Provenance and geochemistry of sedimentary components in the Volcano-Sedimentary Complex, Iberian Pyrite Belt: discrimination between the sill–sediment-complex and volcanic-pile models

Abstract

Two highly contrasting models have been proposed for the palaeovolcanological setting of the massive sulphide deposits in the Iberian Pyrite Belt. The long-standing view of the host rocks is that they are a pile of effusive and pyroclastic rocks but this position has now been challenged by the proposal that highlevel peperitic sills predominate. Discrimination between the volcanic-pile and sill-sediment-complex models is important because they lead to very different conclusions about such key metallogenic features as the timing of mineralization, the nature of the ore-forming convective system and the source of the metals. Sedimentary geochemistry, particularly REE and Ti/Nb, shows that there is no correspondence between the chemistries of mafic igneous sheets and intercalated stratified-volcaniclastic rocks that range from andesite to rhyodacite in composition. Therefore none of the mafic sheets supplied detritus to the sedimentary environment. Sedimentary rocks of continental provenance persist throughout the host-rock sequence, especially in mineralized regions, implying confinement of the majority of primary volcanic facies in the form of high-level intrusions. Some andesitic and felsic intrusions created a minor, stratified volcaniclastic component via hydrovolcanic eruptions. The volcanic-pile model is invalidated because the expected provenance patterns for this volcanic style are not present and the sill-sediment-complex setting of the sulphide deposits is confirmed.

Comment on “A new geodynamic interpretation for the South Portuguese Zone (SW Iberia) and the Iberian Pyrite Belt genesis” by J. Onézime et al.

“…At the time of my initial work in the Iberian Pyrite Belt, previous reports had considered these stratified volcanic breccias to be pyroclastic flow deposits. In stark contrast to the Onézime et al [2003] perspective on my earlier work, I did recognize the importance of stratified volcaniclastic rocks in the Pyrite Belt, and this recognition has continued to the present‐day with an analysis of their chemistry [ Boulter et al , 2004]. This provenance study has supported the proposition that the majority of the volcanic facies in the Rio Tinto district were peperitic intrusions that did not supply detritus to the sedimentary basin.…”

“…Our 2004 provenance study does however preclude widespread distribution of pyroclastic eruption products by subaerial means because of the common occurrence of mudrocks with continental chemistry through the Volcano‐Sedimentary Complex. Also detailed documentation of lateral facies in the stratified felsic volcaniclastic deposits has led to the surprising result that the stratiform sulphide sheets were positive regions immediately postmineralization [ Boulter et al , 2004]; this is a configuration more readily explained in a sill‐sediment complex.…”

Geochemistry and U–Pb dating of felsic volcanic rocks in the Riotinto–Nerva unit, Iberian Pyrite Belt, Spain: crustal thinning, progressive crustal melting and massive sulphide genesis

“…2): (1) a lower mafic-siliciclastic succession of Strunian age (Rodríguez et al 2002), containing a number of dark shale horizons and basaltic rocks, both volcanic and subvolcanic (García-Palomero 1980;Boulter 1993aBoulter ,b, 1996Tornos & Almodóvar 2003;Boulter et al 2004;Mellado et al 2006); (2) a volcanic felsic succession in which volcaniclastic rocks alternate with rhyolitic flows and sills (Boulter 1993a;Pascual et al 2000;Valenzuela et al 2002;Boulter et al 2004); (3) an upper sedimentary succession. The occurrence of rhyolite fragments within this last unit, as well as the chloritic alteration haloes within the felsic succession, indicate that the VHMS deposits in the Riotinto-Nerva unit postdate most of the Volcano-Sedimentary Complex sequence, at least in the Riotinto mining district (García-Palomero 1980).…”

Geochemical characteristics of the Permian marine mudstone and constraints on its provenance and paleoenvironment in the Fenghai area, Fujian Province, southeastern China

“…These are often used as important parameters for analyzing Edited provenance attributes and discriminating tectonic settings. Their main controlling factor was provenance (Boulter et al 2004;Cao et al 2007). Furthermore, V, Cr, Ni, Co and U were active elements in sediments and their content reflected their physical and chemical properties, even the influence of paleo-sedimentary environment and tectonic setting during their formation (Xie et al 2015a;Gao et al 2017).…”