Tectonic evolution and gold mineralisation of the Granites-Tanami Orogen, North Australian Craton

216 Pages·2017·23.09 MB·English

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Tectonic evolution and gold mineralisation
of the Granites-Tanami Orogen, North
Australian Craton

Ben Li
BSc, Msc (Northwest University, China)

This thesis is presented for the degree of Doctor of Philosophy of
The University of Western Australia

Centre for Exploration Targeting,
School of Earth and Environment
The University of Western Australia
Economic Geology 2014
Abstract
ABSTRACT

The multiply deformed Palaeoproterozoic Granites-Tanami Orogen (GTO) located in
the southern part of the North Australian Craton is a significant auriferous province.
This PhD study investigated the magmatism, tectonic and thermal evolution, and gold
mineralisation event of the GTO.
The early Palaeoproterozoic stratigraphic succession in the orogen is the Tanami Group.
The ca 1864 Ma Stubbins, Dead Bullock and Mount Charles formations of the Tanami
Group are correlated and assigned to the Dead Bullock Formation. Pillow basalt and
associated dolerite sills in the Dead Bullock Formation over a wide distance in the GTO
have common geochemical features of enriched back-arc basin basalts. These mafic
rocks are interpreted to be the results of a high degree decompressional melting (5-15%)
of an asthenosphere source in the spinel stability field. The source of the rocks have
primitive mantle signature with input of 3%-4% subduction-related material.
Convective flow operating during subduction circulated the enriched material from
wedge corner into the asthenospheric mantle beneath the Granites-Tanami back-arc
basin and generated the mildly enriched mafic magma that was emplaced as basalt and
dolerite sills.
Widespread younger (ca. 1795 Ma) mafic dykes in the region have geochemical
characteristics of primitive mafic magma with input of crust-derived material. The
interpreted continental-continental collision between the GTO and Arunta Orogen
resulted in the thickening of the lower crust and lithospheric mantle root along the
Willowra Lineament. The thickened lithospheric mantle root, having a higher density
than the upper asthenospheric mantle, lead to gravitational instability and resulted in
convective removal. The detached denser lithospheric mantle root sank into the
asthenosphere triggered upwelling of the hot asthenospheric mantle material and
extension. Melts derived from partial melting of the previously metasomatized
lithospheric mantle with crustal assimilation formed the mafic dykes.
Studies of 40Ar/39Ar geochronology identified three major Palaeoproterozoic tectono-
thermal events in the GTO. The ca. 1840 Ma 40Ar/39Ar cooling age of metamorphic
hornblende from dolerite sills in the Dead Bullock Formation provided precise age
I
Abstract
constraint for the first tectono-thermal event during the evolution of the Granites-
Tanami back-arc basin. This age is consistent with the ca. 1850–1840 Ma subduction
and peak metamorphism events associated with the Halls Creek Orogeny and the
Tennant Orogeny. The 40Ar/39Ar age of 1753 ± 8 Ma for the early biotite from the Dead
Bullock Formation is a cooling age record of the peak greenschist facies metamorphism
during the ca. 1795 Ma Tanami Orogeny, which was associated with gold
mineralisation in the GTO. The biotite recrystallization 40Ar/39Ar age of 1718 ± 8 Ma
revealed the last tectono-thermal overprint to the GTO, which was the distal thermal
influence by the ca. 1723 Ma Strangways Event in the Arunta Orogen.
The Twin Bonanza deposit, which is hosted by the ca. 1795 Ma Buccaneer Porphyry, is
studied as it’s a unique quartz monzonite-hosted gold-only deposit in the GTO. The
Buccaneer Porphyry at the deposit consists of two separate phases of porphyritic quartz
monzonite and abundant mafic microgranular enclaves (MMEs). Geochemical and
zircon geochronological data suggest that the two quartz monzonite phases and MMEs
are products of progressive crystal fractionation of a co-magmatic system. The source
for this gold-rich intrusion complex is the metasomatized lithospheric mantle. Crustal
assimilation with magma that forming the Phase 1 quartz monzonite was considerable,
but minor with the Phase 2 quartz monzonite and MMEs. The magma for these
magmatic units was generated by partial melting of the metasomatized lithospheric
mantle in the post-collisional tectonic setting. The post-collisional magmatism is
approximately synchronously with the ca. 1795–1780 Ma Ma gold mineralisation and
extensive granitic magmatism elsewhere in the GTO.

