Miguel Galliski - Academia.edu (original) (raw)
Papers by Miguel Galliski
Mineralogical Magazine, Jan 19, 2023
This is a 'preproof' accepted article for Mineralogical Magazine. This version may be subject to ... more This is a 'preproof' accepted article for Mineralogical Magazine. This version may be subject to change during the production process.
Canadian Mineralogist, Oct 1, 1995
The fust find of goldichite in Argentina and the third worldwide occurrence is described. The min... more The fust find of goldichite in Argentina and the third worldwide occurrence is described. The mineral was found in a sulfur deposit, the Santa Birbara mine, in iujuy province, formed by present-day activity of thermal springs. The Tioeral occurs with metavoltine, hexahydrite, alunogen, sideronatrite, feninatrite, voltaite, kausite, halotrichite, gypsum and halite. The goldichite @curs as euhedral flattened "ryitats O.:-in lenglh, tabular on { 100}, with t 100}, { 110} and {011} crystallographic forms. The strongest five X-ray powder-diffraction hnJs ld in A(t)(hkt)l are: 10.11(70)(100), 5.11(40X200), 3.072(100)Q02), 2.444A0\h30\. and 2.283i30\e33). The refined unir-cell parameters 6f 1[is 6sn6rslinic mineral arc a 10.397Q), b 10.461(8), c g.tog<qj A, $ rOO.Ootll;, V 972.5(8) A,3. The crystals are transparent, brittle, and have a greenish hue in naturallight and a pale pink'tint onOer uttinaa nght; Orey have a hardness of 2-3, n excellent { 100} cleavage, vitreous luster and white streak. OptiJuUV, goldichite is traasparint, wiih positive elongation, with X colorless, I colorless to very pale yellow, anjlZ very pale y"no*: i j v > x:biaxial (+), 2vbd.\75;,cl 1.584(2), F 1.602Q),y 1,.634Q),X = b, Y'a, Z lt c 9o, v > r, sfong' The chemical composition, obtained by electrotil-microprobe analysii, indicates S, Fe and K as the principal compon€nts, wrJLthe^following ranges in concentration of the oxidei (w.%o):
Canadian Mineralogist, Jul 1, 2016
The syenite pegmatitic segregation veins (SPSV) of the Early Miocene La Peña alkaline complex (LP... more The syenite pegmatitic segregation veins (SPSV) of the Early Miocene La Peña alkaline complex (LPC), Mendoza, Argentina, are emplaced in a malignite body. They occur as veins, parallel layers, and small elliptical bodies 1 to 6 cm wide and 0.2 to 1 m in length. The veins with a pegmatitic to micropegmatitic texture have a thin dark border composed of andradite, potassic-hastingsite, and dark micas and a thicker internal zone of poikilitic Ba-Sr-poor K-feldspar (Or 90.3 Ab 8.9 An 0.8), nepheline (Ne 74.9 Ks 19.4 Qz 5.7 to Ne 78.7 Ks 20.0 Qz 1.3), potassic-hastingsite, dark mica, andradite, scarce clinopyroxene (diopsidehedenbergite), and locally zoned microphenocrysts of Ba-Sr-rich K-feldspar (Or 75.6 Ab 21.7 An 2.7). Accessory fluorapatite, titanite, interstitial sodalite, and magnetite and secondary abundant Na-and K-rich zeolites, calcite, chlorite-group minerals, and possibly cancrinite have been identified. The textural and mineralogical characteristics of the SPSV show genetic links with the host malignite that belongs to the potassic alkaline series. The SPSV were formed from a residual syenitic melt (malignite) extracted from a parental tephritic magma. In the residual malignite, the concentration of primary crystals (apatite, clinopyroxene, Ba-Sr-rich K-feldspar, and nepheline) formed a crystal network (mush) with the open spaces occupied by small amounts of residual melt enriched in Al, Na, K, and volatiles and depleted in Ba and Sr. Deformation (by shear movements plus magmatic pressures) produced microfractures and fractures which were occupied by residual interstitial melt. In situ crystallization within these fractures resulted in the formation of the SPSV.
