A geochemical study of Paleozoic alkaline magmatism in the Selwyn Basin and the potential relationship to Zn-Pb mineralization

• Main Author: Scanlan, Emma
• Other Authors: Geological Sciences and Geological Engineering, Leybourne, Matthew, Layton-Matthews, Daniel
• Format: Thesis
• Language: English
• Published: 2022
• Subjects: igneous petrology; geochemistry; geology; isotope geochemistry; sediment-hosted mineralization; economic geology; Yukon; Canada; Selwyn; Anvil; Keno Hill; Macmillan Pass; Misty Creek; Ocean Island
• Online Access: http://hdl.handle.net/1974/31324

The Selwyn Basin in the Yukon, Canada, has several occurrences of Paleozoic alkaline volcanic rocks that are spatially and temporally associated with Zn-Pb deposits. The volcanics are represented by ocean island basalt (MacMillan Pass, Misty Creek Embayment), enriched mid ocean ridge basalt (Keno Hill) and transitional basalts (Anvil District). The OIB signature indicates the MacMillan Pass and Misty Creek Embayment magmas were derived from small partial melts of an enriched lithospheric mantle during small, shallow, degrees of melting. An increased amount of extension resulted in upwelling of the asthenosphere that was sampled during melting of the transitional basalts in the Anvil District. Strontium isotopes of the Selwyn Basin volcanic rocks show evidence for interaction with Paleozoic seawater and several samples display highly radiogenic 87Sr/86Sr values due to crustal contamination. The volcanic rocks have low 143Nd/144Nd values and are representative of the source region. Mixing occurred between a highly radiogenic and less radiogenic Pb source. The Keno Hill samples plot near MORB values. The isotopes for both MacMillan Pass and Anvil volcanics plot between EMII-like and HIMU-like mantle end members, suggesting melting of a heterogenous lithospheric mantle with two end members; an enriched reservoir (low Nd, average Pb, high Sr) and a highly radiogenic Pb reservoir (high Pb, average Nd, low Sr). A depleted mantle source may be contributing to the Keno Hill samples. Thallium isotopes of the volcanic rocks have negative values that decrease with increasing degree of alteration. The MacMillan Pass samples have the smallest ɛ205Tl compositions while the Anvil samples overlap with OIB and MORB values and the measured ɛ205Tl range of mineralized rocks from Anniv East at Howard’s Pass. Ratios of certain trace elements (Tl, Ba, In, Ag) of host rocks for mineralization at Howard’s Pass and MacMillan Pass trend towards the values of Selwyn volcanic rocks. Mineralized samples plot at the overlap between their host ...