Abstract
The pyrite nodules from ore diagenites of the Urals massive sulfide deposits associated with various background sedimentary rocks are studied using optical and electron microscopy and LA-ICP-MS analysis. The nodules are found in sulfide–black shale, sulfide–carbonate–hyaloclastite, and sulfide–serpentinite diagenites of the Saf’yanovskoe, Talgan, and Dergamysh deposits, respectively. The nodules consist of the core made up of early diagenetic fine-crystalline (grained) pyrite and the rim (±intermediate zone) composed of late diagenetic coarse-crystalline pyrite. The nodules are replaced by authigenic sphalerite, chalcopyrite, galena, and fahlores (Saf’yanovskoe), sphalerite, chalcopyrite and galena (Talgan), and pyrrhotite and chalcopyrite (Dergamysh). They exhibit specific accessory mineral assemblages with dominant galena and fahlores, various tellurides and Co–Ni sulfoarsenides in sulfide-black shale, sulfide–hyaloclastite–carbonate, and sulfide-serpentinite diagenites, respectively. The core of nodules is enriched in trace elements in contrast to the rim. The nodules from sulfide–black shale diagenites are enriched in most trace elements due to their effective sorption by associated organic-rich sediments. The nodules from sulfide–carbonate–hyaloclastite diagenites are rich in elements sourced from seawater, hyaloclastites and copper–zinc ore clasts. The nodules from sulfide–serpentinite diagenites are rich in Co and Ni, which are typical trace elements of ultramafic rocks and primary ores from the deposit.
Highlights
Diagenetic pyrite nodules are one of the types of sedimentary pyrite abundant in sedimentary sequences of various ages, in particular, in those enriched in organic matter [1,2,3,4]
The presence of various associated background sediments is a key factor affecting the diversity of accessory authigenic minerals, which occur inside the pyrite nodules
The core of the nodules formed during early diagenesis, which is evident from the presence of associated framboidal pyrite (Saf’yanovskoe deposit) (Figure 3c), a typical product of early diagenesis of sedimentary rocks [50,51]
Summary
Diagenetic pyrite nodules are one of the types of sedimentary pyrite abundant in sedimentary sequences of various ages, in particular, in those enriched in organic matter [1,2,3,4] They occur in black shale sequences of gold deposits, where they are associated with arsenopyrite, native gold, and Au tellurides [1,2,3]. Recent studies of syngenetic and diagenetic pyrite from black shales have showed that hydrothermal pyrite is a proxy of chemistry of ore-forming fluids, whereas sedimentary pyrite is an indicator of variable chemistry of seawater [8]. It is suggested that these pyrite types trapped trace elements from seawater (As, Hg, Ni, Mn, Pb, Co, Cu, Zn, Sb, Mo, Se, Ag, Tl, Bi, Te, and Au) and detrital matrix
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