commonly found in Banded Iron Formations (BIFs)?
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Which texture is characterized by alternating iron-rich and silica-rich layers in BIFs?
Which texture is characterized by alternating iron-rich and silica-rich layers in BIFs?
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What type of Banded Iron Formation is associated with volcanic sequences and typically has lower iron content?
What type of Banded Iron Formation is associated with volcanic sequences and typically has lower iron content?
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What is the primary characteristic of oolitic or granular texture in BIFs?
What is the primary characteristic of oolitic or granular texture in BIFs?
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What primarily controls the formation of porphyry deposits?
What primarily controls the formation of porphyry deposits?
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Which type of Banded Iron Formation is predominantly Paleoproterozoic in age?
Which type of Banded Iron Formation is predominantly Paleoproterozoic in age?
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What does the term 'microbanding' in BIFs refer to?
What does the term 'microbanding' in BIFs refer to?
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Which metal is typically found in the intermediate zone of a porphyry deposit?
Which metal is typically found in the intermediate zone of a porphyry deposit?
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What process can lead to the recrystallization of iron oxides and chert in BIFs?
What process can lead to the recrystallization of iron oxides and chert in BIFs?
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During metal deposition, what usually causes metals to precipitate out of the hydrothermal fluids?
During metal deposition, what usually causes metals to precipitate out of the hydrothermal fluids?
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Which characteristic is essential for the host rocks in porphyry deposit formation?
Which characteristic is essential for the host rocks in porphyry deposit formation?
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What is a common environmental condition indicated by the presence of sulfides in BIFs?
What is a common environmental condition indicated by the presence of sulfides in BIFs?
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Which type of survey involves detecting chargeability and resistivity anomalies for porphyry exploration?
Which type of survey involves detecting chargeability and resistivity anomalies for porphyry exploration?
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In which zone of porphyry deposits would you typically find high concentrations of As, Sb, and Hg?
In which zone of porphyry deposits would you typically find high concentrations of As, Sb, and Hg?
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What kind of surveys are conducted to identify magnetic anomalies associated with porphyry intrusions?
What kind of surveys are conducted to identify magnetic anomalies associated with porphyry intrusions?
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What process describes the movement of metals like Cu, Mo, and Au within hydrothermal fluids?
What process describes the movement of metals like Cu, Mo, and Au within hydrothermal fluids?
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Study Notes
Classification of Ore Deposits
- Ore deposits are classified based on their origin, mineralogy, host rocks & the processes that formed them.
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Genetic classification:
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Magmatic ore deposits: Crystallized from magmas.
- Examples include: Chromite, magnetite, and platinum group elements in layered mafic intrusions.
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Hydrothermal ore deposits: Formed by hot, metal-rich fluids circulating through rocks.
- Subtypes: Porphyry, Epithermal, Volcanogenic Massive Sulfides (VMS).
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Sedimentary ore deposits: Formed by chemical precipitation or sedimentary processes.
- Examples include: Banded iron formations (BIFs), placer gold deposits, and sediment-hosted copper deposits.
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Metamorphic ore deposits: Formed by metamorphic processes typically involving fluid movement during metamorphism.
- Examples: Gold in orogenic belts, skarn deposits.
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Supergene ore deposits: Formed by the weathering and enrichment of primary mineral deposits near the Earth's surface.
- Examples: Secondary copper deposits, bauxite (aluminum ore).
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Magmatic ore deposits: Crystallized from magmas.
Mineralized Pegmatites
- Coarse-grained igneous rocks known for exceptionally large crystals, often the source of economically important minerals.
- Form during the late stages of magma crystallization.
- Residual melt becomes enriched in water, volatiles, and rare elements.
- Leading to the crystallization of large mineral grains.
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Key features:
- Formation: Form from the final fraction of magma rich in volatile components like water, boron, and fluorine, which lower the crystallization temperature & increase ion mobility.
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Mineralogy: Common minerals include quartz, feldspar, and mica, but contain high concentrations of rare metals.
- Minerals include: lithium (spodumene, lepidolite), tantalum (tantalite), niobium (columbite), beryllium (beryl), tourmaline, and various gemstones.
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Geological setting: Found in orogenic belts, associated with granitic intrusions, and also metamorphic terrains.
- Emplaced as dikes or veins cutting through surrounding rocks.
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Zoning: Often display internal zoning with different minerals concentrated in distinct zones within the pegmatite body.
- Outer zones might consist of large feldspar and quartz crystals, while the inner zones could be enriched in rare-element minerals and gemstones.
Hydrothermal Ore Deposits
- Formed by hot, mineral-rich fluids circulating through fractures and porous rocks in the Earth's crust.
- These fluids, originating from magmatic, metamorphic, or meteoric (surface) water sources, dissolve minerals and transport them to new locations, where they precipitate out to form concentrated deposits of valuable metals and minerals.
