VOLTAITA Y METAVOLTINA DE MINA SANTA BARBARA, JUJUY Y MINA CAPILLITAS, CATAMARCA

GALLISKI M. A. LOMNICZI DE UPTON I. Y MÁRQUEZ-ZAVALÍA M. F.

Revista de la Asociación Argentina de Mineralogía, Petrología y Sedimentología

Lugar: Buenos Aires; Año: 1990 vol. 21 p. 1 - 6

0325-0253

Voltaite and metavoltine from Santa Bárbara and Capillitas minesThe first metavoltine and the second voltaite occurrences in the Argentina Republic are described The minerals werefound in Santa Bárbara mine, Jujuy province and Capillitas mine, Catamarca province. Santa Bárbara mine (23° 50' 40"lat. S and 64° 25' 25" long. W) is a sulphur deposit formad by actual thermal springs, contained in calcareous sandstonesand limestones. The principal minerals are sulphur and gypsum, and several Al, Mg and mainly K or Na and Fe sulphatesare associated to these.The following minerals were identified: hexahydrite, alunogen, sideronatrite, ferrinatrite, krausite, halotrichite andgoldichite.Voltaite occurs around two fumaroles associated to alunogen, halotrichite and scarce krausite, as clusters of crystals.These are C 1 mm and have {103} and {110} its colour varias between greenish gray and shining black, H = 3 andresinous luster. Under microscope it is transparent, almost colourless to greenish gray, isotropic with n 1.595 (3) orwith slightly anisotropic, bxa (—) sectors. its composition is SO3 = 51.29; Al203 = 5.80; Fe 203 = 10.16; Fe0 =7.11;MgO = 4.32; Na20 = 1.05; K 2 0 = 5.28; H 2 O = 15.04 which yields: (K,Na)2.84 (Mg, Fe 2+)41A1, Fe 31.14.6815041i2.4s •16.22 H20. The strongest X-ray diffraction lines are: 3.40 (100); 3.54 175); 5.54 (60) and the calculated cell is a0= 27.12 A.Metavoltine crystals are laminar and hexagonal, intimately associated to goldichite and ferrinatrite. Its colour is saffron yellow when in powdery dusters. and orange-brown in individual cristals. H = 2-2.5, luster resinous and perfect #{0001} . It is transparent, pleochroic, with O = brown and E = light yellow; un iaxic 1—) with E = 1.576 (3); CO=1.58713).Its analysis yielded: SO3 = 44.50; Fe203 = 21.68; Na20 = 8.50; K 2 0 = 8.32; H 2 O = 17.21 and its formula is K3.69Na5.73 Fe 5.67 3. (SO4 ) 11.61 0 1.6 . 19.95 H2O. The strongest lines in its X-ray diffraction pattern are: 9.01 (100); 3.045(90B); 17.6(80); and its unit cell parameters a0 = 9.63 and co = 18.00 A.Capillitas mine (27° 27' lat. S and 66° 30' long. W) is a subvolcanic polimetallic deposit of miocene age. Voltaite isvery scarce and only in Bordon vein was found, associated with other secondary sulphates: gypsum, halotrichite, melanterite,goslarite, ferricopiapite and metavoltine. It is dark oliva green to almost black with vitreous to resinous luster andconchoidal fracture. Under microscope it is transparent, oliva green and isotropic, with n = 1.59413). Metavoltine occursin Bordon, Capillitas, La Argentina and Nueve veins in scarce, rounded aggregates, that are powdery to granular andformed by C 20 /En mustard yellow crystals. It is transparent, pleochroic with X almost colour less, very light yellow,Y x Z = yellow; it is anomalously biaxic (—) with a very small 2V (2-4x) and a = 1.575; Q ter=1.583.The voltaite and metavoltine of Santa Bárbara mine are of fumarolic origin, while the same minerals from Capillitasmine are the alteration product of pyrite by acid waters in subaereal conditions.