| Summary: | The Lake Bond deposit is hosted by Lower Ordovician volcanic rocks of the Robert's Arm Group. Detailed penological studies indicate that there are two generations of superimposed alteration and sulphide deposition. The first generation mineralization is pre-kinematic, and is characterized by pyrite and Cu-Zn sulphides associated with pervasive chloritization and locally intense quartz-sericite alteration. The second generation mineralization occurs in syn- to post-kinematic veins, and comprises locally auriferous Cu-Zn-Pb sulphides in a dominantly Ca-Mg-Fe silicate gangue. First generation mineralization resulted in 5x to 100x enrichments in Cu, Zn, Pb, Au, As, Sb, Cd and Ba, with respect to the probable source basalts. Second generation veins, in contrast, carry 100x to 1000x enrichments in most of these metals (except Sb and Ba), substantial enrichments in Fe and Mn, ?10x enrichment in Ag, and a marked increase in the enrichment of Pb, Au, As and Ag relative to Cu and Zn compared to the first generation mineralization. Sphalerites in second generation veins are enriched in Cd, Mn and Fe relative to first generation sphalerites, parallelling enrichments in the whole rocks. The Ca-Mg-Fe vein silicate assemblage suggests fluid temperatures greater than 200°C and possibly greater than 300°C; abundant calcite in the veins implies that CO2 may have influenced mineralization. Fluid inclusions in second generation sphalerite yield average homogenization temperatures of about 306°C. The timing of deformation and second generation mineralization in the Lake Bond deposit is constrained to the early Silurian by cross-cutting relationships with dated post-tectonic plutons. Comparisons with other deposits in the Robert's Arm Group and deposits elsewhere in central Newfoundland suggest a two-stage metallogenic model comprising: (1) an early volcanogenic event coeval with the Lower Ordovician host rocks; and (2) early Silurian hydrothermal activity related to shearing and movement on major faults. The latter is ...
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