Sulfur and Lead Isotopic Geochemistry of the Shidi Pb-Zn Deposit in Xiushan County, Chongqing

The Shidi Pb-Zn deposit is located in Xiushan County, southern Chongqing, and its orebodies were hosted in marine carbonates of the Cambrian Pingjing Formation. The authors selected sulfide minerals from the deposit for the analysis of sulfur and lead isotopic compositions. Theδ34S values of sulfide minerals vary from 10.8 to 15.6, with an average value of 13.52, indicating these sulfide materials were mainly derived from marine sulfate reduction. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios for sulfide minerals vary within the ranges of 18.319~18.422, 15.740~15.784 and 38.355~38.511, respectively. In the diagrams of Zartman, the Pb isotopic compositions of sulfide minerals fall into the regional upper crust lead zone. According to the characteristics of sulfur and lead isotopic compositions of the Shidi Pb-Zn deposit, the ore-forming materials might have come from the black shales of the Lower Cmabrian Niutitang Formation.

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Status-quo of carbonate cadmium isotope compositions as a paleo-productivity proxy

10.5194/egusphere-egu21-825 ◽

2021 ◽

Author(s):

Simon V. Hohl

Keyword(s):

Isotopic Composition ◽

Isotope Composition ◽

Status Quo ◽

Ambient Seawater ◽

Isotopic Compositions ◽

Marine Carbonates ◽

The Status ◽

State Changes ◽

Underlying Processes ◽

Isotope Systematics

Cadmium (Cd) and isotope systematics are emerging tools for studying the biogeochemical cycling of micronutrients in the oceans, and sedimentary archives, as Cd concentrations in seawater show a nutrient-like behaviour, with surface depletion and deep water enrichments. However, the underlying processes are yet to be fully understood. The Cd concentration and isotopic composition of seawater are set by the balance of Cd inputs (and their isotopic composition) and the fractionation on removal to sedimentary sinks. The most favoured explanation is the Cd utilisation by marine phototrophic biomass, causing the surface water&#8217;s dissolved Cd pool depletion creating a depth gradient of increasing Cd concentrations and lighter isotopic compositions. Under incomplete oxidative recycling, organic matter may act as an effective Cd sink and authigenic minerals may store the ambient seawater&#8217;s Cd isotope composition.Consequently, stable Cd isotope compositions in marine carbonates show broad variations linked to paleo-productivity and redox state changes. Additional fractionation processes govern the Cd isotopic compositions of marine sediments. Besides biological utilisation, experimental Cd partitioning into authigenic calcites or sulphides under variable redox and salinity conditions has been shown. &#160;Therefore, when applying Cd isotopes in carbonates, other geochemical proxies must be evaluated very carefully to understand the involved Cd fractionation processes. This presentation aims to present the status quo of research done on authigenic and biologic carbonates and carbonate leachates in carbonatic shales to show the strengths and pitfalls of this new emerging bio-geoscience isotope proxy and its use for paleoenvironmental reconstructions on Earth and beyond.&#160;&#160;

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Copper, zinc, chromium and osmium isotopic compositions of the Teplá-Barrandian unit black shales and implications for the composition and oxygenation of the Neoproterozoic-Cambrian ocean

Chemical Geology ◽

10.1016/j.chemgeo.2019.05.013 ◽

2019 ◽

Vol 521 ◽

pp. 59-75 ◽

Cited By ~ 5

Author(s):

Lukáš Ackerman ◽

Jan Pašava ◽

Adéla Šípková ◽

Eva Martínková ◽

Eva Haluzová ◽

...

