Granitic Pegmatites of the San Luis Ranges‖
Total Page：16
File Type：pdf, Size：1020Kb
5th International Symposium on Granitic Pegmatites – Field Trip Guidebook 5th INTERNATIONAL SYMPOSIUM ON GRANITIC PEGMATITES PEG2011 ARGENTINA FIELD TRIP GUIDEBOOK ―GRANITIC PEGMATITES OF THE SAN LUIS RANGES‖ Edited by: Miguel Ángel Galliski1 & María Florencia Márquez-Zavalía1. Written by Miguel Ángel Galliski1, María Florencia Márquez-Zavalía1, Viviana Martínez2 & María Belén Roquet3. 1 IANIGLA-CONICET, CCT-Mendoza, Av. A. Ruiz Leal s/n, Parque General San Martín, Mendoza, Argentina. 2 Universidad Nacional de La Pampa. Uruguay 151, 6300 Santa Rosa, La Pampa, Argentina. 3 Departmento de Geología, Universidad Nacional de San Luis, Chacabuco y Pedernera, (5700) San Luis, Argentina. Program …………………………………………………………………………………………………………….. 2 The Pampean pegmatite province (M. A. Galliski) Introduction………………………………………………………………………………………………… 3 The Tectonic Setting………………………………………………………………………………......……. 3 The distribution of the pegmatite fields ……….……….……….………….…………...……………...….. 3 The orogenic pegmatite fields ……….……….…………..……….…….……………………........ 3 The post-orogenic pegmatite fields ……….……….…………..……….…….…………………… 5 Concluding remarks ……….……….……….……….……….………..……………...…………….……… 5 The pegmatite fields of San Luis ranges (M. A. Galliski) ….……….……….……….……….……………..……...… 6 The Totoral pegmatite field ……….……….……….…...….……….……….……….……….…………… 6 The granites ……….……….……….……….……….………...……….……………...........…...… 8 Stop 1: Paso del Rey leucogranite ……….……….……….……….……….……….……….……… 8 Geology and types of pegmatites …….….……….……….……….……….………...…………… 8 Geochemistry……….……….……….……….……….……….……….………………………… 10 Concluding remarks……….……….……….……….……….……….…………...……………... 11 Stop 2: San Luis I and II pegmatites ……….……….……….……….………...….…..…………… 12 Stop 3: Cerro La Torre granite………………………………………………..….……..…………... 16 Stop 4: Santa Ana pegmatite (M. A. Galliski & M. F. Márquez-Zavalía)…………………………...……….........… 17 Stop 5: Independencia Argentina pegmatite (M. A. Galliski & M. F. Márquez-Zavalía)……….………...… 21 The Conlara pegmatite field ……….……….……….……….……….……….……….…….…….…...… 23 Potrerillos subgroup (M. B. Roquet & M. A. Galliski)…….……...…….……….……….…………...………... 23 Stop 6: Rancul pegmatite ……….……….……….……….……….……………….…………......… 26 Stop 7: La Elsa pegmatite ……….……….……….……….……….……….……………................. 27 Stop 8: Las Cuevas pegmatite (V. Martínez & M. A. Galliski)……….……….……………..……....…... 29 The La Estanzuela pegmatite field ……….……….……….……….………………..…….………........... 34 Stop 9: San Elías pegmatite (M. A. Galliski & M. F. Márquez-Zavalía)……….……..……....……..……… 34 Stop 10: La Viquita pegmatite (M. A. Galliski, M. F. Márquez-Zavalía & V. Martínez)..………….……..… 35 References…………………………………………………………………………………………....….… 41 1 Granitic pegmatites of the San Luis ranges PROGRAM Thursday, February 24th, 2011 Departure from Mendoza at 8 am. Arrival to the Hotel Amerian Park, San Luis. Lodging and lunch. Departure to Stop 1: Paso del Rey leucogranite. Stop 2: San Luis I & II pegmatites. Return to the hotel. Friday, February 25th, 2011 Departure to Stop 3: Cerro La Torre leucogranite. Stop 4: Santa Ana pegmatite. Box lunch in the field. Stop 5: Independencia Argentina pegmatite. Return to the hotel. Saturday, February 26th, 2011 Departure to La Toma. Visit stone stores and PG La Toma milling plant of pegmatite raw material. Lunch at La Toma. Stop 6: visit to Potrerillos granite and Rancul pegmatite. Stop 7: La Elsa pegmatite. Stop 8: Las Cuevas pegmatite. Return to the hotel. Sunday, February 27th, 2011 Departure to La Estanzuela pegmatite field. Stop 9: San Elías pegmatite. Box lunch in the field. Stop 10: La Viquita pegmatite. Farewell early dinner. Return to Mendoza. 2 5th International Symposium on Granitic Pegmatites – Field Trip Guidebook THE PAMPEAN PEGMATITE PROVINCE plotted in Figure 1. The muscovite class pegmatites are dominant in three fields aligned in the western side of The Pampean pegmatite province (PPP) was defined to the province, and one in the eastern side. include the economic fields of granitic pegmatites of central and northwestern Argentina (Galliski 1992, The different fields from the rare-element pegmatite belt 1994a, 1994b, 2009). It contains more than 95% of the belong to the LCT (Li, Cs, Ta) petrogenetic family. granitic pegmatites of the country, with mineral They are aligned N-S and mostly hosted in medium- resources that had been mined during the past 80 years, grade metamorphic rocks, preferentially in amphibolite producing the majority of the feldspar, quartz and mica facies from an Abukuma-type metamorphic belt, that plus Be-, Li-, Ta-, Bi- and Rb-bearing minerals. The suffered polyphase deformation during the Pampean and PPP extends discontinuously for more that 800 km N-S Famatinian orogenic cycles. Along