The Ni-Cu-PGE-(Au-Te) potential of the Permo-Triassic boundary between Laurasia and Gondwana

<p>The long-lived geodynamic evolution of the Permo-Triassic boundary between <span>Laurasia</span> and Gondwana may have created the ideal conditions for the genesis of a trans-continental Ni-Cu-PGE-(Au-Te) mineralised belt in Europe. This working hypothesis stems from the recent understanding that orogenic processes play a fundamental role in the onset of chemical and physical triggers for the transport of metals from the metasomatised mantle through to various crustal levels. An insight into our renewed framework for the polyphased genetic evolution of magmatic sulfide mineral systems is provided by a series of mineralised occurrences in the Ivrea Zone of NW Italy, which formed at multiple stages over a > 80 Ma time interval. Between 290-250 Ma, a series of hydrated and carbonated ultramafic alkaline pipes containing Ni-Cu-PGE-(Te-Au) mineralisation was emplaced in the lower continental crust. At ~200 Ma, a subsequent mineralising event occurred in association with the emplacement of the La Balma-Monte Capio (LBMC) intrusion. Modelling of the LBMC parental magma shows derivation from ~30% partial melting of an anhydrous juvenile mantle at moderate pressure (< 7 GPa). The inferred composition of the parental melt is consistent with magmatism associated with the Central Atlantic Magmatic Province (CAMP). However, its tellurium-enriched composition together with the S-C-O isotope signature of the associated magmatic sulfide mineralisation cannot be reconciled with the CAMP source. It is argued that the geochemical and isotopic signature of the LBMC intrusion reflects interaction and mixing of a primitive magma sourced from a juvenile source with localised domains enriched in carbonate and metal-rich sulfides located in the lower crust, consistent with the composition of the Permo-Triassic pipes. Evidence of this magmatic interaction informs on the first-order processes that control enhanced metallogenic fertility along the margins of lithospheric blocks. The scenario depicted here is consistent with reactivation and enrichment of a Gondwana margin Ni-Cu-PGE-(Te-Au) mineral system during the breakup of Pangea. The lessons learnt in the Ivrea Zone natural laboratory may inform on the genesis of other Permo-Triassic magmatic mineral systems in continental Europe, such as the deposits in north-west Czech Republic and southern Spain, which display significant analogies with their counterparts in the Ivrea Zone. We suggest that these systems may have a common DNA related to a metallogenic belt forming at different stages during the complex evolution and multi-phase activation of the margin between <span>Laurasia</span> and Gondwana. The nature and localisation of the magmatic sulfide mineral systems along this belt indicate that enhanced potential for ore formation at lithospheric margins may be due not only to favourable architecture, but also to localised enhanced metal and volatile fertility. Importantly, this hypothesis may explain why ore deposits along the margins of lithospheric blocks are not distributed homogeneously along their entire extension but generally form clusters. As mineral exploration is essentially a search space reduction exercise, this new understanding may prove to be important in predictive exploration targeting for new mineralised camps in Europe and elsewhere globally, as it provides a way to prioritise segments with enhanced fertility along extensive lithospheric block margins.</p>

A high-resolution seismic survey across the Balmuccia Peridotite, Ivrea Zone, Italy - Project DIVE phase two, site investigation

<p>The Ivrea Verbano Zone (IVZ) is one of the most complete crust–upper mantle geological references in the world, and the Drilling the Ivrea-Verbano zone project (DIVE) aims to unravel the uncertainties below this area. Geophysical anomalies detected across the IVZ indicate that dense, mantle-like rocks are located at depths as shallow as ca. 3km. Thus, several geological, geochemical and geophysical studies are planned, including the drilling of a 4km deep borehole that will penetrate the Balmuccia Peridotite (Val Sesia, Italy) to approach and possibly cross the crust–mantle transition zone, and provide, for the first time, geophysical in-situ measurements of the IVZ.</p><p>One of the primary requirements before drilling is a seismic site characterization, to define with precision the correct positioning and orientation of the borehole, to assess potential drilling hazards and to allow for the spatial extrapolation of the borehole logs. For that goal, two joint geophysical surveys were performed in October 2020 in a collaboration of GFZ Potsdam, Université de Lausanne and Montanuniversität Leoben. First: a deep seismic survey, entitled SEIZE (SEismic imaging of the Ivrea ZonE), consisting of two approximately 15km-long seismic lines performed by GFZ Potsdam, that aim to resolve the deeper structure of the IVZ in the area, and second: a static seismic survey at the proposed drill site, entitled HiSEIZE (High-resolution SEismic imaging of the Ivrea ZonE), geared towards providing high-resolution seismic images of the uppermost few km at the proposed drill site.</p><p>The HiSEIZE survey, the subject of this study, was performed with a fixed spread of 200 vertical geophones and 160 3C-sensors, spaced at ca. 11m along three sub-parallel lines spaced 50-80m apart. Vibroseis source points were at 22m stations along a 2.4km line utilizing a high-frequency (12-140 Hz) 10s linear sweep with 3s listening time. In addition to this, the HiSEIZE receiver spread was active during the deep SEIZE survey, information that may be useful in determination of a velocity model through the Balmuccia Peridotite.</p><p>This project will not only provide site characterization for the DIVE project, but also contribute to understanding the structure of the Balmuccia Peridotite, its changes in depth and its relationship with the crustal-mantle transition.</p><p>Here we present the data and discuss the challenges of 3D pre-stack-imaging in an area of extreme topography.</p>