Geochemistry of natural acid rock drainage in the Mt Evans area, Anaconda–Pintler Range, Montana, USA

IF 1 4区地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS

Geochemistry-Exploration Environment Analysis Pub Date : 2021-10-12 DOI:10.1144/geochem2021-068

C. Gammons, M. F. Doolittle, K. Eastman, S. Poulson

{"title":"Geochemistry of natural acid rock drainage in the Mt Evans area, Anaconda–Pintler Range, Montana, USA","authors":"C. Gammons, M. F. Doolittle, K. Eastman, S. Poulson","doi":"10.1144/geochem2021-068","DOIUrl":null,"url":null,"abstract":"This paper investigates natural acid rock drainage in two streams draining either side of Mt Evans, Montana. Bedrock consists of pyrrhotite-bearing schist intruded by granitic dykes and plutons of Late Cretaceous to Tertiary age. The headwaters of both streams are moderately acidic (pH < 5.0) and carry elevated loads of dissolved sulfate, aluminum and other trace metals (Cd, Co, Cu, Mn, Zn) as well as rare earth elements (REEs). Copious aluminum precipitates inferred to be hydrobasaluminite coat boulders of both streams as pH rises > 5, with adsorption of copper and REEs. Concentrations and loads of dissolved sulfate and trace elements are anomalously high in a small tributary that is sourced by meltwater from a rock glacier. The S-isotope composition of dissolved sulfate in both watersheds is similar to that of pyrrhotite in the meta-sediments, but not molybdenite in late porphyry dykes. Calculations of sulfate flux (i.e. sulfate load divided by surface area) indicate a relatively fast rate of sulfide oxidation in the study area, possibly due to exposure of fresh bedrock in the steep and recently glaciated field area. Overall, the geochemistry of the site suggests the possible presence of a metamorphosed sedimentary–exhalative deposit, a possibility that is unlikely to be tested by drilling given the proximity of the site to a federal wilderness area. Supplementary material: All analytical data related to this project, additional maps and photographs, and selected results from geochemical modelling are available at https://doi.org/10.6084/m9.figshare.c.5649850 Thematic collection: This article is part of the Hydrochemistry related to exploration and environmental issues collection available at: https://www.lyellcollection.org/cc/hydrochemistry-related-to-exploration-and-environmental-issues","PeriodicalId":55114,"journal":{"name":"Geochemistry-Exploration Environment Analysis","volume":" ","pages":""},"PeriodicalIF":1.0000,"publicationDate":"2021-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"1","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Geochemistry-Exploration Environment Analysis","FirstCategoryId":"89","ListUrlMain":"https://doi.org/10.1144/geochem2021-068","RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q3","JCRName":"GEOCHEMISTRY & GEOPHYSICS","Score":null,"Total":0}

引用次数: 1

Abstract

This paper investigates natural acid rock drainage in two streams draining either side of Mt Evans, Montana. Bedrock consists of pyrrhotite-bearing schist intruded by granitic dykes and plutons of Late Cretaceous to Tertiary age. The headwaters of both streams are moderately acidic (pH < 5.0) and carry elevated loads of dissolved sulfate, aluminum and other trace metals (Cd, Co, Cu, Mn, Zn) as well as rare earth elements (REEs). Copious aluminum precipitates inferred to be hydrobasaluminite coat boulders of both streams as pH rises > 5, with adsorption of copper and REEs. Concentrations and loads of dissolved sulfate and trace elements are anomalously high in a small tributary that is sourced by meltwater from a rock glacier. The S-isotope composition of dissolved sulfate in both watersheds is similar to that of pyrrhotite in the meta-sediments, but not molybdenite in late porphyry dykes. Calculations of sulfate flux (i.e. sulfate load divided by surface area) indicate a relatively fast rate of sulfide oxidation in the study area, possibly due to exposure of fresh bedrock in the steep and recently glaciated field area. Overall, the geochemistry of the site suggests the possible presence of a metamorphosed sedimentary–exhalative deposit, a possibility that is unlikely to be tested by drilling given the proximity of the site to a federal wilderness area. Supplementary material: All analytical data related to this project, additional maps and photographs, and selected results from geochemical modelling are available at https://doi.org/10.6084/m9.figshare.c.5649850 Thematic collection: This article is part of the Hydrochemistry related to exploration and environmental issues collection available at: https://www.lyellcollection.org/cc/hydrochemistry-related-to-exploration-and-environmental-issues

查看原文本刊更多论文

美国蒙大拿州Anaconda-Pintler山脉埃文斯山地区天然酸性岩石排水的地球化学

本文研究了蒙大拿州埃文斯山两侧的两条溪流中的天然酸性岩石排水。基岩由磁黄铁矿片岩组成，该片岩被晚白垩世至第三纪的花岗岩脉和深成岩体侵入。两条溪流的源头均为中等酸性（pH 5，具有对铜和稀土元素的吸附。在一条由岩石冰川融水形成的小支流中，溶解硫酸盐和微量元素的浓度和含量异常高。两个流域溶解硫酸盐的S同位素组成与变质沉积物中的磁黄铁矿相似，但与晚斑岩脉中的辉钼矿不同。硫酸盐通量（即硫酸盐负荷除以表面积）的计算表明，研究区域的硫化物氧化速度相对较快，这可能是由于陡峭和最近冰川化的野外区域暴露了新鲜基岩。总的来说，该场地的地球化学表明可能存在变质沉积-呼气矿床，鉴于该场地靠近联邦荒野地区，这种可能性不太可能通过钻探进行测试。补充材料：与本项目有关的所有分析数据、其他地图和照片以及地球化学建模的选定结果可在https://doi.org/10.6084/m9.figshare.c.5649850主题集：本文是与勘探和环境问题相关的水化学集的一部分，可在以下网站获取：https://www.lyellcollection.org/cc/hydrochemistry-related-to-exploration-and-environmental-issues

本文章由计算机程序翻译，如有差异，请以英文原文为准。

求助全文

约1分钟内获得全文求助全文

来源期刊

Geochemistry-Exploration Environment Analysis 地学-地球化学与地球物理

CiteScore

3.60

自引率

16.70%

发文量

审稿时长

1 months

期刊介绍： Geochemistry: Exploration, Environment, Analysis (GEEA) is a co-owned journal of the Geological Society of London and the Association of Applied Geochemists (AAG). GEEA focuses on mineral exploration using geochemistry; related fields also covered include geoanalysis, the development of methods and techniques used to analyse geochemical materials such as rocks, soils, sediments, waters and vegetation, and environmental issues associated with mining and source apportionment. GEEA is well-known for its thematic sets on hot topics and regularly publishes papers from the biennial International Applied Geochemistry Symposium (IAGS). Papers that seek to integrate geological, geochemical and geophysical methods of exploration are particularly welcome, as are those that concern geochemical mapping and those that comprise case histories. Given the many links between exploration and environmental geochemistry, the journal encourages the exchange of concepts and data; in particular, to differentiate various sources of elements. GEEA publishes research articles; discussion papers; book reviews; editorial content and thematic sets.