The timing of gold mineralization in White Bay, western Newfoundland: Evidence from 40Ar/39Ar studies of mafic dykes that predate and postdate mineralization

Abstract

The Rattling Brook deposit is a low-grade, disseminated to stockwork-style gold deposit hosted by Precambrian granodiorite and adjacent Cambrian sedimentary rocks. Alteration and gold mineralization also occur in foliated and metamorphosed mafic dykes, likely of late Precambrian age. The auriferous granodiorite is in turn cut by relatively fresh, unaltered, and locally chilled diabase dykes, interpreted as Paleozoic post-mineralization intrusions. A fresh post-mineralization diabase gave a 40 Ar/ 39 Ar amphibole plateau age of 412.9 ± 4.3 Ma, which is interpreted as the time of its crystallization, and which provides a younger limit for the timing of gold mineralization. An altered, metamorphosed dyke of pre-mineralization timing gave an identical 40 Ar/ 39 Ar biotite plateau age of 412.6 ± 2.3 Ma, which is more difficult to interpret. It could represent post-metamorphic cooling, or alternatively, resetting of metamorphic biotite during alteration related to gold mineralization. In the first case, the age provides a reasonable upper limit for the timing of gold mineralization, provided that the ambient temperature during mineralization was not significantly above the closure temperature for Ar in biotite (~ 300 o C). On this basis, gold mineralization at Rattling Brook occurred during the latest Silurian or earliest Devonian, between 415 and 409 Ma. The possibility that mineralization occurred at temperatures above 300 o C, prior to 415 Ma, cannot be completely excluded, but it must be younger than ca. 430 Ma, the time of peak metamorphism in adjacent areas. In conjunction with sparse data on the ages of gold deposits elsewhere in Newfoundland, the results support two discrete episodes of mineralization corresponding to the SilurianDevonian boundary (420-410 Ma) and middle to late Devonian (380-370 Ma). These age groupings resemble those defined by recent Re-Os isotopic studies of sulphides from vein-style gold deposits in the Meguma terrane of Nova Scotia and may in part correspond to the timing of intrusion-related gold in New Brunswick. Given the small amount of data from all of these areas, further interpretation is speculative. However, such hints of discrete orogen-scale episodes of gold mineralization, perhaps correlative with regional tectonothermal events, provide a powerful incentive for further geochronological studies of gold mineralization in the Appalachian orogen. RÉSUMÉLe gîte du ruisseau Rattling est un gîte aurifère à faible teneur qui, de disséminé, devient un stockwerk inclus dans de la granodiorite précambrienne et des roches sédimentaires cambriennes adjacentes. Une altération et une minéralisa-tion aurifère se manifestent également dans des dykes mafiques métamorphisés et feuilletés, remontant probablement au Précambrien tardif. La granodiorite aurifère est à son tour recoupée par des dykes de diabase figés par endroits, non altérés et relativement sains, interprétés en tant qu'intrusions paléozoïques ultérieures à la minéralisation. Une diabase post-minéralisation inaltérée a accu...

Latest Silurian syntectonic sedimentation and magmatism and Early Devonian orogenic gold mineralization, central Newfoundland Appalachians, Canada: Setting, structure, lithogeochemistry, and high-precision U-Pb geochronology

“…Farther west in the Humber Zone along White Bay (Fig. 1), 40 Ar/ 39 Ar geochronology along splays of the Doucers Valley Fault Zone brackets orogenic gold mineralization between 419 Ma and 408 Ma (Kerr and van Breemen, 2007;Minnett et al, 2012). These geochronological data suggest that orogenic gold mineralization along the Baie Verte-Brompton Line and Doucers Valley fault systems may have occurred prior to ca.…”

Overview of age constraints for gold mineralization in central and western Newfoundland and new 40Ar/39Ar ages for muscovite from selected auriferous zones

“…419 to ca. 408 Ma;Kerr and van Breemen 2007;Minnett et al 2012). However, the new data are compatible with a previous age determination for secondary muscovite at White Bay (ca.…”

“…Extant geochronological investigations on gold zones are limited to those from the Hope Brook (Dubé et al 1995) and Cape Ray deposits (Dubé et al 1996;Dubé and Lauzière 1997) and select geochronological studies at the Nugget Pond (Sangster et al 2008) and Hammerdown (Ritcey et al 1995) deposits. Subjects of more recent gold-related, paragenetic, lithogeochemical and geochronological studies include: the Rattling Brook (Kerr and van Breemen 2007) and Thor prospects (Minnett et al 2012) in western Newfoundland (White Bay); the Pine Cove (Ybarra 2020) and Ming (Au-rich VMS) deposits of Baie Verte Peninsula (Pilote et al 2020); and the central Newfoundland gold district (Valentine Lake deposit and Wilding Lake prospect ;Honsberger et al 2022a).…”

Decision support for ore sorting and preconcentration in gold applications

“…Once again the exact mineral assemblage and the strength of the connection between gold and potential proxy minerals is mostly deposit specific. Kerr (2005) reports a description of a specific type of gold mineralisation in Canada. In the paper, correlations between gold and other elements are examined, with the main finding being that there is a strong relationship between Au-As-S and gold enriched areas are also commonly associated with Te and W. Once such relationships are known, for a given deposit, it is a matter to deciding if the presence of these proxies can be detected and if the relationships are sufficiently strong and pervasive to support preconcentration.…”