An assessment of environmental geochemical baseline for Matthews Lake, Northwest Territories

Seabridge Gold Inc.库拉湖勘探项目（SCL）位于北部240公里的耶洛奈夫在中部NT。在SCL索赔范围内，Tundra（1964-1968年）和Salmita（1983-1987年）矿进行了采矿，矿石在现场加工。该湖的砷含量一直超过加拿大环境部长理事会的指导方针。As和其他相关金属的浓度升高（例如，铝、镉、铜、汞）可能是自然风化、过去采矿活动渗漏或两者兼而有之的结果。 目前缺乏对马修斯湖沉积物质量的长期评估，也不知道该区域采矿前活动的基线地球化学。对于SCL场地内的两个先前矿场，确定地球化学基线和过去土地使用对马修斯湖沉积物质量的影响至关重要。由于北方湖泊的沉积速率非常缓慢，因此使用目前用于环境监测的技术几乎不可能区分基线、过去和未来土地利用对马修斯湖的影响。 例如，埃克曼抓斗和Glew岩心取样器通常用于获取湖泊沉积物，以便在场地特征描述和环境监测期间进行分析，它们可以产生可以均匀化长达200年的沉积物积累的样本，有效地混合了采矿之前、期间和之后沉积的沉积物。 我们建议使用一种技术，沉积物冻结原位与冷冻取样器和提取，从而减少或消除所造成的干扰湖泊沉积物的传统取心装置。我们将使用定制设计的切片机以毫米级对冻结沉积物岩心进行切片，以实现相当于每2-10年取样一次的时间采样分辨率。 我们的研究预计将提供特定地点的环境监测，特别强调确定人为和非人为的比例。 如果这一初步研究取得成功，今后可利用对湖周围多个岩心的更详细研究来说明自然变异的来源，以衡量今后的化学变化和土地使用对沉积物质量的影响。

The Seabridge Gold Inc. Courageous Lake exploration project (SCL) is located 240 km north Yellowknife in the central NT. Mining took place within the SCL claim at the Tundra (1964-1968) and Salmita (1983-1987) mines and ore was processed onsite. Levels of Arsenic (As) in the lake have consistently exceeded Canadian Council of the Ministers of the Environment guidelines. Elevated concentrations of As and other metals of concern (e.g., Al, Cd, Cu, Hg) in the lake could be the result of natural weathering, seepage from past mining activities, or a combination of both. A long-term sediment quality assessment of Matthews Lake is lacking and baseline pre-mining activity geochemistry for this region is not known. With two previous mine sites within the SCL site it is critical that geochemical baseline and past land-use impacts on the sediment quality of Matthews Lake be defined. It is nearly impossible to differentiate between baseline, past, and future land-use impacts on Matthews Lake using technologies currently employed for environmental monitoring due to the incredibly slow sedimentation rates within northern lakes. For example, Ekman grabs and Glew corers, commonly used to obtain lake sediments for analysis during site characterization and environmental monitoring, can produce samples that may homogenize up to 200 years of sediment accumulation, effectively mixing sediments deposited prior, during, and post mining. We propose using a technique where sediments are frozen in situ with a freeze corer and extracted, thus reducing or eliminating disturbance of lake sediments caused by traditional coring devices. We will slice frozen sediment cores at mm-scale with a custom designed microtome to achieve a temporal sampling resolution equivalent to a sample every 2-10 years. Our research is expected to provide site-specific environmental monitoring with specific emphasis on determining the proportions of anthropogenic and non-anthropogenic As. If this preliminary research is successful more detailed future research on multiple cores from around the lake may be used to account for sources of natural variability to be used to measure future chemical change and land-use impact on sediment quality.