Metal Sources in the Proterozoic Vazante-Paracatu Sediment-Hosted Zn District, Brazil: Constraints from Pb Isotope Compositions of Meta-Siliciclastic Units

2021 ◽  
Author(s):  
Neil A Fernandes ◽  
Gema R. Olivo ◽  
Daniel Layton-Matthews ◽  
Alexandre Voinot ◽  
Donald Chipley ◽  
...  
Keyword(s):  
Continental Crust ◽  
Isotopic Signature ◽  
Pb Isotope ◽  
Metal Sources ◽  
Upper Continental Crust ◽  
Basement Rocks ◽  
Siliciclastic Rocks ◽  
Brasiliano Orogeny ◽  
Isotope System ◽  
Parallel Arrays

ABSTRACT Different types of sediment-hosted whole-rock Pb isotope (206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb) compositions were determined from phyllites, carbonaceous phyllites (>1% TOC), and meta-litharenites belonging to the Serra do Garrote Formation, which is part of the Proterozoic Vazante Group, Brazil. Results were integrated with lithogeochemistry in order to identify the Pb isotopic signature of Zn enrichment (up to 0.24 wt.% Zn) associated with meta-siliciclastic-hosted sulfide mineralization that formed prior to the Brasiliano Orogeny (850 to 550 Ma) in order to (1) understand the nature of siliciclastic sediment sources, (2) identify possible metal sources in pre-orogenic meta-siliciclastic-hosted Zn mineralization, and (3) evaluate the genetic links between the Zn enrichment in the relatively reduced phyllite package, and different styles of syn-orogenic Zn ± Pb mineralization (hypogene Zn-silicate and Zn-Pb sulfide) in overlying dolomitic carbonates throughout the Vazante-Paracatu Zn District, Brazil. The whole-rock 206Pb/204Pb and 207Pb/204Pb isotope ratios of meta-siliciclastic rocks plot as positively sloping, sub-parallel arrays with radiogenic, upper continental crust compositions, which could represent a detrital contribution from at least two upper continental crust sources. However, the 206Pb/204Pb versus 207Pb/204Pb isotope system does not distinguish between Zn-enriched samples and un-mineralized samples. In the whole-rock 206Pb/204Pb–208Pb/204Pb plot, Zn-enriched samples form a flat trend of lower 208Pb/204Pb values (38.3 to 39.5) compared to the Zn-poor ones that follow common upper crustal trends. Zinc-enriched samples have low whole-rock Th/U values (<4) and higher whole-rock U concentrations compared to unmineralized samples. These support the hypothesis that U (± Pb) was added by pre-orogenic metalliferous fluids, which were in turn derived from underlying Paleoproterozoic and Archean basement rocks. Due to U addition, the original whole-rock thorogenic and uranogenic Pb isotope systems were decoupled in mineralized samples. Pre-orogenic metalliferous fluids have similar present-day first-order characteristics, including: (1) relatively high U/Pb and (2) low Th/U values, when compared to galena in the major carbonate-hosted Zn ± Pb deposits (Vazante, Morro Agudo, Ambrosia, Fagundes) in the Vazante Group. These results support the hypothesis that Zn-rich layers and veins in mineralized carbonaceous phyllites could be linked to the same origins as carbonate-hosted mineral deposits throughout the Vazante Basin, but further data are warranted. We suggest that the tectonic evolution of the Vazante Basin saw multiple phases of Zn-rich mineralization over protracted time periods from around 1200 to 550 Ma.

Pb–Zn occurrences and their Pb-isotopic signatures bearing on metallogeny and mineral exploration—Paleozoic sedimentary rocks, northern Appalachians, Quebec

1988 ◽  
Vol 25 (11) ◽  
pp. 1777-1790 ◽  
Author(s):  
K. Schrijver ◽  
E. Marcoux ◽  
G. Beaudoin ◽  
J. Y. Calvez
Keyword(s):  
Continental Crust ◽  
Mineral Exploration ◽  
Sedimentary Rocks ◽  
Isotope Ratios ◽  
Isotopic Signature ◽  
Coarse Grained ◽  
Pb Isotope ◽  
Isotopic Signatures ◽  
Fine Grained ◽  
Quartz Veins

Galena Pb-isotope ratios of epithermal vein and disseminated sulfide occurrences in the Taconian Orogen and Siluro-Devonian basin cluster around 17.90–18.05 for 206Pb/204Pb and 37.70–38.00 for 208Pb/204Pb. The major source of Pb in most, if not all, occurrences is a fairly common continental crust, a characteristic found in published analyses of Grenville feldspar Pb. A southwest to northeast increase in galena 206Pb/204Pb ratios is ascribed to the supply of several types of detritus from Grenville basement during the Cambro-Ordovician: coarse-grained, K-feldspar-bearing in the southwest, grading into fine-grained phyllitic, and relatively more highly radiogenic in the northeast.Emplacement (i) of Pb–Zn–barite veins and disseminations, commonly of homogeneous crustal Pb-isotopic signature, was late Taconian; (ii) of Pb–Zn–quartz veins, of less homogeneous signature, was post-Taconian; and (iii) of Pb–Zn–carbonate veins, relatively highly radiogenic and commonly homogeneous, was late or post-Acadian. Signatures of the first-mentioned group seem to be most useful in exploration.

