Evaluating Geochemical Discriminants in Archean Gold Deposits: A Superior Province Perspective with an Emphasis on the Abitibi Greenstone Belt

Abstract

Discriminating Archean Au deposit types and related ore-forming processes is challenging but paramount for increasing Au exploration success. This study tests the validity of applying geochemical data generated from conventional bulk versus modern in situ methods as discriminants for classifying Au deposits in the Archean Swayze greenstone belt with further comparison to other deposits in the contiguous Abitibi greenstone belt and Red Lake area (Superior Province, Canada). The study used five well-characterized Au settings, based on new mapping, as a basis for evaluating in situ (δ18Oquartz, δ33, 34Ssulfide, laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analysis of pyrite, electron microprobe analysis of gold), and whole-rock geochemical datasets to resolve whether intrusion-related Au deposits can be discriminated from orogenic-type Au deposits. Results show that the in situ methods provide insight into processes related to Au mineralization, both primary and subsequent remobilization and upgrading, and define elemental and isotopic correlations that cannot be resolved using conventional bulk methods. For example, when comparing the whole-rock to laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) trace metal data, only Ag, Te, and Hg show a consistent positive correlation with Au across deposit types in both data sets. Furthermore, the wholerock datasets combined with in situ isotopic analysis suggest the Archean sanukitoid-associated Au deposits represent a distinct group of intrusion-related deposits with mineralization characterized by low δ34Spyrite (<–5 to –25‰), inferred high fO2, an Hg-Te signature, and hosted in intrusions of <2690 Ma that predate shearing. The data and interpretations presented herein provide a baseline that can be widely utilized in future studies of Au deposits.

Au-Bi-Te(-Cu) Mineralization in the Wawa Gold Corridor (Ontario, Canada): Implications for the Role of Bi-Rich Polymetallic Melts in Orogenic Au Systems

“…The association of Au with Bi and Te is also relevant to whether the progenitor Au-bearing hydrothermal fluids that form some orogenic deposits are of metamorphic and/or magmatic origin [8][9][10][11][12]. Given the apparent similarity in the isotopic and chemical nature of the fluids derived from these two reservoirs [3,8,[13][14][15], the usefulness of the geochemical association of Au with various elements as evidence for a specific fluid source has been a subject of interest (see [16] and references therein), and mineral assemblages and compositions that reflect a Au-Bi-Te association are often taken, in part, to be diagnostic of a magmatic-hydrothermal origin for ore metals [17][18][19][20][21][22][23]. Indeed, both the transport of Au in Bi-rich polymetallic melts and its association with Bi and Te have been repeatedly documented in a variety of magmatic-hydrothermal environments, including skarns [24][25][26][27][28], iron oxide copper-gold (IOCG) and iron oxide cobalt-gold-bismuth deposits [29,30], intrusion-related gold systems [31], greisens [32], and porphyry-epithermal systems [28,33,34].…”