the rare-element belt and 200 km E-W, from 24º30´ to 33º30´S, mostly in the the lithium bearing pegmatites crystallized under Sierras Pampeanas of northwestern and central increasing pressure conditions from the petalite-subtype Argentina (Fig. 1), but the three northern districts are in pegmatites of the El Quemado district in the north, the southern part of Cordillera Oriental and the adjacent passing through the spodumene-subtype pegmatites of mountain block of Puna. Its possible extension to the Ancasti district in the middle, and finishing in the South could be even more than 400 km as indicated by economic pegmatite fields of the San Luis ranges. discontinuous outcrops under recent cover that reach the province of La Pampa. The Conlara, Totoral and La Estanzuela pegmatite fields are located in the San Luis ranges and have an The Tectonic Setting important past record of producing mica, beryl, spodumene, tantalite, and lastly, K-feldspar, albite The orogenic pegmatite fields of the Pampean pegmatite and quartz. These districts are hosted in metamorphic province developed mainly in the early Paleozoic, complexes of medium grade, intruded by orogenic during the Pampean (~550-520 Ma) and especially and postorogenic granites. The medium-sized Famatinian (~500-435 Ma) orogenic cycles, along a pegmatites are representative of several types and pericratonic mobile belt located in the western subtypes as beryl-columbite-phosphate, spodumene, protomargin of Gondwana. The tectonic evolution of albite-spodumene and albite. The K-Ar ages of the this mobile belt is complex and it includes the accretion pegmatites from this belt, except for the Córdoba of several terranes (Cf. Collo et al. 2009). Significant districts, are grouped in the Lower Paleozoic, in good facts in the geological evolution of the pegmatite correlation with the granitic magmatic of the province include: (1) the ensialic deposition of several Famatinian orogenic cycle. They are genetically thousand meters thick psammopelitic succession of linked to a suite of two- mica, or muscovite- sediments, represented by the Puncoviscana Formation tourmaline leucogranite, which usually are small to and equivalent protoliths, during the Late Proterozoic - medium size composite intrusive of variable fabric, Early Cambrian, and (2) the Upper Ordovician collision within the aplite to pegmatite range. They are of the Precordillera terrane. The present tectonic setting peraluminous, low-Ca calc-alkaline rocks that have that exposes the pegmatite province in faulted blocks high LILE and volatile contents, especially B and P. eastward of the Andean Cordillera, results from the flat They have total REE depleted contents and high subduction geometry of the Nazca plate under this initial 87Sr/86Sr ratios (≥ 0.71). Most of these S-type segment of the South America plate. leucogranite and associated pegmatites are syn- to The Distribution of the Pegmatite Fields late-kinematic and were slightly or strongly deformed during the late-stage phases of the Famatinian The orogenic pegmatite fields deformation. The most favored model for the origin of this suite comprises episodic crustal anatexis, The orogenic pegmatite fields encompass pegmatites of produced by muscovite ± biotite dehydration melting, muscovite, muscovite–rare-element and rare-element of dominant Puncoviscana protoliths by shear-heating classes using the classification of Černý & Ercit (2005). during a collisional orogeny, as proposed by Nabelek The distribution of the economic pegmatite fields is & Liu (2004) for other regions (Galliski 2009). 3 Granitic pegmatites of the San Luis ranges Figure 1: Schematic geological map of the Pampean pegmatite province showing the main lithological units and the distribution and classes of the pegmatite economic fields (modified from Galliski & Černý 2006) 4 5th International Symposium on Granitic Pegmatites – Field Trip Guidebook This collisional leucogranite suite is space-related to locally showing K-feldspars with incipient rapakivi- another suite of TTG dominant lithology, which like textures. They are usually high silica, meta- to includes some more basic intrusives; it is also calc- mildly peraluminous, high-K calc-alkaline granites, 87 86 alkaline, peraluminous, and has lower Sr/ Sri ratios with Fe-, Mg-, and Ca-contents higher than the (~0.706). This last suite has been considered of I-type orogenic leucogranites. Commonly, these granites and related to a subduction setting, with variable are moderately LIL and HFSE enriched. The initial lower crust component and possible assimilation of 87Sr/86Sr ratios, if not disturbed, are generally low to supra-crustal protoliths (Pankhurst et al. 2000). medium (0.703-0.706); the contents and normalized REE patterns, and δ 18O values are most likely The post-orogenic