Albitization and redistribution of REE and Y in IOCG systems: Insights from Moonta-Wallaroo, Yorke Peninsula, South Australia

摘要: Abstract Trace element concentrations, particularly rare earth elements and yttrium (REY) in feldspars accessory minerals, have been determined a suite of albitized igneous, metasedimentary metasomatite rocks from the Moonta-Wallaroo district, Olympic Cu–Au Province, South Australia. Results show that changes REY-fractionation trends concentrations common accessories are associated with key textures albite-bearing associations different lithologies. In granitic rocks, pseudomorphic replacement pre-existing is typified by porous albite cleavage-oriented intergrowths sericite pore-attached hematite. These observations comparable albitization features terranes elsewhere. A mineral association (albite-sericite ± chlorite), similar to granitoids, observed as pervasive spots limestone, inferring prograde skarnoid reactions at low fluid/rock ratio an impure carbonate. Na2O content (~ 5–6 wt.%), fine-grained granoblastic suggests growth under high ratios irrespective lithology. such cases, highest REY (ΣREY ~ 200 ppm) accounts for entire budget, e.g., albite–biotite-schist lowest abundance minerals. Nanoscale investigation confirms this be carrier (elements incorporated within crystal lattice); no inclusions observed. contrast, REY-concentration (~ 14 ppm) encountered metasomatite. recording ΣREY (~ 1000 ppm) whole-rock, partitioning favoured among abundant (titanite, apatite) calc-silicates (actinolite, clinozoisite) rather than albite. Comparable low-REY also found granitoid-derived albitite (Na2O ~ 5 wt.%), which discrete REY-minerals formed during account (~ 700 ppm) whole rock. The role coupled dissolution–reprecipitation (CDRR) critical (re)distribution igneous where REY-release early magmatic and/or assists REY-enrichment into late presence nanopore-attached plagioclase demonstrates nanoscale nature CDRR-driven consistent published experimental work on altered granites. Such porosity offers sites entrapment seen new-formed K-feldspar. Similarly, release uptake REY, concurrent albitization, formation coarser (xenotime, bastnasite, synchysite) Fe–Ti-oxides symplectites chlorite Based differences identified between pathways we discuss how proceeds via series complex fluid–mineral reactions, each involving redistribution, accumulation retention REY. defining endowment deportment undergone sodic alteration. Contrary previous models, appears controlled pH redox conditions. Despite regional local geological environment alteration style across initiation hydrothermal alteration, pre-requisite stage Iron-Oxide–Copper–Gold (IOCG) systems. distribution patterns may thus value exploration criteria enabling mineralization distinguished background. Strong without superposition later potassic not, however, automatically linked giant IOCG deposits. Albitization enhances rock permeability strongly faulted structural suitable trap, fluids more readily lost system.