Carbonate Alteration of the Sams Creek Gold Deposit

211 Pages·2016·11.31 MB·English

by  Ryan Lee

http://researchcommons.waikato.ac.nz/

Research Commons at the University of Waikato

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CARBONATE ALTERATION OF THE SAMS
CREEK GOLD DEPOSIT
NW NELSON, NEW ZEALAND

A THESIS SUBMITTED IN PARTIAL FULFILMENT
OF THE REQUIREMENTS FOR THE DEGREE
OF
Masters of Science (Research)
AT THE
UNIVERSITY OF WAIKATO
BY
Ryan John Lee
UNIVERSITY OF WAIKATO
2016

Abstract
Located near Upper Takaka, NW Nelson, the Sams Creek Gold Deposit is host to
significant gold mineralisation, which has been extensively explored since being
first discovered in 1974 by CRA exploration. The gold mineralisation, hosted
largely within the Sams Creek Granite Dyke has since been the focus of continual
ongoing exploration and research by various companies and academia. The dyke is
a peralkaline microgranite, is up to 60 meters wide and has a strike length totalling
7 kilometres. Multiple stages of hydrothermal alteration have affected the granite
dyke which is host to a series of sheeted, stock work and irregular fracture veins.
At the time of writing, Sams Creek is New Zealand’s largest undeveloped gold
project.
Despite extensive research and exploration, the origin of Au bearing fluids and
hence classification of the deposit is still debated. Little is also known about the
role of which the wide spread carbonate alteration has had during the genesis of this
deposit. Siderite/ankerite (carbonate) veins are a common occurrence at Sams
Creek, occurring in both the highly mineralised granite and seemingly unaltered
metasedimentary rock, of which the Sams Creek Granite and various other mafic
dykes intrude.
This study presents a detailed paragenetic study of the multiple phases of carbonate
alteration throughout the prospect. Trace element geochemistry for individual vein
generations was obtained by in-situ analysis of the carbonate vein minerals using
LA-ICP-MS. Oxygen and carbonate stable isotope ratios were also determined for
many of the carbonate minerals.
The carbonate alteration was found to be largely structurally controlled and coeval
with the multiple stages of Au mineralisation and alteration. The veins were often
comprised of multiple siderite and ankerite intergrowths, reflecting temporally
distinct fluids of varying Ca/Fe/Mn/Mg concentrations. Whole vein geochemical
analysis confirmed an overall ankerite composition, contrary to the previous reports
of siderite only veins. Major and trace element signatures showed geochemically
distinct ankerite veins for each host rock. Notably, the geochemistry of the veins
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indicates that the surrounding metasediments are an unlikely fluid source for the
carbonate alteration. This has implications for models which suggest an orogenic
fluid is responsible for the alteration. The fluid likely received its trace element and
isotopic signature from a high temperature, reduced and 18O-depleted fluid source,
consistent with a fluid source that is not metamorphogenic. The carbonate minerals
associated with the mineralisation and/or the dyke have a unique trace element
signature in relation to carbonate of other lithologies.
Overall, this study provides evidence that is in agreement with the Sams Creek
Dyke being classified as an Intrusion Related Gold System. Further implications
for exploration potential are the distinctions between metamorphogenic and
hydrothermal carbonate minerals, which could be easily undertaken using pXRF
based upon anomalous Mn and Mg contents.

