Prepared by Prof. Stefano Naitza - Cagliari University

1. The metallogenic potential of an old mining
district: the case of Sardinia
Stefano Naitza
DSCG - Dipartimento di Scienze Chimiche e Geologiche, Università degli
Studi di Cagliari
Mine Waste Management - IMPEL Project, II meeting
IGLESIAS, 3-4 February 2020

2. • Since 2010, Critical raw materials (CRMs) have been
defined by EU Commission as a list of materials of
high importance for which there are concerns about
supply risks, both for geological and geopolitical
factors.
• The list now comprises 27 CRMs, including large
groups as HREEs, LREEs and PGMs.
• The EU Commission proposed a series of
recommendations regarding EU policies on raw
materials, including the re-evaluation of domestic
mineral resources. In several ancient mining areas of
Europe where old deposits have been mined for
centuries new activities have begun to evaluate their
residual potential in terms of CRMs resources. The
island of Sardinia, the most important mining district
in Italy, represents one of these areas.
Critical raw materials for EU: opportunities in the old European districts?

3. Historical mining activities
• More than 2000 years of mining;
• Iglesiente e Arburèse districts historical productions >
6.0 Mt Pb+Zn concentrates;
• Historical productions of fluorspar concentrates: > 3 Mt ;
• Historical productions of baryte concentrates : > 3.5 Mt
• Historical productions of coal («Sulcis coal»): > 28 Mt
• IM&R current productions.> 2 Mt/year
• Huge volumes of wastes from past mining - > 70 Mm3 in
169 decommissioned mine sites
• Presence of a polluted site of national interest (Sulcis-
Iglesiente) directly connected to past mining activities
• Priority requirement - clean-up / reclamation / restoration
of abandoned mining sites - estimated costs exceeding
630 million euros (Regional Plan 2003)
• Are there any remaining economic (metallogenic)
potential for this district?

4. A residual metallogenic potential?
Three main themes in assessing the residual potential of the Sardinian districts:
- wastes and residues of previous mining (and related metallurgical) activities
- marginal deposits, so far unexploited; deposits, mined for commodities other than
CRMs, considered exhausted or nearing exhaustion;
- new discoveries - deposits so far unexplored, not evaluated or not yet identified
Recognized presence of a large set of CRM in various ores:
• Fluorite
• Sb, W
• In, Ga, Ge
• REE
• Co
• Te
Other resources:
Base and ferrous metals Zn, Pb, Cu, Sn, Mo, Ni, Cd, Bi
Precious metals Au, Ag

5. - with some exceptions, most of the Sardinian deposits are
concentrated in southern Sardinia;
- two large geostructural units:
Paleozoic basement (Cambrian and Variscan metallogenesis)
«Sardinian Rift» (tertiary metallogenesis)
Three main metallogenic peaks:
1) Pre-Sardic Phase (Cambrian – early Ordovician)
2) Variscan (late Carboniferous-early-Permian)
3) Cenozoic (Oligocene-Miocene magmatism)
Geological availability of resources

6. DISTRICTS ORES TYPE
Pre-Sardic phase peak (early Cambrian-early Ordovician)
Iglesiente-Sulcis Ba, Pb Evaporite
Iglesiente-Sulcis Fe-Zn-Pb SEDEX
Iglesiente-Sulcis Pb-Zn MVT
Sardic phase period (middle-late Ordovician)
Iglesiente-Sulcis Ba, Zn-Pb Karst, Supergene
Eastern Sardinia base metals protores Sedimentary, volcanic exhalative
Eo-Variscan period (late Ordovician-late Devonian)
Eastern Sardinia Ti, Zr, LREE Placers
Nurra Fe Oolitic Fe
Iglesiente/Eastern Sardinia base metals, Mn, Au, U, V protores Sedimentary
Variscan peak (Carboniferous – early Permian)
Eastern Sardinia As-Sb-W-Au (Pb-Zn-Cu-Ag) Orogenic Mesothermal
Arburèse/Baronie/Nurra Pb-Zn (Ag, Ga-Ge-In), Ni-Co Hydrothermal granite-related (?) “five
elements-type” veins
Central Sardinia Pb-Zn-Cu (Ag, Au) Skarn, granite-related
Southern Sardinia Mo-W-Sn-F, F-Ba-Pb-Ag Hydrothermal, greisen and skarn granite-
related
Post-Variscan I period (Permian-Triassic)
Southern Sardinia F-Ba-Pb-Ag Low-temperature veins
Iglesiente-Sulcis Ba, Zn-Pb Karst, supergene
Post-Variscan II period (Cretaceous)
Nurra bauxite Paleosoil
Cenozoic peak (Oligocene-Miocene)
Western Sardinia Au-Ag-Te-Cu HS and LS epithermal, porphyry
Sulcis/Logudoro Mn Volcano-Sedimentary/exhalative
Logudoro Cu, Pb Sedimentary

