Italian ore/mineral deposits related to emersion surfaces a summary

Assereto, R.; Brigo, L.; Brusca, C.; Omenetto, Paolo; Zuffardi, P.

doi:10.1007/bf00204479

Cited by 12 publications

(3 citation statements)

References 2 publications

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“…Arera, and Val Riso-Mt. Trevasco areas (Omenetto 1966); (2) dominant fluorite ores in the Paglio Pignolino-Dossena area (Jadoul and Omenetto 1980); (3) barite ores in the Brembana Valley; and (4) fluorite-barite deposits, with subordinate Zn-Pb ores in the Presolana area (Assereto et al 1976(Assereto et al , 1978Brigo et al 1977;Rodeghiero 1977;Jadoul and Omenetto 1980). These ores mainly occur as stratiform bodies in the CMB Formation, at the contact with the black shales of the "Basal Tongue" of the Gorno Formation, or as discordant bodies in the limestones of the underlying Breno Formation (Omenetto 1966;Vailati 1966;Rodeghiero and Vailati 1978).…”

Section: General Features Of the Ore Deposits In The Gorno Districtmentioning

confidence: 99%

From Alpine-type sulfides to nonsulfides in the Gorno Zn project (Bergamo, Italy)

et al. 2019

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Recent exploration of the Gorno Zn-Pb-Ag deposit in northern Italy identified 3.3 Mt of sulfides at 4.9% Zn, 1.3% Pb, and 27.2 g/ t Ag (indicated+inferred resources), and a further mineralized nucleus of mixed sulfides-nonsulfides in the Val Vedra area, currently under evaluation. The ores are hosted in Triassic limestone and shale. Sulfides (sphalerite, Ag-bearing galena, minor pyrite, and chalcopyrite) paragenetically follow Mn-Fe-bearing saddle dolomite and sparry calcite. The mineral association, and the carbon and oxygen isotope ratios of the sparry calcite (avg. δ 13 C = 1.0 ± 0.6‰ V-PDB; avg. δ 18 O = 19.63 ± 1.25‰ V-SMOW), are in agreement with precipitation from hydrothermal fluids in a deep burial setting. Sulfide emplacement occurred before the Alpine orogeny, likely during the Early-Middle Jurassic, in analogy to other Alpine-type deposits. The nonsulfide ore formed at the expense of sulfides, and mainly consists of smithsonite, hydrozincite, hemimorphite, and cerussite. The C-Oisotope values of the early generations of Zn-carbonates are characterized by δ 18 O between 24.1 and 26.8‰ V-SMOW and δ 13 C ratios between − 3.1 and 1.7‰ V-PDB. The later generations have lower δ 18 O (21.9 to 23.9‰) and lower δ 13 C (− 6.2 to − 3.9‰). These compositions, as those measured on cerussite (δ 13 C = −6.3 and − 7.7‰; δ 18 O = 14.0 and 15.3‰), agree with the formation of the nonsulfides in a supergene environment, under climatic conditions warmer than today. The δ 18 O decrease from early to late generations suggests progressive involvement of meteoric water sourced from higher altitudes. These characteristics indicate that the nonsulfides formed during the exhumation of the Gorno area from Miocene to Pliocene.

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Section: General Features Of the Ore Deposits In The Gorno Districtmentioning

confidence: 99%

From Alpine-type sulfides to nonsulfides in the Gorno Zn project (Bergamo, Italy)

et al. 2019

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“…At the top of the Calcare Metallifero Bergamasco, prolonged emersion of the platform results in the erosion of part of the section and the development of an extensive karstic network extending to a depth of 10-30 m Mutti, 1992~). Leadzinc mineralization associated with this exposure occurs throughout the Alpine area (Bechstadt, 1975;Assereto et al, 1976;Bechstadt & Dohler-Hirner, 1983). This period of subaerial exposure marks the demise of the carbonate system, overlain in the mid-Carnian by a volcanoclastic deltaic system prograding from the south (Garzanti, 1985;Gnaccolini & Jadoul, 1990).…”

Section: Ladinian-carnian Unitsmentioning

confidence: 98%

Association of tepees and palaeokarst in the Ladinian Calcare Rosso (Southern Alps, Italy)

