1995 ASPDEN EL ORO METAMORPHIC COMPLEX SP PDF
Preview 1995 ASPDEN EL ORO METAMORPHIC COMPLEX SP
BRITISH GEOLOGICAL SURVEY Number 67 Overseas Geology and The El Oro metamorphic complex, Mineral Resources Ecuador: geology and economic mineral deposits J. A. Aspden, W. Bonilla and P. Duque CONTRIBUTORS Whole rock geochemistry N. J. Fortey and M. G. Gillespie © Crown copyright 1995 First published 1995 ISBN 0 85 272242 7 Keyworth, Nottingham British Geological Survey 1995 Bibliographic reference Aspden J. A., Bonilla W., and Duque P. (1995) The El Oro metamorphic complex, Ecuador: geology and economic mineral deposits. Overseas Geology and Mineral Resources, No. 67. Authors J. A. Aspden British Geological Survey Keyworth Nottingham NG12 5GG United Kingdom W. Bonilla CODIGEM Ministerio de Energía y Minas Quito Ecuador P. Duque Escuela Politécnica Nacional Casilla 2759 Quito Ecuador Contributors N. J. Fortey and M.G. Gillespie British Geological Survey Keyworth Nottingham NG12 5GG United Kingdom Cover photograph Stunted cloud forest, southern Ecuador (C. Mortimer, BGS) CONTENTS Abstract 1 Introduction 1 Background 2 Description of the area 4 Access and map coverage 4 Acknowledgements 4 Geological units of the complex 5 General setting 5 Geology of Sub-province I 6 Tahuín semi-pelitic division 6 El Tigre unit 6 La Victoria unit 9 Depositional age of the Tahuín division 10 Moromoro granitoid complex 10 La Bocana unit 10 La Florida unit 14 Marcabelí and El Prado plutons 16 Age of La Bocana unit and Marcabelí pluton 17 Piedras mafic complex 17 Quebrada Plata unit 17 Age of Quebrada Plata unit 19 Summary of conditions and age of metamorphism south of the Zanjón-Naranjo 20 fault zone Geology of Sub-province II 20 Palenque mélange division 20 Raspas ophiolitic complex 21 Limón Playa and Quera Chico units 24 Unnamed granitoid units 24 Arenillas and Taqui units 24 Unnamed serpentinite units 25 Origin and age of the tectonic inclusions north of the Zanjón-Naranjo fault 25 zone Whole-rock geochemistry 26 Background 26 Moromoro granitoid complex 26 Piedras mafic complex 27 Palenque mélange division 31 Río Panupali unit 32 El Toro unit and unnamed serpentinites 33 Structure 38 General 38 Structure south of the Zanjón-Naranjo fault zone, the ‘Moromoro event’ 40 Zanjón-Naranjo fault zone 42 Structure north of the Zanjón-Naranjo fault zone, the ‘Palenque event’ 42 Structural limits of the El Oro metamorphic complex 44 Geological interpretation 44 Regional context within the Northern Andes 44 Origin of the El Oro metamorphic complex 45 Age of accretionary complex and rotation of the El Oro metamorphic complex 45 Economic geology 47 General 47 Metallic mineral occurrences 47 Cerro Pelado area 47 Loma Larga mine 49 Manganese mine 49 Sacachispas gold mining area 49 Alluvial gold 49 Magnetite 49 Chromium, nickel and platinum group metals 49 Non-metallic mineral occurrences 49 Jerusalem feldspar mine 49 Quarrying operations 50 Brick clays 50 Sand and gravel 50 Ornamental stone 50 Stream sediment sampling programme 50 Introduction 50 Gold and silver 50 Arsenic, antimony, bismuth and tellurium 52 Copper, lead, zinc, cadmium and barium 59 Chromium, nickel, cobalt and vanadium 59 Molybdenum, tin and tungsten 60 Lanthanum and yttrium 60 References 62 PLATES 1 Angular unconformity of Cretaceous Alamor basin sequence and El Tigre unit 8 2 Slump folding in turbiditic El Tigre unit 9 3 Migmatitic paragneiss, La Victoria unit 10 4 Texturally heterogenous granitoid, La Bocana unit 11 5 Texturally heterogenous foliated granitoid, La Bocana unit 11 6 Migmatitic granite gneisses, La Bocana unit of Moromoro complex 12 7 Migmatitic granite gneisses, La Bocana unit of Moromoro complex 12 8 Unfoliated, late-stage granitic pegmatite cross-cutting foliated granite, La Bocana unit 13 9 Irregular pegmatitic apophysis, comprising feldspar, quartz, biotite, muscovite and 13 tourmaline, La Bocana unit 10 Megacrystic alkali feldspar biotite granite, La Florida unit 14 11 Megacrystic alkali feldspar biotite granite, La Florida unit 14 12 Xenolith of migmatitic granite gneiss in La Florida unit 15 13 Metasedimentary xenoliths with chilled margins, La Florida unit 15 