Keyword(s):

Black Shales ◽

Isotopic Compositions ◽

Copper Zinc

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Elemental Geochemical Characterization of Sedimentary Conditions and Organic Matter Enrichment for Lower Cambrian Shale Formations in Northern Guizhou, South China

Minerals ◽

10.3390/min10090793 ◽

2020 ◽

Vol 10 (9) ◽

pp. 793

Author(s):

Shuangbiao Han ◽

Yuanlong Zhang ◽

Jie Huang ◽

Yurun Rui ◽

Zhiyuan Tang

Keyword(s):

Organic Matter ◽

Deposition Rate ◽

Black Shale ◽

South China ◽

Shale Gas ◽

Geochemical Data ◽

Shale Formations ◽

Average Value ◽

Geochemical Elements ◽

Niutitang Formation

The black shale deposited in the Niutitang Formation and its adjacent strata is considered to be a favorable source rock in northern Guizhou of south China and has become a target horizon for shale gas exploration in recent years. Based on SQ-1 and CY-1 core samples, the organic matter properties and geochemical elements were obtained through experimental analysis. Provenance, paleoredox, paleoclimate, paleoproductivity and deposition conditions were analyzed, and the sedimentary effects on organic matter enrichment were discussed. The results show that total organic carbon (TOC) is between 0.22–10.10 wt.% in SQ-1, with an average of 2.60 wt.%, and TOC is between 0.23–7.7 wt.% in CY-1, with an average of 1.45 wt.%. The geochemical data of the samples indicate that the black shale of the Niutitang Formation and adjacent strata are deposited in the tectonic background of the passive continental margin. The provenance shows moderate weathering, with hot and humid paleoenvironmental characteristics and fast deposition rate. Using multiple ancient redox indicators, it is concluded that the formation has undergone changes in the oxidizing environment and anaerobic environment during deposition. According to the (La/Yb)N value (the average value of SQ-1 is 1.23 and the average value of CY-1 is 1.26), it shows a faster deposition rate of the two wells and shortens the residence time of organic matter in the microbial degradation zone. The Babio indicates that the bottom has a high paleoproductivity when deposited. Considering the influencing factors, the paleoproductivity mainly controls the organic matter enrichment, followed by ancient redox conditions and the deposition rate. The research results provide a reference for deepening sedimentary understanding and shale gas exploration in the study area.

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Ferro-andesites in the Grande Ronde Basalt: their composition and significance in studies of the origin of the Columbia River Basalt Group

Canadian Journal of Earth Sciences ◽

10.1139/e95-036 ◽

1995 ◽

Vol 32 (4) ◽

pp. 424-436 ◽

Cited By ~ 2

Author(s):

R. StJ. Lambert ◽

V. E. Chamberlain ◽

J. G. Holland

Keyword(s):

Chemical Composition ◽

Columbia River ◽

Special Consideration ◽

Negative Slope ◽

Magma Chambers ◽

Uppermost Mantle ◽

Average Value ◽

Isotopic Compositions ◽

Columbia River Basalt ◽

Columbia River Basalt Group

Flows from the Grande Ronde Basalt of the Columbia River Basalt Group include several with the chemical composition of ferro-andesites. These flows have SiO2 > 55%, MgO < 4%, and also have higher Fe/Mg than the average value for Grande Ronde Basalt. They are also distinctly richer in Cs, Rb, K, Ba, La, Ce, Th, and U than the remainder of the Grande Ronde Basalt flows, and possess small negative Eu anomalies. Their Pb isotopic compositions define a mixing line with a negative slope on a 206Pb/204Pb versus 207Pb/204Pb plot. Their Nd isotopic compositions lie between 143Nd/144Nd = 0.51252 and 0.51264, and their Sr isotopic compositions lie between 87Sr/86Sr = 0.7055 and 0.7060. These values define the enriched end of the Columbia River Basalt Group spectrum on a Sr–Nd epsilon diagram (excluding the Saddle Mountains Basalt). These ferro-andesite flows also form a compositional end member of the Columbia River Basalt Group and are sufficiently distinctive to warrant special consideration. We compare them with lavas from other tholeiitic provinces. Petrogenetically, they can be related to the Grande Ronde Basalt low-Mg basalts by plagioclase fractionation, or by clinopyroxene fractionation in partially melted eclogites. However, the situation may not be that simple, as their unique isotopic compositions are closely related to those of parental mantle materials, perhaps thus requiring separate reservoirs and (or) sources. Extending this argument to other parts of the Columbia River Basalt Group suggests that the origin of these basalts may be in a system of comparatively small magma chambers in the uppermost mantle, frequently replenished from a variety of sources.

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