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  Mineralogical and Isotopic Characteristics of Sodic-Calcic Alteration in the Highland Valley Copper District, British Columbia, Canada: Implications for Fluid Sources in Porphyry Cu Systems

Byrne, K., Trumbull, R., Lesage, G., Gleeson, S. A., Ryan, J., Kyser, K., Lee, R. G. (2020): Mineralogical and Isotopic Characteristics of Sodic-Calcic Alteration in the Highland Valley Copper District, British Columbia, Canada: Implications for Fluid Sources in Porphyry Cu Systems. - Economic Geology, 115, 4, 841-870.
https://doi.org/10.5382/econgeo.4740

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Byrne, Kevin, Autor
Trumbull, R.1, Autor              
Lesage, G., Autor
Gleeson, S. A.1, Autor              
Ryan, J., Autor
Kyser, K., Autor
Lee, R. G., Autor
GFZ SIMS Publications, Deutsches GeoForschungsZentrum, Autor              
Affiliations:
13.1 Inorganic and Isotope Geochemistry, 3.0 Geochemistry, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum, ou_146040              

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 Zusammenfassung: The Highland Valley Copper porphyry Cu (±Mo) district is hosted in the Late Triassic Guichon Creek batholith in the Canadian Cordillera. Fracture-controlled sodic-calcic alteration is important because it forms a large footprint (34 km2) outside of the porphyry Cu centers. This alteration consists of epidote ± actinolite ± tourmaline veins with halos of K-feldspar–destructive albite (1–20 XAn) ± fine-grained white mica ± epidote. The distribution of sodic-calcic alteration is strongly influenced by near-orthogonal NE- and SE-trending fracture sets and by proximity to granodiorite stocks and porphyry dikes. Multiple stages of sodic-calcic alteration occurred in the district, which both pre- and postdate Cu mineralization at the porphyry centers. The mineral assemblages and chemical composition of alteration minerals suggest that the fluid that caused sodic-calcic alteration in the Guichon Creek batholith was Cl bearing, at near-neutral pH, and oxidized, and had high activities of Na, Ca, and Mg relative to propylitic and fresh-rock assemblages. The metasomatic exchange of K for Na, localized removal of Fe and Cu, and a paucity of secondary quartz suggest that the fluid was thermally prograding in response to magmatic heating. Calculated δ18Ofluid and δDfluid values of mineral pairs in isotopic equilibrium from the sodic-calcic veins and alteration range from 4 to 8‰ and −20 to −9‰, respectively, which contrasts with the whole-rock values for least altered magmatic host rocks (δ18O = 6.4–9.4‰ and δD = −99 to −75‰). The whole-rock values are suggested to reflect residual magma values after D loss by magma degassing, while the range of hydrothermal minerals requires a mixed-fluid origin with a contribution of magmatic water and an external water source. The O-H isotope results favor seawater as the source but could also reflect the ingress of Late Triassic meteoric water. The 87Sr/86Srinital values of strongly Na-Ca–altered rocks range from 0.703416 to 0.703508, which is only slightly higher than the values of fresh and potassic-altered rocks. Modeling of those data suggests the Sr is derived predominantly from a magmatic source, but the system may contain up to 3% seawater Sr. Supporting evidence for a seawater-derived fluid entrained in the porphyry Cu systems comes from boron isotope data. The calculated tourmaline δ11Bfluid values from the sodic-calcic domains reach 18.3‰, which is consistent with a seawater-derived fluid source. Lower tourmaline δ11Bfluid values from the other alteration facies (4–10‰) suggest mixing between magmatic and seawater-derived fluids in and around the porphyry centers. These results imply that seawater-derived fluids can infiltrate batholiths and porphyry systems at deep levels (4–5 km) in the crust. Sodic ± calcic alteration may be more common in rocks peripheral to porphyry Cu systems hosted in island-arc terranes and submarine rocks than currently recognized.

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Sprache(n): eng - Englisch
 Datum: 2020-06-042020
 Publikationsstatus: Final veröffentlicht
 Seiten: -
 Ort, Verlag, Ausgabe: -
 Inhaltsverzeichnis: -
 Art der Begutachtung: -
 Identifikatoren: GFZPOF: p3 PT5 Georesources
DOI: 10.5382/econgeo.4740
 Art des Abschluß: -

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Titel: Economic Geology
Genre der Quelle: Zeitschrift, SCI, Scopus
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Seiten: - Band / Heft: 115 (4) Artikelnummer: - Start- / Endseite: 841 - 870 Identifikator: CoNE: https://gfzpublic.gfz-potsdam.de/cone/journals/resource/journals110
Publisher: Society of Economic Geologists (SEG)