Origin and metamorphic reworking of the Buca della Vena Tl-rich orebody (Alpi Apuane, Italy)

2020 ◽  
Author(s):  
Simone Vezzoni ◽  
Diego Pieruccioni ◽  
Andrea Dini ◽  
Giancarlo Molli ◽  
Cristian Biagioni
Keyword(s):  
Structural Investigation ◽  
Hydrothermal Activity ◽  
Low Grade ◽  
Ore Formation ◽  
Origin And Evolution ◽  
Fe Oxides ◽  
Lower Ordovician ◽  
Geological Evolution ◽  
Metamorphic Terrane ◽  
Host Rocks

<p>The origin and evolution of an orebody hosted in metamorphic terrane is a prime topic in economic geology because they have implications on exploration as well as on related potential geo-environmental health hazards. The Alpi Apuane orebodies has long been known; however, their ore genesis and the relationships with the Apenninic age deformation and metamorphism is still a matter of debate. Indeed, they are still an interesting field of research, as proved by the recent discovery of a remarkable Tl anomaly associated to the baryte ± pyrite ± Fe-oxides ores of southern Alpi Apuane, northern Tuscany, Italy [1]. The present work reports a new detailed field and underground geological-structural investigation, performed from cartographic- to microscopic-scale, integrated by available drill-logs data, of one of these Tl-rich orebodies - the Buca della Vena ore.</p><p>The present study gives new insights on some aspect of the ore-forming events and discusses previous interpretations. According to our investigations, the ore settings were acquired during successive geological events related to an early hydrothermal-magmatic phase, likely of Permian age, and to the more recent Apenninic deformations. We suggest that the proto-ore was produced by hydrothermal activity related to the post-Variscan magmatic cycle (documented by the Permian age “Fornovolasco metarhyolite” Fm [2]), causing ore-formation, tourmalinization and hydrothermal alteration halo in the Cambrian-Lower Ordovician phyllites host-rocks. In our model, the ores were then partially exhumed suffering supergene alteration with development of minor Fe-oxides sedimentary mineralizations during the upper Norian-Hettangian. Finally, the previous hydrothermal and sedimentary ores, along with the host-rocks, were involved in the Apenninic orogenesis, and were recrystallized, and partially remobilized acquiring the current mineralogical, textural, and structural settings.</p><p>References:</p><p>[1] Biagioni, C., D’Orazio, M., Vezzoni, S., Dini, A., Orlandi, P., 2013. Mobilization of Tl-Hg-As-Sb-(Ag,Cu)-Pb sulfosalt melts during low-grade metamorphism in the Alpi Apuane (Tuscany, Italy). Geology, 41, 747-750.</p><p>[2] Vezzoni, S., Biagioni, C., D’Orazio, M., Pieruccioni, D., Galanti, Y., Petrelli, M., Molli, G., 2018. Evidence of Permian magmatism in the Alpi Apuane metamorphic complex (Northern Apennines, Italy): New hints for the geological evolution of the basement of the Adria plate. Lithos, 318-319, 104-123.</p>

Paleomagnetism and the Origin of Mississippi Valley-Type Ore Deposits

1974 ◽  
Vol 11 (2) ◽  
pp. 211-223 ◽  
Author(s):  
F. W. Beales ◽  
J. C. Carracedo ◽  
D. W. Strangway
Keyword(s):  
Natural Remanent Magnetization ◽  
Ore Deposits ◽  
The Other ◽  
Mississippi Valley ◽  
Ore Formation ◽  
Lower Ordovician ◽  
Southeast Missouri ◽  
Host Rocks ◽  
Mississippi Valley Type ◽  
Valley Type

Paleomagnetism can provide useful information about the stratigraphic relationships between the host rocks and the ore of some ore deposits.Four North American mines with stratabound ore deposits of Mississippi Valley type were sampled and the direction and intensity of the natural remanent magnetization (NRM) were measured. Two of the sites sampled (Newfoundland Zinc Co. property near Daniel's Harbour in western Newfoundland and the St. Joe Minerals Co., #8 Mine in southeast Missouri) had a weak, but measurable NRM in both host and ore rocks. This magnetization proved to be highly stable upon alternating field (AF) demagnetization. The other two mines (Magmont Mine, southeast Missouri, and Pine Point Mine, Northwest Territories, Canada) had intensities of magnetization too low to be measured after demagnetization.The pole positions computed for the ores and their corresponding hosts are identical within the statistical uncertainty, strongly suggesting that the ore and the host are, geologically speaking, of roughly the same age. This study gives two reliable pole positions, one for late lower Ordovician dolostone and sphalerite ore from Newfoundland of 26 °N, 126 °E, and the other for the upper Cambrian, based on the Bonneterre dolostone and galena ore from southeast Missouri of 35 °S, 170 °W.Within the present limitations of the method the results agree with published opinions concerning the age of the ore, i.e. that host rock and ore formation were relatively close in time. Therefore, when significant time differences occur between epigenetic ores and their host rocks, the method may be expected to define this. The method will become progressively more valuable as the apparent polar wandering curves for various continental areas become better defined.

