Hydrothermal Mineral Deposits: Principles and Fundamental Concepts for the Exploration Geologist

720 Pages·1992·15.57 MB·English

by  Professor Dr. Franco Pirajno (auth.)

A photograph made from the submersible ALVIN in May 1986 during the first dives to observe
black smoker geysers that were initially discovered in the Atlantic Ocean by the NOAA VENTS
Program in 1985. The photograph shows vent shrimp (individual length 2 to 5 centimeters) of a new
variety swarming over a chimney (heigh about 2 meters) built of polymetallic sulfide minerals
through which a black smoker geyser is venting. The scene occurs at a water depth of 3,630 meters
(12,000 feet) about 3,300 kilometers (1,800 miles) due east of Miami, Florida at the Mid-Atlantic
Ridge, a submerged volcanic mountain range that extends along the center of the Atlantic Ocean.
The photograph was made by a research team of scientists from the National Oceanic and
Atmospheric Administration (NOAA), the Woods Hole Oceanographic Institution (WHOI), and
the Massachusetts Institute of Technology (MIT). This photograph, and its caption, were kindly
supplied by Dr. P. . Rona, of the Oceanic and Atmosphere Administration (USA), and published in
EOS. 18th of November issue (vol. 67, No. 46).
Franco Pirajno
Hydrothermal
Mineral Deposits
Principles and Fundamental Concepts
for the Exploration Geologist
With 288 Figures
Springer-Verlag
Berlin Heidelberg New York London Paris
Tokyo Hong Kong Barcelona Budapest
Professor Dr. FRANCO PIRAJNO
Rhodes University
Department of Geology
Mineral Exploration
P.O. Box 94
Grahmstown 6140
South Africa
Present address:
2/34 Kennedy Street
Maylands 6051
Western Australia
ISBN-13:978-3-642-75673-3 e-ISBN-13:978-3-642-75671-9
001: 10.1007/978-3-642-75671-9
Library of Congress Cataloging-in-Publication Data. Pirajno, Franco, 1939-Hydrothermal mineral
deposits: principles and fundamental concepts for the exploration geologist / Franco Pirajno. p. cm.
Includes bibliographical references and index. ISBN-13:978-3-642-75673-3
I. Hydrothermal deposits. 2. Prospecting. l. Title. TN263.P58 1992 622'.159--dc20 91-34466
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©! Springer-Verlag Berlin Heidelberg 1992
Softcover reprint of the hardcover I st edition 1992
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Media conversion: Elsner & Behrens GmbH, D-6836 Oftersheim
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To my parents
Edgardo and Carmen Pirajno
Preface
This book is intended primarily for exploration geologists and post
graduate students attending specialist courses in mineral exploration.
Exploration geologists are engaged not only in the search for new mineral
deposits, but also in the extension and re-assessment of existing ones. To
succeed in these tasks, the exploration geologist is required to be a
"generalist" of the Earth sciences rather than a specialist. The exploration
geologist needs to be familiar with most aspects of the geology of ore
deposits, and detailed knowledge as well as experience play an all
important role in the successful exploration for mineral commodities. In
order to achieve this, it is essential that the exploration geologist be up to
date with the latest developments in the evolution of concepts and ideas in
the Earth sciences. This is no easy task, as thousands of publications
appear every year in an ever increasing number of journals, periodicals
and books. For this reason it is also difficult, at times, to locate
appropriate references on a particular mineral deposit type, although this
problem is alleviated by the existence of large bibliographic data bases of
geological records, abstracts and papers on computers. During my
teaching to explorationists and, indeed, during my years of work as an
explorationist, the necessity of having a text dealing with the fundamental
aspects of hydrothermal mineral deposits has always been compelling.
Metallic mineral deposits can be categorised into three great families,
namely: (I) magmatic; (2) sedimentary and residual; (3) hydrothermal.
This book deals with the hydrothermal family. Hydrothermal activity, in
its broadest sense, is responsible for a very wide range and variety of
metallic ore deposits. The intent of this book, however, is not to provide a
classification of hydrothermal mineral deposits, for which the reader is
referred to Guilbert and Park (1986). The main purpose of this book is to
guide the exploration geologist to the most economically and geologically
important hydrothermal systems, their possible origin and nature, and the
nature of their products, i.e. the ore deposits - and the geotectonic setting
in which they occur.
As mentioned above there is today a large number of published works
dealing with specific aspects of hydrothermal mineral deposits. In general,
a great deal of emphasis is placed on laboratory data, such as experimental
studies, isotope systematics and geochemistry. As a consequence, field
geological observations have suffered a decline. Many of these works are
collected into edited volumes, which treat hydrothermal deposits by
VIII Preface
district or regions, environments of ore deposition, or by geological age.
Although by no means exhaustive, I have endeavoured to record in this
book the fundamentals of the geology of hydrothermal ore deposits, and
the most recent conceptual models which, however imperfect or incom
plete, attempt to explain their origin. These models are based on the
available evidence and clearly, as more information is published, they will
need to be refined, modified or changed altogether. In so doing, I have
drawn heavily from the published work of specialists and therefore the
theories, concepts and ideas presented are the result of many years of
research by Earth scientists from all over the world.
Some of the information presented in this book is drawn from
unpublished and published works carried out whilst I worked as an
exploration geologist in southern Africa, Southeast Asia, Australia, New
Zealand and the southwest Pacific islands. Much of the information on
southern African deposits was gained during my years as Professor of
