Association Between Strike-Slip Fault Tectonics and ... - Cmi Capital

Association Between Strike-Slip Fault
Tectonics and the Occurrence of
Porphyry Copper and Polymetallic Vein
Deposits
By
Lawrence J. Drew
U.S. Geological Survey

BEGININGS
• In the 1970s, 1980s, and early 1990s, the
U.S. Geological Survey (USGS) undertook
the assessment of undiscovered mineral
resources in:
• 1. Proposed wilderness areas
• 2. Natural forests
• 3. Public lands
•4. USA

Recently
• Individual countries
• Globally for several types of mineral
deposits

Proposed Wilderness Areas in
1983

Many Deposit Types
But
Porphyry Copper Deposits
Were Very Important

Observation
Porphyry copper and associated deposits
such as polymetallic veins, skarns,
replacement deposits, are very important
in the assessment of undiscovered
minerals.

Titley’s Model

Apuseni Mountains, Romania
(Borcos, 1962)

Northern Hungary
(MAFI-USGS 1995-1998 study)

Mátra Mountains, Hungary
(MAFI-USGS 1995-1998 study)

Mátra Mountains

Mátra Mountains

Apuseni Mountains

Observations
(Seraphim and Hollister, 1976)
Mineralized porphyry stocks are:
• Small and nearly cylindrical in shape
• Cross-section, approximately 1 square kilometer
• Often near-surface emplacement
• Possible extreme vertical extents, up to 7 kilometers
• Co-eval strike-slip system nearby

A Model for Earthquake Swarms in
Volcanic Regions
(Hill, 1977)
• Clusters of magma-filled dikes exist in the
crust.
• These dikes are oriented according to the
greatest regional principal stress.
• The tips of the dikes are connected to
each other by shear faults.

Earthquake Swarm--Continued
• The dike swarms are closely associated
with strike-slip faults.
• Volcanism and igneous intrusions are
closely associated.

Hill’s Extensional-Shear Mesh

Adaptation to Mineral Deposits
(Sibson, 1985)
• Dilatational jogs (fault duplexes) in strike-slip
fault systems are common host of
mineralization.
• Fault duplexes are vertical conduits for
hydrothermal fluid flow.
• Earthquakes trigger the flow. Deposition is
episodic.

Sibson’s Extensional-Shear Mesh

The Mesh Is a Common Ore Host
Chuquicamata, Chile
Martha Lode, New Zealand
Sibson, 1985

Synthesis Using Laboratory
Model Studies
• Segall and Pollard (1980)
• Connolly and Cosgrove (1999)

Segall and Pollard

Connolly and Cosgrove
(1999)

The Classical Magmatic-Hydrothermal
Model for Porphyry Copper Deposits
after Burnham, 1979

A Porphyry Deposit
• It is created in a reaction containment
vessel that produces a large volume of
silica that forms a carapace that is
repeatedly fractured.
• A “quiet” extensional environment (little or
no shear) is a basis requirement.

The Sequence of Deposition
• Far-field stress nullified locally—
porphyry copper emplacement
• Far-field stress reestablished —
acid sulfate veins followed by
quartz adularia veins

Location of fault duplexes where porphyry
copper and polymetallic vein deposits may
occur in an orogen
Members of the porphyry
copper and polymetallic vein
family of deposits occur in close
spatial and temporal
association with strike-slip fault
duplexes.
Location of strike-slip
duplex structures along an
active tectonic-plate
margin (modified from
Bally and Oldow, 1985).

The Structure of Oblique Subduction
Systems
(de Saint Blanquat and others, 1998)

Central Europe
• Application of a tectonic model for the spatial occurrence of
porphyry copper and polymetallic vein deposits.
• Cretaceous deposits in the Srednogorie-Timok
Timok-Banat
region
in Bulgaria, Serbia, and Romania.
• Miocene deposits in the Apuseni Mountains, Romania, and in
the central Slovakian volcanic field, Slovakia.

Location of and Application of the Tectonic
Occurrence Model to the Late Cretaceous
Porphyry Copper Deposits of Central
Europe

Tectonic Reconstruction
(Csontos and Nagymarosy, 1998)

“Straightening” Out the Orogen
(Willingshoper, 2000; Ciobanu and others, 2002)

Cretaceous Age Porphyry Copper
Deposits in Central Europe
(modified from Singer and others, 2002)

Satellite Images Used as a Basis for
Compilation in the Srednogorie Region

Locations of Deposits and Strike-Slip
Faults

Registration of Geology
(modified from Geografski Institute of Bulgaria, 1973; Bogaonov, 1983;
Bayraktarov, 1994; Strashimirov and others, 2002)

Registration of Faults
(Modified from Geografski Institute of Bulgaria, 1973; Bogdanov, 1983;
Bayraktarov, 1994); Ivanov and others, 2002; and Strashimov and others,
2002)

An Interpretation
• Polymetallic vein deposits are deposited in
an “active” tectonic environment—
extension and shear.
• Generally, porphyry copper deposits are
emplaced in a “quiet” tectonic
environment—extension, but no shear.

Duplexes and Deposits

Tectonic Interpretation in the Timok Duplex,
Serbia
Basin development,
volcanic rocks, and
granitoid intrusions
(Modified from Yugoslavia
Federal Geological
Institute, 1970; Jankovic,
1990; and Karamata and
others, 1997. Porphyry
copper and vein deposit
locations from Kozelj and
Jelenkovic, 2001)

Right Lateral Sense of Shear Identified at
Majdanpek in the Timok region of Serbia
(Jankovic and others, 1983)

Strike-Slip Faults
(Milovanovi,, 1968)

Location of Porphyry Copper Deposits in Strike-
Slip Fault Duplexes Between Older Thrust Faults
in the Banat Region of Romania
(Map modified from Codarcea,
1967); Codareca and Dimitrescu,
1967; Codarcea and Raileanu,
1968; Nastaseanu and Maier, 1972;
Maier and others,1973; and
Nastaseanu and others, 1975)

Shear Reversal Interpretation
of Gravitational Collapse and Block Rotation

Location of and Application of the Tectonic
Occurrence Model to the Miocene Porphyry
Copper Deposits of Central Europe

Miocene Copper Porphyry Deposits in the
Apuseni Mountains
(Modified from
Ghitulescu and
Socolescu,1941;
Borcos, 1994;
Berberleac and
others, 1995)

Strike-Slip Duplex Interpretation
(modified from Fodor and others, 1999)

Recent Data
The sense of shear is not left lateral,
but
right lateral.
Written
communication
from Gary
O’Connor, Gabriel
Resources Ltd,
October 2004.
This fits the observed occurrence better.

Strike-Slip Duplex Interpretation
Empirically,
If the sense
of shear is
left lateral,
then
expect a
porphyry
copper
deposit here

Application of the Model to
Central Slovakia
(modified from Marsina (1995) and Lexa and others (1999)

Conclusions
The tectonic model for the spatial occurrence of
porphyry copper and polymetallic vein deposits can
account for the locations of:
• Cretaceous porphyry copper and polymetallic
vein deposits in the Srednogorie, Timok, and
Banat regions, and
• Miocene porphyry copper and polymetallic vein
deposits in Apuseni Mountains, and central
Slovakia, and
• Sites for exploration and
Can help assess undiscovered resources.