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Cresson Project Hvdroaeochemistry AdrianBrown <br />Fracture intensity in the volcanics is highly variable, and so the hydraulic conductivity is <br />similarly variable. In particular, it appears that the hydraulic conductivity of the eastern volcanic <br />overflow apron (see location on Plate 4) is lower than in other parts of the Diatreme. This is <br />consistent with the absence of gold mineralization in this area, as hydrothermal gold <br />emplacement requires high rockmass permeability and porosity. It is also consistent with the <br />generally lower downward hydraulic gradient in this area, indicative of higher resistance to <br />vertical flow than in other parts of the Diatreme. Vertical hydraulic conductivity is likely <br />dominated by the strong vertical jointing and faulting in this rockmass, generally striking <br />approximately NW -SE. As all the test holes are vertical, these features are likely under- <br />represented in the testing. Accordingly, it is expected that the effective vertical hydraulic <br />conductivity of the volcanics is at least an order of magnitude higher than the horizontal <br />hydraulic conductivity. <br />Tertiary horizontal hydraulic conductivity: <br />Tertiary vertical hydraulic conductivity: <br />General Overflow Apron <br />2x10 " cm/sec 2x10 cm/sec <br />2x10 cm/sec 2x10 cm/sec <br />4. Precambrian. The Precambrian age materials surrounding the Diatreme comprise granite, <br />granodiorite, schist, and gneiss (Plate 3). The measured horizontal hydraulic conductivity values <br />of this material have a geometric mean of 1x10 cm/sec, with values ranging from 3x10 " cm/sec <br />to 3x10 -3 cm/sec. Intact Precambrian rock is impermeable, and the rockmass derives its <br />permeability from fracturing, faulting, and flow along bedding /schistosity planes. The <br />permeability is increased by alteration, which intensifies as the Precambrian interface with the <br />diatremal rocks is approached. This can be seen in the vertical hydraulic head gradient, which is <br />very strong close to the steeply dipping diatremal wall, indicating that the Precambrian rock is <br />more permeable close to the steep walls of the Diatreme. Vertical hydraulic conductivity is not <br />expected to differ significantly from horizontal hydraulic conductivity, as there is no observed <br />preferential joint direction in the Precambrian rock. Both horizontal and vertical hydraulic <br />conductivity are expected to be reasonably similar to the measured hydraulic conductivity. <br />General Beside Diatreme <br />Precambrian horiz. hydraulic conductivity: 2x1 cm/sec 2x1 -5 cm/sec <br />Precambrian vert. hydraulic conductivity: 2x10 -6 cm/sec 2x10 cm/sec <br />2.5 Hydrology Model <br />The Diatreme is made up of three main vertical volcanic feeder tubes, one to the north, one to the west, <br />and one to the east. The Carlton Tunnel penetrates and directly drains the regional ground water regime <br />in the relatively high permeability eastern and southern feeders, which are geologically connected at <br />tunnel level. The Carlton Tunnel indirectly drains the regional ground water regime in the north feeder, <br />by drawing flow to the south feeder through the relatively low permeability Precambrian rock curtains <br />that separate them. Thus the conceptual model of the hydrology of the District is a large diameter "well" <br />(the Diatreme) that collects infiltrating precipitation from the surface of the Diatreme and adjacent <br />1385L.20120125 10 <br />