Valeriy V. Maslennikov

Two Palaeozoic Hydrothermal Vent Communities from the Southern Ural Mountains, Russia

The Sibay and Yaman Kasy massive sulphide deposits contain macrofossil assemblages that represent some of the oldest known hydrothermal vent communities. The deposits are hosted respectively by Middle Devonian and Silurian arc-related volcanic rocks in the Ural Mountains of Russia, and formed under the same environmental constraints as modern vent sulphides. The Sibay palaeocommunity comprises, in order of decreasing abundance, tubes of an indeterminate ?annelid and the vestimentiferan Tevidestus serrriformis Shpanskaya, Maslennikov and Little and articulated specimens of the modiomorphid bivalve Sibaya ivanovi gen. et sp. nov. The Yaman Kasy palaeocommunity comprises, in order of decreasing abundance, tubes of the ?polychaete Eoalvinellodes annulatus gen. et sp. nov. and the vestimentiferan Yamankasia rifeia Shpanskaya, Maslennikov and Little, and specimens of the ?kirengellid tergomyan Themoconus shadlunae gen. et sp. nov., the lingulate brachiopod Pyrodiscus lorrainae gen. et sp. nov., an indeterminate vetigastropod, and the ambonychiid bivalve Mytilarca sp. Some of these taxa have affinities to endemic taxa at modern hydrothermal vent sites and some belong to taxa that are typical of Palaeozoic non-vent marine palaeocommunities. Therefore, there has been movement of taxonomic groups in and out of the vent ecosystem through the Phanerozoic.

Mineralogical-geochemical features of sulfide ores from the Broken Spur hydrothermal vent field

A representative collection of hydrothermal sediments was sampled practically from all the hydrothermal mounds of the Broken Spur hydrothermal vent field from the Mir manned submersibles during three cruises of R/V Akademik Mstislav Keldysh. Mineral associations characteristic of different morphological types of sulfide ores from hydrothermal pipes, plates, and diffusers are assessed. Particular attention is paid to the distribution of minor elements and their distribution patterns determined by the mineralogical zonation. The measured isotopic value of the sulfur in the sulfide minerals appeared to vary from 0.4 to 5.2‰, which indicates their similarity with the ores from the Snake Pit vent field and is related to the dilution of hot ore-bearing solutions by seawater and reduction of the water sulfate ions to H2S with a heavy isotopic composition.

Sulfide minerals in the Menez Gwen nonmetallic hydrothermal field (Mid-Atlantic Ridge)

Mineralogy and geochemistry of the sulfide-bearing rocks and ores discovered in the Menez Gwen field are studied. Samples were taken during the expedition of the Shirshov Institute of Oceanology (cruise 49, R/V Akademik Mstislav Keldysh. The mineral composition of rocks and ores were studied by the traditional methods of optical microscopy, scanning electron microscopy (CAMSCAN), and microprobe analysis (EPMA SX-50). Contents of trace elements were determined by the laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS). The Zn-Cu ore comprises zonal sulfide chimney intergrowths. Numerous Se-rich copper ore fragments occur in the volcanomictic layered gritstones and/or barite slabs. The mineral composition, zonality, and association of trace elements in ore are typical of “black smokers” formed at the basalt base near the Azores Triple Junction in the MAR. The results obtained make it possible to reconstruct formation history of the Menez Gwen hydrothermal field into the high-temperature (Cu-Se association in ore clasts), medium-temperature (Zn-Cu-As association in ore), and recent (Ba-SiO2 association) stages.

Biomorphic textures in the ferruginous-siliceous rocks of massive sulfide-bearing paleohydrothermal fields in the urals

The work is dedicated to first finds of bacteriomorphic and microfaunal textures in the ferruginous-siliceous rocks that are widespread among volcanosedimentary complexes of the massive sulfide-bearing paleohydrothermal fields in the Urals. The bacteriomorphs are represented by: (1) single filaments with a diameter of 8–10 μm across and 80–90 μm long; (2) fascicles of branched or twisted-fibrous hematitequartz filaments 1–4 μm in diameter and up to 100 μm long; (3) microtubular textures, 20–30 μm across and up to 500 μm long, closely interlaced with thin hematite-quartz filaments (3–5 μm in diameter); (4)and hematite-quartz filaments (with the axial channel 1 μm across) formed by chains of elongated-oval lumps. These textures closely associate in the ferruginous-siliceous rocks with the fossilized tubular organisms (60–120 μm in diameter), tentaculites, remains of radiolarian skeletons, foraminifers, and others. It has been established that accumulation of various elements, such as Fe, Si, Ca, P, Mn, Ba, Ti, and K that are associated with biomorphic structures, was accompanied by the formation of their own mineral forms. Biomorphic textures in the gossanites (ferruginous-siliceous rocks forming haloes around destroyed massive sulphide mounds) differ from jasperites (not associating with sulfide ores ferruginouse-siliceous rocks), in terms of abundance, diversity, and development of tubular organisms and tentaculites.Biomineralization of different degrees of preservation in the Paleozoic ferruginous-siliceous rocks can indicate the microbial influence on geochemical processes during the decomposition of initial hyaloclastic sediments, which contain an admixture of sulfides and carbonates, under low-temperature conditions accompanied by the formation of iron and silica.