In situ U-Pb geochronology and Sm-Nd isotope data of hydrothermal monazite
associated with gold-enclosing arsenopyrite from disseminated ore at the Twin Bonanza
gold deposit have a weighted mean 207Pb/206Pb age of 1788 ± 8 Ma (interpreted as the
age of the gold mineralisation), and ε (t) values identical with the ca. 1795 host quartz
Nd
monzonites. The synchronicity and identical ε (t) values indicate that gold was
Nd
precipitated from the magmatic hydrothermal fluid that sourced from the metasomatized
lithospheric mantle. Our study also suggest the episode of ca. 1795–1780 Ma was a
single major gold mineralisation event that took place across the GTO and the Pine
Creek Orogen.
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Acknowledgement
ACKNOWLEDGEMENT

This thesis involved contributions from many people, and without them, this could not
have been achieved.
First and foremost, I would like to thank Min Liu, my wife, and Alma, my little angel,
for their unconditional support, encouragement, understanding and patience throughout
my studies for this degree.
This study was mainly supervised by Dr Leon Bagas. I am grateful to him for being
very positive, supportive and inspiring all the time. His solid knowledge of the study
area kept me always on the right track. I believe we will be in close collaboration for the
following decades. Professor T. Campbell McCuaig is thanked for all the constructive
suggestions and valuable advice from the beginning when I applied for the PhD position.
Doctors Anthony I. S. Kemp, Fred Jourdan, Luis A. Gallardo, John Miller, Nuru Said,
Yongjun Lu and Professors Richard J. Goldfarb are thanked for their insightful
comments and help, which greatly improved the quality of this thesis. Doctors Joao
Orestes Santos, Chunrong Diwu, John Cliff, Janet Muhling, Malcolm Roberts, Matt R.
Kilburn, Paul Guagliardo, David Adams, Wenqiang Yang, Cristina Talavera, Peter
Duncan, and many other people are thanked for their help with various analyses I used
in this research project. Professors Peter Cawood, John Greenough, Marco Scambelluri
and Jochen Kolb are thanked for their helpful comments on my publications.
I gratefully acknowledge AMIRA International and the industry sponsors, including
AusAid and the ARC Linkage Project LP110100667 for their support of the WAXI
project (P934A). I also acknowledge the SIRF Scholarship of The University of
Western Australia granted to me. This contribution is also a product of collaboration
between Centre for Exploration Targeting (CET) at the University of Western Australia,
and the ARC Centre of Excellence for Core to Crust Fluid Systems (CCFS).
I acknowledge the state-of-the-art facilities, and the scientific and technical assistance of
the Australian Microscopy & Microanalysis Research Facility at the Centre for
Microscopy, Characterisation & Analysis, The University of Western Australia, John de
Laeter Centre, Curtin University, Advanced Analytical Centre, James Cook University,
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Acknowledgement
and State Key Laboratory of Continental Dynamics, Department of Geology, Northwest
University.
Last but not least, Newmont Mining Corporation, ABM Resources NL and Tanami
Gold NL are thanked for helping with sample collections and constructive discussions
whilst in the field.
IV
Statement of candidate contribution
STATEMENT OF CANDIDATE CONTRIBUTION

This thesis consists of 7 chapters and 7 appendices. Except for Chapters 1 and 7, the
other chapters are written as a series of journal papers, among which, Chapters 2, 3 and
4 are published while Chapters 5 and 6 are under review. All the chapters (papers)
composing the thesis are in a logical order and strongly linked together.
All authors involved in this thesis have given permission for me to include the work in
the thesis. The relative contribution of the co-authors and the candidate for each chapter
is listed as follows:
Chapter 1. Introduction
Ben Li (100%)

Chapter 2. Regional geology and stratigraphy
This chapter is written in the format of a journal article: Paleoproterozoic stratigraphy
and gold mineralisation in the Granites-Tanami Orogen, North Australian Craton:
Australian Journal of Earth Sciences, 2014, 60, 497–508.
Leon Bagas (60 %), Rodney Boucher (15%), Ben Li (15%), John Miller, Pascal Hill, G.
Depauw, J. Pascoe, B. Eggers. (collective total 10%)

