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

Seabbridge Gold Inc.勇敢湖勘探项目(SCL)位于新界中部耶洛奈夫以北240公里处。采矿是在SCL声称的苔原(1964-1968年)和Salmita(1983-1987年)矿进行的，矿石在现场加工。该湖中的砷水平一直超过加拿大环境部长理事会的指导方针。湖中砷和其他令人关注的金属(如铝、镉、铜、汞)的浓度升高可能是自然风化、过去采矿活动的渗漏或两者兼而有之的结果。缺乏对马修斯湖沉积物质量的长期评估，也不知道该地区开采前的基线活动。对于沙中湖遗址内以前的两个矿场，确定地球化学基线和过去土地利用对马修斯湖沉积物质量的影响是至关重要的。由于北部湖泊的沉积速度非常慢，使用目前用于环境监测的技术几乎不可能区分基线、过去和未来对马修斯湖的土地利用影响。例如，Ekman Grabs和Glew Corers通常用于获取湖泊沉积物，以便在现场鉴定和环境监测期间进行分析，它们可以产生可能使长达200年的沉积物积累均一化的样品，有效地混合开采之前、开采期间和开采后沉积的沉积物。我们建议使用一种技术，即用冷冻取样器将沉积物就地冻结并提取，从而减少或消除传统取芯设备对湖泊沉积物的干扰。我们将用定制设计的切片机对冻结的沉积物岩心进行毫米级切片，以达到相当于每2-10年采样一次的时间采样分辨率。我们的研究有望提供特定地点的环境监测，特别强调确定人为和非人为As的比例。如果这项初步研究取得成功，未来对湖泊周围多个岩心进行的更详细的研究可能被用来解释自然可变性的来源，用于衡量未来的化学变化和土地利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.