Chimneys in Paleozoic massive sulfide mounds of the Urals VMS deposits: Mineral and trace element comparison with modern black,grey, white and clear smokers |
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| Institution: | 1. Institute of Mineralogy, Ural Branch, Russian Academy of Sciences, Miass, Chelyabinsk District 456317, Russia;2. Department of Geology, South Urals State University, 8 Oktyabrya str. 16, Miass 456301, Russia;3. ARC Centre of Excellence in Ore Deposits, University of Tasmania, Hobart, Australia;4. Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, United Kingdom;5. Institute of Oceanology, Russian Academy of Sciences, Nakhimosvsky av., 36, Moscow 117997, Russia;6. John de Laeter Centre, Department of Imaging and Applied Physics, Curtin University, GPO Box U 1987, Perth 6845, Western Australia, Australia;1. Seafloor Hydrothermal Activity Laboratory of the Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China;2. Laboratory for Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China;3. University of Chinese Academy of Sciences, Beijing 100049, China;4. Qingdao Collaborative Innovation Center of Marine Science and Technology, Qingdao 266071, China;5. Department of Earth Sciences, University of Durham, Durham DH1 3LE, UK;1. National Deep Sea Center, State Oceanic Administration, Qingdao 266237, China;2. Ocean University of China, Qingdao 266100, China;1. School of Physical Sciences, University of Adelaide, Adelaide, SA 5005, Australia;2. School of Chemical Engineering, University of Adelaide, Adelaide, SA 5005, Australia |
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| Abstract: | In the Urals, a wide range of well-preserved chimneys are found in VMS deposits, which are associated with ultramafic (Atlantic type: Dergamysh), mafic (Cyprus type: Buribay), bimodal mafic (Uralian type: Yubileynoye, Sultanovskoye, Yaman-Kasy, Molodezhnoye, Uzelga-4, Valentorskoye) and bimodal felsic (Kuroko or Baymak type: Oktyabrskoye, Tash-Tau, Uselga-1, Talgan, Alexandrinskoye) sequences. Chimneys have also been found in the Safyanovskoye deposit (Altay type) that is hosted by intercalated felsic lavas and carbonaceous shales. A combination of geological, mineralogical and trace element data provide a general outline for comparison between chimneys from the Urals deposits and modern vent sites. The chimneys from the Dergamysh deposit show a broad affinity with those from the Rainbow and other vent sites associated with serpentinites of the Mid-Atlantic Ridge. The chimneys from the Buribay deposit are similar to the black smokers of the EPR vent sites including the scarcity of rare minerals. The chimneys from the Urals type of the VMS deposits show some similarities with grey smokers from the Brother Volcano and PACMANUS sites. The chimneys from the Baymak type of the VMS deposits resemble grey and white smokers of the PACMANUS and grey smokers of the Suiyo vent sites. The chimneys from the Safyanovskoye deposit are similar to the black and clear smokers from the Okinawa Trough. Mineral assemblages are controlled by the combination of host rock composition and physico-chemical conditions of the ore-forming processes. Amount of colloform pyrite, isocubanite and pseudomorphic pyrite and marcasite after pyrrhotite decreases in the chimneys across the range from ultramafic and mafic to felsic-hosted deposits and is concomitant with increase in the contents of sphalerite, galena, bornite, fahlores, native gold and barite across this range. The chimneys from the Urals type contain abundant tellurides and sulfoarsenides, while these minerals are rare (except for hessite) in the Baymak type deposits. In the same range, the buffering capacity of host rocks decreases in contrast to the increase in ?S2 and ?O2. With the exception of the Safyanovskoye deposit, trace element assemblages in chalcopyrite vary to reflect the host rock: ultramafic (high Se, Sn, Co, Ni, Ag and Au) → mafic (high Co, Se, Mo and low Bi, Au and Pb) → bimodal mafic (high Te, Au, Ag, Bi, Pb, Co, moderate Se, and variable As and Sb) → bimodal felsic (high As, Sb, Mo, Pb, moderate Bi, and low Co, Te and Se). In sphalerite of the same range, the contents of Bi, Pb, Ag, Au and Sb increase versus Fe, Se and Сo. The variations in trace elements in colloform pyrite coincide with these changes. The specific mineral changes in the local ranges from Cu- to Zn-rich chimneys in each VMS deposit are similar to the general changes in the range of host rock classes of the deposits. However, the local T, ?S2 and ?O2 changes can broadly be interpreted in terms of contribution of variable oxygenated cold seawater to the subseafloor and seafloor hydrothermal processes. |
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