Revista de la Asociación Geológica Argentina, Jun 1, 2007
Angelelli 1984), agrupa un conjunto de yacimientos con una metalogénesis predominante de Cu-Au, v... more Angelelli 1984), agrupa un conjunto de yacimientos con una metalogénesis predominante de Cu-Au, vinculados genéticamente con un complejo volcánico-intrusivo de edad miocena superior y naturaleza calcoal
Canadian Mineralogist, Dec 1, 2014
Ishiharaite is a new sulfide mineral, (Cu,Ga,Fe,In,Zn)S, discovered at the Nueva Esperanza vein, ... more Ishiharaite is a new sulfide mineral, (Cu,Ga,Fe,In,Zn)S, discovered at the Nueva Esperanza vein, Capillitas mine (27º20´43″ S, 66º23´17″ W, 3290 m osl) an epithermal ore deposit belonging to the Farallón Negro Mining District, northwestern Argentina. The mineral occurs as subhedral, equidimensional, individual grains (20 to 50 μm in size) included in tennantite. It is a dark gray metallic mineral, opaque and non-fluorescent. Under polarizing-reflected light, it is an isotropic mineral, and its color is burgundy brown with a faint violet hue in air and violet-burgundy in oil.
Canadian Mineralogist, Feb 1, 2010
Canadian Mineralogist, Dec 1, 2012
ABSTRACT
Canadian Mineralogist, Jun 1, 2004
Journal of South American Earth Sciences, 1988
... Universidad Nacional de Tucu-m~n (Jujuy, Argentina), Instituto de Geologia y Mineria, Publica... more ... Universidad Nacional de Tucu-m~n (Jujuy, Argentina), Instituto de Geologia y Mineria, Publica-ci6n 474, 65 p. Barberi, F., Santacroce, R., and Varet, ,J. 1982. Chemical aspects of rift magmatism. ... Universi-dad Nacional (Jujuy, Argentina), Instituto de Geologia, in press. ...
Canadian Mineralogist, Sep 1, 2018
Canadian Mineralogist, Feb 1, 2010
Journal of South American Earth Sciences, Apr 1, 2016
The La Peña alkaline igneous complex (LPC) is located in the Precordillera (32 41 0 34 00 S-68 59... more The La Peña alkaline igneous complex (LPC) is located in the Precordillera (32 41 0 34 00 S-68 59 0 48 00 W) of Mendoza province, Argentina, above the southern boundary of the present-day flat-slab segment. It is a 19 km 2 and 5 km diameter subcircular massif emplaced during the Miocene (19 Ma) in the Silurian-Devonian Villavicencio Fm. The LPC is composed of several plutonic and subvolcanic intrusions represented by: a cumulate of clinopyroxenite intruded by mafic dikes and pegmatitic gabbroic dikes, isolated bodies of malignite, a central intrusive syenite that develops a wide magmatic breccia in the contact with clinopyroxenite, syenitic and trachytic porphyries, a system of radial and ring dikes of different compositions (trachyte, syenite, phonolite, alkaline lamprophyre, tephrite), and late mafic breccias. The main minerals that form the LPC, ordered according to their abundance, are: pyroxene (diopside, hedenbergite), calcium amphibole (pargasite, ferro-pargasite, potassic-ferro-pargasite, potassic-hastingsite, magnesio-hastingsite, hastingsite, potassic-ferro-ferri-sadanagaite), trioctahedral micas (annite-phlogopite series), plagioclase (bytownite to oligoclase), K-feldspar (sanidine and orthoclase), nepheline, sodalite, apatite group minerals (fluorapatite, hydroxylapatite), andradite, titanite, magnetite, spinel, ilmenite, and several CueFe sulfides. Late hydrothermal minerals are represented by zeolites (scolecite, thomsonite-Ca), epidote, calcite and chlorite. The trace element patterns, coupled with published data on Sr-Nd-Pb isotopes, suggest that the primary magma of the LPC was generated in an initially depleted but later enriched lithospheric mantle formed mainly by a metasomatized spinel lherzolite, and that this magmatism has a subduction-related signature. The trace elements pattern of these alkaline rocks is similar to other Miocene calc-alkaline occurrences from the magmatic arc of the Southern Central Andes. Mineral and whole-rock chemical compositions support the interpretation that a first batch of a tephritic magma produced a cumulate of clinopyroxenite (clinopyroxene þ magnetite þ apatite) and a residual melt that crystallized as malignite at a shallow emplacement level (<5 km). Fractional crystallization in a deep chamber, coupled with rock assimilation, produced successive magma pulses that gave the composite central syenite, the syenitic and trachitic porphyries, and trachytic dikes. The latest rocks (phonolites) reflect an extreme fractionation with Ca, Al and K removal by feldspars. Mingling relationships between tephrites-basanites and trachytes-phonolites, plus compositional variations linked to the reabsorption surface observed in the K-feldspar from the phonolitic dikes, suggest recharge events with local mixing in the late-stages of the LPC evolution.
