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<p>Detailed core logging, combined with TESCAN TIMA mineral quantification at two globally significant, high-grade porphyry deposits – Resolution, USA, and Hugo Dummett North, Mongolia – indicate that most chalcopyrite ± bornite-pyrite is intergrown with muscovite that overprints earlier potassic alteration assemblages containing biotite and/or K-feldspar. Copper grades increase with the intensity of muscovite overprint on primary potassic assemblages supporting a link between high-grade Cu mineralization and phyllic alteration. Another zone of high-grade Cu mineralization occurs in the upper parts of the phyllic alteration zone and/or within later advanced argillic alteration, associated with high-sulfidation bornite ± digenite ± covellite ± chalcocite-pyrite assemblages, that partly replace earlier chalcopyrite. These two high grade domains have comparable features in many other significant high-grade Cu porphyry deposits (Chuquicamata, Rosario, MMH, Onto, Butte) – all strongly telescoped systems that host significant amounts of high-grade Cu mineralization in phyllic and/or advanced argillic alteration that overprint potassic alteration. We suggest there are at least three reasons for the development of high-grade hypogene ore in telescoped porphyry systems: (1) rapid unroofing and exhumation can generate steep thermal gradients, promoting a rapid decrease in Cu solubility and efficient precipitation of sulfides; (2) rapid, syn-mineralization exhumation and magma doming when the rock mass behaves in an increasingly brittle fashion, create significant permeability in late stages of porphyry systems; (3) telescoping during syn-mineralization exhumation leads to overprinting of early sulfide assemblages by late-stage acidic and oxidized hydrothermal fluids that remobilize and concentrate early Cu, leading to the precipitation of sulfides with high Cu/S ratios. We conclude that the coincidence of rapid exhumation and long-lived hydrothermal activity exerts a first order control on the formation of high-grade hypogene porphyry Cu mineralization.</p>

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Formation of giant high-grade hypogene porphyry copper deposits during phyllic to advanced argillic alteration: textural evidence from automated SEM mapping at the Resolution and Hugo Dummett North deposits

  • 期刊论文

  • 发表日期：

    2025年11月4日

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  • Chao Yang,
  • Jamie J. Wilkinson

摘要

Detailed core logging, combined with TESCAN TIMA mineral quantification at two globally significant, high-grade porphyry deposits – Resolution, USA, and Hugo Dummett North, Mongolia – indicate that most chalcopyrite ± bornite-pyrite is intergrown with muscovite that overprints earlier potassic alteration assemblages containing biotite and/or K-feldspar. Copper grades increase with the intensity of muscovite overprint on primary potassic assemblages supporting a link between high-grade Cu mineralization and phyllic alteration. Another zone of high-grade Cu mineralization occurs in the upper parts of the phyllic alteration zone and/or within later advanced argillic alteration, associated with high-sulfidation bornite ± digenite ± covellite ± chalcocite-pyrite assemblages, that partly replace earlier chalcopyrite. These two high grade domains have comparable features in many other significant high-grade Cu porphyry deposits (Chuquicamata, Rosario, MMH, Onto, Butte) – all strongly telescoped systems that host significant amounts of high-grade Cu mineralization in phyllic and/or advanced argillic alteration that overprint potassic alteration. We suggest there are at least three reasons for the development of high-grade hypogene ore in telescoped porphyry systems: (1) rapid unroofing and exhumation can generate steep thermal gradients, promoting a rapid decrease in Cu solubility and efficient precipitation of sulfides; (2) rapid, syn-mineralization exhumation and magma doming when the rock mass behaves in an increasingly brittle fashion, create significant permeability in late stages of porphyry systems; (3) telescoping during syn-mineralization exhumation leads to overprinting of early sulfide assemblages by late-stage acidic and oxidized hydrothermal fluids that remobilize and concentrate early Cu, leading to the precipitation of sulfides with high Cu/S ratios. We conclude that the coincidence of rapid exhumation and long-lived hydrothermal activity exerts a first order control on the formation of high-grade hypogene porphyry Cu mineralization.