The Pb-Zn-Ag vein system at Montevecchio-Ingurtosu, southwestern Sardinia, Italy: A summary of previous knowledge and new mineralogical, fluid inclusion, and isotopic data

M. Moroni, S. Naitza, G. Ruggieri, A. Aquino, P. Costagliola, G. De Giudici, S. Caruso, E. Ferrari, M. L. Fiorentini, P. Lattanzi

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Abstract

The Montevecchio-Ingurtosu district (SW Sardinia) was among the largest historical Pb-Zn producers of Italy, with significant Ag output, and yields of metallic byproducts such as Cd, Co, Cu, Bi, Sb, Ge, In, and Ga. Despite this importance, detailed descriptions of orebodies and mineral assemblages are surprisingly scarce and old. Here we summarize all previously available information and contribute new textural, microchemical, fluid inclusion, and C-O isotopic data deriving from a recent sampling of currently exposed orebodies. Mineralization occurs as steeply dipping veins extending for almost 20 km at the northern and western flanks of the Variscan Arbus pluton; veins are hosted in phyllites of the Arburese Unit close to the thermometamorphic aureole. Ore enrichments range from massive to coarsely nodular, stockwork and brecciated. Vein filling consists of siderite (locally Zn-rich), quartz, sphalerite, galena (remarkably rich in micro-inclusions), with accessory chalcopyrite, fahlore, bournonite, barite, and Ni-Co sulfarsenides. Vein assemblages may vary, even within a single vein, from sphalerite- to galena-dominated. Cu-rich assemblages (fahlore + chalcopyrite) were locally observed. Wallrock is affected by silicification, sericitization and pyrite dissemination. Sphalerite shows a complex mineral chemistry, with marked variations in Fe (0.08 to 8.9 mol% FeS) and in Cd contents (from <0.05 to >1 wt%). Trace element analyses (LA-ICP-MS) document the presence of measurable amounts of Ga, Ge, In, Ag, Ni, Co, Tl and Mo. Fahlore varies from the Sb (tetrahedrite) and the As (tennantite) endmembers, with Ag-rich compositions corresponding to Sb endmembers. The occurrence of Cd-rich tetrahedrite (up to 14.5 wt%) is remarkable. Fluid inclusion studies on sphalerite and quartz are in agreement with previous literature data, and indicate comparatively low (in the range 90°–130 °C) homogenization temperatures (Th) and high salinities (14 to 25 equiv. mass % NaCl); both microthermometric data and SEM/EDS analyses of decrepitated inclusions indicate the presence of Ca and K beside Na. Pressure correction to Th is presumably low (in the order of 10 °C), considering a hydrostatic pressure regime. Application of the sphalerite-based GGIMFiS thermometer provided temperatures in excellent agreement with fluid inclusion data for the Montevecchio mineralization. Isotopic data on Montevecchio carbonates define mildy negative δ13CPDB values (between −1 and −5 per mil), and a larger spread of δ18OSMOW values, between +14 and +20 per mil. Other isotopic data from literature include a limited set of δ34S values for galena, sphalerite and pyrite, and a fairly large body of Pb isotopic data on galena. Comparatively narrow ranges for sulfur isotope signatures suggest a homogeneous, possibly igneous, sulfur source, whereas the large spread in Pb isotope signatures reflects the large-scale character of the hydrothermal process and indicates that the Arbus pluton may have been just one of the sources of ore lead. The Montevecchio vein system shows affinities with other late to post Variscan European deposits. The nature of the mineralizing fluids at Montevecchio is analogous to low temperature, basinal brines, and typical of several regional-scale, late to post-Variscan hydrothermal events across Europe. Mineralization at Montevecchio obviously postdates the emplacement of the Arbus plutonic complex, but its exact age remains unknown.

