We compare three poorly known, historical Ni�Co-bearing hydrothermal deposits in different geological settings in Italy: The Ni-Co-As-Sb-Au-bearing Arburese vein system (SW Sardinia),the Co-Ni-As-rich Usseglio vein system (Piedmont), and the small Cu-Ag-Co-Ni-Pb-Te-Se stockwork at Piazza (Liguria).These deposits share various (mineralogical, chemical, thermal, andstable isotopic) similarities to the Five Element Vein-type ores but only the first two were economic for Co-Ni. The Sardinian Ni-rich veins occur in Paleozoic basement near two Variscan plutons. Like theCo-rich Usseglio vein system, the uneconomic Piazza deposit is hostedin an ophiolite setting anomalous for Co. The Sardinian and Usseglio deposits share a polyphasic assemblage with Ni-Co-As-Sb-Bi followed by Ag-base metal sulfides, in siderite-rich gangue, whereas Piazza shows As-free, Ag-Pb-Te-Se-bearing Co-Ni-Cu sulfides, in prehnite-chlorite gangue. Fluid inclusions indicated Co-Ni arsenide precipitation at ≈170 °C for Usseglio, whereas forthe Sardinian system late sulfide deposition occurred within the 5 -126 °C range. Ore fluids in both systems are NaCl-CaCl2-bearing basinal brines. The chlorite geothermometer at Piazza provides the range of 200-280 °C for ore deposition from CO2-poor fluids. Enrichments in Se and negative °13C in carbonates suggest interaction withcarbonaceous shales. These deposits involve issues about source rocks,controls on Co/Ni and possible role of arsenic and carbonate components towards economic mineralization.
Factors Controlling Hydrothermal Nickel and Cobalt Mineralization—Some Suggestions from Historical Ore Deposits in Italy / M. Moroni, P. Rossetti, S. Naitza, L. Magnani, G. Ruggieri, A. Aquino, P. Tartarotti, A. Franklin, E. Ferrari, D. Castelli, G. Oggiano, F. Secchi. - In: MINERALS. - ISSN 2075-163X. - 9:7(2019 Jul 01), pp. 429-470. [10.3390/min9070429]
Factors Controlling Hydrothermal Nickel and Cobalt Mineralization—Some Suggestions from Historical Ore Deposits in Italy
M. Moroni
Primo
Writing – Original Draft Preparation
;L. Magnani;P. TartarottiInvestigation
;
2019
Abstract
We compare three poorly known, historical Ni�Co-bearing hydrothermal deposits in different geological settings in Italy: The Ni-Co-As-Sb-Au-bearing Arburese vein system (SW Sardinia),the Co-Ni-As-rich Usseglio vein system (Piedmont), and the small Cu-Ag-Co-Ni-Pb-Te-Se stockwork at Piazza (Liguria).These deposits share various (mineralogical, chemical, thermal, andstable isotopic) similarities to the Five Element Vein-type ores but only the first two were economic for Co-Ni. The Sardinian Ni-rich veins occur in Paleozoic basement near two Variscan plutons. Like theCo-rich Usseglio vein system, the uneconomic Piazza deposit is hostedin an ophiolite setting anomalous for Co. The Sardinian and Usseglio deposits share a polyphasic assemblage with Ni-Co-As-Sb-Bi followed by Ag-base metal sulfides, in siderite-rich gangue, whereas Piazza shows As-free, Ag-Pb-Te-Se-bearing Co-Ni-Cu sulfides, in prehnite-chlorite gangue. Fluid inclusions indicated Co-Ni arsenide precipitation at ≈170 °C for Usseglio, whereas forthe Sardinian system late sulfide deposition occurred within the 5 -126 °C range. Ore fluids in both systems are NaCl-CaCl2-bearing basinal brines. The chlorite geothermometer at Piazza provides the range of 200-280 °C for ore deposition from CO2-poor fluids. Enrichments in Se and negative °13C in carbonates suggest interaction withcarbonaceous shales. These deposits involve issues about source rocks,controls on Co/Ni and possible role of arsenic and carbonate components towards economic mineralization.File | Dimensione | Formato | |
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