7. Iglesiente-Sulcis
Pb-Zn-Ba
«anello
metallifero»
Arburèse Pb-Zn
Montevecchio-
Ingurtosu-
Gennamari
Sarrabus Ag-Pb e F-Ba
«Sarrabus silver lode»
Gerrei Sb-W-As e F-Ba
Villasalto-Ballao district
Silius district
Barbagia-Ogliastra Cu-Zn-Pb
Funtana Raminosa– skarn
Baronie Pb-Zn
Lula
Nurra Pb-Zn, Cu
Argentiera;
Calabona
Just to remember… the «classical» sardinian districts

8. The potential of waste deposits: Iglesias valley Data and potential of the district:
- Original size of the deposits : 120-150 Mt
of Pb-Zn sulfides
- Mining operations ceased since 1999
- Few residual or marginal ores related to
major deposits (e.g. barite)
- Huge wastes deriving from mining and
metallurgical activities in the district (over
13,000,000 m3 only in the Iglesias valley)
However…
Data from mine wastes characterization
integrated with data on ores from old
mines indicate a low potential in terms of
CRMs (Ga, Ge, In, etc.)

9. "Red muds" of Monteponi - Iglesias • residues from zinc metallurgy (electrolytic
sludge)
• feeding: non-sulfide zinc ores ("calamine")
• mainly consisting of goethite (50%),
smithsonite and gypsum
total area: 68,000 m2
total volume: 800,000 m3
tons (d = 3.5): 2.800.000
Metal contents
Zn (range conc. %) ton metal
min. 6% 168.000
max. 17% 475.000
aver. 10% 280.000
Fe (range conc. %) ton metal
min. 18% 500.000
max. 37% 1.040.000
aver. 30% 840.000
Cd (ppm) 124 -860
100 μm
100 μm
100 μm
100 μm
However…
Data from mine waste characterization integrated with data
on ores from old mines (Società di Monteponi and
Montevecchio)
indicate a low potential in terms of CRMs (Ga, Ge, In, etc.)

10. The Montevecchio district: the link between ores and waste resources
• Mine activities ceased in 1991
• Historical production: 1,700,000 t of Pb
and > 1,200,000 t of Zn in addition to
unspecified quantities of Ag, Bi, Sb, Cu,
Cd, Ge, Ga, In recovered in the
metallurgical cycle.
• In the bulk ore (data from exploration
campaigns of Società di Montevecchio):
up to 220 ppm Ga, 290 ppm Ge, 140 ppm
In
• Large deposits of waste rocks, tailings
and hydrogravimetric residues at the two
main beneficiation plants >9,000,000 m3
• Severe problems of environmental heavy
metals and metalloids (As) pollution
“Levante” wastes and tailings “Ponente” wastes

11. The Montevecchio district: CRMs in the ore
Recent studies on Montevecchio ores identified diffuse micro-inclusions in galena-sphalerite ores as potential
sources of CRMs, as Co and Sb. Euhedral gersdorffite crystals with As-bearing pyrite cores, tetrahedrite and
chalcopyrite blebs in galena (c) Droplets of native Sb associated with tetrahedrite and chalcopyrite in galena

12. The Montevecchio district: the Ni-Co minerals
Gersdorffite crystals with pyritic cores in the
sphalerite – chalcopyrite ore (e) and in quartz (f)

13. Southern Arburèse: «Five elements» veins: Ni-Co (Bi, Ag, REE etc.)
Miniera di Pira Inferida
The Southern Arburese district include
an extended veinfield of Ni-Co
arsenide-sulfarsenide veins
interpreted as the southern branch of
the Montevecchio system. Several
small dumps with Ni-Co, Bi, Pb-Zn-Cu
and REE minerals are scattered along
old mineworks

14. The metallogenic heritage of Variscan granitoids: Sn-W-Mo

15. Perda Niedda tin skarn ore –SW SardiniaMonte Tamara tungsten skarn ore –SW Sardinia
New perspectives in skarn and greisen deposits of Southern Sardinia: Sn-W-Mo (In, Nb,Ta)

16. The eastern districts: a wide CRMs potential
• Mines of the "Sarrabus silver lode"
(base metals, Ag in mine wastes.)
• Sb ores in the Villasalto-Ballao district
(Sb in metallurgical wastes)
• F-Ba–Pb and LREE ores (of Silius and
Sarrabus vein systems)
• Mesothermal Au-W ores ("Variscan
orogenic gold" -type)
• Ti-Zr-LREE paleoplacers (monazite) in
late Ordovician metasediments
• Skarn ores ("Funtana Raminosa type":
base metals, Au, LREE, etc.)

