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Classification of VMS deposits: lessons from the South Uralides

Classification of VMS deposits: lessons from the South Uralides
Classification of VMS deposits: lessons from the South Uralides
VMS deposits of the South Urals developed within the evolving Urals palaeo-ocean between Silurian and Late Devonian times. Arc-continent collision between Baltica and the Magnitogorsk Zone (arc) in the south-western Urals effectively terminated submarine volcanism in the Magnitogorsk Zone with which the bulk of the VMS deposits are associated. The majority of the Urals VMS deposits formed within volcanic-dominated sequences in deep seawater settings. Preservation of macro and micro vent fauna in the sulphide bodies is both testament to the seafloor setting for much of the sulphides but also the exceptional degree of preservation and lack of metamorphic overprint of the deposits and host rocks. The deposits in the Urals have previously been classified in terms of tectonic setting, host rock associations and metal ratios in line with recent tectono-stratigraphic classifications. In addition to these broad classes, it is clear that in a number of the Urals settings, an evolution of the host volcanic stratigraphy is accompanied by an associated change in the metal ratios of the VMS deposits, a situation previously discussed, for example, in the Noranda district of Canada.
Two key structural settings are implicated in the South Urals. The first is seen in a preserved marginal allochthon west of the Main Urals Fault where early arc tholeiites host Cu–Zn mineralization in deposits including Yaman Kasy, which is host to the oldest macro vent fauna assembly known to science. The second tectonic setting for the South Urals VMS is the Magnitogorsk arc where study has highlighted the presence of a preserved early forearc assemblage, arc tholeiite to calc-alkaline sequences and rifted arc bimodal tholeiite sequences. The boninitc rocks of the forearc host Cu–(Zn) and Cu–Co VMS deposits, the latter hosted in fragments within the Main Urals Fault Zone (MUFZ) which marks the line of arc-continent collision in Late Devonian times. The arc tholeiites host Cu–Zn deposits with an evolution to more calc-alkaline felsic volcanic sequences matched with a change to Zn–Pb–Cu polymetallic deposits, often gold-rich. Large rifts in the arc sequence are filled by thick bimodal tholeiite sequences, themselves often showing an evolution to a more calc-alkaline nature. These thick bimodal sequences are host to the largest of the Cu–Zn VMS deposits.
The exceptional degree of preservation in the Urals has permitted the identification of early seafloor clastic and hydrolytic modification (here termed halmyrolysis sensu lato) to the sulphide assemblages prior to diagenesis and this results in large-scale modification to the primary VMS body, resulting in distinctive morphological and mineralogical sub-types of sulphide body superimposed upon the tectonic association classification.
It is proposed that a better classification of seafloor VMS systems is thus achievable using a three stage classification based on (a) tectonic (hence bulk volcanic chemistry) association, (b) local volcanic chemical evolution within a single edifice and (c) seafloor reworking and halmyrolysis.
South Urals, VMS, classification, halmyrolysis, tectonic setting, volcanic chemistry
0169-1368
203-237
Herrington, R.
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Maslennikov, V.
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Zaykov, V.
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Seravkin, I.
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Kosarev, A.
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Buschmann, B.
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Oregeval, J.J.
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Holland, N.
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Tesalina, S.
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Nimis, P.
cd277f1a-a2b9-4a1c-98cf-337fa517ad13
Armstrong, R.
c1cf75df-a0d8-4416-a8b8-3b75736ff8aa
Herrington, R.
40a3682c-debf-4944-b4c7-6cdfee6c79f5
Maslennikov, V.
627c7820-67c7-41c9-a395-4fbdd6bf93d9
Zaykov, V.
ef18db60-c7f9-4828-b0b2-7523d7771891
Seravkin, I.
7511edf1-9766-4ef8-99b5-c33401f034af
Kosarev, A.
0dbe156e-3d25-492d-950c-1ff355344013
Buschmann, B.
414fabdd-da8c-47b3-b1e2-119def61c1a8
Oregeval, J.J.
ebb1538f-826d-418a-9944-57e27fdf419a
Holland, N.
66a9a527-44e0-4364-a668-24117ba19bfb
Tesalina, S.
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Nimis, P.
cd277f1a-a2b9-4a1c-98cf-337fa517ad13
Armstrong, R.
c1cf75df-a0d8-4416-a8b8-3b75736ff8aa

