The association qingheiite-beusite-lithiophilite in the Santa Ana pegmatite, San Luis, Argentina

GALLISKI M. A. CERNÝ P. OYARZÁBAL J. CHAPMAN R. Y MÁRQUEZ-ZAVALÍA M. F.

Universidad de Buenos Aires

Congreso; 6º Congreso de Mineralogía y Metalogenia; 2002

Qingheiite, the Mg end-member of the wyllieite family of primary peginatitic phosphates, with aformula Na2 Na Mn2 Mg2 (AI,Fe), (PO4)6 and known so far froin only the typc locality, was discovcred in anew occurrencc and association. It occurs in Santa Ana mine (32° 53´ 32" S y 65° 55´ 43" W) in a beryl typc,beryl-columbite-phosphate subtype of rare-element pegmatite. Qingheiite occurs as :50.5-cm thick irregulargranular veinlets or patches of deep jade-green color, úi a nodule of beusite interlaminated with Iithiophilite.The average of four chemical analysis gives PO 4 45.19, Al203 5.17, Mn0 24.27, FeO 10.05, MgO 6.13,ZnO 0.18, Ca0 0.51, Sr0 0.02, BaO 0.02, Na20 9.22, K20 0.02, F 0.05, C1 . 0.01, total 100.84. Assuming thesarne Fe31 /Fe2´, ratio and partition of cations ás in the type specimen, the formula obtained gives (Na l :7o ~0.226K0.004 SI0.002 ga0.001)).2.0(N) Na (IvInn.9<liCa 0.085 Na0.014) E1.000 (141.423 Fe0.277M110,300) E2.000 (A10 .9.49 Fe3f.0.474 Zn0.021Fe24 0.556) Ez.000 (PO4)5.952. Least-squa res refinement of X-ray powder-diffraction data of qingheiite gives10.900(2), h 12.420(3), c 6.433(1) A, fi 97.97 (2)°, V = 862.52(2) A 3 . The p ost beusite has the forniula(Mn i.733 Feo.660 Ca0.412 Mgo.123) 5.2.928 (PO4)2.012 and a 8.790(3), b 11.475(2), c 6.156(2) A, f3 99.11 (2)°, V=613.11(2) A 3 . Lithiophilite composition is Li (Mno. s ii Fe2+ 0., 99Mgo.171) E0,981 (P0,4) 1.003 and a 6.063(2), h10.324(6), c 4.712(2) A, V= 294.94 A3.The Santa Ana paragenesis is unusual and hybtid arnong the primary phosphate associationsrecognized by Moore and Molin Case (1974) in pegrnatit(s where P and transition metals are available. Ingeneral, triphylite-lithiophilite series tend to predominate :n Li-rich pegmatites, wyllieite and dickinsonitearrojaditeseries are dominant in Na-rich pegmatites, and graftonite-beusite and sarcopside prevail in Ca-richpegmatites.ReferenccsMoorc P.B. Molin Case J. A., 1974. Contribution to pegmatite phosphatc giant crystal paragcnesis: 11. The crystalchemistry of wyllicitc, Na 2Fc3-´ 2A1 (PO4)3, a primary phasc. Ame´, Miner. 59.3-4: 280-290.157