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Metal deposition:
- As the hydrothermal fluids move away from the cooling magma, they begin to cool and react with surrounding rocks.
- Metals such as Cu, Mo, and Au are transported as complexes (e.g., chloride complexes) and precipitate out of the solution due to changes in temperature, pressure, or chemical environment.
- Resulting in the formation of disseminated mineralization within the host rock, with metal concentrations often increasing around the stock or core of the intrusion.
Porphyry Deposits Formation
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Controls:
- Subduction zone tectonics: Plate convergence, arc magmatism
- Magmatic processes: Magmatic differentiation, volatile exsolution, intrusive activity (porphyritic intrusions)
- Hydrothermal fluid flow: Hydrothermal circulation, temperature and pressure fluctuation
- Host rock characteristics: Fracture systems (permeability), reactive host rocks (e.g., limestone)
- Metal precipitation mechanisms: Cooling of hydrothermal fluids, chemical reactions (pH, redox changes)
- Tectonic uplift: Post-magmatic tectonics (uplift, erosion)
Metal Zoning in Porphyry Deposits
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Core zone:
- High concentrations of Mo & W, near the central intrusion.
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Intermediate zone:
- Rich in Cu and sometimes Au, typically the most economically valuable zone.
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Outer zones:
- Dominated by Pb, Zn, & Ag, farther from the core.
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Distal zones:
- Includes As, Sb, & Hg, at the outermost edges, possibly transitioning into epithermal systems.
Exploration for Porphyry Deposits
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Methods:
- Geological mapping: Identifying intrusive rocks and alteration zones and extensive structures.
- Geochemical surveys: Soil sampling (analyzing surface soils) and stream sediment sampling.
- Geophysical surveys: Magnetic surveys, induced polarization (IP), and gravity surveys.
- Key features: Layering: Alternating bands of iron oxides and silica.
Banded Iron Formations (BIF)
- Layering: Alternating bands of iron oxides and silica, which can be millimeters to centimeters thick.
- Composition: Iron-rich layers are primarily hematite or magnetite, while silica-rich layers consist of chert or quartz.
- Origin: Formed in ancient oceans, where dissolved iron precipitated out of seawater in response to increasing oxygen levels, a process linked to the Great Oxidation Event.
Tectonic Settings for BIF Formation
- Cratonic basins: Stable, ancient continental regions that hosted large, shallow seas during the Precambrian.
- Mid-Ocean ridges and back-arc basins: Tectonically active settings where hydrothermal activity was prevalent.
- Passive margins: Large continental shelves where upwelling and sedimentation occurred over long periods.
Models of Formation of BIF Deposits
- Hydrothermal model: Formation from iron-rich hydrothermal fluids at mid-ocean ridges or back-arc basins, in tectonically active regions.
- Volcanic-sedimentary model: Formation from volcanic activity releasing iron, with subsequent sedimentation in shallow marine environments, in island arcs, continental rifts, or other volcanically active regions.
- Upwelling model: Formation from upwelling of iron-rich deep waters into oxygenated surface waters, in passive continental margins or large epicontinental seas.
- Chemocline model: Formation at the boundary between oxygenated surface waters and anoxic deep waters (chemocline), in large, stable marine basins with strong stratification.
- Oxidation model (Great Oxidation Event): Formation linked to the rise of atmospheric oxygen, leading to iron oxidation and precipitation, in various settings, dependent on global changes in ocean chemistry.
Banded Iron Formations (BIF) Mineralogy
- Iron oxides: Magnetite, hematite, goethite.
- Silicate: Chert (microcrystalline quartz), jasper.
- Carbonates: Siderite, ankerite.
- Other minerals: Clay minerals, sulfides.
Banded Iron Formations (BIF) Textures
- Banded: Alternating layers of iron-rich and silica-rich layers.
- Granular: Oolitic or granular textures, where iron minerals form small, rounded grains (ooids) within a chert matrix.
- Laminated: Fine lamination of iron oxides and chert, indicating slow deposition in a quiet marine environment.
- Recrystallization: Metamorphic alteration leading to recrystallization of iron oxides and chert.
- Microbanding: Sub-millimeter bands of iron and silica.
Banded Iron Formations (BIF) Types
- Algoma-type BIFs: Associated with volcanic and sedimentary sequences, typically in greenstone belts, mostly Archean in age, formed in small, deep marine basins, often near volcanic centers, typically lower iron content than Superior-type BIFs.
- Superior-type BIFs: Found in large, stable cratonic basins, predominantly Paleoproterozoic in age.
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Description
This quiz covers the classification of ore deposits based on their origins and processes. Topics include magmatic, hydrothermal, sedimentary, metamorphic, and supergene deposits. Test your knowledge of examples and subtypes within these categories.