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Acknowledgements
Firstly, a huge thanks to my chief supervisor Dr. Shaun Barker for the great support
and wisdom throughout this project. I am also very grateful for the support of Paul
Angus and MOD Resources, whom made this research possible by providing access
to drill core, exploration data and facilities.
A special thanks to Richard Jongens and Rose Turnbull for all of the knowledge
and assistance provided, especially the long day spent out in the field. Also Mark
McCulloch, Michael Southern and Bob Brathwaite for helping with this project.
The NZ Branch of AusIMM have given me tremendous financial and professional
support throughout my studies. In particular, through the G B O’Malley Medal,
Jock Braithwaite Award and EET Scholarship. Also The University of Waikato for
the Masters Research Scholarship and the other awards and contributions which I
have received during my study. ARANZ Geo for providing me with and supporting
my use of Leapfrog Geo software. I would also like to acknowledge support from
the NZ Ministry of Business Innovation & Employment and GNS science.
A big thanks to my fellow students of GHOSTED Research Group: Rosie Hughes,
John Mering, Ben Andrew and Anna Eames. Also, the many technicians who
helped me gather data; Annette Rodgers, Renat Radosinsky and Helen Turner.
Finally, I would like to thank my Mum and dad, friends and family for all the
support I have received during my time at university.
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Table of Contents
Abstract .................................................................................................................. iii
Acknowledgements ................................................................................................ iii
Table of Contents ................................................................................................... iii
List of Figures ........................................................................................................ iii
List of Tables ......................................................................................................... iii
CHAPTER 1 INTRODUCTION ............................................................................. 1
1.1 Overview ....................................................................................................... 1
1.2 Study Objectives ........................................................................................... 3
1.3 Deposit Models ............................................................................................. 4
1.3.1 Intrusion related .................................................................................... 5
1.3.1.1 Sams Creek – IRGS ...................................................................... 6
1.3.1.2 IRGS and Carbonate Veins ........................................................... 7
1.3.2 Orogenic ................................................................................................ 8
1.3.2.1 Sams Creek –Orogenic/Metamorphic ........................................... 9
1.3.3 Mineralising fluid Origin Debate .......................................................... 9
1.4 Oxygen and Carbon stable isotopes ............................................................ 13
1.4.1 Oxygen ................................................................................................ 14
1.4.2 Carbon ................................................................................................. 15
1.4.3 Stable isotopes of hydrothermal systems ............................................ 16
1.5 Carbonate Trace Element Geochemistry .................................................... 17
CHAPTER 2 GEOLOGICAL SETTING .............................................................. 21
2.1 Regional Geology ....................................................................................... 21
2.2 Deposit Geology ......................................................................................... 23
2.2.1 Stratigraphy ......................................................................................... 28
2.2.1.1 Metasediments............................................................................. 28
2.2.1.2 Mafic Dykes ................................................................................ 33
2.2.1.3 Lamprophyre ............................................................................... 33
2.2.1.4 Hornfels ....................................................................................... 38
2.2.1.5 Diorite ......................................................................................... 39
2.2.2 Structure and Deformation .................................................................. 42
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2.2.3 Mineralogy and geochemistry of the SCD ......................................... 46
2.2.3.1 A-type classification .................................................................... 47
CHAPTER 3 PREVIOUS EXPLORATION AND RESEARCH ......................... 49
3.1 History of Mineral Exploration .................................................................. 49
3.2 Academic Research .................................................................................... 52
3.2.1 Timing of dyke emplacement and mineralisation .............................. 52
3.3 Exploration Models .................................................................................... 54
3.3.1 Deformation (folding) Model ............................................................. 54
3.3.2 Faulting Model ................................................................................... 56
3.3.3 IRGS Exploration Model .................................................................... 57
CHAPTER 4 CARBONATE ALTERATION & PARAGENESIS ...................... 59
4.1 Methods ...................................................................................................... 59
4.2 Alteration and Mineralisation of the Sam’s Creek Dyke ........................... 60
4.2.1 TYPE 1 Magnetite-Carbonate Alteration ........................................... 62
4.2.2 TYPE 2 Quartz-Carbonate-Pyrite Alteration...................................... 63
4.2.3 TYPE 3 Au-bearing Arsenopyrite Alteration & Mineralisation......... 64
4.2.4 TYPE 4 Au-Bearing Base Metal Mineralisation ................................ 67
4.2.5 TYPE 5 Au-Bearing Quartz Carbonate veins ..................................... 68
4.3 Carbonate Alteration .................................................................................. 69
4.3.1 Carbonate species control ................................................................... 70
4.3.2 Carbonate species appearance ............................................................ 72
4.4 Carbonate Paragenesis ............................................................................... 73
4.4.1 Host rock carbonates .......................................................................... 74
4.4.2 Sams Creek Granite Dyke Carbonates ............................................... 80
4.4.2.1 TYPE 1 ........................................................................................ 80
4.4.2.2 TYPE 2 ........................................................................................ 81
4.4.2.3 TYPE 3 ........................................................................................ 82
4.4.2.4 TYPE 4 ........................................................................................ 83
4.4.2.5 TYPE 5 ........................................................................................ 84
4.4.3 Lamprophyre Carbonates ................................................................... 84
4.4.4 Diorite carbonate ................................................................................ 89
4.4.5 Discussion ........................................................................................... 89
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4.4.6 Conclusions ......................................................................................... 92
CHAPTER 5 GEOCHEMISTRY .......................................................................... 97
5.1 Introduction ................................................................................................. 97
5.1.1 Exploration Drill Assays ..................................................................... 97
5.2 Methods .................................................................................................... 100
5.2.1 Introduction ....................................................................................... 100
5.2.2 X-RAY FLUORESCENCE .............................................................. 100
5.2.3 Stable Isotopes .................................................................................. 101
5.2.4 Laser-ablation inductively coupled plasma mass spectrometry ........ 103
5.2.4.1 LA-ICP-MS data reduction using Iolite® ................................. 106
5.3 Carbonate Geochemistry........................................................................... 108
5.3.1 XRF ................................................................................................... 108
5.3.2 LA-ICP-MS ....................................................................................... 113
5.3.2.1 Raw LA-ICP-MS data ............................................................... 113
5.3.2.2 LA-ICP-MS Data Reduction ..................................................... 117
5.3.2.3 Major Elements ......................................................................... 120
5.3.2.4 Trace Elements .......................................................................... 125
5.4 Stable Isotopes .......................................................................................... 136
5.4.1 Introduction ....................................................................................... 136
5.4.2 Results ............................................................................................... 138
5.5 Conclusions ............................................................................................... 144
CHAPTER 6 DISCUSSION ................................................................................ 147
6.1 Introduction ............................................................................................... 147
6.2 Carbonate Mineral Paragenesis ................................................................ 148
6.3 Geochemistry ............................................................................................ 149
6.3.1 Carbonate Species ............................................................................. 149
6.3.2 LREE Depletion and HREE Enrichment .......................................... 149
6.3.3 Carbonate Mineral Accessory REE Phases ....................................... 151
6.3.4 Europium Anomaly ........................................................................... 152
6.3.5 Source of the carbonate alteration ..................................................... 156
6.3.5.1 Trace elements .......................................................................... 157
6.3.5.2 Stable isotopes ........................................................................... 160
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