TY - JOUR

T1 - The genesis of sulfide assemblages in the former Wilhelmine mine, Spessart, Bavaria, Germany

AU - Okrusch, Martin

AU - Lorenz, Joachim A.

AU - Weyer, Stefan

PY - 2007/8

Y1 - 2007/8

N2 - The vein-type copper mineralization in the abandoned Wilhelmine copper mine, Sommerkahl, Spessart, northwestern Bavaria, Germany, is hosted by metamorphic rocks of the Spessart Crystalline Complex. These are overlain by Permo-Triassic sedimentary rocks, including the stratabound base-metal mineralization of the Kupferschiefer. Ore textures in the sulfide veins demonstrate three stages of mineralization: (i) An early stage (I) is characterized by colloform textures, documented by spherical, cockadelike or garland-shaped, mononfineralic or polymineralic aggregates of tennanrite I, enargite I, pyrite I, chalcopyrite I, bornite I and digenite I. (ii) During a subsequent stage of recrystallizarion (II), the colloform textures were overgrown by, or enclosed in, anhedral grains of tennantite II, enargite II, bomite II, digenite II, pyrite II and chalcopyrite II. Minimum temperatures of about 175°C for this stage can be estimated from the bulk composition of fine-grained to submicroscopic digenite-bornite intergrowths, exsolved from an initial la solid solution with up to 55 mole % of bornite. Conversely, tbe assemblage pyrite + chalcopyrite + tennantite provides an uppermost temperature limit of ∼440°C [at an a(S2) = 10-5]. (iii) A late stage of alterarion (III) led to the replacement of the primary sulfides by yarrowite, spionkopite and rare covellite, together with goethite, under decreasing temperatures and rising acrivity of sulfur. The close sparial association of the Sommerkahl vein-type Cu deposit with the overlying Kupferschiefer suggests that this metal-rich bituminous shale played an important role in the formation of the ore veins. Sulfur isotope analyses yielded negative δ34S of-12.8 to -23.9%o, which indicate that the sulfur was derived from the overlying Kupferschiefer, presumably by hydrothermal leaching. Such a low-temperature mobilization could also be discussed for all or part of the metals forming the Wilhelmine ore, wbich later on recrystallized in response to hydrothermal acrivity (modified hydrothermal model). However, we prefer a strictly hydrothermal model, according to which all or most of the metals were derived from deep-seated sources, transported upward by hydrothermal fluids, and precipitated by thermochemical reduction of sulfate due to interaction with the sulfur-bearing organic matter and the pyrite of the Kupferschiefer. Formation of the sulfide ore veins in the former Wilhelmine mine is related to post-Variscan hydrothermal activity that affected the Spessart area in Middle Jurassic to late Early Cretaceous time.

AB - The vein-type copper mineralization in the abandoned Wilhelmine copper mine, Sommerkahl, Spessart, northwestern Bavaria, Germany, is hosted by metamorphic rocks of the Spessart Crystalline Complex. These are overlain by Permo-Triassic sedimentary rocks, including the stratabound base-metal mineralization of the Kupferschiefer. Ore textures in the sulfide veins demonstrate three stages of mineralization: (i) An early stage (I) is characterized by colloform textures, documented by spherical, cockadelike or garland-shaped, mononfineralic or polymineralic aggregates of tennanrite I, enargite I, pyrite I, chalcopyrite I, bornite I and digenite I. (ii) During a subsequent stage of recrystallizarion (II), the colloform textures were overgrown by, or enclosed in, anhedral grains of tennantite II, enargite II, bomite II, digenite II, pyrite II and chalcopyrite II. Minimum temperatures of about 175°C for this stage can be estimated from the bulk composition of fine-grained to submicroscopic digenite-bornite intergrowths, exsolved from an initial la solid solution with up to 55 mole % of bornite. Conversely, tbe assemblage pyrite + chalcopyrite + tennantite provides an uppermost temperature limit of ∼440°C [at an a(S2) = 10-5]. (iii) A late stage of alterarion (III) led to the replacement of the primary sulfides by yarrowite, spionkopite and rare covellite, together with goethite, under decreasing temperatures and rising acrivity of sulfur. The close sparial association of the Sommerkahl vein-type Cu deposit with the overlying Kupferschiefer suggests that this metal-rich bituminous shale played an important role in the formation of the ore veins. Sulfur isotope analyses yielded negative δ34S of-12.8 to -23.9%o, which indicate that the sulfur was derived from the overlying Kupferschiefer, presumably by hydrothermal leaching. Such a low-temperature mobilization could also be discussed for all or part of the metals forming the Wilhelmine ore, wbich later on recrystallized in response to hydrothermal acrivity (modified hydrothermal model). However, we prefer a strictly hydrothermal model, according to which all or most of the metals were derived from deep-seated sources, transported upward by hydrothermal fluids, and precipitated by thermochemical reduction of sulfate due to interaction with the sulfur-bearing organic matter and the pyrite of the Kupferschiefer. Formation of the sulfide ore veins in the former Wilhelmine mine is related to post-Variscan hydrothermal activity that affected the Spessart area in Middle Jurassic to late Early Cretaceous time.

KW - Anilite

KW - Bornite

KW - Digenite

KW - Germany

KW - Hydrothermal activity

KW - Kupferschiefer

KW - Spessart

KW - Spionkopite

KW - Sulfur isotopes

KW - Tennantite

KW - Thermochemical sulfate reduction

KW - Vein-type Cu mineralization

KW - Yarrowite

UR - http://www.scopus.com/inward/record.url?scp=35748947783&partnerID=8YFLogxK

U2 - 10.2113/gscanmin.45.4.723

DO - 10.2113/gscanmin.45.4.723

M3 - Article

AN - SCOPUS:35748947783

VL - 45

SP - 723

EP - 750

JO - Canadian Mineralogist

JF - Canadian Mineralogist

SN - 0008-4476

IS - 4

ER -