Original languageEnglish
Article number103194
JournalOre Geology Reviews
Volume115
DOIs
Publication statusPublished - 1 Dec 2019

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fluid inclusion
sphalerite
fahlore
Fluids
galena
Hercynian orogeny
Quartz
tetrahedrite
Ores
mineralization
Minerals
Sulfur Isotopes
chalcopyrite
pluton
pyrite
Barium Sulfate
Brines
quartz
tennantite
Thermometers

Cite this

@article{f38e2c0015134495b345bad8d0a98fdf,
title = "The Pb-Zn-Ag vein system at Montevecchio-Ingurtosu, southwestern Sardinia, Italy: A summary of previous knowledge and new mineralogical, fluid inclusion, and isotopic data",
abstract = "The Montevecchio-Ingurtosu district (SW Sardinia) was among the largest historical Pb-Zn producers of Italy, with significant Ag output, and yields of metallic byproducts such as Cd, Co, Cu, Bi, Sb, Ge, In, and Ga. Despite this importance, detailed descriptions of orebodies and mineral assemblages are surprisingly scarce and old. Here we summarize all previously available information and contribute new textural, microchemical, fluid inclusion, and C-O isotopic data deriving from a recent sampling of currently exposed orebodies. Mineralization occurs as steeply dipping veins extending for almost 20 km at the northern and western flanks of the Variscan Arbus pluton; veins are hosted in phyllites of the Arburese Unit close to the thermometamorphic aureole. Ore enrichments range from massive to coarsely nodular, stockwork and brecciated. Vein filling consists of siderite (locally Zn-rich), quartz, sphalerite, galena (remarkably rich in micro-inclusions), with accessory chalcopyrite, fahlore, bournonite, barite, and Ni-Co sulfarsenides. Vein assemblages may vary, even within a single vein, from sphalerite- to galena-dominated. Cu-rich assemblages (fahlore + chalcopyrite) were locally observed. Wallrock is affected by silicification, sericitization and pyrite dissemination. Sphalerite shows a complex mineral chemistry, with marked variations in Fe (0.08 to 8.9 mol{\%} FeS) and in Cd contents (from <0.05 to >1 wt{\%}). Trace element analyses (LA-ICP-MS) document the presence of measurable amounts of Ga, Ge, In, Ag, Ni, Co, Tl and Mo. Fahlore varies from the Sb (tetrahedrite) and the As (tennantite) endmembers, with Ag-rich compositions corresponding to Sb endmembers. The occurrence of Cd-rich tetrahedrite (up to 14.5 wt{\%}) is remarkable. Fluid inclusion studies on sphalerite and quartz are in agreement with previous literature data, and indicate comparatively low (in the range 90°–130 °C) homogenization temperatures (Th) and high salinities (14 to 25 equiv. mass {\%} NaCl); both microthermometric data and SEM/EDS analyses of decrepitated inclusions indicate the presence of Ca and K beside Na. Pressure correction to Th is presumably low (in the order of 10 °C), considering a hydrostatic pressure regime. Application of the sphalerite-based GGIMFiS thermometer provided temperatures in excellent agreement with fluid inclusion data for the Montevecchio mineralization. Isotopic data on Montevecchio carbonates define mildy negative δ13CPDB values (between −1 and −5 per mil), and a larger spread of δ18OSMOW values, between +14 and +20 per mil. Other isotopic data from literature include a limited set of δ34S values for galena, sphalerite and pyrite, and a fairly large body of Pb isotopic data on galena. Comparatively narrow ranges for sulfur isotope signatures suggest a homogeneous, possibly igneous, sulfur source, whereas the large spread in Pb isotope signatures reflects the large-scale character of the hydrothermal process and indicates that the Arbus pluton may have been just one of the sources of ore lead. The Montevecchio vein system shows affinities with other late to post Variscan European deposits. The nature of the mineralizing fluids at Montevecchio is analogous to low temperature, basinal brines, and typical of several regional-scale, late to post-Variscan hydrothermal events across Europe. Mineralization at Montevecchio obviously postdates the emplacement of the Arbus plutonic complex, but its exact age remains unknown.",
keywords = "Basinal brines, Geothermometry, Pb-Zn-Ag veins, Sardinian metallogeny, Sphalerite composition",
author = "M. Moroni and S. Naitza and G. Ruggieri and A. Aquino and P. Costagliola and {De Giudici}, G. and S. Caruso and E. Ferrari and Fiorentini, {M. L.} and P. Lattanzi",
year = "2019",
month = "12",
day = "1",
doi = "10.1016/j.oregeorev.2019.103194",
language = "English",
volume = "115",
journal = "Ore Geology Reviews",
issn = "0169-1368",
publisher = "Pergamon",

}

The Pb-Zn-Ag vein system at Montevecchio-Ingurtosu, southwestern Sardinia, Italy : A summary of previous knowledge and new mineralogical, fluid inclusion, and isotopic data. / Moroni, M.; Naitza, S.; Ruggieri, G.; Aquino, A.; Costagliola, P.; De Giudici, G.; Caruso, S.; Ferrari, E.; Fiorentini, M. L.; Lattanzi, P.

