Hydrothermal evolution of volcanogenic Zn-Cu-Pb deposits, Taylors Brook showing, Stirling Belt, southeastern Cape Breton Island, Nova Scotia

• Main Author: LeBlanc, Haley D.
• Other Authors: Hanley, Jacob James, 1976-
• Format: Text
• Language: English
• Published: Halifax, N.S. : Saint Mary's University 2016
• Subjects: Canada; Breton Island; Stirling; Taylors Brook
• Online Access: http://library2.smu.ca/handle/01/26619

1 online resource (vi, 64 p.) : ill. (chiefly col.), col. maps Includes abstract and appendices. Includes bibliographical references (p. 50-54). The Taylors Brook showing is a suspected volcanogenic massive sulfide (VMS) occurrence (Zn-Pb-Cu-Au-Ag) that occurs within the ~680 Ma Stirling volcanosedimentary-plutonic belt, southeastern Cape Breton Island, Nova Scotia, Canada. In addition to mineralized mudstones, there are 7 associated hydrothermal vein types, characterized using three criteria: vein-filling mineral composition and alteration style, cross cutting relationships and mineralization. Mineralized (Zn-Cu-Pb-Sc-Y-Ag-Te) veins show propylitic and potassic alteration assemblages. Compositional zoning in epidote and a pyrrhotite-smythite replacement reaction indicate that the hydrothermal fluid was experiencing fluctuations in /O2 and cooling, respectively, rendering the metals less soluble causing their precipitation. Bulk rock geochemistry indicates mineralization anomalies are associated with host rock Zn-Pb anomalies in pyritic mudstone units and Cu anomalies in type IA (epidote-actinolite-calcite-K-feldspar-quartz-pyrite) veins. Fluid inclusion data from two generations of calcite in later type V veins suggest a CaCl2-rich hydrothermal brine responsible for metal transport and deposition with bulk salinities ranging between 43-54 wt% total salt (absolute: 33-50 wt% CaCl2 and up to 20 wt % NaCl). The homogenization temperatures for calcite A-hosted inclusions range from 106-306[degree]C (n=21) and in calcite B-hosted inclusions from 212-331[degree]C (n=91). Isochore ranges were plotted using microthermometric data, paired with a po-py equilibrium boundary constraint limits trapping conditions to a maximum of 400[degree]C and 5kbar. The distinct Ca-Cl-rich brine composition can only be formed naturally under specific conditions. There are four conceivable explanations for this Ca rich fluid: boiling, cation exchange between Na and Ca, evaporation of Ca-rich paleoseawater and dissolution of ...