Canadian Mineralogist, Aug 1, 2012
Petr Cerný certainly needs no introduction to the students and professional scientists who study ... more Petr Cerný certainly needs no introduction to the students and professional scientists who study granitic pegmatites. Cerný's prolific career of research on these rocks has spanned over forty years, with important contributions in the areas of 1) the mineralogy, geochemistry and petrology of
Chemical Geology, Dec 1, 2021
Canadian Mineralogist, Jul 1, 2016
Three samples of minerals belonging to the wyllieite mineral group were structurally investigated... more Three samples of minerals belonging to the wyllieite mineral group were structurally investigated: wyllieite from the Buranga pegmatite, Rwanda (A); wyllieite from the Malpensata pegmatite, Italy (B); and qingheiite from the Santa Ana pegmatite, Argentina (C). Their crystal structures were refined, based on single-crystal X-ray diffraction data, to R 1 ¼ 2.72% (A), 3.53% (B), and 2.46% (C). Unit-cell parameters are:
Canadian Mineralogist, Jun 1, 2002
The crystal structure of ushkovite, triclinic, a 5.3468(4), b 10.592(1), c 7.2251(7) Å, ␣ 108.278... more The crystal structure of ushkovite, triclinic, a 5.3468(4), b 10.592(1), c 7.2251(7) Å, ␣ 108.278(7),  111.739(7), ␥ 71.626(7)°, V 351.55(6) Å 3 , Z = 2, space group P1, has been refined to an R index of 2.3% for 1781 observed reflections measured with MoK␣ X-radiation. The crystal used to collect the X-ray-diffraction data was subsequently analyzed with an electron microprobe, to give the formula (Mg 0.97 Mn 2+ 0.01) (H 2 O) 4 [(Fe 3+ 1.99 Al 0.03) (PO 4) (OH) (H 2 O) 2 ] 2 (H 2 O) 2 , with the (OH) and (H 2 O) groups assigned from bond-valence analysis of the refined structure. Ushkovite is isostructural with laueite. Chains of corner-sharing {Fe 3+ O 2 (OH) 2 (H 2 O) 2 } octahedra extend along the c axis and are decorated by (PO 4) tetrahedra to form [Fe 3+ 2 O 4 (PO 4) 2 (OH) 2 (H 2 O) 2 ] chains. These chains link via sharing between octahedron and tetrahedron corners to form slabs of composition [Fe 3+ 2 (PO 4) 2 (OH) 2 (H 2 O) 2 ] that are linked by {Mg O 2 (H 2 O) 4 } octahedra.
Canadian Mineralogist, Sep 1, 2018
Journal of Geosciences, Apr 7, 2021
is a small selenide occurrence situated to the WNW of Jagüé, a small town of the General Sarmient... more is a small selenide occurrence situated to the WNW of Jagüé, a small town of the General Sarmiento department, La Rioja province, Argentina. This occurrence, also called El Chire in recent years, is located (28°35'46.10"S, 68°44'35.78"W, 3120 m. a. s. l.) in the Precordillera environment, to the furthermost southwestern corner of the selenium ore district of Los Llantenes, defined as one of the representative metallogenic belts of the Gondwanic episodes. The selenide minerals occur as veinlets up to few centimeters or as patches or fine inclusions, widespread in calcite. We have identified eleven hypogene Se-bearing minerals (naumannite, tiemannite, chrisstanleyite, jagüéite, eucairite, clausthalite, fischesserite, umangite, athabascaite, berzelianite and bellidoite) mainly associated with gold, silver, hematite and various supergene minerals, including malachite, chalcomenite, and molybdomenite. The paragenesis should have formed from low temperature (< 133 °C), neutral to mildly alkaline pH and highly oxidizing fluids with increasing sulfur fugacity. The country-rock, rich in graptolite-fauna, could be considered, at least in part, the source for the Se and associated metals forming the minerals of this paragenesis, although this hypothesis has yet to be tested.