In: Ore Geology Reviews, Vol. 115, 103194, 01.12.2019.

Research output: Contribution to journalArticle

TY - JOUR

T1 - The Pb-Zn-Ag vein system at Montevecchio-Ingurtosu, southwestern Sardinia, Italy

T2 - A summary of previous knowledge and new mineralogical, fluid inclusion, and isotopic data

AU - Moroni, M.

AU - Naitza, S.

AU - Ruggieri, G.

AU - Aquino, A.

AU - Costagliola, P.

AU - De Giudici, G.

AU - Caruso, S.

AU - Ferrari, E.

AU - Fiorentini, M. L.

AU - Lattanzi, P.

PY - 2019/12/1

Y1 - 2019/12/1

N2 - The Montevecchio-Ingurtosu district (SW Sardinia) was among the largest historical Pb-Zn producers of Italy, with significant Ag output, and yields of metallic byproducts such as Cd, Co, Cu, Bi, Sb, Ge, In, and Ga. Despite this importance, detailed descriptions of orebodies and mineral assemblages are surprisingly scarce and old. Here we summarize all previously available information and contribute new textural, microchemical, fluid inclusion, and C-O isotopic data deriving from a recent sampling of currently exposed orebodies. Mineralization occurs as steeply dipping veins extending for almost 20 km at the northern and western flanks of the Variscan Arbus pluton; veins are hosted in phyllites of the Arburese Unit close to the thermometamorphic aureole. Ore enrichments range from massive to coarsely nodular, stockwork and brecciated. Vein filling consists of siderite (locally Zn-rich), quartz, sphalerite, galena (remarkably rich in micro-inclusions), with accessory chalcopyrite, fahlore, bournonite, barite, and Ni-Co sulfarsenides. Vein assemblages may vary, even within a single vein, from sphalerite- to galena-dominated. Cu-rich assemblages (fahlore + chalcopyrite) were locally observed. Wallrock is affected by silicification, sericitization and pyrite dissemination. Sphalerite shows a complex mineral chemistry, with marked variations in Fe (0.08 to 8.9 mol% FeS) and in Cd contents (from <0.05 to >1 wt%). Trace element analyses (LA-ICP-MS) document the presence of measurable amounts of Ga, Ge, In, Ag, Ni, Co, Tl and Mo. Fahlore varies from the Sb (tetrahedrite) and the As (tennantite) endmembers, with Ag-rich compositions corresponding to Sb endmembers. The occurrence of Cd-rich tetrahedrite (up to 14.5 wt%) is remarkable. Fluid inclusion studies on sphalerite and quartz are in agreement with previous literature data, and indicate comparatively low (in the range 90°–130 °C) homogenization temperatures (Th) and high salinities (14 to 25 equiv. mass % NaCl); both microthermometric data and SEM/EDS analyses of decrepitated inclusions indicate the presence of Ca and K beside Na. Pressure correction to Th is presumably low (in the order of 10 °C), considering a hydrostatic pressure regime. Application of the sphalerite-based GGIMFiS thermometer provided temperatures in excellent agreement with fluid inclusion data for the Montevecchio mineralization. Isotopic data on Montevecchio carbonates define mildy negative δ13CPDB values (between −1 and −5 per mil), and a larger spread of δ18OSMOW values, between +14 and +20 per mil. Other isotopic data from literature include a limited set of δ34S values for galena, sphalerite and pyrite, and a fairly large body of Pb isotopic data on galena. Comparatively narrow ranges for sulfur isotope signatures suggest a homogeneous, possibly igneous, sulfur source, whereas the large spread in Pb isotope signatures reflects the large-scale character of the hydrothermal process and indicates that the Arbus pluton may have been just one of the sources of ore lead. The Montevecchio vein system shows affinities with other late to post Variscan European deposits. The nature of the mineralizing fluids at Montevecchio is analogous to low temperature, basinal brines, and typical of several regional-scale, late to post-Variscan hydrothermal events across Europe. Mineralization at Montevecchio obviously postdates the emplacement of the Arbus plutonic complex, but its exact age remains unknown.