scholarly journals Geochemistry, Paragenesis, and Wall-Rock Alteration of the Qatruyeh Iron Deposits, Southwest of Iran: Implications for a Hydrothermal-Metasomatic Genetic Model

2014 ◽  
Vol 2014 ◽  
pp. 1-25 ◽  
Author(s):  
Sina Asadi ◽  
Mohammad Ali Rajabzadeh
Keyword(s):  
Genetic Model ◽  
Wall Rock ◽  
Hydrothermal Activity ◽  
Low Grade ◽  
Wall Rock Alteration ◽  
Propylitic Alteration ◽  
Iron Deposits ◽  
Geochemical Analyses ◽  
Southwest Of Iran ◽  
Host Rocks

The Qatruyeh iron deposits, located on the eastern border of the NW-SE trending Sanandaj-Sirjan metamorphic zone, southwest of Iran, are hosted by a late Proterozoic to early Paleozoic sequence dominated by metamorphosed carbonate rocks. The magnetite ores occurred as layered to massive bodies, with lesser amounts of disseminated magnetite and hematite-bearing veins. Textural evidences, along with geochemical analyses of the high field strengths (HFSEs), large ion lithophiles (LILEs), and rare earth elements (REEs), indicate that the main mineralization stage occurred as low-grade layered magnetite ores due to high-temperature hydrothermal fluids accompanied by Na-Ca alteration. Most of the main ore-stage minerals precipitated from an aqueous-carbonic fluid (3.5–15 wt.% NaCl equiv.) at temperatures ranging between 300° and 410°C during fluid mixing process, CO2 effervescence, cooling, and increasing of pH. Low-temperature hydrothermal activity subsequently produced hematite ores associated with propylitic alteration. The metacarbonate host rocks are LILE-depleted and HFSE-enriched due to metasomatic alteration.

Pressure, temperature, and composition history of syntectonic fluids in a low-grade metamorphic terrane

Geology ◽  
2005 ◽  
Vol 33 (5) ◽  
pp. 421 ◽  
Author(s):  
Arthur Goldstein ◽  
Bruce Selleck ◽  
John W. Valley
Keyword(s):  
Low Grade ◽  
History Of ◽  
Metamorphic Terrane ◽  
Composition History

scholarly journals The Role of Hydrothermal Activity in the Formation of Karst-Hosted Manganese Deposits of the Postmasburg Mn Field, Northern Cape Province, South Africa

Minerals ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 408
Author(s):  
Brenton J. Fairey ◽  
Martin J. Timmerman ◽  
Masafumi Sudo ◽  
Harilaos Tsikos
Keyword(s):  
Hydrothermal Fluid ◽  
Hydrothermal Activity ◽  
Ore Deposits ◽  
Manganese Ore ◽  
High Grade ◽  
Ore Formation ◽  
Manganese Ores ◽  
Manganese Deposits ◽  
Northern Cape

