Paragenesis and origin of staurolite from a palladium-rich gabbronorite: an unusual occurrence from the Lukkulaisvaara layered intrusion, Russian Karelia
Barkov, Andrei Y.; Martin, R. F.; Laajoki, K. V. O.; Alapieti, T. T.; Iljina, M. J.
published: Dec 1, 1999
ArtNo. ESP154017502004, Price: 29.00 €
Microcrystalline staurolite and other highly aluminous secondary minerals (Cl-rich pargasitic amphiboles, almandine, epidote, chlorite, Zn-rich hercynite, phlogopite, corundum, Al2SiO5 and AlO (OH) phases) occur in altered coarse-grained gabbronorite (ACGG) that is associated with a sill-like body of microgabbronorite within the layered series of the Early Proterozoic Lukkulaisvaara intrusion, Russian Karelia. The ACGG and a related plagioclase-bearing pyroxenite contain various basemetal sulphides (BMS) and platinum-group minerals (PGM). The magmatic texture and relics of primary minerals are preserved in the staurolite-bearing rock. The composition of primary minerals in the ACGG is indistinguishable from that in the pristine host microgabbronorite, and indicates the existence of a close relationship between these rocks. Textural data imply that the Al-rich assemblage largely formed at the expense of the plagioclase. The content of chlorine of the Al-rich amphiboles in the ACGG is unusually high (up to 4.5 wt. % Cl), including the amphibole closely associated with the PGM. Inclusions of phlogopite in chalcopyrite also are Cl-rich (up to 1.1 wt. % Cl). Thus, Cl was prominent in the fluid causing the alteration. The ACGG formed by crystallisation of isolated volumes of H2O-saturated melt, in situ, during solidification of the microgabbronorite. The Al-rich amphibole-garnet-staurolite assemblage appears to have formed in the range 560 to 670 °C at a deuteric stage. Ultimate loss of the fluid phase, which had dissolved the original minerals incongruently, shifted the bulk composition of the gabbronorite to a corundum-bearing assemblage on the scale of tens of centimetres. Textural evidence shows that both the BMS and PGM were mobile during the alteration event; their mobility was rather restricted, however, in spite of an elevated Cl concentration in the fluid phase.
staurolite • aluminium-rich minerals • chlorine-rich minerals • platinum-group minerals • platinum-group elements • mobility • alteration • layered intrusion • Lukkulaisvaara • Russian Karelia • Fennoscandian Shield