Canadian Mineralogist, Nov 1, 2020
ABSTRACT We describe an unusual example of rhythmically layered peraluminous granitic pegmatite l... more ABSTRACT We describe an unusual example of rhythmically layered peraluminous granitic pegmatite locally developed in the intragranitic Potrerillos NYF pegmatites derived from the A-type host granites of the Las Chacras–Potrerillos batholith, Sierra de San Luis, Argentina. The strikingly rhythmic layers in the Zebra pegmatite consist of units of albite–K-feldspar–quartz–K-feldspar–albite, with accessory tourmaline and minor muscovite. The layers crystallized from a boron-bearing melt ponded and thermally insulated in the intermediate zone. A layer of low albite 1–2 cm thick was followed by coarser-grained K-feldspar, then well-ordered microcline, which gives way to quartz grains, also coarser-grained, in optical continuity. Zoned prismatic crystals of schorl nucleated in the feldspathic layer in random orientation. Muscovite is scarce. The rock has a granitic composition enriched in Rb, Cs, and B, and is depleted in the rare-earth elements compared to its precursor. We contend that the normative composition, 35.3% Or, 38.1% Ab, and 21.3% Q, was close to the eutectic in the granite system modified by dissolved H2O, F, and B, at a P(H2O) close to 3.5 kbar and a temperature in the range 575–600 °C. Repeated incursions from the field of Ab + Or to the field of quartz and back again as the melt was producing bubbles of H2O can account for the rhythmic crystallization and the local truncation or merging of the feldspathic layers. Occasional larger crystals of K-feldspar may have become detached from the wall or roof of the chamber.
Acta Crystallographica Section A, Aug 16, 2009
Mineralogical Magazine, Jan 19, 2023
This is a 'preproof' accepted article for Mineralogical Magazine. This version may be subject to ... more This is a 'preproof' accepted article for Mineralogical Magazine. This version may be subject to change during the production process.
Canadian Mineralogist, Oct 1, 1995
The fust find of goldichite in Argentina and the third worldwide occurrence is described. The min... more The fust find of goldichite in Argentina and the third worldwide occurrence is described. The mineral was found in a sulfur deposit, the Santa Birbara mine, in iujuy province, formed by present-day activity of thermal springs. The Tioeral occurs with metavoltine, hexahydrite, alunogen, sideronatrite, feninatrite, voltaite, kausite, halotrichite, gypsum and halite. The goldichite @curs as euhedral flattened "ryitats O.:-in lenglh, tabular on { 100}, with t 100}, { 110} and {011} crystallographic forms. The strongest five X-ray powder-diffraction hnJs ld in A(t)(hkt)l are: 10.11(70)(100), 5.11(40X200), 3.072(100)Q02), 2.444A0\h30\. and 2.283i30\e33). The refined unir-cell parameters 6f 1[is 6sn6rslinic mineral arc a 10.397Q), b 10.461(8), c g.tog<qj A, $ rOO.Ootll;, V 972.5(8) A,3. The crystals are transparent, brittle, and have a greenish hue in naturallight and a pale pink'tint onOer uttinaa nght; Orey have a hardness of 2-3, n excellent { 100} cleavage, vitreous luster and white streak. OptiJuUV, goldichite is traasparint, wiih positive elongation, with X colorless, I colorless to very pale yellow, anjlZ very pale y"no*: i j v > x:biaxial (+), 2vbd.\75;,cl 1.584(2), F 1.602Q),y 1,.634Q),X = b, Y'a, Z lt c 9o, v > r, sfong' The chemical composition, obtained by electrotil-microprobe analysii, indicates S, Fe and K as the principal compon€nts, wrJLthe^following ranges in concentration of the oxidei (w.%o):
