Geochemical and Tectonic Evolution of Arc-Backarc Hydrothermal Systems: Implication for the Origin of Kuroko and Epithermal Vein-Type Mineralizations and the Global Geochemical Cycle

479 Pages·2003·21.43 MB·English

by  Naotatsu Shikazono (Eds.)

Developments in Geochemistry 8
Geochemical and Tectonic Evolution
of lrc-Backarc Hydrothermal Systems
Implication for the Origin of Huroko and
fpithermal Vein-Type lllineralizations and
the Global Geochemical Cycle
Developments in Geochemistrg
1. W.S. Fyfe, N.J. Price and A.B. Thompson
FLUIDS IN THE EARTH’S CRUST
2. P. Henderson (Editor)
RARE EARTH ELEMENT GEOCHEMISTRY
3. B.A. Mamyrin and I.N. Tolstikhin
HELIUM ISOTOPES IN NATURE
4. B.O. Mysen
STRUCTURE AND PROPERTIES OF SILICATE MELTS
5. H.A. Das, A. Faanhof and H.A. van der Sloot
RADIOANALYSIS IN GEOCHEMISTRY
6. J. Berthelin
DIVERSITY OF ENVl RON M ENTAL BIOGEOCH EMISTRY
7. L.W. Lake, S.L. Bryant and A.N. Araque-Martinez
GEOCHEMISTRY AND FLUID FLOW
Developments in Geochemistry 8
Geochemical and Tectonic Evolution
of flrc-Backarc Hydrothermal Systems
Implication for the Origin of Huroko and
fpithermal Vein-Type mineralizations and
the Global Geochemical Cycle
BY
Naotatsu Shikazono
2003
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Preface
In and near the Japanese Islands many Neogene hydrothermal ore deposits have
been formed from the middle Miocene to the present time, and many subaerial active
geothermal systems occur. Some of them are associated with base-metal (Cu, Zn, Pb, Fe,
Mn) and precious-metal (Au, Ag) mineralizations.
Representative types of Neogene deposits include Kuroko and epithermal vein-type
deposits.
Kuroko deposits, which are strata-bound massive sulfide-sulfate deposits, are well-
known because (1) many studies have been done and many papers (more than 1,000) have
been published since the work by Ohashi (1919), (2) original ore textures are preserved
due to the absence of metamorphism, and (3) geological and physicochemical environ-
ments of ore deposition were well-elucidated. Summaries of previous studies on Kuroko
deposits have been published in the 1970s and early 1980s (Ishihara, 1974; Ohmoto and
Skinner, 1983). However, no summary written in English after the early 1980s has been
published, although considerable works on ore deposits have been carried out.
Epithermal vein-type deposits in Japan have also been well-studied. More than
1,000 papers (mostly in Japanese) have been published. However, a general overview of
the ore deposits is not yet available in English.
Previous work on Kuroko and epithermal vein-type deposits in Japan will be sum-
marized in Chapter 1. The descriptions of individual vein-type and Kuroko deposits are not
covered in this book; they can be found in the references listed at the end of each chapter.
By integrating geological (e.g., distribution of ore deposits, age of ore formation,
host and country rocks, associated volcanic activity, tectonics, paleogeography), miner-
alogical (opaque, gangue, and hydrothermal alteration minerals), and geochemical (fluid
inclusions, stable and radiogenic isotopes, minor elements of ore and country rocks,
thermochemical calculations) data on the two types of deposits, the genesis, depositional
mechanism and origin of ore deposits are described and discussed in Chapter 1. Temporal
and spatial relationships between the two types of deposits and the evolution of tectonics
and hydrothermal systems associated with the mineralization during the Neogene age in
and around the Japanese Islands are considered.
During the last three decades, subaerial geothermal areas in the Japanese Islands
have been explored considerably and geothermal energy plants were developed. It was
recognized that some active geothermal systems are accompanied by present-day base-
metal and precious-metal mineralizations.
In 1990s, hydrothermal venting and mineralization were discovered on the sea
floor of the back-arc basin, back-arc rift, and island arc surrounding the Japanese Islands
as well as other western Pacific regions.
vi Preface
In Chapter 2, a geochemical, geological and mineralogical summary of active
subaerial and submarine back-arc basin hydrothermal systems and mineralizations is
given. The characteristic features of above-fossil and active subaerial and submarine
hydrothermal systems are compared with fossil hydrothermal systems (epithermal vein-
type and Kuroko deposits), and the causes for the differences in the characteristic features
are considered. Characteristic features of Paleozoic-Mesozoic volcanogenic stratiform
Cu deposits (Besshi-type deposits) are compared with those of midoceanic ridge deposits
and Kuroko deposits.
In Chapter 3, hydrothermal and volcanic gas fluxes from submarine back-arc
basins and island arc are estimated. These fluxes are compared with midoceanic ridge
hydrothermal fluxes. Particularly, hydrothermal flux of CO2 is considered and the
influences of this flux on global long-term carbon cycle and climate change in Tertiary-
Quaternary ages are discussed in Chapter 4.
Acknowledgements
Several acknowledgements are in order.
I am very much indebted to the late Professors Emeriti T. Tatsumi of the University
