Mixing line isochrons; a new interpretation of galena lead isotope data from southeastern British Columbia

Abstract

Galena lead isotope data from Ainsworth-Bluebell, Slocan, and Moyle camps in southeastern British Columbia can be interpreted in terms of mixing of lead from two different sources, both of which follow simple growth-curve lead evolution. The more radiogenic source can be approximated using the three-stage shale curve of Godwin and Sinclair (1982) which is thought to represent evolution of lead in the upper crustal, continentally derived sedimentary rocks which host these deposits. The two-stage Bluebell growth curve through the Bluebell datum provides an estimate of the uranium-poor lead source which may be the lower crust, the upper mantle, or a mixture of both. The Bluebell curve departs from Stacey and Kramers' (1975) average growth curve at 3.77 b.y., with a •t value of 9.23.Mixing line isochrons drawn between these two curves at ages corresponding to the best estimates for the mineralization ages at these three mining camps closely fit the lead isotope data. This supports the age estimates for all three camps and, in particular, substantiates a Lower Cambrian age for the original mineralization in the Ainsworth and Bluebell deposits. Mixing is assumed to take place at the time of mineralization and may be attributed to magmatic activity in the Moyie and Slocan camps. Additional data from deposits in the Purcell anticlinorium in Idaho and Montana (Zartman and Stacey, 1971), the Carmi and Tillicum Mountain gold-silver camps in south-central BritishColumbia, and the Galena Hill silver veins in the Yukon Territory demonstrate the applicability of this model to a large part of the Omineca belt and show how it may be used to date both epigenetic and syngenetic or penecontemporaneous deposits of unknown age.

Genesis of the Lass vein system, Beaverdell silver camp, south-central British Columbia

“…1, which are represented by gold veins at Carmi, 7 km north of Beaverdell. The recent "shale" (Godwin and Sinclair 1982), "Bluebell, " and "mixing-line isochrons" (Andrew et al 1984) models confirm the tentative interpretation by Watson et a/. (1982) that all the Beaverdell silver-rich vein mineralization is Tertiary and distinct from Carmi-type, gold-rich vein mineralization related to the Jurassic Westkettle batholith.…”

“…Granodiorite of the Westkettle batholith, believed by Little (1961), Peatfield (1978, Watson et nl. (1982), andAndrew et al (1984) to be correlative with Jurassic Nelson intrusions, underlies much of the area. This batholith has been intruded by small stocks that have been dated by biotite K-Ar methods at Carmi Moly, Eugene Creek, and Tuzo Creek as Tertiary (49.5 -57.3 + 2 Ma: Fig.…”

Quantifying an early signature of the industrial revolution from lead concentrations and isotopes in soils of Pennsylvania, USA

“…Dashed gray lines show the values for Pb ores from Mexico and Peru, which were not used as gasoline additives in the Great Lakes region (Graney et al, 1995). Data sources are Chow and Earl (1972), Andrews et al (1984), Cumming and Richards (1975), Cumming et al (1979), Doe and Delevaux (1972), Gulson et al (1981), Gunnesch et al (1990), Heyl et al (1974), Thompson and Beaty (1990) and Graney et al (1995). early 1900s, coal was supplying more than 100,000 ovens to make coke, mostly in western Pennsylvania and northwestern West Virginia (Eggert, 1994).…”

Lead- and strontium-isotope geochemistry of Paleozoic Sicker Group and Jurassic Bonanza Group volcanic rocks and Island Intrusions, Vancouver Island, British Columbia

“…Thus Sicker Group material cannot uniquely be identified as the crustal end member because many other continental and crustal and ocean sediment compositions would be suitable candidates. It is, however, possible to rule out contamination by sediments that were derived from the rniogeosynclinal part of the Canadian Cordillera, which are characterized by high 207Pb/204Pb values (Godwin and Sinclair 1982;Andrew et al 1984).…”