Transcript GEOL363_1 - Geological Sciences, CMU

GEOL. 363 : Mineral Deposits
3(3/3-0/0)
MWF 0800-0900 GB 200 /110
“ Formation, characteristics and distribution of
metallic and non-metallic mineral deposits ”
Introduction
Genesis of Mineral Deposits
Geology of Mineral Deposits
Excursion : Sat. 11 Aug. 2001
5 hrs.
10 ,,
30 ,,
Introduction
• Definition of mineral deposits and related terms
• Morphology of mineral deposits
• Modes of mineral deposition.
• Plate tectonics and mineralization
• Classifications of mineral deposits
What is a mineral deposit ?
A mineral deposit is a place where valuable mass of
economic mineral (or minerals) is formed in varying
size, shape and orientation.
The ore body or valuable mass of economic minerals is
normally outlined by cut-off grade.
Morphology of an ore body can be: tabular, cylindrical,
pipe, massive, lenses, nest, massive etc.
How is a mineral’s concentration factor determined?
Concentration factor, the increase in concentration
of a mineral required to form an ore.
What is the difference between ore and gangue?
• Ore is rock that contains economic concentrations
of metallic minerals.
• Gangue is non-economic minerals associated with
ores.
Pyrrhotite-rich, magmatic sulfide blebs partly altered to
chalcopyrite. Little Stobie Mine, Sudbury
Massive pyrrhotite (Po; tan and yellow) and pentlandite (Pn; white)
Sudbury massive ores in reflected light under crossed polars. Pentlandite grains
are intergrown with pyrrhotite and constitute the main nickel mineral for which
t h e s e
o r e s
a r e
m i n e d.
Some of the ores from the Sudbury nickel district contain significant amounts of
cubanite (CuFe2S3). Cubanite forms a complete solid solution series with
chalcopyrite, and the single solid formed at high temperatures may exsolve with
d e c l i n i n g
t e m p e r a t u r e s.
What is the difference between a reserve and a resource?
• Reserves are resources that can be economically
extracted using existing technology
•The volume of reserves is much less than the volume
of resources
Morphology of Mineral deposits
An orebody is a mixture of valuable minerals and waste rock.
Each orebody, which has a definite size and shape, is a mass
that contains enough valuable mineral to be mined and
p r o c e s s e d
a t
a
p r o f i t.
S h a p e s o f o r e b o d i e s c a n b e c l a s s i f i e d a s:
1. D i c s c o r d a n t
2. C o n c o r d a n t
i.e.
vein
type
deposits
i.e. stratiform ore deposits
A: Discordant Orebodies
Regularly shaped bodies
Tabular orebodies
Tubular orebodies
Irregularly shaped bodies
Disseminated deposits
Irregular replacement deposits
B: Concordant Orebodies
Sedimentary host rocks
Igneous host rocks
Volcanic hosts
Plutonic hosts
Metamorphic host rocks
Residual deposits
Supergene enrichment
Skarn
A replacement of
limestone (calcium
carbonate) or other
carbonate-rich rocks
adjacent to an
intrusive contact by
calc-silicate minerals
usually through the
addition of Si and
o t h e r e l e m e n t s.
Massive Sulfide Orebody
Anticlinal fold in sandstones and shales, United Kingdom. The
white material in the hinge of the fold at the center of the
photograph is quartz, and fills a void that opened up during
folding. Such filled-in features are called saddle reefs.
How can minerals deposits be formed?
Magmatic mineral deposits concentrated in igneous rocks;
Residual mineral deposits formed by weathering reactions
at the earth’s surface.
Placer deposits are sorted and distributed by flow of
transporting media such as water, wind and ice;
Sedimentary mineral deposits are precipitated from a
solution, typically sea water;
Metamorhogenic mineral deposits form in association with
metamorphism
Hydrothermal mineral deposits form in association with
magma and water;
Distribution of major tectonic plates
Classifications of Mineral Deposits