Exploration Geology at Rhodes University in Grahamstown. During this
time, I directed and co-ordinated post-graduate courses in exploration
geology, which include field-based studies of ore deposits, their genesis
and tectonic settings. This afforded me the unique and pleasurable
opportunity of examining and studying a wide range and a great number
of mineralised environments, such as only southern Africa can offer.
Consequently, two biases - which reflect my experience and provinciality
- are discernable in the text. One bias is geographic, as many of the
examples discussed are from southern Africa and Oceania. However, I
make no apology for this geographical bias, because these land masses are
endowed with a wide spectrum of hydrothermal mineral deposits. The
other bias is on the selection of topics. These I have chosen largely on the
basis of what I believe to be interesting and useful for the explorationist.
Finally, the reader must note that I take full responsibility for the
contents of this book. If some of the ideas and concepts taken from the
literature have been misrepresented, this was unintentional, and in no way
reflects a disregard of the original author(s), work.
Reference
Guilbert J M, Park C F (1986) The geology of ore deposits. Freeman, San Francisco,
985pp
Acknowledgements
The compilation of this book has benefited from my association with
colleagues and post-graduate students in New Zealand, South Africa and
Namibia.
I lived and worked in New Zealand as an exploration geologist for
many years, and I wish to acknowledge the influence that this country and
its friendly people have had in shaping my philosophy of life and the
benefit derived from my association with its geological community. In
particular, lowe gratitude to Drs. I. Speden and R. L. Brathwaite of the
Geological Survey, and the late Prof. N. Brothers of the University of
Auckland. The "boys" of Gold Mines of New Zealand Ltd.: Greg Walker,
Geoff Taylor, Terry Bates, Ian McKenzie, Paul Rutheford, Chris Torrey,
Simon Henderson, Phil Bentley, Kajava Davui, are thanked for contribut
ing to a very stimulating professional life. John Kernick (Exploration
Manager, Australian Anglo American Ltd.) Dick Lay (Chief Geologist)
and John Lawrey (Director) made it all possible. lowe gratitude to the
community of the village of Reeft on (Westland) for its hospitality, in
particular I wish to thank my friends Graeme Jacobs, Maria and Ivan
Wilson.
The many and detailed field trips undertaken in South Africa and
Namibia have provided invaluable experience and knowledge of a
treasure house of ore deposits unique in the world. South African mining
companies - Anglo American Corp., Gold Fields of South Africa,
Genmin, Anglo Vaal and Johannesburg Consolidated Investments - are
thanked for their generous support of these field trips, as are their on-site
geologists, who proved enthusiastic hosts, and have shared their knowl
edge and experience with us, frequent visitors from Rhodes University. A
special debt of gratitude is owed Gold Fields Namibia and their
geologists, Anton Esterhuizen, Volker Petzel, Louis Kruger, Pat Vickers,
Ehrart Kostlin and Dudley Corbett, for their continued support of my
work in Namibia - a beautiful country and a paradise for any natural
scientist.
I also wish to acknowledge the contribution of: Prof. R.E. Jacob, Drs.
I. Reynolds, J.S. Marsh and R. Scoon; Messrs. C. Mallinson, R. Rossiter,
P.J. Ash, V.F.W. Petzel, N. Franey, J. Misiewicz, I. de Klerk, B. Joubert
and D. Whitfield of Rhodes University; Drs. A.A. de Gasparis and H.
Gewald of Anglo American Corporation; F. Badenhorst and K.H.
Hoffmann of the Geological Survey of Namibia. My secretary at Rhodes,
x
Acknowledgements.
Lori Wades on draughted most of the illustrations, while Amanda Butcher
read the manuscript and helped with the editing. The last chapter was
completed in Perth, Australia, and I wish to express my gratitude to an old
friend - Murray Surtees - for having made available the facilities of his
office.
My wife, Mariateresa, accompanied, supported and encouraged me
throughout this long journey.
FRANCO PIRAJNO
Contents
I Introduction ............................................ .
Part I Nature and Types of Hydrothermal Solutions
and Systems
1 Water and Solutions 5
1.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2 Water: Its Origin and Significance ...................... 5
1.2.1 Planetary Evolution and the Origin of Water ............. 6
1.2.2 Water - Past and Present. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.2.3 Water in Subduction Zones. . . . . . . . . . . . . . . . . . . . . . . . . . .. 12
1.2.4 Water in the Crust ................................... 13
1.3 Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 14
1.4 Solubility and Boiling ................................ 15
1.5 Acid-Base Nomenclature. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 16
1.6 Structure of Water - Hydrolysis and Hydration. . . . . . . . . .. 17
1.7 Redox Potential (Eh) ................................. 18
1.8 Chemical Potential, Chemical Activity and Fugacity ....... 20
References ................................................ 21
2 Hydrothermal Solutions ............................... 23
2.1 Introduction ........................................ 23
2.2 Water of Hydrothermal Solutions ...................... 23
2.3 Oxygen and Hydrogen Isotope Systematics
of Hydrothermal Fluids. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 25
2.4 Fluid Inclusions ..................................... 28
2.5 Dissolved Constituents and Metals Partitioning
into Hydrothermal Solutions. . . . . . . . . . . . . . . . . . . . . . . . . .. 31
2.5.1 Partitioning of Metallic Elements
into Hydrothermal Solutions. . . . . . . . . . . . . . . . . . . . . . . . . .. 33
2.6 Metal Transport ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 33
2.6.1 Complex Ions and Ligands ............................ 34
2.6.2 Complex Ions in Hydrothermal Solutions . . . . . . . . . . . . . . .. 37
2.7 Metal Deposition .................................... 39
References ................................................ 40