The Postmasburg Manganese Field (PMF), Northern Cape Province, South Africa, once represented one of the largest sources of manganese ore worldwide. Two belts of manganese ore deposits have been distinguished in the PMF, namely the Western Belt of ferruginous manganese ores and the Eastern Belt of siliceous manganese ores. Prevailing models of ore formation in these two belts invoke karstification of manganese-rich dolomites and residual accumulation of manganese wad which later underwent diagenetic and low-grade metamorphic processes. For the most part, the role of hydrothermal processes and metasomatic alteration towards ore formation has not been adequately discussed. Here we report an abundance of common and some rare Al-, Na-, K- and Ba-bearing minerals, particularly aegirine, albite, microcline, banalsite, sérandite-pectolite, paragonite and natrolite in Mn ores of the PMF, indicative of hydrothermal influence. Enrichments in Na, K and/or Ba in the ores are generally on a percentage level for most samples analysed through bulk-rock techniques. The presence of As-rich tokyoite also suggests the presence of As and V in the hydrothermal fluid. The fluid was likely oxidized and alkaline in nature, akin to a mature basinal brine. Various replacement textures, particularly of Na- and K- rich minerals by Ba-bearing phases, suggest sequential deposition of gangue as well as ore-minerals from the hydrothermal fluid, with Ba phases being deposited at a later stage. The stratigraphic variability of the studied ores and their deviation from the strict classification of ferruginous and siliceous ores in the literature, suggests that a re-evaluation of genetic models is warranted. New Ar-Ar ages for K-feldspars suggest a late Neoproterozoic timing for hydrothermal activity. This corroborates previous geochronological evidence for regional hydrothermal activity that affected Mn ores at the PMF but also, possibly, the high-grade Mn ores of the Kalahari Manganese Field to the north. A revised, all-encompassing model for the development of the manganese deposits of the PMF is then proposed, whereby the source of metals is attributed to underlying carbonate rocks beyond the Reivilo Formation of the Campbellrand Subgroup. The main process by which metals are primarily accumulated is attributed to karstification of the dolomitic substrate. The overlying Asbestos Hills Subgroup banded iron formation (BIF) is suggested as a potential source of alkali metals, which also provides a mechanism for leaching of these BIFs to form high-grade residual iron ore deposits.

scholarly journals Introduction to the special issue on the Flatreef PGE-Ni-Cu deposit, northern limb of the Bushveld Igneous Complex

2020 ◽  
Author(s):  
Wolfgang D. Maier ◽  
Marina Yudovskaya ◽  
Pedro Jugo
Keyword(s):  
Ore Deposits ◽  
Special Issue ◽  
Ore Formation ◽  
Igneous Complex ◽  
Northern Limb ◽  
Pge Mineralization ◽  
World Class ◽  
Bushveld Igneous Complex ◽  
Mine Development ◽  
Host Rocks

AbstractMore than 30 years ago, Cox and Singer (1986) suggested that magmatic platinum-group element (PGE)-Ni-Cu deposits are amongst the best understood of ore deposits, yet the origin of PGE mineralization in the Bushveld Igneous Complex (BIC) remains controversial after a century of study. In the northern limb of the BIC, the unravelling of ore formation proved particularly difficult due to relatively poor outcrop, which is typically affected by contamination of the intruding magmas with the host rocks and expressed in the form of abundant xenoliths, footwall rafts and disturbance of magmatic stratigraphy. In this thematic issue, we present contributions on the Flatreef, a recently discovered world-class PGE-Ni-Cu deposit constituting a downdip extension of the mineralized unit of the Platreef of the northern limb. Two deep shafts are currently being sunk, making the Flatreef one of the most significant new mine development on the Bushveld in several decades.

scholarly journals Ore Formation During Jurassic Subduction of the Tethys Along the Eurasian Margin: Constraints from the Kapan District, Lesser Caucasus, Southern Armenia

2019 ◽  
Vol 114 (7) ◽  
pp. 1251-1284 ◽  
Author(s):  
Johannes Mederer ◽  
Robert Moritz ◽  
Massimo Chiaradia ◽  
Richard Spikings ◽  
Jorge E. Spangenberg ◽  
...  
Keyword(s):  
Middle Jurassic ◽  
Late Jurassic ◽  
Ore Deposits ◽  
Sulfide Deposit ◽  
Short Time Interval ◽  
Ore Formation ◽  
Magmatic Arc ◽  
Argillic Alteration ◽  
Lesser Caucasus ◽  
Host Rocks

