Correlation of massive sulfide deposits in the Appalachian-Caledonian orogen on the basis of paleotectonic setting

Abstract

Over 70 major (>1 million metric tons) strata-bound and stratiform sulfide deposits of late Proterozoic and early Paleozoic age in the fragmented Appalachian-Caledonian orogen are correlated on the basis of their palcotectonic setting. The latter is defined in terms of two parameters, the plate tectonic palcosetting and the palcogeographic location relative to various cratonic margins. Attention is focused on geochemical data from mafic volcanic and high-level intrusive rocks associated with massive sulfide deposits, as well as on structural settings and regional tectonostratigraphic correlations. Host-rock data for over 20 key deposits or groups of deposits are discussed. Massive sulfides formed in intraplate (ensialic) as well as ocean-floor and convergent plate boundary settings are recognized in the orogen. The intraplate (ensialic) setting involves environments marginal to the Laurentian and Baltoscandian cratons; it includes both sedimentary and volcanic host-rock sequences and is interpreted as an incipientdivergent plate boundary. The ocean-floor setting includes massive sulfides in ophiolites formed either at a major ocean spreading axis or within back-or interarc basins, as well as deposits hosted by sequences of mafic volcanics, graphitic phyllite, and chert possibly formed in an off-axis (intraplate) situation; deposits in this setting are restricted to the northern Appalachians and the Norwegian Caledonides. The convergent plate boundary setting includes massive sulfides hosted by subduction-related volcanics, and by postarc and post-early collision volcano-sedimentary sequences. Both ensimatic and ensialic subarc crustal environments are represented, the latter recognized outboard (northwest) of the Avalonian platform in the Appalachians and its equivalent in the United Kingdom-Ireland Caledonides. The majority of massive sulfide deposits in the orogen formed within a convergent plate boundary setting. Assessment of the host-rock data in connection with the correlation theme has revealed:(1) the presence of both regional and sulfide-localized alterations in volcanic host rocks and the occurrence of sulfide-localized alteration in several of the sediment-hosted deposits; (2) evidence for an extensional tectonic regime either during or immediately after deposition of many of the massive sulfide deposits, including some of those formed in a convergent plate boundary setting (rifted-arc, postarc, and post-early collision sequences); (3) the likelihood that massive sulfides were deposited during a single cycle of ocean basin opening and closure, although possible reservations to this model are raised by volcanic-hosted deposits in the southern Appalachians; and (4) possible target areas for future mineral exploration.

Lead-isotope study of the sulphide ore and alteration zone, Bleikvassli zinc-lead deposit, northern Norway

“…This suggests a depletion of uranium from this whole rock specimen during the 464 Ma event defined by the Rb-Sr dating. The position of the Bleikvassli galena lead on the orogen growth curve reflects a relatively large proportion of upper crustal lead, which is consistent with its identity as one of the most continental members among the stratiform sulphide deposits in the Caledonides, as previously suggested by Stephens et al (1984) and Vokes (1988). A continental extensional environment is further supported by its metasedimentary host rocks and the within-plate affinity of the associated mafic rocks (Ramberg 1967;Skauli 1990).…”

Intergrowths of hexagonal and monoclinic pyrrhotites in some sulphide ores from norway

“…On the basis of their metal contents these ores may be described as either Cu, Cu-Zn or Zn-Pb-(Cu) types though the majority fall into the Cu-Zn type. They were generated in several different palaeotectonic environments during the course of the Caledonian orogenic cycle and deformed/metamorphosed during this cycle (Vokes, 1968(Vokes, , 1988Stephens et al, 1984).…”

Geochemical evidences of sedimentary-exhalative origin of the shale-hosted PGE–Ag–Au–Zn–Cu occurrences of the Prades Mountains (Catalonia, Spain): trace-element abundances and Sm–Nd isotopes

“…Feldspar layers of different composition have been reported in several exhalative deposits worldwide, with ages ranging from Precambrian to Paleozoic. Many examples of albite occurrences are known: Thackaringa, in Australia (Plimer, 1977), Cinco Villas, in the Basque Country, Spain (Pesquera and Velasco, 1993), Sullivan, in Canada (Shaw and Jodgson, 1986), Foz-Barreiros, in Galicia, Spain (Roel, 1994), in Roná district, Czech Republic (Kříbek et al, 2002), and in several deposits of the CaledonianAppalachian Orogeny (Stephens et al, 1984). However, anorthite-bearing layers have only been reported in few deposits; the most known are in Dachang, China .…”