Hydrogeochemical and isotopic characterization of groundwaters in the Myra-Price Hillsides and Thelwood Valley, Myra Falls mining camp, Vancouver Island, British Columbia, Canada.

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Title: Hydrogeochemical and isotopic characterization of groundwaters in the Myra-Price Hillsides and Thelwood Valley, Myra Falls mining camp, Vancouver Island, British Columbia, Canada.
Authors: Phipps, Graham Charles.
Date: 1998
Abstract: Chemical and isotope characteristics of surface and ground waters were investigated within portions of the Myra Falls (Zn-Cu-Pb) mining camp, Vancouver Island (49° 35' N, 125° 34' W). This site was selected to characterize ground waters, investigate metal mobility, develop ground water exploration methods, and to elucidate ground water circulation in mountainous terrain with high rainfall. A broad spectrum of water characteristics were found and have been subdivided into water facies which correspond to hydrologic regimes within the mining camp: (1) local precipitation and surface runoff have Ca2+-HCO 3-- composition. (2) Ca2+-HCO 3-- shallow ground waters are of recent meteoric origin, contain tritium, have low total dissolved solids (TDS) (<200 ppm), and are nearly saturated with respect to dissolved oxygen (DO). These ground waters are mainly limited to the fractured rock carapace of the Myra-Price ridge, and shallow zones within Thelwood Valley. Many of these waters contact sulphide mineralization but have near neutral pH and SO4 2' remains subordinate to HCO3--. (3) Ca2+-Na+-HCO3-- and Na+-Ca2+-HCO3 -- are meteoric waters occurring within the central core of the Myra-Price ridge. They have gained Na+ by cation exchange in rocks previously saturated with Na+-Ca2+-Cl -- water. These ground waters have TDS similar to Ca2+ -HCO3-- ground waters. (4) Na +-Ca2+-Cl-- saline ground waters (TDS >30,000 ppm) were discovered in areas undisturbed by mining operations. These waters are reducing, have alkaline pH, contain very low HCO3 --, are most likely 14C-free, and contain a high volume of helium. The unique chemical and isotope character of the Cl -- waters imply they are exotic to this setting. (5) Na +-Ca2+-SO42-- and Ca 2+-SO42-- ground waters, of meteoric origin, occur at intermediate depth in areas underlying previously mined areas and in areas where dissolution of anhydrite has dominated the anion chemistry. (6) Mg2+- SO42-- runoff waters result from intense weathering of mined waste-rock. Thelwood Valley is unaffected by mine development. Ground waters in this area exhibit a narrow mixing interface between modern Ca 2+-HCO3-- and saline waters, and have little cation exchange. The pH of ground waters related to the Myra Falls mineral deposits is generally near neutral, and acidic ground waters with high metal loads are extremely rare. Amorphous oxy-hydroxides composed primarily of Fe oxy-hydroxides but also including Mn and Al. Zinc displays the strongest and most reliable anomaly contrasts for hydrogeochemical exploration in the dominantly bicarbonate and sulphate ground waters associated with the Zn-Cu-Pb mineralization of the Price ore-deposit. (Abstract shortened by UMI.)
URL: http://hdl.handle.net/10393/4513
http://dx.doi.org/10.20381/ruor-10297
CollectionTh├Ęses, 1910 - 2010 // Theses, 1910 - 2010
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