17. F-Ba (Ag, Pb-Zn-Cu) of SE Sardinia districts – “Sarrabus silver lode":
• exploited in 1860-1920: now exhausted
• Pb, Zn, Cu sulfide ore, with abundant Ag minerals, barite e fluorite
• relevant mine wastes are still present in some minesites ( 300.000 m3
at Monte Narba mine) – small mine dumps are scattered in the area
• wastes still retain good potential for Ag, fluorite and barite;
• LREE potential at the district scale is still unevaluated.
Discariche laveria Monte Narba - Studio CNR e Progemisa S.p.A. (2001)
Potential targets in mining wastes in eastern districts:
some examples

18. Villasalto-Ballao antimony district:
• operating in 1880-1984.
• mesothermal ores with Sb-As (Pb, Zn, Cu) sulfides, W (scheelite) and native Au
• main metallurgical plant in Italy for antimony (Villasalto)
• about 250.000 m3 of mine and metallurgical wastes
• high Sb grades in the wastes (up to 6%) – high pollution of the area
Villasalto- Ballao antimony district

19. • Exploited for over 50 years in the Genna Tres Montis/Muscadroxiu mine – now still operating but in stand-
by - it has been one of the largest fluorite deposit in Europe.
• two large F-Pb (fluorite-galena) hydrothermal veins
• more than 2.000.000 ton of ore still in place, at 34.5% CaF2 (727,495 ton fluorspar) and 3.2% Pb (67,724
Pb ton in galena).
• LREE minerals (synchisite-Ce and xenotime) in the carbonate gangue have been evaluated as potential
byproduct, with an average grade of 951 ppm ΣREE and a potential of 1220 ton of REE in 750.000 ton of old
carbonate wastes (Mondillo et al., 2017) .
The Silius deposit

20. The Ordovician REE metallotect: the Punta Serpeddì Formation
• The late Ordovician Punta Serpeddì
Formation is a 70-150 m –thick sequence
of shallow marine siliciclastic
metasediments (low-grade
metasandstones and metasiltstones).
• It includes several heavy minerals
paleoplacers, enriched in Ti-minerals,
zircon and monazite.
• Monazite-rich layers reach high grades of
Ce, La and other REEs (ΣREE>5000 ppm)
• Due to its extension, this Formation may
be considered as a relevant Ordovician
REE metallotect

21. • Gamma-ray logging allowed to identify the monazite-rich
layers
• Several monazite-rich paleoplacer zones have been
recognized in the succession

22. Remobilization of REE ores: a new target for
explorations? Examples from central Sardinia
• New conventional and
gamma-logging surveys
recognized the
Ordovician paleoplacers
in central Sardinia
• The LREE-bearing ores
display evidences of
remobilization related to
late Variscan granitoid
intrusions

23. Nurra
Argentiera: Ge-Ga-
In, Co, Sb
Mesozoic bauxite:
LREE
Gerrei
Villasalto-Ballao district: Sb, W
Silius district: F-Ba-LREE
Quirra granitoids: Mo-W-Sn
Sarrabus
Granitoids: F-Ba, LREE
Ordovician paleoplacers LREE
Sarrabus
Granitoids: F-Ba, LREE
Ordovician paleoplacers LREE
Barbagia-Ogliastra
Funtana Raminosa skarn– LREE, W
Ordovician paleoplacers - LREE
Granitoids - Mo
Baronie
Lula: Ge-Ga-In, Co
Granitoids: Mo-W
So…What about CRMs in Sardinia?
Arburèse
Montevecchio-
Ingurtosu-Gennamari
Ge-Ga-In, Ni-Co, LREE
Southern Arburèse
Ni-Co, LREE
Linas and Sulcis
Granitoids: Mo-W-Sn, F-Ba,
LREE
South Sardinia
Cenozoic volcanics Au ores: Te

24. Some conclusive remarks
• Among the old mining regions of western Europe, Sardinia stands out for the variety of its
mineralized deposits.
• New studies on Sardinian geology and metallogeny suggest many possible targets for
future explorations of different mineral resources, including several CRM’s.
• They include primarily the mining waste dumps of the old districts and numerous marginal
or under-explored deposits.
• New data from geological and metallogenic studies indicate possible new exploration
themes and suggest that Sardinian districts still retain a metallogenic potential for the
years to come.

25. Thank you!!
Mine Waste Management - IMPEL Project, II meeting
IGLESIAS, 3-4 February 2020