New approaches to crustal evolution studies and the origin of granitic rocks: what can the Lu-Hf and Re-Os isotope systems tell us?

1996 ◽  
Vol 87 (1-2) ◽  
pp. 339-352 ◽  
Author(s):  
Clark M. Johnson ◽  
Steven B. Shirey ◽  
Karin M. Barovich
Keyword(s):  
Continental Crust ◽  
Isotope Ratios ◽  
Granitic Rocks ◽  
Nd Isotope ◽  
Volcanic Arcs ◽  
Depleted Mantle ◽  
Os Isotopes ◽  
Isotope System ◽  
Os Isotope

ABSTRACT:The Lu-Hf and Re-Os isotope systems have been applied sparsely to elucidate the origin of granites, intracrustal processes and the evolution of the continental crust. The presence or absence of garnet as a residual phase during partial melting will strongly influence Lu/Hf partitioning, making the Lu–Hf isotope system exceptionally sensitive to evaluating the role of garnet during intracrustal differentiation processes. Mid-Proterozoic (1·1–1·5Ga ) ‘anorogenic’ granites from the western U.S.A. appear to have anomalously high εHf values, relative to their εNd values, compared with Precambrian orogenic granites from several continents. The Hf-Nd isotope variations for Precambrian orogenic granites are well explained by melting processes that are ultimately tied to garnet-bearing sources in the mantle or crust. Residual, garnet-bearing lower and middle crust will evolve to anomalously high εHf values over time and may be the most likely source for later ‘anorogenic’ magmas. When crustal and mantle rocks are viewed together in terms of Hf and Nd isotope compositions, a remarkable mass balance is apparent for at least the outer silicate earth where Precambrian orogenic continental crust is the balance to the high-εHf depleted mantle, and enriched lithospheric mantle is the balance to the low-εHf depleted mantle.Although the continental crust has been envisioned to have exceptionally high Re/Os ratios and very radiogenic Os isotope compositions, new data obtained on magnetite mineral separates suggest that some parts of the Precambrian continental crust are relatively Os-rich and non-radiogenic. It remains unclear how continental crust may obtain non-radiogenic Os isotope ratios, and these results have important implications for Re-Os isotope evolution models. In contrast, Phanerozoic batholiths and volcanic arcs that are built on young mafic lower crust may have exceptionally radiogenic Os isotope ratios. These results highlight the unique ability of Os isotopes to identify young mafic crustal components in orogenic magmas that are essentially undetectable using other isotope systems such as O, Sr, Nd and Pb.

scholarly journals Paleofluids and Recent fluids in the upper continental crust: Results from the German Continental Deep Drilling Program (KTB)

1997 ◽  
Vol 102 (B8) ◽  
pp. 18233-18254 ◽  
Author(s):  
P. Möller ◽  
S. M. Weise ◽  
E. Althaus ◽  
W. Bach ◽  
H. J. Behr ◽  
...  
Keyword(s):  
Continental Crust ◽  
Deep Drilling ◽  
Upper Continental Crust ◽  
Continental Deep Drilling

scholarly journals The silicon isotope composition of the upper continental crust

2013 ◽  
Vol 109 ◽  
pp. 384-399 ◽  
Author(s):  
Paul S. Savage ◽  
R. Bastian Georg ◽  
Helen M. Williams ◽  
Alex N. Halliday
Keyword(s):  
Continental Crust ◽  
Isotope Composition ◽  
Silicon Isotope ◽  
Upper Continental Crust

Pb-Nd-Sr Isotope Geochemistry of Metapelites from the Iberian Pyrite Belt and Its Relevance to Provenance Analysis and Mineral Exploration Surveys

2021 ◽  
Author(s):  
Filipa Luz ◽  
António Mateus ◽  
Ezequiel Ferreira ◽  
Colombo G. Tassinari ◽  
Jorge Figueiras
Keyword(s):  
Isotope Geochemistry ◽  
Mineral Exploration ◽  
Hanging Wall ◽  
Massive Sulfide ◽  
Iberian Pyrite Belt ◽  
Isotopic Signature ◽  
Sr Isotope ◽  
Provenance Analysis ◽  
Basement Rocks ◽  
World Class

