Volcanology and geochemistry of the Lundberg volcanogenic massive sulphide zone, Buchans, Newfoundland
Abstract
The Buchans mining camp is characterized by a number of unusually high grade low-tonnage volcanogenic massive sulphide deposits (VMS) hosted by a bimodal calc-alkaline continental arc sequence. The mining camp produced a total of 16.2 Mt of ore at an average grade of 14.5% zinc, 7.6% lead, 1.3% copper, 126g/t Ag, and 1.37g/t Au rivalling most other VMS districts. Recent exploration has been focused on the Lundberg zone located in the hanging wall of the Lucky strike orebody, providing an excellent opportunity to explore the relationships between volcanology, sedimentation and mineralization in closely spaced drillcore. Four main volcanic and volcano-sedimentary units have been identified including two different rhyolites (both geochemical and textural constraint), dacite, basalt and late diabase. These units can be correlated across the entire Lundberg zone and provide an excellent testable stratigraphy. The stratigraphy of the Lundberg zone is characterized by a lower basaltic hyaloclastite with locally developed scoreaceous textures. Overlying the basalt is a volcano-sedimentary unit consisting of a rhyolite>dacite>siltstone>basalt framework breccia with a pyritic sandstone matrix, and rare sphalerite, galena, pyrite clasts and isolated massive sulphide (i.e., 20cm) and barite beds. These are structurally or stratigraphically overlain by a feldspar>>quartz phyric, green- pale yellow-red, +/- flow banded, coherent rhyolite and quartz>feldspar phyric, pale beige to red-dark green rhyolite with large quartz phenocrysts. The sequence is intruded by diabase sills. The basalt is extensively altered and cut by stockwork chlorite-pyrite, polymetallic and chalcopyrite rich veins which may form the stockwork to the overlying massive and transported sulphides. Some of the polymetallic veins contain extensive bladed calcite and quartz, suggesting local boiling may have occurred. Determination of the detailed volcanic stratigraphy, geochemical and mineralization characteristics of the Lundberg zone provides a predicative model that can be applied to exploration in this mining camp. On a broader scale, the presence of epithermal characteristics in the Buchans VMS camp provides clues to the origin of these high-grade, low tonnage deposits.
- Publication:
-
AGU Spring Meeting Abstracts
- Pub Date:
- May 2009
- Bibcode:
- 2009AGUSM.V31B..24V
- Keywords:
-
- 8424 Hydrothermal systems (0450;
- 1034;
- 3017;
- 3616;
- 4832;
- 8135)