Publication Type:Book Chapter
Source:Irish-type Zn-Pb deposits around the World volume ("The Lime Green Book"), Irish Association for Economic Geology, p.629-656 (2023)
Keywords:British Colombia and Alberta, MVT-deposits, mineralogy, mineral textures, fluid inclusions, stable iso-, topic data.
<p>A comprehensive study of samples from MVT–type base-metal (Zn-Pb) deposits from across the Canadian Cordillera was done to compare and contrast features and assess their relevance in the context of sulphide mineralization. Petrography and supported CL imaging indicates early host rock dissolution to form secondary fine-grained dolostone during marine cementation is followed by multiple generations of dolomite cements (low T, fine-grained to coarser, higher T varieties) that overlaps with Zn-Pb sulphides which is succeeded by a later barren calcite stage. Ore-stage dolomite is often rich in Fe (<1.3 wt. % FeO) and hosts small sphalerite inclusions. Sphalerite-hosted fluid inclusions record Th values (77–214°C) and salinities (1–28 wt. % equiv. NaCl±CaCl2) that reflect fluid mixing with no single fluid type related to sulphide mineralization. In situ SIMS δ18OVSMOW data for dolomite and calcite (13 to 33‰) suggest involvement of several fluids (i.e., seawater, basinal, meteoric) over a large temperature range at varying fluid-rock ratios. In situ SIMS δ34SVCDT data for sphalerite and pyrite indicate a large variation (8 to 33‰), but with smaller ranges (<2 to 3‰) for the settings studied, and suggest reduced S was produced dominantly via TSR processes from homogeneous sulphur reservoirs. Together the datasets suggest involvement of several fluids in the mineralizing process with mixing of a S-poor, metal-bearing fluid with a metal-poor, S-bearing fluid.</p>