A distinctive Pd-Hg signature in detrital gold derived from alkalic Cu-Au porphyry systems

Abstract

22This study comprises the first systematic classification of native gold geochemistry within 23 alkalic porphyry Cu-Au systems and the placer expression of such systems. The 24 geochemistry and mineral associations of gold from four alkalic porphyry deposits in British

A new indicator mineral methodology based on a generic Bi-Pb-Te-S mineral inclusion signature in detrital gold from porphyry and low/intermediate sulfidation epithermal environments in Yukon Territory, Canada

“…Previous studies have established the correlation between hypogene gold-bearing mineralization and the suite of inclusions observed within gold grains derived from that mineralization a b c (e.g., Chapman et al 2000Chapman et al , 2017. This general result was replicated in the present study and the associations are summarized below.…”

“…Consequently, the mineralogical associations reported here in the Bi-Pb-Te-S system in relation to calcalkalic porphyry systems of Yukon are a useful discriminant by which to identify gold derived from calc-alkalic porphyry systems as compared to orogenic gold sources. Chapman et al (2017) established a strong generic Pd-Hg signature in detrital gold formed in alkalic porphyry systems in British Columbia, which is absent in gold from Yukon calcalkalic porphyry deposits. Whereas bismuth tellurides were observed as inclusions in detrital gold from alkalic porphyry systems (Chapman et al 2017) the Bi-Pb-Te-S signature of gold from the calc-alkalic systems described in the present study is far more pronounced.…”

“…For example, Gammons and Williams-Jones (1997) describe the stripping of gold from pre-existing auriferous chalcopyrite-bornite ore and both Bower et al (1995) and Hart and Langdon (1997) observed the removal of both Au and Cu during the phyllic overprint of the potassic zone at Casino and Cyprus, respectively. Elsewhere Palacios et al (2001) reported gold associated with sericitic (phyllic) veins at Cerro Casale, and Chapman et al (2017) identified gold grains in propylitically altered rocks at the Mount Milligan alkalic porphyry in British Columbia. In some cases, the Ag content of gold alloy decreases with successive alteration environments (e.g., Cerro Casale: Palacios et al 2001;Pebble, Alaska: Gregory et al 2013), whereas in other cases, the opposite trend has been recorded (e.g., Santo…”

“…Milligan, B.C., constituted an example of this relationship. Chapman et al (2017) suggested that the majority of gold grains in the placer environment local to alkalic porphyry deposits in British Columbia were derived from such late stage veins. Corbett and Leach (1995) described vertical zonation in low sulfidation epithermal systems from deeper Au-Cu-dominated mineralogy to shallower, later Au-Ag mineralization, and it seems probable that the microchemical signatures of gold from such low sulfidation environments would be sympathetic to this compositional progression.…”

“…The microchemical signature may be applied to evaluate variation within a single style of mineralization in a specific area (e.g., Chapman et al 2010a, b, Chapman and or to investigate a specific signature associated with a particular style of Au mineralization (e.g., Chapman et al 2009). This approach has proved particularly valuable in the study of gold from alkalic porphyry systems in which gold is precipitated in different hydrothermal settings within the evolving system (Chapman et al 2017). In some cases, the ranges of alloy compositions of populations of gold grains from different styles of mineralization overlap, but the associated mineralogy represented in the inclusion assemblage may provide a useful discriminant.…”