The Origin of Hyper-Enriched Black Shales and Their Relationship to Hydrocarbon Generation

Author:

Henderson Kyle M.1,Williams-Jones Anthony E.1,Clark James R.1

Affiliation:

1. McGill University, Earth and Planetary Sciences, 3450 University Street, Montreal, Quebec, H3A 0E8

Abstract

Abstract The Richardson Trough in northern Yukon hosts several occurrences of polymetallic hyper-enriched black shales (HEBS), comprising semimassive sulfide layers with metal concentrations several orders of magnitude above those of average black shales. Models seeking to explain the origin of such spectacular metal concentrations have focused on syndepositional, early diagenetic processes, proposing that the mineralization is entirely prelithification. These models do not provide satisfactory explanations for the mineral textures, paragenesis, and mineral chemistry and thus fail to capture the full story of HEBS formation. We present a new model for HEBS formation that explains mineral textures unaccounted for in previous genetic models. The sulfide fraction in HEBS is dominated by three types of pyrite: Ni-enriched framboidal pyrite (Py1a), euhedral pyrite (Py1b), and an As-enriched anhedral overgrowth (Py2). Two generations of millerite (NiS) have been identified. The first is blebby, disseminated millerite (Mlr1a) and interstitial millerite (Mlr1b), which replaced preexisting features in pyrite. The second millerite generation encases preexisting pyrite and locally replaced sphalerite (Mlr2a). It also forms laths in veinlets with cryptocrystalline quartz and bitumen and in fractures that crosscut bedding-parallel pyritic layers (Mlr2b). Some secondary millerite occurs in sulfide nodules (Mlr2c) containing sphalerite and gersdorffite. Much of the HEBS consists of biogenic quartz, detrital and diagenetic feldspar, and minor illite. The feldspars comprise K-, Ba-, and NH4-rich varieties. Detrital K-feldspar was altered to buddingtonite (Bud) during early diagenesis and to hyalophane (Hya-B) during late diagenesis. Authigenic hyalophane (Hya-A) precipitated concurrently with Hya-B, from pore-fluids in the HEBS matrix, or formed nodules (Hya-C) and veneers (Hya-D) on preexisting sulfides. We propose that the HEBS formed in three stages. Stage 1 involved extensive pyrite precipitation and significant accumulation of metal-rich organic material. Stage 2 coincided with the cessation of pyrite precipitation and the release of nickel and zinc from organic material to precipitate millerite and sphalerite. Stage 3 proceeded via reactions within the oil window that converted clay minerals to authigenic feldspar and released acid, partially dissolving sphalerite. Organic-hosted nickel reacted with sulfur released by sphalerite dissolution to precipitate the second generation of millerite. Our model provides the first explanation for the millerite-sphalerite textures, accounts for the multiple generations of millerite, and explains the various metal enrichments that characterize HEBS. It also demonstrates how diagenetic mineral reactions can strongly influence metal concentrations in black shale.

Publisher

Society of Economic Geologists, Inc.

Reference115 articles.

1. Significance of δ34S and evaluation of its imprint on sedimentary organic matter: I. The role of reduced sulfur species in the diagenetic stage: A conceptual review;Aizenshtat,2004

2. Redox classification and calibration of redox thresholds in sedimentary systems;Algeo;Geochimica et Cosmochimica Acta,2020

3. A re-assessment of elemental proxies for paleoredox analysis;Algeo;Chemical Geology,2020

4. Mo-total organic carbon covariation in modern anoxic marine environments: Implications for analysis of paleoredox and paleohydrographic conditions;Algeo;Paleoceanography,2006

5. Environmental analysis of paleoceanographic systems based on molybdenum-uranium covariation;Algeo;Chemical Geology,2009

同舟云学术

1.学者识别学者识别

2.学术分析学术分析

3.人才评估人才评估

"同舟云学术"是以全球学者为主线,采集、加工和组织学术论文而形成的新型学术文献查询和分析系统,可以对全球学者进行文献检索和人才价值评估。用户可以通过关注某些学科领域的顶尖人物而持续追踪该领域的学科进展和研究前沿。经过近期的数据扩容,当前同舟云学术共收录了国内外主流学术期刊6万余种,收集的期刊论文及会议论文总量共计约1.5亿篇,并以每天添加12000余篇中外论文的速度递增。我们也可以为用户提供个性化、定制化的学者数据。欢迎来电咨询!咨询电话:010-8811{复制后删除}0370

www.globalauthorid.com

TOP

Copyright © 2019-2024 北京同舟云网络信息技术有限公司
京公网安备11010802033243号  京ICP备18003416号-3