Ore Genesis Theories and Processes Midterm Exam

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Questions and Answers

What is the branch of applied geology dealing with the genetic study of ore deposits?

Ore Geology

Define ore and ore deposits.

Ore: metalliferous mineral or an aggregate of metalliferous minerals, more or less mixed with gangue, that can be won at a profit. Ore Deposits: contain an unusually high concentration of particular element(s) or parts of the crust where ores are concentrated.

What are ore minerals and gangue minerals?

Ore minerals have economic value and are those from which metals are extracted, e.g. chalcopyrite and galena. Gangue minerals are usually worthless, non-metallic minerals of a deposit.

What does the term 'syngenetic' refer to in the context of ore deposits?

Ore deposits that form at the same time as their host rocks. Signup and view all the answers

What is metallogeny and metallotect?

Metallogeny is the study of the genesis of mineral deposits, and metallotect refers to any geological, tectonic, lithological, or geochemical feature that has played a role in the concentration of elements in the Earth's crust. Signup and view all the answers

What is the specific gravity of gold?

19gm/cc Signup and view all the answers

Name one economically important placer deposit mineral other than gold.

Diamonds (carbon) Signup and view all the answers

What chemical process can concentrate minerals through chemical weathering and erosion?

Progressive dissolution of silica from clays in wet soils Signup and view all the answers

What is the specific gravity of Cr spinel compared to basaltic magma?

Cr spinel: 4800 kg/m3, Basaltic magma: 2500 kg/m3 Signup and view all the answers

What type of melt can be rich in niobium, tantalum, rare earths, copper, thorium, and phosphorous?

Carbonate melts Signup and view all the answers

What are the primary mechanisms for concentrating minerals into ores?

Sorting by density or sorting by solubility Signup and view all the answers

What are the three main steps for making a placer deposit?

A. Weathering removes mineral particles from country rock. B. Kinetic energy of high-velocity stream transports mineral particles. C. Where kinetic energy drops suddenly, high-density particles stop, lower density particles continue Signup and view all the answers

What is the geochemical anomaly that characterizes an ore?

An ore is a geochemical anomaly resulting from the removal, transport, and concentration of specific elements, compounds, or minerals from ordinary rock. Signup and view all the answers

Give an example of how mechanical weathering and erosion can concentrate minerals.

Quartz sand typically mined from ancient beaches, sand bars, etc. Signup and view all the answers

What are placer deposits, and how are they formed?

Placer deposits are deposits of heavy mineral particles in a stream bed, formed through the steps of weathering, transportation, and density contrasts. Signup and view all the answers

Study Notes

Economic Geology

Economic geology is the branch of applied geology that deals with the genetic study of ore deposits.

Ore and Ore Deposits

Ore is a naturally occurring mineral or rock from which a valuable substance, such as a metal, can be extracted at a profit.
Ore deposits are naturally occurring concentrations of ore that can be economically extracted.

Ore Minerals and Gangue Minerals

Ore minerals are minerals that contain valuable elements, such as metals, that can be extracted for profit.
Gangue minerals are minerals that are found in ore deposits but do not contain valuable elements.

Syngenetic

Syngenetic refers to the formation of ore deposits simultaneously with the formation of the surrounding rocks.

Metallogeny and Metallotect

Metallogeny is the study of the origin and distribution of ore deposits.
Metallotect refers to the tectonic processes that control the formation of ore deposits.

Physical Properties

The specific gravity of gold is 19.3.
The specific gravity of Cr spinel compared to basaltic magma is higher.

Placer Deposits

Placer deposits are deposits of sand and gravel that contain valuable minerals, such as gold, that have been concentrated by water or wind.
Cassiterite (tin oxide) is an economically important placer deposit mineral other than gold.

Concentration of Minerals

Chemical weathering and erosion can concentrate minerals through the process of residual enrichment.
Mechanical weathering and erosion can also concentrate minerals, for example, through the formation of placer deposits.
The primary mechanisms for concentrating minerals into ores are magmatic segregation, metasomatism, and hydrothermal activity.
The three main steps for making a placer deposit are: • Weathering and erosion of source rocks • Transportation of minerals by water or wind • Deposition and concentration of minerals in a new location

Geochemical Anomaly

A geochemical anomaly that characterizes an ore is an unusual concentration of a particular element or elements in the rocks.

Formation of Placer Deposits

Placer deposits are formed through the concentration of heavy minerals, such as gold or cassiterite, in streams, rivers, and coastal areas.
A type of melt that can be rich in niobium, tantalum, rare earths, copper, thorium, and phosphorous is a carbonate-rich magma.

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Description

Test your knowledge of major theories of ore genesis, ore forming processes, texture and structure of ore and gangue minerals, fluid inclusions, wall rock alteration, geothermometry, geobarometry, plate tectonics, and magmatic-hydrothermal ore-forming processes.