Canadian Mineralogist, Jul 1, 2016
The syenite pegmatitic segregation veins (SPSV) of the Early Miocene La Peña alkaline complex (LP... more The syenite pegmatitic segregation veins (SPSV) of the Early Miocene La Peña alkaline complex (LPC), Mendoza, Argentina, are emplaced in a malignite body. They occur as veins, parallel layers, and small elliptical bodies 1 to 6 cm wide and 0.2 to 1 m in length. The veins with a pegmatitic to micropegmatitic texture have a thin dark border composed of andradite, potassic-hastingsite, and dark micas and a thicker internal zone of poikilitic Ba-Sr-poor K-feldspar (Or 90.3 Ab 8.9 An 0.8), nepheline (Ne 74.9 Ks 19.4 Qz 5.7 to Ne 78.7 Ks 20.0 Qz 1.3), potassic-hastingsite, dark mica, andradite, scarce clinopyroxene (diopsidehedenbergite), and locally zoned microphenocrysts of Ba-Sr-rich K-feldspar (Or 75.6 Ab 21.7 An 2.7). Accessory fluorapatite, titanite, interstitial sodalite, and magnetite and secondary abundant Na-and K-rich zeolites, calcite, chlorite-group minerals, and possibly cancrinite have been identified. The textural and mineralogical characteristics of the SPSV show genetic links with the host malignite that belongs to the potassic alkaline series. The SPSV were formed from a residual syenitic melt (malignite) extracted from a parental tephritic magma. In the residual malignite, the concentration of primary crystals (apatite, clinopyroxene, Ba-Sr-rich K-feldspar, and nepheline) formed a crystal network (mush) with the open spaces occupied by small amounts of residual melt enriched in Al, Na, K, and volatiles and depleted in Ba and Sr. Deformation (by shear movements plus magmatic pressures) produced microfractures and fractures which were occupied by residual interstitial melt. In situ crystallization within these fractures resulted in the formation of the SPSV.
Revista de la Asociación Geológica Argentina, Jun 1, 2007
Angelelli 1984), agrupa un conjunto de yacimientos con una metalogénesis predominante de Cu-Au, v... more Angelelli 1984), agrupa un conjunto de yacimientos con una metalogénesis predominante de Cu-Au, vinculados genéticamente con un complejo volcánico-intrusivo de edad miocena superior y naturaleza calcoal
Canadian Mineralogist, Dec 1, 2014
Ishiharaite is a new sulfide mineral, (Cu,Ga,Fe,In,Zn)S, discovered at the Nueva Esperanza vein, ... more Ishiharaite is a new sulfide mineral, (Cu,Ga,Fe,In,Zn)S, discovered at the Nueva Esperanza vein, Capillitas mine (27º20´43″ S, 66º23´17″ W, 3290 m osl) an epithermal ore deposit belonging to the Farallón Negro Mining District, northwestern Argentina. The mineral occurs as subhedral, equidimensional, individual grains (20 to 50 μm in size) included in tennantite. It is a dark gray metallic mineral, opaque and non-fluorescent. Under polarizing-reflected light, it is an isotropic mineral, and its color is burgundy brown with a faint violet hue in air and violet-burgundy in oil.
Canadian Mineralogist, Feb 1, 2010
Canadian Mineralogist, Dec 1, 2012
ABSTRACT
Canadian Mineralogist, Jun 1, 2004
Journal of South American Earth Sciences, 1988
... Universidad Nacional de Tucu-m~n (Jujuy, Argentina), Instituto de Geologia y Mineria, Publica... more ... Universidad Nacional de Tucu-m~n (Jujuy, Argentina), Instituto de Geologia y Mineria, Publica-ci6n 474, 65 p. Barberi, F., Santacroce, R., and Varet, ,J. 1982. Chemical aspects of rift magmatism. ... Universi-dad Nacional (Jujuy, Argentina), Instituto de Geologia, in press. ...
