A RECENTLY DISCOVERED TRACHYTE-HOSTED RARE EARTH ELEMENT-NIOBIUM-ZIRCONIUM OCCURRENCE IN NORTHERN MAINE, USA

Abstract Reported here are geological, geophysical, mineralogical, and geochemical data on a previously unknown trachyte-hosted rare earth element (REE)-Nb-Zr occurrence at Pennington Mountain in northern Maine, USA. This was newly discovered by regional multiparameter, airborne radiometric survey that revealed anomalously high equivalent Th (eTh) U (eU), confirmed detailed ground portable X-Ray fluorescence (pXRF) whole-rock analyses of representative rock samples. The mineralized area occurs within an elongate trachyte body (~1.2 km2) intrudes Ordovician volcanic rocks. Geologic constraints suggest the is also age. eastern lobe (~900 × ~400 m) pervasively brecciated with matrix containing seams, lenses, veinlets composed mainly potassium feldspar, albite, fine-grained zircon monazite. Barite locally abundant. Minor minerals include columbite, bastnäsite, euxenite, chlorite, pyrite, sphalerite, magnetite. pXRF 22 samples (App. Table A1) collected from demonstrate this entire part highly mineralized. Whole-rock for document average contents Zr (1.17 wt %), Nb (1,656 ppm), Ba (3,132 Y (1,140 Hf (324 Ta (122 (124 (36.5 Zn (689 Sn (106 ppm). Among light REE, highest concentrations shown La (763 ppm) Ce (1,479 For heavy REE (HREE), Dy Er most abundant (167 114 ppm, respectively). No HREE-rich such as xenotime have been identified; HREE may reside chiefly monazite zircon. Very strong positive correlations (R2) 0.92 to 0.98 exist between Zr, Nb, Y, Ce, Yb, Sn, indicating eTh valid proxies these metals Trachyte-hosted REE-Nb-Zr deposits like known Australia south Qinling belt Central China. Based comparisons deposits, lack geologic mapping region, we other rare-metal occurrences contained elsewhere more widely Appalachian-Caledonian orogen where subvolcanic trachytes recognized.