02548nas a2200253   4500008004100000245016300041210006900204260001600273300000700289490000600296520173400302653002502036653001602061653001702077653001302094100001602107700002202123700002402145700002602169700002202195700001802217700001802235856004102253       2019                        eng d00aAge and Origin of Monazite Symplectite in an Iron Oxide-Apatite Deposit in the Adirondack Mountains, New York, USA: Implications for Tracking Fluid Conditions0 aAge and Origin of Monazite Symplectite in an Iron OxideApatite D  cJan-21-2019  a650 v93 a<p>Monazite crystals, intergrown with allanite, fluorapatite, and quartz from the Cheever Mine iron oxide-apatite (IOA-type) deposit in Essex County, New York, USA, display rare symplectite textures. Electron probe wavelength-dispersive spectrometry (WDS) mapping and major and trace element characterization of these features reveal a natural experiment in fluid-mediated monazite recrystallization. Two types of monazite with symplectite intergrowths have been recognized (Type I and II). Both types of symplectite development are associated with a decrease in HREE, Si, Ca, Th, and Y, but an increase in both La and Ce in monazite. Electron microprobe Th-U-total Pb analysis of Type I monazite with suitable ThO2 concentrations yielded a weighted mean age of 980  5.8 Ma (MSWD: 3.3), which is interpreted as the age of monazite formation and the onset of symplectite development. Both types of monazite formed during a series of reactions from fluorapatite, and possibly britholite, to produce the final assemblage of monazite, allanite, and fluorapatite. Monazite formation was likely a response to evolving fluid conditions, which favored monazite stability over fluorapatite at ca. 980 Ma, possibly a NaCl brine. A subsequent transition to a Ca-dominated fluid may have then promoted the consumption of monazite to produce another generation of allanite and fluorapatite. Our results indicate that recrystallized monazite formed during fluid-mediated processes that, over time, trended towards an increasingly pure end-member composition. Regionally, these data are consistent with a magmatic-origin followed by fluid-mediated remobilization of select phases at subsolidus conditions for the Adirondack IOA deposits.</p>
10aAdirondack Mountains10aIOA-deposit10ametasomatism10amonazite1 aRegan, Sean1 aLupulescu, M., V.1 aJercinovic, Michael1 aChiarenzelli, Jeffrey1 aWilliams, Michael1 aSinger, Jared1 aBailey, David  uhttp://www.mdpi.com/2075-163X/9/1/65