Economic Geology

Question 1

What are Cu and Al used for?

Answer 1

wire, construction (aluminum)

Question 2

What is Ge used for?

Answer 2

Semiconductors, transistors, and optics

Question 3

Where does gold occur?

Answer 3

hydrothermal deposits, placers

Question 4

Where are lead and magnesium found?

Answer 4

hydrothermal deposits

Question 5

Where do most valuable metals occur?

Answer 5

most occur as atomic substitutions in more abundant rock-forming minerals

Question 6

Where are most ore minerals found as?

Answer 6

Sulphides

Question 7

ore minerals such as iron, tin, and tungsten occur as…

Answer 7

oxides

Question 8

Define gangue

Answer 8

non-valuable minerals that metals occur in

Question 9

Define hydrothermal mineral deposits?

Answer 9

minerals are concentrated by hot aqueous solutions flowing through fractures and pores in the substrate

Question 10

Define magmatic mineral deposits

Answer 10

Formed by concentration of magmatic processes within a body of igneous

Question 11

Define sedimentary mineral depostis

Answer 11

formed by precipitation from concetrated, modified sea water

Question 12

How are placers formed?

Answer 12

Concentration by flowing surface water in streams

or along the shore

Question 13

How residual minerals deposits are formed

Answer 13

Concentration by weathering processes

Question 14

What three rules govern the formation of concentrated minerals

Answer 14

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

Question 15

Where are mineral deposits found?

Answer 15

Mineral deposits are found in a variety of plate
tectonic settings depending on where these
processes operate

Question 16

Describe magmatic deposits from gravitational setting

Answer 16

heavy minerals that crystallize early, settle
and concentrate on the bottom of the magma
chamber

Question 17

Some of the most important accumulations of

metals?

Answer 17

Associated with magma that forms igneous rocks

Question 18

Describe magmatic deposits from immiscibility

Answer 18

• segregation of metal-rich (sulphide) liquid from the
crystallizing magma
• dense, metal-sulfide melt settles to the bottom of
the crystallizing magma chamber

Question 19

Describe magmatic deposits in pegmatites

Answer 19

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

Question 20

What are especially reactive carbonate-rich rocks which act as a chemical trap for metals

Answer 20

skarns

Question 21

How are skarns made?

Answer 21

magma flows to marble like rocks, and the minerals are extracted out of the magma into the marble

Question 22

Describe hydrothermal ore deposits

Answer 22

1. generated from hot water
2. originate from hot, metal-rich fluids
   expelled from crystallizing intrusions
3. Fluids move along fractures, cool, and
   precipitate the metallic ions to produce vein
   deposits

Question 23

Where are vein deposits concentrated?

Answer 23

areas of intense faulting

Question 24

What are the two most common vein minerals?

Answer 24

quartz and calcite

Question 25

Three places hydrothermal fluids come from?

Answer 25

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