AB - The Montevecchio-Ingurtosu district (SW Sardinia) was among the largest historical Pb-Zn producers of Italy, with significant Ag output, and yields of metallic byproducts such as Cd, Co, Cu, Bi, Sb, Ge, In, and Ga. Despite this importance, detailed descriptions of orebodies and mineral assemblages are surprisingly scarce and old. Here we summarize all previously available information and contribute new textural, microchemical, fluid inclusion, and C-O isotopic data deriving from a recent sampling of currently exposed orebodies. Mineralization occurs as steeply dipping veins extending for almost 20 km at the northern and western flanks of the Variscan Arbus pluton; veins are hosted in phyllites of the Arburese Unit close to the thermometamorphic aureole. Ore enrichments range from massive to coarsely nodular, stockwork and brecciated. Vein filling consists of siderite (locally Zn-rich), quartz, sphalerite, galena (remarkably rich in micro-inclusions), with accessory chalcopyrite, fahlore, bournonite, barite, and Ni-Co sulfarsenides. Vein assemblages may vary, even within a single vein, from sphalerite- to galena-dominated. Cu-rich assemblages (fahlore + chalcopyrite) were locally observed. Wallrock is affected by silicification, sericitization and pyrite dissemination. Sphalerite shows a complex mineral chemistry, with marked variations in Fe (0.08 to 8.9 mol% FeS) and in Cd contents (from <0.05 to >1 wt%). Trace element analyses (LA-ICP-MS) document the presence of measurable amounts of Ga, Ge, In, Ag, Ni, Co, Tl and Mo. Fahlore varies from the Sb (tetrahedrite) and the As (tennantite) endmembers, with Ag-rich compositions corresponding to Sb endmembers. The occurrence of Cd-rich tetrahedrite (up to 14.5 wt%) is remarkable. Fluid inclusion studies on sphalerite and quartz are in agreement with previous literature data, and indicate comparatively low (in the range 90°–130 °C) homogenization temperatures (Th) and high salinities (14 to 25 equiv. mass % NaCl); both microthermometric data and SEM/EDS analyses of decrepitated inclusions indicate the presence of Ca and K beside Na. Pressure correction to Th is presumably low (in the order of 10 °C), considering a hydrostatic pressure regime. Application of the sphalerite-based GGIMFiS thermometer provided temperatures in excellent agreement with fluid inclusion data for the Montevecchio mineralization. Isotopic data on Montevecchio carbonates define mildy negative δ13CPDB values (between −1 and −5 per mil), and a larger spread of δ18OSMOW values, between +14 and +20 per mil. Other isotopic data from literature include a limited set of δ34S values for galena, sphalerite and pyrite, and a fairly large body of Pb isotopic data on galena. Comparatively narrow ranges for sulfur isotope signatures suggest a homogeneous, possibly igneous, sulfur source, whereas the large spread in Pb isotope signatures reflects the large-scale character of the hydrothermal process and indicates that the Arbus pluton may have been just one of the sources of ore lead. The Montevecchio vein system shows affinities with other late to post Variscan European deposits. The nature of the mineralizing fluids at Montevecchio is analogous to low temperature, basinal brines, and typical of several regional-scale, late to post-Variscan hydrothermal events across Europe. Mineralization at Montevecchio obviously postdates the emplacement of the Arbus plutonic complex, but its exact age remains unknown.

KW - Basinal brines

KW - Geothermometry

KW - Pb-Zn-Ag veins

KW - Sardinian metallogeny

KW - Sphalerite composition

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U2 - 10.1016/j.oregeorev.2019.103194

DO - 10.1016/j.oregeorev.2019.103194

M3 - Article

VL - 115

JO - Ore Geology Reviews

JF - Ore Geology Reviews

SN - 0169-1368

M1 - 103194

ER -