Canadian Mineralogist, Sep 1, 2018
Canadian Mineralogist, Feb 1, 2010
Journal of South American Earth Sciences, Apr 1, 2016
The La Peña alkaline igneous complex (LPC) is located in the Precordillera (32 41 0 34 00 S-68 59... more The La Peña alkaline igneous complex (LPC) is located in the Precordillera (32 41 0 34 00 S-68 59 0 48 00 W) of Mendoza province, Argentina, above the southern boundary of the present-day flat-slab segment. It is a 19 km 2 and 5 km diameter subcircular massif emplaced during the Miocene (19 Ma) in the Silurian-Devonian Villavicencio Fm. The LPC is composed of several plutonic and subvolcanic intrusions represented by: a cumulate of clinopyroxenite intruded by mafic dikes and pegmatitic gabbroic dikes, isolated bodies of malignite, a central intrusive syenite that develops a wide magmatic breccia in the contact with clinopyroxenite, syenitic and trachytic porphyries, a system of radial and ring dikes of different compositions (trachyte, syenite, phonolite, alkaline lamprophyre, tephrite), and late mafic breccias. The main minerals that form the LPC, ordered according to their abundance, are: pyroxene (diopside, hedenbergite), calcium amphibole (pargasite, ferro-pargasite, potassic-ferro-pargasite, potassic-hastingsite, magnesio-hastingsite, hastingsite, potassic-ferro-ferri-sadanagaite), trioctahedral micas (annite-phlogopite series), plagioclase (bytownite to oligoclase), K-feldspar (sanidine and orthoclase), nepheline, sodalite, apatite group minerals (fluorapatite, hydroxylapatite), andradite, titanite, magnetite, spinel, ilmenite, and several CueFe sulfides. Late hydrothermal minerals are represented by zeolites (scolecite, thomsonite-Ca), epidote, calcite and chlorite. The trace element patterns, coupled with published data on Sr-Nd-Pb isotopes, suggest that the primary magma of the LPC was generated in an initially depleted but later enriched lithospheric mantle formed mainly by a metasomatized spinel lherzolite, and that this magmatism has a subduction-related signature. The trace elements pattern of these alkaline rocks is similar to other Miocene calc-alkaline occurrences from the magmatic arc of the Southern Central Andes. Mineral and whole-rock chemical compositions support the interpretation that a first batch of a tephritic magma produced a cumulate of clinopyroxenite (clinopyroxene þ magnetite þ apatite) and a residual melt that crystallized as malignite at a shallow emplacement level (<5 km). Fractional crystallization in a deep chamber, coupled with rock assimilation, produced successive magma pulses that gave the composite central syenite, the syenitic and trachitic porphyries, and trachytic dikes. The latest rocks (phonolites) reflect an extreme fractionation with Ca, Al and K removal by feldspars. Mingling relationships between tephrites-basanites and trachytes-phonolites, plus compositional variations linked to the reabsorption surface observed in the K-feldspar from the phonolitic dikes, suggest recharge events with local mixing in the late-stages of the LPC evolution.
Canadian Mineralogist, Aug 1, 2012
Petr Cerný certainly needs no introduction to the students and professional scientists who study ... more Petr Cerný certainly needs no introduction to the students and professional scientists who study granitic pegmatites. Cerný's prolific career of research on these rocks has spanned over forty years, with important contributions in the areas of 1) the mineralogy, geochemistry and petrology of
Chemical Geology, Dec 1, 2021
Canadian Mineralogist, Jul 1, 2016
Three samples of minerals belonging to the wyllieite mineral group were structurally investigated... more Three samples of minerals belonging to the wyllieite mineral group were structurally investigated: wyllieite from the Buranga pegmatite, Rwanda (A); wyllieite from the Malpensata pegmatite, Italy (B); and qingheiite from the Santa Ana pegmatite, Argentina (C). Their crystal structures were refined, based on single-crystal X-ray diffraction data, to R 1 ¼ 2.72% (A), 3.53% (B), and 2.46% (C). Unit-cell parameters are:
Canadian Mineralogist, Jun 1, 2002
The crystal structure of ushkovite, triclinic, a 5.3468(4), b 10.592(1), c 7.2251(7) Å, ␣ 108.278... more The crystal structure of ushkovite, triclinic, a 5.3468(4), b 10.592(1), c 7.2251(7) Å, ␣ 108.278(7),  111.739(7), ␥ 71.626(7)°, V 351.55(6) Å 3 , Z = 2, space group P1, has been refined to an R index of 2.3% for 1781 observed reflections measured with MoK␣ X-radiation. The crystal used to collect the X-ray-diffraction data was subsequently analyzed with an electron microprobe, to give the formula (Mg 0.97 Mn 2+ 0.01) (H 2 O) 4 [(Fe 3+ 1.99 Al 0.03) (PO 4) (OH) (H 2 O) 2 ] 2 (H 2 O) 2 , with the (OH) and (H 2 O) groups assigned from bond-valence analysis of the refined structure. Ushkovite is isostructural with laueite. Chains of corner-sharing {Fe 3+ O 2 (OH) 2 (H 2 O) 2 } octahedra extend along the c axis and are decorated by (PO 4) tetrahedra to form [Fe 3+ 2 O 4 (PO 4) 2 (OH) 2 (H 2 O) 2 ] chains. These chains link via sharing between octahedron and tetrahedron corners to form slabs of composition [Fe 3+ 2 (PO 4) 2 (OH) 2 (H 2 O) 2 ] that are linked by {Mg O 2 (H 2 O) 4 } octahedra.
