Fractionation of Cu and Mo isotopes caused by vapor-liquid partitioning, evidence from the Dahutang W-Cu-Mo ore field

Yao, Jincao; Mathur, Ryan; Sun, Weidong; Song, Wei-Le; Chen, Hong‐Yuan; Mutti, Laurence; Xiao, Xiang; Luo, Xiaomei

doi:10.1002/2016gc006328

Cited by 44 publications

(15 citation statements)

References 73 publications

(157 reference statements)

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“…Reported values are an average of 1 block of 30 ratios, measured at separate times in the analytical session. An in house standard (USA cent from 1838, reported in Mathur et al [21] and Yao et al [51]) was interleaved throughout the session and the δ 65 Cu = −0.04‰ ± 0.07‰ (n = 5, 2σ), which overlapped the previous values reported. The error of the NIST 976 bracketed by itself throughout the measuring session varied 0.09‰ (n = 56, 2σ).…”

Section: Methodssupporting

confidence: 57%

Copper Isotope Constraints on the Genesis of the Keweenaw Peninsula Native Copper District, Michigan, USA

Bornhorst

Mathur

2017

Minerals

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Abstract:The Keweenaw Peninsula native copper district of Michigan, USA is the largest concentration of native copper in the world. The copper isotopic composition of native copper was measured from stratabound and vein deposits, hosted by multiple rift-filling basalt-dominated stratigraphic horizons over 110 km of strike length. The δ 65 Cu of the native copper has an overall mean of +0.28‰ and a range of −0.32‰ to +0.80‰ (excluding one anomalous value). The data appear to be normally distributed and unimodal with no substantial differences between the native copper isotopic composition from the wide spread of deposits studied here. This suggests a common regional and relatively uniform process of derivation and precipitation of the copper in these deposits. Several published studies indicate that the ore-forming hydrothermal fluids carried copper as Cu 1+ , which is reduced to Cu 0 during the precipitation of native copper. The δ 65 Cu of copper in the ore-forming fluids is thereby constrained to +0.80‰ or higher in order to yield the measured native copper values by reductive precipitation. The currently accepted hypothesis for the genesis of native copper relies on the leaching of copper from the rift-filling basalt-dominated stratigraphic section at a depth below the deposits during burial metamorphism. Oxidative dissolution of copper from magmatic source rocks with magmatic δ 65 Cu of 0‰ ± 0.3‰ is needed to obtain the copper isotopic composition of the metamorphogenic ore-forming hydrothermal fluids. In order to accommodate oxidative dissolution of copper from the rift-filling basalt source rocks, the copper needs to have been sited in native copper. Magmatic native copper in basalt is likely stable when the magma is low in sulfur. Low sulfur is predicted by the lack of sulfide minerals in the ore deposits and in the rift-filling basalt-dominated section, which are source rocks, the same rocks through which the ore fluids moved upwards, and the host rocks for the native copper ores. When combined with geologic evidence and inferences, the copper isotopic composition of native copper helps to further constrain the genetic model for this unique mining district.

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Section: Methodssupporting

confidence: 57%

Copper Isotope Constraints on the Genesis of the Keweenaw Peninsula Native Copper District, Michigan, USA

Bornhorst

Mathur

2017

Minerals

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“…Thus, the isotopic values of subsequent minerals are lighter and lighter [101,102]. This Rayleigh distillation model is supported by the following evidence: (1) The vapour-liquid partitioning and related isotopic fractionation for transition metal elements (e.g., Cu and Mo) have been confirmed by previous research in the Dahutang W-Cu-Mo ore field [103]; (2) minerals typically precipitate from the liquid phase; however, according to the previous literature [58], in unique cases the vapour phase containing metal can even directly condensate to form solid phases from high-temperature ore-forming system (e.g., VMS and volcano related system), which can demonstrate the existence of the vapour phase for metal elements. As for the Zhaxikang deposit, the theoretical calculated oreforming temperature from Fe isotopic data is 500∼800 ∘ C [26], and thus there should be a transitory high-temperature period, making the vapour-liquid partitioning possible; (3) the fluid inclusion data demonstrate that Mn-Fe carbonates and sulfides exist in three types of inclusions: A gas-liquid two-phase water inclusions (W type, more than 90%), B pure liquid inclusions (L type), and C pure CO 2 inclusions (PG type) [104] from Zhaxikang deposit.…”

