The origin of pyrite mineralization: Implications for Late Cambrian geology of the Holy Cross Mountains (south-central Poland)

Abstract

This paper presents results of a petrographic, mineralogical and geochemical study of ore, gangue and rock-forming minerals that occur within the Upper Cambrian (Furongian)-age siliciclastic rocks of the Wiśniówka massif (western part of the Main Range, Holy Cross Mountains, south-central Poland). This area is characterized by the presence of ubiquitous pyrite that makes up two stratiform mineralization zones assigned to the early and middle Late Cambrian, giving rise to acid mine drainage. The oldest zone comprises additionally sedimentary breccias with intraclast-supported pyrite cement. The predominant microscopic (colloform) and partly framboidal pyrite typically shows high concentrations of As (up to 8.23 wt%) and a distinct enrichment in the light sulfur isotope (δ34S from −41.4 to −23.6‰). The occurrences of large amounts of As-rich pyrite showing strongly negative δ34S values are rather uncommon in Paleozoic sedimentary formations worldwide that exhibit distinctly smaller amounts of As and mostly enrichments in heavier sulfur isotope (δ34S up to 63‰). Another specific feature of the Wiśniówka rock series is the presence of REE-bearing aluminophosphate and phosphate minerals that occur primarily in clayey-silty shales and bentonites. Based on the results obtained, a sequence of hydrothermal index minerals was discriminated, including pyrite (whose grains are usually made of alternating arsenic-rich and arsenic-poor bands), as well as paragenetic assemblages of dickite, nacrite, xenotime and the crandallite series of aluminum-phosphate-sulfate minerals. Both mineral composition and specific microtextures are indicative of multistage hydrothermal activity that took place in the Wiśniówka depositional basin during the Late Cambrian time. This is in distinct contrast to the remaining part of the Main Range, which is devoid of the hydrothermal pyrite imprint. Moreover, the results of this study give insight into the complex sedimentary and early diagenetic history of the southwestern passive margin of the Baltica craton. This currently makes up a part of the Łysogóry Block (Terrane) that borders on the Trans-European Suture Zone separating the Precambrian East-European Craton from the Paleozoic Platform of Central Europe. This study is important because we still lack the full knowledge about the hydrothermal processes that took place in Early Paleozoic depositional basins.