Canadian Mineralogist, Sep 1, 2018
Journal of Geosciences, Apr 7, 2021
is a small selenide occurrence situated to the WNW of Jagüé, a small town of the General Sarmient... more is a small selenide occurrence situated to the WNW of Jagüé, a small town of the General Sarmiento department, La Rioja province, Argentina. This occurrence, also called El Chire in recent years, is located (28°35'46.10"S, 68°44'35.78"W, 3120 m. a. s. l.) in the Precordillera environment, to the furthermost southwestern corner of the selenium ore district of Los Llantenes, defined as one of the representative metallogenic belts of the Gondwanic episodes. The selenide minerals occur as veinlets up to few centimeters or as patches or fine inclusions, widespread in calcite. We have identified eleven hypogene Se-bearing minerals (naumannite, tiemannite, chrisstanleyite, jagüéite, eucairite, clausthalite, fischesserite, umangite, athabascaite, berzelianite and bellidoite) mainly associated with gold, silver, hematite and various supergene minerals, including malachite, chalcomenite, and molybdomenite. The paragenesis should have formed from low temperature (< 133 °C), neutral to mildly alkaline pH and highly oxidizing fluids with increasing sulfur fugacity. The country-rock, rich in graptolite-fauna, could be considered, at least in part, the source for the Se and associated metals forming the minerals of this paragenesis, although this hypothesis has yet to be tested.
Canadian Mineralogist, Nov 1, 2020
ABSTRACT We describe an unusual example of rhythmically layered peraluminous granitic pegmatite l... more ABSTRACT We describe an unusual example of rhythmically layered peraluminous granitic pegmatite locally developed in the intragranitic Potrerillos NYF pegmatites derived from the A-type host granites of the Las Chacras–Potrerillos batholith, Sierra de San Luis, Argentina. The strikingly rhythmic layers in the Zebra pegmatite consist of units of albite–K-feldspar–quartz–K-feldspar–albite, with accessory tourmaline and minor muscovite. The layers crystallized from a boron-bearing melt ponded and thermally insulated in the intermediate zone. A layer of low albite 1–2 cm thick was followed by coarser-grained K-feldspar, then well-ordered microcline, which gives way to quartz grains, also coarser-grained, in optical continuity. Zoned prismatic crystals of schorl nucleated in the feldspathic layer in random orientation. Muscovite is scarce. The rock has a granitic composition enriched in Rb, Cs, and B, and is depleted in the rare-earth elements compared to its precursor. We contend that the normative composition, 35.3% Or, 38.1% Ab, and 21.3% Q, was close to the eutectic in the granite system modified by dissolved H2O, F, and B, at a P(H2O) close to 3.5 kbar and a temperature in the range 575–600 °C. Repeated incursions from the field of Ab + Or to the field of quartz and back again as the melt was producing bubbles of H2O can account for the rhythmic crystallization and the local truncation or merging of the feldspathic layers. Occasional larger crystals of K-feldspar may have become detached from the wall or roof of the chamber.
Acta Crystallographica Section A, Aug 16, 2009