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Chemical and boron isotope compositions of tourmaline in the Hadamiao porphyry gold deposit, Inner Mongolia, China

Qiao, X, Li, W, Zhang, LJ, White, NC, Zhang, F and Yao, Z 2019 , 'Chemical and boron isotope compositions of tourmaline in the Hadamiao porphyry gold deposit, Inner Mongolia, China' , Chemical Geology: An International Journal, vol. 519 , pp. 39-55 , doi: 10.1016/j.chemgeo.2019.04.029.

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The Hadamiao porphyry gold deposit in Inner Mongolia, China, is located in the northern margin of the NorthChina Craton (NCC). Tourmaline is a common mineral in hydrothermal veins and granitic rocks contemporaneous with the mineralized granite porphyry in this deposit. The tourmaline can be divided into sixtypes, including magmatic tourmaline (Tur-M1) in granite porphyry dikes, magmatic-hydrothermal transitionaltourmaline (Tur-M2) in nodular granitic rocks, and hydrothermal tourmalines in early tourmaline veins (TurV1), gold-bearing quartz-tourmaline-chalcopyrite veins (Tur-V2), breccia cements (Tur-V3) and late carbonatequartz veins (Tur-V4). The gold mineralization is closely related to the occurrence of Tur-V2. Almost all the tourmalines from the Hadamiao deposit belong to the alkali group and show a schorlitic–-dravitic composition, except for some Tur-M1 belonging to uvite. The concentrations of most elements in different tourmaline types overlap. Tur-M1 has higher Ca, W, Th, U, Pb, Mn, and Zr contents than other types, andthe hydrothermal tourmalines (V1–V4) show slightly higher Ba, Cu and Y contents than Tur-M1 and Tur-M2. Theconcentration of Au in Tur-M1 and Tur-M2 can reach up to 80 ppb and is higher than that in Tur-V1; the Aucontent in Tur-V2 is an order of magnitude higher than that in other stages of tourmaline. Systematic contrasts inmajor and trace element compositions between magmatic and hydrothermal tourmalines are attributed to theassimilation of the country rock by the magmatic-hydrothermal system.The six types of tourmaline exhibit variable δ11B values ranging from −8.7‰ to +21.2‰. Tur-M1 shows thehighest δ11B values of +15.1‰ to +21.2‰, and Tur-V2 yields the lowest values ranging from−8.7‰ to−5.4‰. The boron probably came from two sources with different isotopic compositions, one with high positiveδ11B values and the other with negative δ11B values. Magmatic hydrothermal fluids could have provided isotopically light boron for hydrothermal tourmalines, whereas the heavy boron in magmatic tourmaline wasprobably derived from marine carbonates that are widespread in the study area. The magma related to themineralization and the one containing magmatic tourmaline may have experienced different degrees of interaction with wall rocks, resulting in the diversity of δ11B values in Hadamiao tourmaline.

Item Type: Article
Authors/Creators:Qiao, X and Li, W and Zhang, LJ and White, NC and Zhang, F and Yao, Z
Keywords: porphyry gold deposit, tourmaline, Mineral chemistry, boron isotopes, magmatic–hydrothermal evolution, material source
Journal or Publication Title: Chemical Geology: An International Journal
Publisher: Elsevier Science Bv
ISSN: 0009-2541
DOI / ID Number: 10.1016/j.chemgeo.2019.04.029
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© 2019 Elsevier B.V. All rights reserved.

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