Abstract The Kapan mining district in the southernmost Lesser Caucasus is one of the few locations along the central Tethyan metallogenic belt where ore-forming processes were associated with magmatic arc growth during Jurassic Tethys subduction along the Eurasian margin. Three ore deposits of the Kapan district were investigated in this study: Centralni West, Centralni East, and Shahumyan. The ore deposits are hosted by Middle Jurassic andesitic to dacitic volcanic and volcaniclastic rocks of tholeiitic to transitional affinities below a late Oxfordian unconformity, which is covered by calc-alkaline to transitional Late Jurassic-Early Cretaceous volcanic rocks interlayered with sedimentary rocks. The mineralization consists of veins, subsidiary stockwork, and partial matrix replacement of breccia host rocks, with chalcopyrite, pyrite, tennantite-tetrahedrite, sphalerite, and galena as the main ore minerals. Centralni West is a dominantly Cu deposit, and its host rocks are altered to chlorite, carbonate, epidote, and sericite. At Centralni East, Au is associated with Cu, and the Shahumyan deposit is enriched in Pb and Zn as well as precious metals. Both deposits contain high-sulfidation mineral assemblages with enargite and luzonite. Dickite, sericite, and diaspore prevail in altered host rocks in the Centralni East deposit. At the Shahumyan deposit, phyllic to argillic alteration with sericite, quartz, pyrite, and dickite is dominant with polymetallic veins, and advanced argillic alteration with quartz-alunite ± kaolinite and dickite is locally developed. The lead isotope composition of sulfides and alunite (206Pb/204Pb = 18.17–18.32, 207Pb/204Pb = 15.57–15.61, 208Pb/204Pb = 38.17–38.41) indicates a common metal source for the three deposits and suggests that metals were derived from magmatic fluids that were exsolved upon crystallization of Middle Jurassic intrusive rocks or leached from Middle Jurassic country rocks. The δ18O values of hydrothermal quartz (8.3–16.4‰) and the δ34S values of sulfides (2.0–6.5‰) reveal a dominantly magmatic source at all three deposits. Combined oxygen, carbon, and strontium isotope compositions of hydrothermal calcite (δ18O = 7.7–15.4‰, δ13C = −3.4−+0.7‰, 87Sr/86Sr = 0.70537–0.70586) support mixing of magmatic-derived fluids with seawater during the last stages of ore formation at Shahumyan and Centralni West. 40Ar/39Ar dating of hydrothermal muscovite at Centralni West and of magmatic-hydrothermal alunite at Shahumyan yield, respectively, a robust plateau age of 161.78 ± 0.79 Ma and a disturbed plateau age of 156.14 ± 0.79 Ma. Re-Os dating of pyrite from the Centralni East deposit yields an isochron age of 144.7 ± 4.2 Ma and a weighted average age of the model dates of 146.2 ± 3.4 Ma, which are younger than the age of the immediate host rocks. Two different models are offered, depending on the reliability attributed to the disturbed 40Ar/39Ar alunite age and the young Re-Os age. The preferred interpretation is that the Centralni West Cu deposit is a volcanogenic massive sulfide deposit and the Shahumyan and Centralni East deposits are parts of porphyryepithermal systems, with the three deposits being broadly coeval or formed within a short time interval in a nascent magmatic arc setting, before the late Oxfordian. Alternatively, but less likely, the three deposits could represent different mineralization styles successively emplaced during evolution and growth of a magmatic arc during a longer time frame between the Middle and Late Jurassic.

A Discussion on natural strain and geological structure - The control of ductility on the deformation of pebbles and conglomerates

1976 ◽  
Vol 283 (1312) ◽  
pp. 109-128 ◽  
Keyword(s):  
Confining Pressure ◽  
Geological Structure ◽  
Metamorphic Rocks ◽  
Tectonic Deformation ◽  
Low Grade ◽  
Rock Types ◽  
Gravitational Loading ◽  
The Matrix ◽  
Host Rocks

Pebbles are commonly used parameters for the determination of finite strain in deformed rocks. In high grade metamorphic environments, rocks probably behave as viscous fluids and a theory exists which relates the deformation experienced by a pebble to that of the host rocks. However, some deformed conglomerates are found in low grade metamorphic rocks where the assumption of viscous behaviour is unrealistic The deformation of artificial conglomerates made of geological materials, at room temperature and varying confining pressure is described. In these experiments, pebbles deform by cataclasis at surprisingly low applied loads and large finite strains are achieved. The amount of deformation experienced by pebbles of different rock types depends mainly on their yield strengths and ductility contrasts with respect to the matrix. A theoretical analysis assuming that pebble and matrix behave as workhardening Bingham materials during deformation relates the strain experienced by a pebble to that of the host rock. The results suggest that significant pebble deformation can occur during gravitational loading of sediments. An attempt is made to verify this idea by analysing the shape of pebbles in conglomerates of the Upper Witwatersrand System. At some sites the pebbles appear to have deformed during gravitational compaction while at others a tectonic deformation has been superimposed upon the pre-tectomic strain.