14 Steep, east-west-trending, ductile shear zone in Marcabelí pluton 16 15 Relict igneous banding, Quebrada Plata unit 18 16 Vertical banding with concordant mafic enclaves, Quebrada Plata unit 18 17 Finely Banded greenschist tectonite with centimetre-scale (Z) kink bands, Quebrada Plata 19 unit 18 Photomicrographs of La Chilca unit blueschist 22 19 Photomicrographs of La Chilca unit eclogite 23 20 Horizontal (dextral) slickensides on vertical surface, El Tigre unit 40 21 Mylonitic L-S tectonites La Victoria unit, Tahuín division, Río Moromoro 41 22 Mylonitic L-S tectonites La Victoria unit, Tahuín division, north of Las Lajas 41 23 Boudinaged quartz veins indicating dextral movement, low-grade portion of La Victoria 42 unit 24 Dextral winged inclusion, high-grade portion of La Victoria unit 42 25 Boudinaged pegmatitic vein and small-scale Z-folds (right centre) indicating dextral 43 movement, high-grade portion of La Victoria unit 26 Dextral S-C (Type 1) mylonite, La Bocana unit 43 FIGURES 1 Location map 3 2 Summary of stratigraphic nomenclature 5 3 Comparison of pre-existing stratigraphic nomenclature with that used in the present 7 study 4 Physiographic setting 8 5 Sm/Nd isochron diagram for garnet-bearing paragneiss, La Bocana unit, Moromoro 16 complex, Río Piedras 6 U/Pb concordia diagram for Marcabelí pluton 16 7 U/Pb zircon concordia diagram for Quebrada Plata unit, Piedras complex, Río Piedras 18 8 Location map of whole-rock samples 27 9 QAP ternary diagram based on the CIPW normative values for Moromoro complex 30 10 Aluminosity index v. SiO2 for Moromoro complex 30 11 K2O v. Na2O diagram for Moromoro complex 30 12 ACF ternary diagram for Moromoro complex 30 13 ROCK/ORG normalised spider diagram for Marcabelí pluton, Moromoro complex 31 14 ROCK/ORG normalised spider diagram for La Bocana unit, Moromoro complex 31 15 ROCK/ORG normalised spider diagram for El Prado pluton, Moromoro complex 31 16 Rb v. Y+Nb diagram for Moromoro complex 31 17 K2O v. SiO2 classification diagram for Piedras complex and Raspas ophiolitic complex 34 18 Na2O + K2O v. SiO2 classification diagram for Piedras complex and Raspas ophiolitic 34 complex 19 Zr/Ti v. Nb/Y classification diagram for Piedras complex and Raspas ophiolitic complex 34 20 AFM ternary diagram for Piedras complex and Raspas ophiolitic complex 34 21 TiO2 and Sr v. MgO diagrams for Piedras complex and Raspas ophiolitic complex 35 22 Zr and Y vs. MgO diagrams for Piedras complex and Raspas ophiolitic complex 35 23 ROCK/MORB normalized spider diagram for Quebrada Plata unit, Piedras complex 35 24 ROCK/MORB normalised spider diagram for Arenillas and Taqui units, Piedras 35 complex 25 Zr/Y vs. Zr discriminant plot for Piedras complex and Raspas ophiolitic complex 35 26 Ti vs. Zr discriminant plot for Piedras complex and Raspas ophiolitic complex 35 27 Zr-Ti/100-Y × 3 discriminant plot for Piedras complex and Raspas ophiolitic complex 35 28 ROCK/MORB normalised spider diagram for Río Panupali unit, Raspas ophiolitic 35 complex 29 Cr vs. TiO2 discriminant plot for El Toro and other serpentinites of Palenque division 38 30 Sketch of eastern portion of Northern Andean accretionary complex, Ecuador segment 46 31 Areas of established mining and distribution of anomalous stream sediment gold values 48 32 Stream sediment sample location map 61 TABLES 1 Selected climatic data from El Oro Province 4 2 K-Ar determinations for Moromoro granitoid complex 17 3 K-Ar determinations for Piedras mafic complex 19 4 Moromoro granitoid complex whole-rock analyses 28 5 Moromoro granitoid complex normative mineral compositions and geochemical indices 29 6 Piedras mafic complex whole-rock analyses 32 7 Piedras mafic complex normative mineral composit ion and geochemical whole-rock 33 analyses 8 Palenque mélange division (inclusions) whole-rock analyses 37 9 Palenque mélange division (inclusions) normative mineral compositions and 39 geochemical indices 10 List of stream sediment samples and heavy minerals concentrates 51 11 Stream sediment sample geochemistry 53 MAPS 1 1:100000 scale geological map of El Oro metamorphic complex in pocket
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