Associations of trace elements in the sulfides of black smokers from the Broken Spur, Menez Gwen, and Snake Pit hydrothermal fields

Thorough processing of a huge amount of analytical data from Electron-Probe Microanalyses (EPMA) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) allowed us to define several trace-element associations in sulfides from three hydrothermal vent fields at the Mid-Atlantic Ridge (Broken Spur, Menez Gwen, and Snake Pit). The presence of such association may indicate the occurrence of certain mineral phases at the micro- and/or nano-scales.

Biomineralization in ferruginous-siliceous sediments of massive sulfide deposits of the Urals

193 Ferruginous–siliceous sediments, associated with Silurian and Devonian massive sulfide deposits of the Urals, preserved the textural–structural and geochemi cal features of their halmyrolitic, apohyaloclastic, and aposulfide origin [1]. These rocks are made mainly of hematite, quartz, carbonates, chlorite, and rarely manganese and sulfide minerals. In these rocks two types of deposits are distinguished: jasperites and gos sanites. It was shown that jasperites formed as a result of halmyrolysis of hyaloclastites in the presence of an admixture of calcareous material. As for gossanites, oxidized sulfide particles took part in their formation, along with the hyaloclastic material [1].

Initial stage of the hydrothermal ore accumulation within the field at 9°50′ N on the East Pacific Rise

In 2003, several hydrothermal mounds located at 9°50′ N on the East Pacific Rise were described and sampled during the expedition of R/V Akademik Mstislav Keldysh during dives of Mir deep-sea manned submersibles. These hydrothermal mounds were formed during a few recent years after the volcanic activity in this region that occurred in 1991. The studies of the chemical and mineralogical compositions of the hydrothermal deposits of these mounds and of the chemical composition of the principal sulfide minerals helped to describe the initial stage of the formation of the hydrothermal circulation system and the initiation of the hydrothermal ore formation.

Se and In minerals in the submarine oxidation zone of a massive sulfide orebody of the molodezhnoe copper–zinc massive sulfide deposit, Southern Urals

For the first time, extremely high Se and In contents were determined for the pinches of massive sulfide orebodies that are composed of small-clastic layered sulfide sediments transformed during submarine supergenesis. Se (clausthalite and naumannite) and In (roquesite) minerals were found. Hydrothermal chalcopyrite, a significant amount of which is present in the clasts of paleohydrothermal black smoker chimneys, was the source of Se. Most of the amount of In was contributed during dissolution of clasts of hydrothermal sphalerite, which is unstable in the submarine oxidation zone in the presence of oxidized pyrite.

Covellite of the Semenov-2 hydrothermal field (13°31.13′ N, Mid-Atlantic Ridge): Enrichment in trace elements according to LA ICP MS analysis

As a result of LA ICP MS analysis of sulfides of the Semenov-2 hydrothermal field, it is established that covellite, which replaces Zn sulfides, is enriched in most trace elements. The Ga, Ni, and In contents in it do not vary, whereas Mn, Co, and Cd are lower than in sphalerite. The distribution of trace elements in covellite, which replaces Cu–Fe sulfides, is distinct: it is enriched in Cd, Sb, Pb, and Bi, whereas the contents of other elements are either lower or invariant. Covellite, which replaces Zn sulfides, is enriched in all trace elements relative to that replacing Cu–Fe sulfides. Enrichment of covellite in trace elements relative to primary sulfides was favored by oxidation of the hydrothermal fluid by seawater, which is similar to the processes of submarine oxidation of ancient massive sulfide deposits. Covellite is also a host to invisible gold and silver in ores of the Semenov-2 field along with toxic elements such as As, Se, Te, Tl, and Cd.

Evidence of Biogenic Activity in Quartz-Hematite Rocks of the Urals VMS Deposits

The textural, mineralogical, and geochemical features of quartz-hematite rocks associated with Urals VMS deposits indicate that the tube microfossils are responsible for immobilization and accumulation of chemical elements during precipitation of authigenic minerals. The crystallization of authigenic minerals is a result of submarine transformation of mixed hyaloclastitic, sulfide, and carbonate sediments and diagenetic processes, which modify the mineralogy and geochemistry of sediments. The tube microfossils about 100 μm across and up to 1 mm long consist of the external rim made up of fine-disperse hematite or hematite-quartz aggregates and of the internal channel filled with hematite and/or transparent quartz, fine-disperse hematite-quartz aggregates, leucoxene, rare sulfides, apatite, Fe-chlorite, and Mn-calcite. The carbon isotopic composition of calcite from quartz-hematite rocks with tube microfossils (up to −26.2 ‰) indicates its biogenic origin. The habitat conditions of the tube microfossils favored the mineral precipitation. The newly formed apatite, rutile, illite, monazite, dolomite, ankerite, siderite, monheimite, REE carbonates, anatase, leucoxene, Mn-oxides, titanomagnetite, and hematitized framboidal pyrite are observed in quartz-hematite matrix with abundant tube organisms in contrast to quartz-hematite rocks free of tube microfossils. Biomorphic hematite contains high contents of Mn (up to 9393 ppm), As (up to 1872 ppm), V (up to 779 ppm), W (up to 1091 ppm), Mo (up to 40 ppm), and U (up to 8.68 ppm), which are indicative of biological mechanisms of accumulation and conservation of these metals in the system.