The Kokanee Range Ag-Pb-Zn vein field (southeastern B.C.) formed during Eocene crustal extension and unroofing of the Valhalla metamorphic core complex. Extension was accommodated along the low-angle Slocan Lake Fault zone which is the western boundary of the vein field. In Slocan Group slates, the veins are in a fault system that comprises a major E-W, S-dipping, low-angle normal fault, the "Main Lode", and several NE-SW steeply-dipping faults that are located in the hangingwall of the Slocan Lake Fault. In the Nelson batholith, faults and fractures display dominant NE and NW orientations but are more sparsely distributed.

        In Slocan Group slates, vein minerals oxygen isopleths are concentric about the "Main Lode" with a NE-SW deflection, and abut on the Slocan Lake Fault. No systematic oxygen isotope zonation is found in the Nelson batholith. The oxygen isotope regional zonation in Slocan Group slates reveals the pattern of fracture-controlled hydrothermal fluid flow, fluid mixing, and fluid-rock exchange. Oxygen isotope and salinity data indicate mixing between a deep-seated, metamorphic fluid and an upper crustal fluid dominated by evolved meteoric water. Fluid inclusion data show no temperature gradient. Fluid-rock exchange is recorded in the oxygen isotope composition of Slocan Group slates which display a regional depletion consistent with the vein oxygen isopleths.

        Our objective is to simulate the oxygen isotope compositions and zonations observed in the Kokanee Range Ag-Pb-Zn vein field.  The hypotheses are that the oxygen isotope compositions and zonations are produced by infiltration of a deep-seated fluid (d¹⁸O = 8 ‰) along the Slocan Lake Fault at the base of the continental crust. A hydraulic head gradient forces the fluid to flow towards higher crustal levels where the fluid enters the fractures in the Slocan Group slates (d¹⁸O = 18 ‰). Fractures in the Slocan Group slates are connected to the Slocan Lake Fault and filled with evolved meteoric water (d¹⁸O = 3 ‰). Isothermal conditions are assumed at the temperature recorded by fluid inclusions (350°C). We use a finite-element model, FRAC3DVS, which simulates 3D-isothermal fluid flow and advective-dispersive transport in discretely-fractured porous media. The model has been modified to allow calculation of oxygen isotope compositions during equilibrium and kinetically-controlled exchange between the fluids and the rock mass. The porous matrix is discretized with 3D elements and is intersected by vertical and inclined (45°) interconnected planar fractures that schematically reproduce the fracture pattern in Slocan Group slates. Material properties and boundary conditions are adjusted to reproduce the Kokanee Range data and to derive useful parameters describing fluid flow and mass transport in the hydrothermal system.