Spatial and Metallogenic Relationships between Different Hydrothermal Vein Systems in the Southern Arburèse District (SW Sardinia)

Matteo Luca Deidda,Marilena Moroni,Ignazio Scano,Dario Fancello,Stefano Naitza

doi:10.3390/iecms2021-09363

Matteo Luca Deidda, Marilena Moroni + Show 3 more

Open Access

https://doi.org/10.3390/iecms2021-09363

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Publication Date: Feb 25, 2021
Citations: 1	License type: CC BY 4.0

Affiliation: University of Milan, University of Cagliari

Abstract

The SW Sardinian basement hosts various ore deposits linked to geological processes active from Cambrian to post-Variscan times. In particular, the Southern Arburèse district hosts several granite-related W-Sn-Mo deposits and a 10 km-long system of Ni-Co-As-Bi-Ag ± Au bearing five-element veins. New investigations into the eastern and central parts of the district (Pira Inferida mine sector) were performed to understand the poorly documented spatial and metallogenic relationships between these systems. The granite-related deposits consist of massive wolframite-quartz (W-Bi-Te-Au) and molybdenite-quartz veins, linked to the early Permian (289 ± 1 Ma) Mt. Linas granite, that are cross-cut by the five-element veins. The wolframite-quartz veins, observed by optical and electron (SEM-EDS) microscopy, show abundant native Bi, Bi-Te phases and native Au suggesting a W-Bi-Te-Au hydrothermal system. The five-element veins exhibit breccia and cockade textures, enveloping clasts of the Ordovician host-rocks and locally small fragments of the earlier W-Mo-quartz veins. The five-element vein paragenesis includes three main stages, from older to younger: (1) native elements (Bi ± Au); (2) Ni-Co arsenides-sulfarsenides in quartz gangue; and (3) Pb-Zn-Cu ± Ag sulfides in siderite gangue. The mineralogical, geochemical and isotopic features of the five-element vein swarm are closely comparable to five-element deposits elsewhere in Europe (Germany, Switzerland, Italian Alps). While the source of Ni and Co is still unknown, the high Bi contents, as well as Au enrichment in the five-element veins, suggest selective remobilization of these elements, and perhaps others, from the granite-related W-Bi-Te-Au veins. The five-element vein system was likely formed during a post-289 ± 1 Ma and post-Variscan metallogenic event.

Highlights

In recent years the five element (Ni-Co-As-Bi-Ag) class of hydrothermal vein deposits [1] has been the object of renewed interest, primarily due to its relevant contents in critical elements such as Co and Bi [2]
New mapping and sampling, Optical Microscopy (OM) and SEM-EDS analyses allow us to envisage a relationship between the wolframite-bearing veins and the polymetallic fiveelement vein system of the Pira Inferida mine sector and to locate these vein systems within a framework of successive mineralizing events that occurred in the Southern Arburèse district during and after the emplacement of the Monte Linas granite
The wolframite-bearing veins are part of the magmatic hydrothermal systems of Monte Linas pluton, which belongs to a suite of early Permian (289 ± 1 Ma) F-bearing, ilmenite-series granites widely represented in SW Sardinia and associated with several Mo-W-Sn skarn, greisen and vein deposits [10]

Summary

Introduction

In recent years the five element (Ni-Co-As-Bi-Ag) class of hydrothermal vein deposits [1] has been the object of renewed interest, primarily due to its relevant contents in critical elements such as Co and Bi [2]. Past and current mining surveys and exploitation in the major districts worldwide (e.g., Cobalt, Ontario; Great Bear Lake, WT; Bou Azzer, Morocco; Kongsberg, Norway; Erzgebirge, Germany; Jachimov, Czech Republic, Batopilas, Mexico, etc.) revealed the metallogenic intricacies of these systems, commonly characterized by a complex geochemical association ( including Sb, U, Hg and base metals), by exceptional enrichments of Ni-Co arsenides-sulfarsenides and native elements (Ag, Bi) and by a typical carbonate gangue [3] These peculiar characters raised several questions about the sources of these metals, the chemo-physical conditions regulating their regional-scale transport by low-temperature hydrothermal fluid systems and their deposition in vein-type deposits at shallow crustal levels. New surveys and mineralogical studies were performed in the area to acquire new data on both types of ores and to investigate their mutual and hitherto poorly constrained spatial and metallogenic relationships

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