The Skaergaard PGE and Gold Deposit: the Result of in situ Fractionation, Sulphide Saturation, and Magma Chamber-scale Precious Metal Redistribution by Immiscible Fe-rich Melt

• Published in: Journal of Petrology
• Main Authors: Nielsen, TFD, Andersen, Jens, Holness, MB, Keiding, JK, Rudashevsky, NS, Rudashevsky, VN, Salmonsen, LP, Tegner, C, Veksler, IV
• Format: Article in Journal/Newspaper
• Language: English
• Published: Oxford University Press 2015
• Subjects: Greenland
• Online Access: http://hdl.handle.net/10871/18921; https://doi.org/10.1093/petrology/egv049

This is a pre-copyedited, author-produced PDF of an article accepted for publication in the Journal of Petrology following peer review. The version of record is available online at: http://petrology.oxfordjournals.org/content/56/8/1643.abstract. The Skaergaard intrusion, Greenland, is the type locality for Skaergaard-type mineralizations. Mineralization levels are perfectly concordant with igneous layering, up to 5 m thick, internally fractionated, and contain crystallized sulphide droplets and precious metal alloys, sulphides, arsenides and telluride. Immiscible Cu-rich sulphide droplets, formed in a mush zone below the roof, scavenged precious metals. They were subsequently dissolved and transported to the floor in late-formed, immiscible, Fe-rich mush melts. Mineralized stratigraphic intervals of floor gabbro formed in ‘proto-macrolayers‘, owing to local sulphide saturation in melt concentrated between floating plagioclase and sinking clinopyroxene. The floor mineralization is divided into four stratigraphic sections. Formation of the Lower Platinum Group Element Mineralization (LPGEM) involved: (1) crystallization of the bulk liquid liquidus paragenesis and in situ fractionation; (2) sulphide saturation and formation of sulphide droplets in melt in the upper part of ‘proto-macrolayers‘. After further in situ fractionation, the following steps occurred: (3) the onset of silicate–silicate immiscibility and the consequent loss of buoyant and immiscible Si-rich melt; (4) dissolution of unprotected droplets of sulphide melt present in the Fe-rich mush melt; (5) compaction-driven upwards loss of residual mush melt enriched in, for example, Au. The LPGEM preserves upward increasing bulk Pd/Pt (∼6–13) owing to a continued supply of PGE and Au, with high Pd/Pt. The further development of the LPGEM ceased as the supply of precious metals to the floor waned. The Upper PGE Mineralization (UPGEM) subsequently formed from precious metals recycled in the floor. The UPGEM is characterized by increasing Au substitution in ...