Economic Geology Flashcards
What are Cu and Al used for?
wire, construction (aluminum)
What is Ge used for?
Semiconductors, transistors, and optics
Where does gold occur?
hydrothermal deposits, placers
Where are lead and magnesium found?
hydrothermal deposits
Where do most valuable metals occur?
most occur as atomic substitutions in more abundant rock-forming minerals
Where are most ore minerals found as?
Sulphides
ore minerals such as iron, tin, and tungsten occur as…
oxides
Define gangue
non-valuable minerals that metals occur in
Define hydrothermal mineral deposits?
minerals are concentrated by hot aqueous solutions flowing through fractures and pores in the substrate
Define magmatic mineral deposits
Formed by concentration of magmatic processes within a body of igneous
Define sedimentary mineral depostis
formed by precipitation from concetrated, modified sea water
How are placers formed?
Concentration by flowing surface water in streams
or along the shore
How residual minerals deposits are formed
Concentration by weathering processes
What three rules govern the formation of concentrated minerals
1. Source rocks or magma enriched in metals that can be supplied to the “ ore-forming” system 2. Transport melt or fluid that can carry metals from a source to a site of deposition 3. Trap physical or chemical process that concentrates the metals into an ore deposit
Where are mineral deposits found?
Mineral deposits are found in a variety of plate
tectonic settings depending on where these
processes operate
Describe magmatic deposits from gravitational setting
heavy minerals that crystallize early, settle
and concentrate on the bottom of the magma
chamber
Some of the most important accumulations of
metals?
Associated with magma that forms igneous rocks
Describe magmatic deposits from immiscibility
• segregation of metal-rich (sulphide) liquid from the
crystallizing magma
• dense, metal-sulfide melt settles to the bottom of
the crystallizing magma chamber
Describe magmatic deposits in pegmatites
Made from melt remaining in last stages of crystalization of granitic magma which is rich in minerals. This liquid flows into cracks and creates large crystals
What are especially reactive carbonate-rich rocks which act as a chemical trap for metals
skarns
How are skarns made?
magma flows to marble like rocks, and the minerals are extracted out of the magma into the marble
Describe hydrothermal ore deposits
- generated from hot water
- originate from hot, metal-rich fluids
expelled from crystallizing intrusions - Fluids move along fractures, cool, and
precipitate the metallic ions to produce vein
deposits
Where are vein deposits concentrated?
areas of intense faulting
What are the two most common vein minerals?
quartz and calcite
Three places hydrothermal fluids come from?
Some originate when water dissolved in magma is
released as the magma crystallizes
• Some are formed from rainwater that circulates deep
in the crust, close to hot intrusions
• In the oceans, such as near midocean ridges, hot
seawater is circulated into the ocean crust