Chapter 3. Palaeoproterozoic back-arc and post-collisional magmatism and tectonic
evolution
This chapter is written in the format of a journal article: Back-arc and post-collisional
volcanism in the Palaeoproterozoic Granites-Tanami Orogen: Precambrian Research,
2013, 224, 570–587.
Ben Li (85%), Leon Bagas (5%), Luis A. Gallardo (5%), Nuru Said, Chunrong Diwu, T.
Campbell McCuaig (collective total 10%)

V
Statement of candidate contribution
Chapter 4. Tectono-thermal evolution
This chapter is written in the format of a journal article: Tectono-thermal evolution of
the Palaeoproterozoic Granites-Tanami Orogen, North Australian Craton: Implications
from hornblende and biotite 40Ar/39Ar geochronology: Lithos, 2014, in press.
Ben Li (90%), Leon Bagas (5%), Fred Jourdan (5%)

Chapter 5. Gold mineralisation associated with the post-collisional tectonic setting
This chapter is written in the format of a journal article: Geology, geochemistry, Sr–Nd
and zircon Hf–O isotopic compositions of the Palaeoproterozoic Buccaneer Porphyry in
the Granites-Tanami Orogen: Evidence for a post-collisional lithospheric mantle source
for magma associated with the Twin Bonanza gold deposit in the North Australian
Craton: Precambrian Research, in review.
Ben Li (85%), Leon Bagas (4%), Anthony I. S. Kemp (4%), T. Campbell McCuaig
(4%), John Cliff (3%)

Chapter 6. Timing and source for gold
This chapter is written in the format of a journal article: In situ U–Pb geochronology
and Sm–Nd isotope systematics of hydrothermal monazite: Revealing the post-
collisional metasomatized lithospheric mantle source for gold, North Australian Craton:
Geology, pending for submission.
Ben Li (82%), Anthony I.S. Kemp (5%), Joao Orestes Santos (3%), Leon Bagas (3%),
T. Campbell McCuaig (3%) , Malcolm Roberts, Matt R. Kilburn, Paul Guagliardo
(collective total 3%)

Chapter 7. Discussion and conclusions
Ben Li (100%)

VI
Statement of candidate contribution
Signatures
co-author signature date
Leon Bagas 26 Nov, 2014
Anthony I.S. Kemp
T. Campbell McCuaig
Joao Orestes Santos 25/11/2014
Luis A. Gallardo
Fred Jourdan 24/11/2014
John Cliff
Nuru Said 24/11/2014
Malcolm Roberts
Matt R. Kilburn
Paul Guagliardo
Chunrong Diwu
John Miller
P. Hill
G. Depauw
J. Pascoe
B. Eggers
VII
Table of contents

TABLE OF CONTENTS
1. Introduction ........................................................................................ 1
1.1. Problem identification and objectives of this study ....................... 1
1.2. Location ........................................................................................... 2
1.3. Methodology and approach ............................................................. 4
1.3.1. Field work .................................................................................. 4
1.3.2. Laboratorial studies and analytical methods .............................. 4
1.4. Terminology ...................................................................................... 6
1.5. Thesis organization .......................................................................... 7
2. Regional geology and stratigraphy ................................................... 15
3. Palaeoproterozoic back-arc and post-collisional magmatism and
tectonic evolution ............................................................................. 39
4. Tectono-thermal evolution ................................................................ 58
5. Gold mineralisation associated with the post-collisional tectonic
setting ............................................................................................... 74
6. Timing and source for gold ............................................................. 142
7. Discussion and conclusions ............................................................ 160

VIII
Table of contents

Appendices
1. Major element and trace element compositions of pillow basalts,
dolerite sills and doleritic dykes from the Tanami Group ............. 171
2. Ar isotopic data corrected for blank, mass discrimination, radioactive
decay and results ............................................................................ 176
3. Monazite SHRIMP U-Pb dating results ........................................ 184
4. In situ monazite LA-MC-ICP-MS Sm-Nd analytical results ........ 186
5. Monazite chemistry EPMA analytical results ................................ 187
6. Selected BSE images of monazite and associated mineral assemblage
......................................................................................................... 199
7. Selected mages of NanoSIMS gold mapping for arsenopyrite ....... 201

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