Mutti

1994

Sedimentology

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The Ladinian Calcare Rosso of the Southern Alps provides a rare opportunity to examine the temporal relationships between tepees and palaeokarst. This unit comprises peritidal strata pervasively deformed into tepees, repeatedly capped by palaeokarst surfaces mantled by terra rossa. Palaeokarsts, characterized by a regional distribution across the Southern Alps, occur at the base and at the top of the unit. Local palaeokarsts, confined to this part of the platform, occur within the Calcare Rosso and strongly affected depositional facies. Tepee deformation ranges from simple antiformal structures (peritidal tepees) to composite breccias floating in synsedimentary cements and internal sediments (senile tepees). Peritidal tepees commonly occur at the top of one peritidal cycle, in association with subaerial exposure at the cycle top, while senile tepees affect several peritidal cycles, and are always capped by a palaeokarst surface. Cements and internal sediments form up to 80% of the total rock volume of senile tepees. The paragenesis of senile tepees is extremely complex and records several, superimposed episodes of dissolution, cement precipitation (fibrous cements, laminated crusts, mega‐rays) and deposition of internal sediments (marine sediment and terra rossa). Petrographical observations and stable isotope geochemistry indicate that cements associated with senile tepees precipitated in a coastal karstic environment under frequently changing conditions, ranging from marine to meteoric, and were altered soon after precipitation in the presence of either meteoric or mixed marine/meteoric waters. Stable isotope data for the cements and the host rock show the influence of meteoric water (average δ18O= ‐ 5·8‰), while strontium isotopes (average 87Sr/86Sr=0·707891) indicate that cements were precipitated and altered in the presence of marine Triassic waters. Field relationships, sedimentological associations and paragenetic sequences document that formation of senile tepees was coeval with karsting. Senile tepees formed in a karst‐dominated environment in the presence of extensive meteoric water circulation, in contrast to previous interpretations that tepees formed in arid environments, under the influence of vadose diagenesis. Tepees initiated in a peritidal setting when subaerial exposure led to the formation of sheet cracks and up‐buckling of strata. This porosity acted as a later conduit for either meteoric or mixed marine/meteoric fluids, when a karst system developed in association with prolonged subaerial exposure. Relative sea level variations, inducing changes in the water table, played a key role in exposing the peritidal cycles to marine, mixed marine/meteoric and meteoric diagenetic environments leading to the formation of senile tepees. The formation and preservation in the stratigraphic record of vertically stacked senile tepees implies that they formed during an overall period of transgression, punctuated by different orders of sea level variations, which allowed formation and later freezing...

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“…1A), several Pb-Zn occurrences are known, among them, the stock-like Argentiera deposit that was been in production until 1971, producing 1 million tonnes of oxide ore @ 6% Zn, 1% Pb (Cerny, 1989). Breccia ores are mostly hosted by the Anisian Upper Sarl Dolomite, and are exclusively structure-controlled (Assereto et al, 1976).…”

Section: Apt Deposits In the Southalpinementioning

confidence: 99%

Carbonate-hosted “Alpine-type” Zn-Pb deposits in the Eastern and Southern Alps – trace element geochemistry and isotopic data of sulphides

Melcher,

Bertrandsson-Erlandsson,

Gartner

et al. 2023

Irish-Type Zn-Pb Deposits Around the World

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More than 500 occurrences of carbonate-hosted Pb-Zn ores are documented in the Eastern and Southern Alps. They are invariably hosted by shallow lagoonal and reef carbonates of Middle and more frequently Upper Triassic (Anisian and Carnian) age and are collectively termed “Alpine-type” deposits. The local palaeogeography and synsedimentary structures influenced ore mineralization. Although they occur in a wide region, they share common features such as a simple mineralogical composition, complex ore textures, light sulphur isotopic compositions, Late Palaeozoic Pb model ages, and similar trace element compositions in sphalerite, galena and pyrite. Sphalerite records a low-temperature (60-140°C) precipitation. It is low in Fe, Mn, Co, Ag and In, but commonly contains elevated Cd, Ge, As, Tl and Pb. Galena is Ag-poor, although both sphalerite and galena tend to higher Ag concentrations towards the northern Districts. Minor Fe sulphides are low in Co and Ni but carry considerable As and Tl. Rb-Sr dating of sphalerite from the type locality Bleiberg reveals an age of ≈229 Ma for ores of the Raibl Group, and ages of ≈207 and ≈201 Ma for trace element-rich breccia ore in the western part of the Bleiberg deposit. The older age corresponds to U-Pb ages obtained on calcite associated with the Pb-Zn mineralization at the Gorno deposit (Southalpine). The younger age suggests fluid flow within the carbonate sequence in an extensional tectonic regime due to fracturing of the carbonate platform during initial rifting of the Penninic Ocean.

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Italian ore/mineral deposits related to emersion surfaces a summary

Cited by 12 publications

References 2 publications

From Alpine-type sulfides to nonsulfides in the Gorno Zn project (Bergamo, Italy)

From Alpine-type sulfides to nonsulfides in the Gorno Zn project (Bergamo, Italy)

Association of tepees and palaeokarst in the Ladinian Calcare Rosso (Southern Alps, Italy)

Carbonate-hosted “Alpine-type” Zn-Pb deposits in the Eastern and Southern Alps – trace element geochemistry and isotopic data of sulphides

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