Abstract The boundary in the Iberian Pyrite Belt is a world-class metallogenic district developed at the Devonian-Carboniferous boundary the Iberian Variscides that currently has seven active mines: Neves Corvo (Cu-Zn-Sn) and Aljustrel (Cu-Zn) in Portugal, and Riotinto (Cu), Las Cruces (Cu), Aguas Teñidas (Cu-Zn-Pb), Sotiel-Coronada (Cu-Zn-Pb), and La Magdalena (Cu-Zn-Pb) in Spain. The Iberian Pyrite Belt massive sulfide ores are usually hosted in the lower sections of the volcano-sedimentary complex (late Famennian to late Visean), but they also occur in the uppermost levels of the phyllite-quartzite group at the Neves Corvo deposit, stratigraphically below the volcano-sedimentary complex. A Pb-Nd-Sr isotope dataset was obtained for 98 Iberian Pyrite Belt metapelite samples (from Givetian to upper Visean), representing several phyllite-quartzite group and volcano-sedimentary complex sections that include the footwall and hanging-wall domains of ore horizons at the Neves Corvo, Aljustrel, and Lousal mines. The combination of whole-rock Nd and Sr isotopes with Th/Sc ratios shows that the siliciclastic components of Iberian Pyrite Belt metapelites are derived from older quartz-feldspathic basement rocks (–11 ≤ εNdinitial(i) ≤ –8 and (87Sr/86Sr)i up to 0.727). The younger volcano-sedimentary complex metapelites (upper Tournaisian) often comprise volcanic-derived constituents with a juvenile isotopic signature, shifting the εNdi up to +0.2. The Pb isotope data confirm that the phyllite-quartzite group and volcano-sedimentary complex successions are crustal reservoirs for metals found in the deposits. In Neves Corvo, where there is more significant Sn- and Cu-rich mineralization, the higher (206Pb/204Pb)i and (207Pb/204Pb)i values displayed by phyllite-quartzite group and lower volcano-sedimentary complex metapelites (up to 15.66 and 18.33, respectively) suggest additional contributions to the metal budget from a deeper and more radiogenic source. The proximity to Iberian Pyrite Belt massive sulfide ore systems hosted in metapelite successions is observed when (207Pb/204Pb)i >15.60 and Fe2O3/TiO2 or (Cu+Zn+Pb)/Sc >10. These are important criteria that should be considered in geochemical exploration surveys designed for the Iberian Pyrite Belt.

scholarly journals The zirconium isotope composition of the mantle and upper continental crust through time

2021 ◽  
Author(s):  
Shengyu Tian ◽  
Frédéric Moynier ◽  
Edward Inglis ◽  
Roberta L. Rudnick ◽  
Fang Huang ◽  
...  
Keyword(s):  
Continental Crust ◽  
Isotope Composition ◽  
Upper Continental Crust

scholarly journals Preliminary Description of the Origin of a Sedimentary – Exhalative Ore Deposit, in Molango, Hidalgo Mexico

2018 ◽  
Author(s):  
Eduardo Cerecedo-Sáenz ◽  
Ventura Rodríguez-Lugo ◽  
Juan Hernández-Ávila ◽  
Demetrio Mendoza-Anaya ◽  
Ma. Isabel Reyes-Valderrama ◽  
...  
Keyword(s):  
Continental Crust ◽  
Rare Earths ◽  
Mineral Deposit ◽  
Base Metals ◽  
Sulfur Deficiency ◽  
Ore Deposit ◽  
Upper Continental Crust ◽  
Distribution Of Elements ◽  
Hydrothermal Remobilization ◽  
Preliminary Description

This work shows the preliminary description of the origin of a sedimentary - exhalative outcrop of Jurassic Lower Pliensbachian. The location of this deposit was achieved by applying an examination based in the identification of sedimentary transgressions of heterochronies ages and the identification of a Rift – type mega –structure. According with the methodology, it was carried out a study of the discordant relationships between two types of sediments: continental and marine. According the characterization, it was noted the existence of light rare earths, in values that show positive anomalies in comparison with the distribution of elements in upper continental crust according to the Clarke [1], reflecting so a felsic affinity of the mineral deposit. Also, positive anomalies of platinum and Pd, were determined with marginal contents of Au and Ag; and finally the base metals Zn, Pb and Cu were detected in low contents, which could be due to the presence of altered shale. According to the sedimentary lithology found, which was of siliciclastic type; to the exhalative roots observed during the fieldwork; the presence of quartz minerals such as biotite and muscovite; the presence of minerals of hydrothermal remobilization like chalcopyrite with some base metals, altered shale, as well as sulfur deficiency; this mineral reservoir could be defined as a SEDEX – type.

Lithium isotopic composition and concentration of the upper continental crust

2004 ◽  
Vol 68 (20) ◽  
pp. 4167-4178 ◽  
Author(s):  
F.-Z. Teng ◽  
W.F. McDonough ◽  
R.L. Rudnick ◽  
C. Dalpé ◽  
P.B. Tomascak ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Continental Crust ◽  
Upper Continental Crust
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