Preliminary observations on styles of mineralization and sulphide-mineral zonation in the Cambrian Zn-Pb-Cu-Ag-Au Lemarchant volcanogenic massive-sulphide deposit, Newfoundland and Labrador

The precious-metal-bearing, polymetallic, bimodal felsic Lemarchant volcanogenic massive-sulphide deposit is located in the Tally Pond belt, Dunnage Zone, Newfoundland Appalachians and consists of a stratiform, massive to semimassive sulphide zone and an underlying stringer sulphide zone. Five principal types of mineral assemblage are present: 1) semimassive white (low-Fe) sphalerite–granular barite–recrystallized pyrite–galena–minor tetrahedrite; 2A) bornite-galena-stromeyerite±chalcopyrite; 2B) bladed barite–coarse-grained tetrahedrite–galena-electrum-colusite±bournonite-polybasite-miargyrite; 3) massive red (high-Fe) sphalerite–fineto medium-grained pyrite–chalcopyrite–galena; and 4) chalcopyritepyrite±orange sphalerite stringers. The stratiform sulphide zone contains the type 1 assemblage, which is crosscut by the type 2A and type 2B assemblages. The type 3 assemblage overprints the type 1 assemblage at the top of the stratiform zone. The basal stringer zone is host to the type 4 assemblage. The type 3 and type 4 assemblages represent minor zone refinement of the stratiform and stringer zones, as the hydrothermal fluids from which they were deposited were relatively hotter (>300°C) than the lower temperature fluid (<250°C) from which the type 1 and type 2 assemblages were deposited. The Lemarchant deposit shows zone refinement typical of Kuroko-style volcanogenic massive-sulphide mineralization; however, the precious-metal–enriched low-Fe sphalerite, bornite, electrum, and sulphosaltrich type 2 assemblages suggest processes analogous to high-sulphidation epithermal-style volcanogenic massive-sulphide mineralization early in the evolution of the deposit. A direct magmatic contribution to the hydrothermal fluid and intermittent boiling during deposition of the type 1 and type 2 assemblages may be partially responsible for precipitation of epithermal-suite minerals and precious-metal enrichment.