Contributions from mafic alkaline magmas to the Bingham porphyry Cu-Au-Mo deposit, Utah, USA

Abstract

The Bingham porphyry Cu-Au-Mo deposit, Utah, may only be world-class because of substantial contributions of sulfur and metals from mafic alkaline magma to an otherwise unremarkable calc-alkaline system. Volcanic mafic alkaline rocks in the district are enriched in Cr, Ni, and Ba as well as Cu, Au, platinum group elements (PGE), and S. The bulk of the volcanic section that is co-magmatic with ore-related porphyries is dacitic to trachytic in composition, but has inherited the geochemical signature of high Cr, Ni, and Ba from magma mixing with the mafic alkaline rocks. The volcanic section that most closely correlates in time with ore-related porphyries is very heterogeneous containing clasts of scoriaceous latite, latitic, and minette, and flows of melanephelinite, shoshonite, and olivine latite in addition to volumetrically dominant dacite/trachyte. Bingham ore-related porphyries show ample evidence of prior mixing with mafic alkaline magmas. Intrusive porphyries that have not been previously well-studied have several chemical and mineralogical indications of magma mixing. These ''mixed'' lithologies include the hybrid quartz monzonite porphyry, biotite porphyry, and minette dikes. Even some of the more silicic latite and monzonite porphyries retain high Cr and Ba contents indicative of mixing and contain trace amounts of sapphire (<1 mm). The heterogeneous block and ash flow deposits also contain sapphire and are permissively correlated with the intrusions based on chemical, mineralogical, and isotopic data. Magma mixing calculations suggest about 10% of the monzonitic/latitic orerelated magma may have been derived from mafic alkaline magma similar to the melanephelinite. If the original S content of the mafic magma was about 2,000-4,000 ppm, comparable with similar magmas, then the mafic magma may have been responsible for contributing more than half of the S and a significant portion of the Cu, Au, and PGE in the Bingham deposit.

Amphibole and apatite insights into the evolution and mass balance of Cl and S in magmas associated with porphyry copper deposits

“…These data suggest that no specific S enrichment is required to form this economic porphyry copper deposit. This view contrasts with findings from other systems where critical amounts of S are thought to have been sourced by co-magmatic basalts (Keith et al 1997;Hattori and Keith 2001;Maughan et al 2002;Halter et al 2002Halter et al , 2005Nadeau et al 2010Nadeau et al , 2016Steinberger et al 2013;Blundy et al 2015). Nevertheless, this concurs with the lack of evidence for mafic magma associated with the porphyries at Coroccohuayco (Chelle-Michou et al 2015a).…”

Geochemical differences between subduction- and collision-related copper-bearing porphyries and implications for metallogenesis

“…1), the majority of samples in this study (with the exception of a few ultrapotassic samples in the Bingham district; Maughan et al, 2002), including limited data for Miocene ultrapotassic rocks of the EPRIM (Kay et al, 1994;Redwood and Rice, 1997;Sandeman and Clark, 2004;Maria and Luhe, 2008;Gómez-Tuena et al, 2011) and southern Tibet (Miller et al, 1999;Ding et al, 2003Ding et al, , 2006Williams et al, 2004;Gao et al, 2007b;Zhao et al, 2009;Chen et al, 2012), do not contain high concentrations of Cu (<130 ppm). However, these mantle-derived potassic and ultrapotassic magmas are typically enriched in the LILE, LREE, and volatiles such as H 2 O, CO 2 , F, and Cl (e.g., Rock, 1987;Rock et al, 1990;Behrens et al, 2009), all of which likely enhance the solubility of chalcophile elements, such as Cu and Au, in high-temperature aqueous fluids (e.g., Heinrich et al, 1992;Pokrovski et al, 2005Pokrovski et al, , 2008Simon et al, 2005Simon et al, , 2006Zajacz et al, 2008Zajacz et al, , 2011Seo et al, 2009).…”

“…3h), suggesting that magmas associated with porphyry Cu deposits contain mantle-derived components (Rapp and Watson, 1995). For example, the high-grade Bingham porphyry Cu (-Mo-Au) deposit on the EPRIM is the product of mixing between an evolving magmatic system and injections of mafic alkaline magmas (e.g., Keith et al, 1997;Hattori and Keith, 2001;Maughan et al, 2002;Pettke et al, 2010). In addition, the presence of porphyry mineralization and both alkalic and adakitic rocks in post-collisional settings are considered to be related with mafic alkalic magmatism (e.g., Richards, 1995;Shafiei et al, 2009;Yang et al, 2014 (Yang et al, 2014).…”

The nature of “quartz eyes” hosted by dykes associated with Au-Bi-As-Cu, Mo-Cu, and Base-metal-Au-Ag mineral occurrences in the Mountain Freegold region (Dawson Range), Yukon, Canada

“…In fact, in Cu-(Au-Mo) and porphyry Au deposits, co-mingling of mafic with silicic magma had been reported to increase the Au budget of the deposits (e.g., at Bingham, Keith et al 1998;Tarkian and Stribrny 1999;Hattori and Keith 2001;Maughan et al 2002). Quartz textures also indicate that the dykes from the study area probably cooled rapidly.…”