Thermochronologic constraints on ore formation at the Gays River Pb–Zn deposit, Nova Scotia, Canada, from apatite fission track analysis

1990 ◽  
Vol 27 (8) ◽  
pp. 1013-1022 ◽  
Author(s):  
Dennis C. Arne ◽  
Ian R. Duddy ◽  
Don F. Sangster
Keyword(s):  
Nova Scotia ◽  
Fission Track ◽  
Track Length ◽  
Late Paleozoic ◽  
Apatite Fission Track ◽  
Ore Formation ◽  
Sulphide Mineralization ◽  
Fission Track Ages ◽  
Uplift And Erosion ◽  
Host Rocks

Fission tracks in detrital apatites from the Cambro-Ordovician metasedimentary basement in the vicinity of the Carboniferous-hosted Gays River Pb–Zn deposit, Nova Scotia, provide a record of final cooling during uplift and erosion of the Meguma Zone and constrain the timing of ore formation. Apatite fission track ages range from 203 to 241 Ma, with typical uncertainties of ± 10 Ma. Mean confined track lengths generally vary between 12.0 and 13.4 μm and indicate that the apatites record "apparent" ages only. An inferred thermal history involving regional heating to paleotemperatures > 110 °C during late Paleozoic burial followed by cooling to ~ 110 °C prior to 240–220 Ma is suggested. A more recent phase or regional heating to paleotem-peratures probably in the range of 60–80 °C during Late Cretaceous – early Tertiary (ca. 100–50 Ma) burial is also indicated by the track length data. Apatite fission track ages and mean track lengths from drill-core samples immediately beneath the Gays River orebody are similar to those for regional outcrop samples. At minimum temperatures > 200 °C estimated for ore formation, sulphide mineralization must either have preceded or accompanied regional heating to paleotemperatures > 110 °C during the late Paleozoic. Sulphide mineralization at Gays River must therefore have taken place at some time after ca. 330 Ma (the stratigraphic age of the lower Windsor Group host rocks) but before ca. 240–220 Ma (the last cooling of Meguma Group basement below 110 °C). These constraints on the timing of ore formation at Gays River are compatible with previous suggestions that Pb–Zn mineralization of Carboniferous strata in Nova Scotia occurred at ca. 300 Ma.

scholarly journals Amethyst occurrences in Tertiary volcanic rocks of Greece: mineralogical and genetic implications

2013 ◽  
Vol 47 (1) ◽  
pp. 477 ◽  
Author(s):  
P. Voudouris ◽  
I. Psimis ◽  
C. Mavrogonatos ◽  
C. Kanellopoulos ◽  
M. Kati ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Hydrothermal Activity ◽  
Hydrothermal Fluids ◽  
Calc Alkaline ◽  
Northern Greece ◽  
Volcanic Arc ◽  
Quartz Veins ◽  
High Sulfidation ◽  
Host Rocks ◽  
Of Greece

Epithermal-altered volcanic rocks in Greece host gem-quality amethyst veins in association with various silicates, carbonates, oxides, sulfides and halides. Host rocks are Oligocene to recent calc-alkaline to shoshonitic lavas and pyroclastics of intermediate- to acid composition. The amethyst-bearing veins occur in the periphery of porphyry-type and/or high-sulfidation epithermal mineralized centers in northern Greece (e.g. Sapes, Kirki, Kornofolia/Soufli, Lesvos island) and on Milos island in the active Aegean Volcanic Arc. Hydrothermal alteration around the quartz veins includes sericitic, K-feldspar (adularia), argillic, propylitic and zeolitic types. Precipitation of amethyst in the northern Greece occurrences, took place during the final stages of the magmatic-hydrothermal activity from near-neutral to alkaline fluids, as indicated by the presence of gangue adularia, calcite, smectite, chlorite, sericite, pyrite, zeolites (laumontite, heulandite, clinoptilolite), analcime and minor amounts of barite, halite, epidote and fluorite in the quartz veins. Amethyst at Milos Island (Chondro Vouno and Kalogries-Vani areas), is accompanied by barite, smectite and lepidocrocite. Colloform-crustiform banding with alternations of amethyst, chalcedony and/or carbonates is a common characteristic of the studied amethyst-bearing veins. Fluid inclusion- and mineralogical data suggest that the studied amethyst were formed at: 174-246 °C (Sapes area), 100-175 °C (Kirki and Kornofolia areas) and 223-234°C (Lesvos island). The amethyst formation requires oxidizing conditions and is probably the result of mixing between meteoric or seawater with upwelling hydrothermal fluids. The involvement of seawater in the studied mineralization is supported by the presence of halite and abundant barite in the veins. Finally, the studied amethyst deposits should be evaluated as potential gemstone sources in Greece.

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