of Tokyo, advisor of my Ph.D. thesis, and T. Watanabe of the University of Tokyo for their
valuable advice to study epithermal vein-type and Kuroko deposits in Japan. I learned
from them an importance of the integration of geochemistry, geology and mineralogy
for studying the genesis of hydrothermal ore deposits. I acknowledge the late Professors
T. Fujii of Tsukuba University and A. Tsusue of Kumamoto University who taught me
applications of thermodynamics, kinetics and hydrodynamics to ore genesis. Professors
T. Nakamura, K. Nagasawa and S. Takenouchi's papers on the detailed mineralogical and
fluid inclusion studies of vein-type deposits in Japan were especially valid and useful
to writing this book. Discussions with Professors Dick Holland, Ulrich Petersen, Ei
Horikoshi, Hiroshi Ohmoto, Clif Farrel and Udo Fehn on the genesis of Kuroko deposits
during my stay at Harvard University as a Post-Doctoral Fellow (1979-1981) contributed
very much to my research on Kuroko deposits. I appreciated Dick Holland's hospitality
while I stayed at Harvard University during my 1997-1998 sabbatical year (during which
parts of the draft of this book were written) from Keio University. Keio University
provided a grant for my one-year stay at Harvard.
This volume is indebted a great deal to many people of the Geology Department
of the University of Tokyo, the Applied Chemistry Department of Keio University,
and Geology Department of Tokyo Gakugei University. I particularly would like to
mention Drs. J.T. Iiyama, E. Hirokoshi, M. Utada, T. Sato, H. Shimazaki, Y. Kajiwara,
M. Watanabe, J. Date, K. Kase, S. Doi, T. Urabe, T. Mizuta, K. Hattori, M. Aoki,
R. Kouda, M. Shimizu, K. Takeuchi, E. Uchida, Y. Shibue, N. Takeno, Y. Morishita,
M. Tamura, S. Nakashima, H. Kawahata, K. Fujimoto, Y. Kato, A. Imai, T. Nagayama,
O. Ishizuka, M. Hoshino, S. Kimura, Y. Ishikawa, H. Kashiwagi, Y. Ogawa, H. Honma
and M. Nakata. I very much appreciate Miss M. Aizawa for her skillful and patient word
processing.
Preface vii
Finally, I would like to dedicate the book to my wife, Midori Shikazono, daughters,
Chikako and Hisako Shikazono, and parents, Naoharu and Yoshiko Shikazono, for their
moral support of my academic research.
Naotatsu Shikazono
Keio University
References
Ishihara, S. (ed.) (1974) Geology of the Kuroko Deposits. Mining Geology Special Issue, 6, 437 pp.
Ohashi, R. (1919) On the origin of Kuroko of the Kosaka mine. J. Geol. Soc. Japan, 26, 107-132 (in
Japanese).
Ohmoto, H. and Skinner, B.J. (eds.) (1983) The Kuroko and Related Volcanogenic Massive Sulfide Deposits.
Econ. Geol. Mon., 5, 604 pp.
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ix
Table of Contents
Preface ......................................................................... V
Chapter 1 . Miocene-Pliocene Hydrothermal Ore Deposits in and around the
Japanese Islands ................................ ............ 1
1.1. General overview of metallogeny and tectonics in the Japanese Islands ....... 1
1.2. General overview and classification of hydrothermal ore deposits of Neogene
age ............................................... ................ 6
1.3. Kuroko deposits ...................... ............................ 15
1.3.1. Geological characteristics ........................................ 15
1.3.1.1. Distribution ................................................ 15
1.3.1.2. General geology, country rocks and tectonic setting ........... 15
1.3.1.3. Age of mineralization ....................................... 19
1.3.1.4. Metals enriched and metal ratios ............................. 20
1.3.2. Mineralogical characteristics .......... ............................ 23
1.3.2.1. Metal zoning, and ore and gan minerals .................. 23
1.3.2.2. Hydrothermal alteration ..................................... 30
1.3.3. Geochemical characteristics ......................... 38
1.3.3.1. Fluid inclusions ............................................. 39
1.3.3.2. Gas fugacities ........ .......................... 41
1.3.3.3. Chemical compositions 48
1.3.3.4. Stable isotopes ........ ......................... 51
1.3.3.5. Radiogenic isotopes ............................. 54
1.3.4. Depositional mechanism and origin of ore fluids ...................... 61
1.3.4.1. Depositional mechanism ......................... 61
1.3.4.2. Origin of ore flui ...................................... 77
1.4. Epithermal vein-type deposits ........... ................................. 83
1.4.1. Geological characteristics ...................................... 84
1.4.1.1. Distribution ............................... ............. 84
1.4.1.2. Age of mineralization .... .......................... 84
1.4.1.3. Volcanic activity related to mineralization .................... 87
1.4.1.4. Metal enriched and metal ratios .............................. 88
1.4.2. Mineralogical characteristics ......................................... 88
1.4.2.1. Metal zoning ..... ................................... 88
1.4.2.2. Ore minerals ...... ...................................... 88
1.4.2.3. Gangue minerals ............................................ 94
I .4.2.4 . Hydrothermal alteration zoning .............................. 98