REE-composition on pegmatitic feldsaprs and muscovites from Maz¨¢n range, Northwestern Argentina

SARDI, F., BAEZ, M. Y LOZANO FERNANDEZ, R.

Heidelberg, Alemania

Congreso; 22nd LAK (LateiAmerika Kolloquium); 2011

Four K-feldspars (KF), two Na-feldspars (NF) and two muscovites (Ms) of pegmatites from Maz¨¢n range, Argentina, were analyzed for REE using ICP-MS methodology. The Maz¨¢n peraluminous Granite of Ordovician age with S-type affinity is the host-rock of the pegmatites. These have a simple zoning with aplite on the border, following towards the center of the bodies an intermediate zone composed of feldspars and finally a quartz-core. They have andalusite as accessory mineral, but rare-elements minerals (like Be and Li) had not been found so far. The ¦²REE is variable on the analyzed minerals, being between 0.71 y 3.34 ppm on KF, 4.91 and 6.40 ppm on NF, and 7.05 and 14.7 ppm on Ms. The gradient of the chrondrite-normalized pattern on these minerals is markedly positive, with Lan/Ybn values of 6.35 to 22.07 on KF, 14.88 and 41.79 on NF, and 6.74 and 7.36 on Ms. Both ¦²REE and Lan/Ybn values are greement with the same minerals from pegmatites from other places. However, the Eu-anomaly on NK and Ms is negative being the Eu/Eu* values lesser than 1 (0.12 and 0.14, and 0.41 and 0.53, respectively). On KF, it is very variable due to on two samples of them, the result is negative (Eu/Eu* 0.31 and 0.68), but the other two samples is positive (Eu/Eu* 2.51 and 11.43). The mineral samples are from different pegmatites of Maz¨¢n range or different sectors of the intermediate zone of the same pegmatite. For this reason, the different Eu/Eu* values is attributed to the variability on the chemical conditions (especially the fO2) in the pegmatite generating-melting. from Maz¨¢n range, Argentina, were analyzed for REE using ICP-MS methodology. The Maz¨¢n peraluminous Granite of Ordovician age with S-type affinity is the host-rock of the pegmatites. These have a simple zoning with aplite on the border, following towards the center of the bodies an intermediate zone composed of feldspars and finally a quartz-core. They have andalusite as accessory mineral, but rare-elements minerals (like Be and Li) had not been found so far. The ¦²REE is variable on the analyzed minerals, being between 0.71 y 3.34 ppm on KF, 4.91 and 6.40 ppm on NF, and 7.05 and 14.7 ppm on Ms. The gradient of the chrondrite-normalized pattern on these minerals is markedly positive, with Lan/Ybn values of 6.35 to 22.07 on KF, 14.88 and 41.79 on NF, and 6.74 and 7.36 on Ms. Both ¦²REE and Lan/Ybn values are greement with the same minerals from pegmatites from other places. However, the Eu-anomaly on NK and Ms is negative being the Eu/Eu* values lesser than 1 (0.12 and 0.14, and 0.41 and 0.53, respectively). On KF, it is very variable due to on two samples of them, the result is negative (Eu/Eu* 0.31 and 0.68), but the other two samples is positive (Eu/Eu* 2.51 and 11.43). The mineral samples are from different pegmatites of Maz¨¢n range or different sectors of the intermediate zone of the same pegmatite. For this reason, the different Eu/Eu* values is attributed to the variability on the chemical conditions (especially the fO2) in the pegmatite generating-melting.