Lithostratigraphy and alteration at the Rävliden North VMS deposit, Skellefte district, Sweden

• Main Author: Simán, Filip
• Format: Master Thesis
• Language: English
• Published: LuleÃ¥ tekniska universitet, Geovetenskap och miljöteknik 2024
• Subjects: Geology; Geologi; Northern Sweden
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-103843

Technological and societal developments in the past century have greatly increased our society’s demand for metals, many which occur in polymetallic ores mined in the Skellefte district, northern Sweden. Near-surface deposits are becoming depleted and as such targeting of deep deposits is needed, which places special demand on effective management, processing and interpretation of geological data obtained from exploration drill holes. New exploration tools and software solutions utilizing machine learning to assist data analysis are becoming increasingly important. However, to get the most of these new tools, a solid geological understanding of prospective areas must first be established. This thesis uses the Rävliden North Zn-Pb-Ag-Cu volcanic massive sulphide (VMS) deposit as a study location to understand its lithostratigraphy and enveloping alteration. The Skellefte district VMS deposits are mainly located at the lithostratigraphic contact between the metavolcanic 1.89 – 1.88 Ga Skellefte group (SG) and the stratigraphically overlying metasiliciclastic 1.89 – 1.87 Ga Vargfors group (VG) rocks. The VMS deposits are commonly enveloped by a zoned alteration with variable alteration intensity and mineral assemblages of quartz, sericite, chlorite and talc at different distance to mineralisation. Sixteen lithofacies and eight precursors can be defined in the Rävliden North host succession, where the SG dominantly contains coherent and volcaniclastic facies of rhyolite, dacite and andesite. The VG contains graphitic phyllite interbedded with polymict breccia-conglomerates, andesitic turbidites and mafic mass-flow deposits. Immobile element lithogeochemistry reveals four rhyolitic (Rhy I – IV), two dacitic (Dac I and II), an andesitic (And I), and a basaltic (Bas I) precursors. The VMS deposits are hosted by graphitic phyllite Tr-rich calc-silicate rock, and a Chl>Ser±Tlc±Qz-altered rock in the contact between the SG and VG. Four alteration types are recognised and spatially associated to mass ...