Herrington, R., Maslennikov, V., Zaykov, V., Seravkin, I., Kosarev, A., Buschmann, B., Oregeval, J.J., Holland, N., Tesalina, S., Nimis, P. and Armstrong, R. (2005) Classification of VMS deposits: lessons from the South Uralides. Ore Geology Reviews, 27 (1-4), 203-237. (doi:10.1016/j.oregeorev.2005.07.014).

Record type: Article

Abstract

VMS deposits of the South Urals developed within the evolving Urals palaeo-ocean between Silurian and Late Devonian times. Arc-continent collision between Baltica and the Magnitogorsk Zone (arc) in the south-western Urals effectively terminated submarine volcanism in the Magnitogorsk Zone with which the bulk of the VMS deposits are associated. The majority of the Urals VMS deposits formed within volcanic-dominated sequences in deep seawater settings. Preservation of macro and micro vent fauna in the sulphide bodies is both testament to the seafloor setting for much of the sulphides but also the exceptional degree of preservation and lack of metamorphic overprint of the deposits and host rocks. The deposits in the Urals have previously been classified in terms of tectonic setting, host rock associations and metal ratios in line with recent tectono-stratigraphic classifications. In addition to these broad classes, it is clear that in a number of the Urals settings, an evolution of the host volcanic stratigraphy is accompanied by an associated change in the metal ratios of the VMS deposits, a situation previously discussed, for example, in the Noranda district of Canada.
Two key structural settings are implicated in the South Urals. The first is seen in a preserved marginal allochthon west of the Main Urals Fault where early arc tholeiites host Cu–Zn mineralization in deposits including Yaman Kasy, which is host to the oldest macro vent fauna assembly known to science. The second tectonic setting for the South Urals VMS is the Magnitogorsk arc where study has highlighted the presence of a preserved early forearc assemblage, arc tholeiite to calc-alkaline sequences and rifted arc bimodal tholeiite sequences. The boninitc rocks of the forearc host Cu–(Zn) and Cu–Co VMS deposits, the latter hosted in fragments within the Main Urals Fault Zone (MUFZ) which marks the line of arc-continent collision in Late Devonian times. The arc tholeiites host Cu–Zn deposits with an evolution to more calc-alkaline felsic volcanic sequences matched with a change to Zn–Pb–Cu polymetallic deposits, often gold-rich. Large rifts in the arc sequence are filled by thick bimodal tholeiite sequences, themselves often showing an evolution to a more calc-alkaline nature. These thick bimodal sequences are host to the largest of the Cu–Zn VMS deposits.
The exceptional degree of preservation in the Urals has permitted the identification of early seafloor clastic and hydrolytic modification (here termed halmyrolysis sensu lato) to the sulphide assemblages prior to diagenesis and this results in large-scale modification to the primary VMS body, resulting in distinctive morphological and mineralogical sub-types of sulphide body superimposed upon the tectonic association classification.
It is proposed that a better classification of seafloor VMS systems is thus achievable using a three stage classification based on (a) tectonic (hence bulk volcanic chemistry) association, (b) local volcanic chemical evolution within a single edifice and (c) seafloor reworking and halmyrolysis.

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Published date: 2005
Keywords: South Urals, VMS, classification, halmyrolysis, tectonic setting, volcanic chemistry

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Local EPrints ID: 24135
URI: http://eprints.soton.ac.uk/id/eprint/24135
ISSN: 0169-1368
PURE UUID: 48f13292-1ba9-4f11-85c0-e82c3c370ac0

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Date deposited: 22 Mar 2006
Last modified: 15 Mar 2024 06:53

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Contributors

Author: R. Herrington
Author: V. Maslennikov
Author: V. Zaykov
Author: I. Seravkin
Author: A. Kosarev
Author: B. Buschmann
Author: J.J. Oregeval
Author: N. Holland
Author: S. Tesalina
Author: P. Nimis
Author: R. Armstrong

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