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Geology and metallogeny of volcanic-hosted massive sulfide deposits: variations through geologic time and with tectonic setting

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Huston, DL and Pehrsson, S and Eglington, BM and Zaw, K (2010) Geology and metallogeny of volcanic-hosted massive sulfide deposits: variations through geologic time and with tectonic setting. Economic Geology, 105 (3). pp. 571-591. ISSN 0361-0128

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Abstract

Analysis of metallogenic data, including grade and tonnage, host-rock succession, ore and alteration mineralogy,
and lead and sulfur isotope data, indicates significant secular changes in the character of volcanic-hosted
massive sulfide (VHMS) deposits, which appear to be related to changes in tectonic processes, tectonic cycles,
and changes in the composition of the hydrosphere and atmosphere. The distribution of these deposits,
whether measured in number of deposits, tons of ore, or tons of metal, is episodic, with major peaks at 2740 to
2690, 1910 to 1840, 510 to 460, and 390 to 355 Ma. These peaks correspond to the assembly of major continental
land masses, including Kenorland, Nuna, Gondwana, and Pangea, respectively. Periods when fewer
VHMS deposits formed correspond to periods of supercontinent and/or supercraton stability. The VHMS
deposits do not form during supercontinent and/or supercraton breakup; rather, these intervals are associated
with deposition of clastic-dominated sediment-hosted zinc-lead deposits. The main exception to these generalizations
is the amalgamation of Rodinia, which was not accompanied by significant VHMS formation.
Rodinian amalgamation may have been dominated by advancing accretionary orogenesis, whereby the overriding
plate did not go into extension. In this case, slab rollback and the associated extension to form back-arc
basins would not have been common, a setting typically conducive to the formation and preservation of VHMS
deposits.
Large ranges in source 238U/204Pb (μ) that characterized VHMS deposits in the Archean and Proterozoic indicate
early (Hadean to Paleoarchean) differentiation of the Earth. A progressive decrease in μ variability may
indicate homogenization with time of these differentiated sources. Secular increases in the amount of lead and
decreases in 100Zn/(Zn+Pb) relate to an increase in felsic rock-dominated successions as hosts to deposits and
to an apparent absolute increase in the abundance of lead in the crust with time.
The increase in the abundance of barite and other sulfate minerals in VHMS deposits, from virtually absent
in the Mesoarchean and Neoarchean to relatively common in the Phanerozoic, relates to the progressive oxidation
of the atmosphere and hydrosphere. The total sulfur content of the oceans also increased, resulting in the
enhanced importance of seawater sulfur in VHMS ore fluids with time. In Archean to Paleoproterozoic deposits,
the bulk of the sulfur was derived by leaching rocks underlying the deposits, with little contribution from
seawater, resulting in uniform, near-zero per mil values of δ34Ssulfide. In contrast, the more variable δ34Ssulfide
values of younger deposits reflect the increasing importance of seawater sulfur in the hydrothermal systems.
Unlike Mesoarchean and Neoarchean deposits, Paleoarchean deposits contain abundant barite. This sulfate
is inferred to have been derived from photolytic decomposition of atmospheric SO2 and does not reflect overall
oxidized oceans.
Archean and Proterozoic seawater was significantly more saline than that in the Phanerozoic, particularly
upper Phanerozoic seawater. The VHMS ore fluids reflect this, being on average more saline in Archean and
Proterozoic deposits. This variability introduces uncertainty into genetic models advocating brine pools or magmatic-
hydrothermal contributions based on high-salinity ore fluids.

Item Type: Article
Journal or Publication Title: Economic Geology
Page Range: pp. 571-591
ISSN: 0361-0128
Identification Number - DOI: 10.2113/gsecongeo.105.3.571
Additional Information:

© 2010 Society of Economic Geologists

Date Deposited: 09 Dec 2010 01:23
Last Modified: 18 Nov 2014 04:15
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