Geology, Mineralogy, and Lithogeochemistry of Metalliferous Mudstones Associated with the Lemarchant Volcanogenic Massive Sulfide Deposit, Tally Pond Belt, Central Newfoundland

Abstract

The Cambrian Lemarchant Zn-Pb-Cu-(Au-Ag) bimodal felsic volcanogenic massive sulfide (VMS) deposit, Tally Pond group, central Newfoundland, Canada, contains metalliferous mudstones that occur either immediately on top or laterally along strike from massive sulfide mineralization, or as interflow mudstones within hanging-wall basaltic rocks. The mudstones are brown to black, graphite rich, and locally have intercalations of siliciclastic, volcaniclastic and/or amorphous chert layers, and, in some cases, fine lamina of organic matter. The main sulfide phases are pyrite (framboidal and euhedral) and pyrrhotite, with minor chalcopyrite, sphalerite, arsenopyrite, and galena; barite is a common sulfate.The metalliferous mudstones occur at various stratigraphic levels and have variable inputs of hydrothermal (high Fe/Al and base metal values) and detrital components (lower Fe/Al and base metal values) with positive shale normalized Eu anomalies (Eu/Eu* ≥1), negative Ce anomalies (Ce/Ce* ≤1), and an average Y/Ho ratio of ~28.3. These signatures suggest precipitation from reduced, high-temperature hydrothermal vent fluids in an oxygenated water column, coupled with the hydrothermal particles having a short residence time within the hydrothermal plume (i.e., a vent proximal setting). Deposition from an oxygenated water column is also supported by the presence of abundant barite in both the Lemarchant massive sulfides and the metalliferous mudstones, as well as locally preserved marcasite in the mudstones. Redox-sensitive trace elements (As, U, V, Mo, Cr, Ni, and Co) were scavenged as oxyanions onto Fe oxyhydroxides during mudstone formation, and these elevated levels of scavenged redox-sensitive trace elements cause apparent anoxic signatures. Immobile element systematics (La-Th-Zr/10 and Th-La-Sc) indicate that the detrital components of the Lemarchant mudstones were mixtures of both continental and mafic sources, most likely deposited within a pericontinental rifted arc environment. Our research illustrates that the lithogeochemistry of metalliferous mudstones can identify vent proximity and provides insights into the physiochemical conditions of the deposit formation and the ambient environment. These results have implications for similar precious metal-bearing VMS deposits globally.

Multiple sulphur and lead sources recorded in hydrothermal exhalites associated with the Lemarchant volcanogenic massive sulphide deposit, central Newfoundland, Canada

“…Lemarchant, and the rare-earth element patterns in the Lemarchant exhalites, are 608 consistent with deposition from an oxygenated water column (Lode et al 2015). This is supported by both paragenetic relationships, e.g., that galena is paragenetically 630 and spatially associated with chalcopyrite (Fig.…”

Hydrothermal alteration and lithogeochemistry of the Boundary volcanogenic massive sulphide deposit, central Newfoundland, Canada

“…Base metals (Cu, Zn, Pb), transition metals (Sc, Ti, V, Cr, Mn, Co, Ni), volatile elements (As, Cd, Sn, Sb), and the LFSE (Sr, Ba, Th) were determined by multi-acid dissolution and analyzed by inductively coupled plasma-mass spectrometry (ICP-MS). The whole-rock dissolution process was a modified version of that described by Jenner et al (1990) and Longerich et al (1990) and is described in detail by Lode et al (2015). The REE and HFSE were determined by means of sodium peroxide (Na 2 O 2 ) sinter and analyzed using the same ICP-MS at Memorial University using the following procedure: sintering of a 0.2 g sample aliquot with Na 2 O 2 , dissolution of the sinter cake by addition of deionized water and subsequent REE precipitate formation, separation by centrifuge, and acid dissolution of precipitate prior to ICP-MS analysis.…”

“…The complete method can be found in Longerich et al (1990). Precision and accuracy of the various methods have been previously reported in Piercey and Colpron (2009) for Actlabs, Jenner et al (1990) and Lode et al (2015) for multi-acid dissolution, and Longerich et al (1990) for Na 2 O 2 sinter. Representative values are displayed in Table 1.…”

Exceptional sulfur and iron isotope enrichment in millimetre-sized, early Palaeozoic animal burrows

“…In conjunction with the low measured TOC values (the majority of samples is well below 1.0 wt.%) 21 , suggests that early Paleozoic mudstones at this specific location originally contained little bioavailable organic matter, except in sediment portions in which mucous-lined burrows provided high-quality EPS for microbial sulfate and iron reduction. A possible alteration of pyrite-hosted stable S and Fe isotope signatures via hydrothermal, sulfide-rich fluids can be excluded, since such an alteration would have resulted in the precipitation other sulfur phases (i.e., barite, metal sulfides) throughout the sediment matrix 19,44 .…”