Section: Fe-zn Isotopicsupporting

confidence: 61%

The Fe-Zn Isotopic Characteristics and Fractionation Models: Implications for the Genesis of the Zhaxikang Sb-Pb-Zn-Ag Deposit in Southern Tibet

et al. 2018

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The genesis of the Zhaxikang Sb-Pb-Zn-Ag deposit remains controversial. Three different geological environments have been proposed to model mineralization: a hot spring, a magmatic-hydrothermal fluid, and a sedimentary exhalative (SEDEX) overprinted by a hot spring. Here, we present the electron probe microanalysis (EPMA) and Fe-Zn isotopic data (microsampled) of four samples from the first pulse of mineralization that show annular textures to constrain ore genesis. The Zn/Cd ratios from the EPMA data of sphalerite range from 296 to 399 and overlap the range of exhalative systems. The δ56Fe values of Mn-Fe carbonate and δ66Zn values of sphalerite gradually decrease from early to late stages in three samples. A combination of the EPMA and isotopic data shows the Fe-Zn contents also have different correlations with δ66Zn values in sphalerite from these samples. Rayleigh distillation models this isotope and concentration data with the cause of fractionation related to vapour-liquid partitioning and mineral precipitation. In order to verify this Rayleigh distillation model, we combine our Fe-Zn isotopic data with those from previous studies to establish 12 Fe-Zn isotopic fractionation models. These fractionation models indicate the δ56Fei and δ66Zni values (initial Fe-Zn isotopic compositions) of the ore-forming system are in the range of -0.5‰ ~−1‰ and -0.28‰ ~0‰, respectively. To conclude, the EPMA data, Fe-Zn isotopic characteristics, and fractionation models support the SEDEX model for the first pulse of mineralization.

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“…Previous studies have shown that significant Mo isotope fractionation occurs during both fluid evolution and molybdenite precipitation (Mathur et al, 2010;Greber et al, 2011;Shafiei et al, 2015;Yao et al, 2016). Therefore, the details of how Mo isotopes fractionate during fluid evolution and molybdenite precipitation are of interest.…”

Section: Grain-scale Mo Isotope Heterogeneity Governed By Rayleigh Frmentioning

confidence: 99%

“…Decompression-induced boiling also facilitates Mo isotope fractionation, and isotopically heavy Mo will preferentially enter the vapor phase over the liquid phase (Yao et al, 2016). Molybdenum is usually withheld in the liquid phase during boiling (Zajacz et al, 2017), and the vapor phase tends to rise above the porphyry-style mineralization site.…”

Section: Hydrothermal Controls On Mo Isotope Fractionation Through Timementioning

confidence: 99%

Controlling Mechanisms for Molybdenum Isotope Fractionation in Porphyry Deposits: The Qulong Example

McCoy-West

Zhang

et al. 2019

Economic Geology

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Molybdenite-bearing porphyry deposits are the predominant supplier of molybdenum to industrialized society and one of the main hosts of Mo in the upper continental crust. The Mo isotope compositions (δ98/95Mo, normalized to NIST3134 equals 0‰) of molybdenite show considerable variation (–1.62 to +2.27‰), but the factors controlling this variability remain poorly constrained. This information is critical for underpinning genetic models of porphyry deposits, understanding elemental cycling, and utilizing the δ98/95Mo of marine sediments as a paleoredox proxy. Using the well-characterized Qulong porphyry Cu-Mo deposit (Tibet) as an example, here we discuss how rapid cooling, facilitated by mixing hot magmatic fluid with cold meteoric water, can be a controlling factor on efficient mineralization, and then tackle how fluid evolution regulates molybdenum isotope fractionation. Molybdenites, which preferentially partition isotopically light Mo (Rayleigh fractionation), precipitated from a single fluid will develop a heavier δ98/95Mo composition over time, and this also creates heterogeneous δ98/95Mo between molybdenite grains. Whereas a fluid undergoing multiple episodes of intensive boiling will gradually lose its isotopically heavy Mo to the vapor phase, molybdenites crystallizing successively from the residual liquid will then have lighter δ98/95Mo over time. However, when mineralization efficiency becomes too low, a negligible variation in δ98/95Mo of molybdenite is observed. Given that the mineralization efficiency (i.e., the amount of Mo crystallized as molybdenite from the fluid) rarely reaches 100% and molybdenite favors isotopically light Mo, the presence of a residual fluid with isotopically heavy Mo is inevitable. This residual fluid may then become trapped in alteration halos; hence, δ98/95Mo has the potential to aid in locating the mineralization center (e.g., lighter δ98/95Mo toward the orebody). The residual fluid may also feed surface hydrological systems and eventually impact Mo cycling. Our study highlights that understanding the controls of isotope fractionation is critical to bridge the gap between ore formation and elemental cycling, and that other transition metals (e.g., Cu, Fe, and Zn) may follow similar trajectories.

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Fractionation of Cu and Mo isotopes caused by vapor-liquid partitioning, evidence from the Dahutang W-Cu-Mo ore field

Abstract: ing of fluids do not appear to cause the isotopic shifts measure. Related equilibrium processes associated with the partitioning of metal between the vapor-fluid in the hydrothermal system could be the probable cause for the relationship seen between the two isotope systems.

Cited by 44 publications

References 73 publications

Copper Isotope Constraints on the Genesis of the Keweenaw Peninsula Native Copper District, Michigan, USA

Copper Isotope Constraints on the Genesis of the Keweenaw Peninsula Native Copper District, Michigan, USA

The Fe-Zn Isotopic Characteristics and Fractionation Models: Implications for the Genesis of the Zhaxikang Sb-Pb-Zn-Ag Deposit in Southern Tibet

Controlling Mechanisms for Molybdenum Isotope Fractionation in Porphyry Deposits: The Qulong Example

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