Contribution of New Airborne Geophysical Information to the Geological Knowledge of Eastern Colombia
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Volume 1 Quaternary Chapter 2 Neogene https://doi.org/10.32685/pub.esp.35.2019.02 Contribution of New Airborne Geophysical Published online 17 April 2020 Information to the Geological Knowledge of Eastern Colombia Paleogene Ismael Enrique MOYANO–NIETO1* , Renato CORDANI2 , Lorena Paola 1 [email protected] Servicio Geológico Colombiano 3 4 CÁRDENAS–ESPINOSA , Norma Marcela LARA–MARTÍNEZ , Oscar Eduardo Dirección de Recursos Minerales Diagonal 53 n.° 34–53 5 6 Cretaceous ROJAS–SARMIENTO , Manuel Fernando PUENTES–TORRES , Diana Lorena Bogotá, Colombia 7 8 OSPINA–MONTES , Andrés Felipe SALAMANCA–SAAVEDRA , and Gloria 2 [email protected] 9 RECONSULT Geofisica PRIETO–RINCÓN Cerqueira César, Rua Augusta, 2690–loja 322, CEP 01412–100 Abstract Airborne geophysics is an easy way to increase and complement the geo- São Paulo–SP, Brasil Jurassic logical knowledge of large areas, especially very remote areas like the Colombian 3 [email protected] Carrera 8 n.° 58–67 Amazonia. For this objective and to identify areas of interest for mineral resources, Cali, Colombia the Colombian government has made extensive efforts to fly the Andean and eastern 4 [email protected] Servicio Geológico Colombiano parts of the country, collecting more than 400 000 linear km of magnetic and gamma Dirección de Recursos Minerales spectrometric information over the Colombian Amazonia. This document focuses on Diagonal 53 n.° 34–53 Triassic Bogotá, Colombia describing the potential of these data to increase the geological knowledge of the 5 [email protected] Amazonian region. It presents a methodology to interpret the geophysical data and its Servicio Geológico Colombiano Dirección de Recursos Minerales application over a specific area in the eastern Guainía Department. It was possible to Diagonal 53 n.° 34–53 Bogotá, Colombia identify Paleoproterozoic to Mesoproterozoic igneous and metamorphic rocks of the Permian 6 [email protected] Guiana Shield (Mitú Complex, Parguaza Granite) and several lineaments and structural Servicio Geológico Colombiano Dirección de Recursos Minerales trends that have not been previously reported. These crystalline basement rocks are Diagonal 53 n.° 34–53 partially covered by Miocene sedimentary rocks, recent alluvial deposits, and dense Bogotá, Colombia rainforest coverage, which make geological mapping very difficult. The results increase 7 [email protected] Servicio Geológico Colombiano Dirección de Recursos Minerales the relevance of this type of geophysical interpretation to the geoscientific knowledge Carboniferous Diagonal 53 n.° 34–53 about Colombia. This paper also highlights the training of Colombian geoscientists in Bogotá, Colombia modern geophysical interpretation techniques. 8 [email protected] Gidco SAS Keywords: geophysical interpretation, magnetics, gamma spectrometry, Colombian Amazonia. Carrera 20 n.° 70ª–21 Bogotá, Colombia Devonian 9 [email protected] Resumen Usar la geofísica aerotransportada es una forma sencilla de aumentar y Servicio Geológico Colombiano complementar el conocimiento geológico de grandes áreas, especialmente si son muy Dirección de Recursos Minerales Diagonal 53 n.° 34–53 remotas como la Amazonia colombiana. Para lograr este objetivo y además identificar Bogotá, Colombia áreas de interés para recursos minerales, el Gobierno colombiano realizó esfuerzos * Corresponding author Silurian para sobrevolar las zonas andina y oriental del país y adquirió más de 400 000 km lineales de información magnetométrica y gamma espectrométrica sobre la Amazonia colombiana. Este documento se centra en describir el potencial de estos datos geofí- sicos para aumentar el conocimiento geológico sobre la región Amazónica. Presenta la metodología que se utilizó para la interpretación de los datos geofísicos adquiridos y Ordovician Citation: Moyano–Nieto, I.E., Cordani, R., Cárdenas–Espinosa, L.P., Lara–Martínez, N.M., Rojas– Sarmiento, O.E., Puentes–Torres, M.F., Ospina–Montes, D.L., Salamanca–Saavedra, A.F. & Prie- to–Rincón, G. 2020. Contribution of new airborne geophysical information to the geological knowledge of eastern Colombia. In: Gómez, J. & Mateus–Zabala, D. (editors), The Geology of Cambrian Colombia, Volume 1 Proterozoic – Paleozoic. Servicio Geológico Colombiano, Publicaciones Geológicas Especiales 35, p. 17–36. Bogotá. https://doi.org/10.32685/pub.esp.35.2019.02 17 Proterozoic MOYANO–NIETO et al. su aplicación en un área específica ubicada al oriente del departamento de Guainía, donde la interpretación geofísica permitió diferenciar las rocas ígneas y metamórfi- cas paleoproterozoicas a mesoproterozoicas del Escudo de Guayana (Complejo Mitú y Granito de Parguaza) y varios lineamientos y tendencias estructurales que no han sido reportados anteriormente. Estas rocas cristalinas del basamento se encuentran par- cialmente cubiertas por rocas sedimentarias del Mioceno, algunos depósitos aluviales recientes y una densa cobertura vegetal, la cual hace muy difícil el mapeo geológico. Los resultados aumentan la relevancia de este tipo de interpretaciones geofísicas para el conocimiento geocientífico de Colombia. Adicionalmente, en este trabajo se resalta el entrenamiento de geocientíficos colombianos en las técnicas modernas de interpretación geofísica. Palabras clave: interpretación geofísica, magnetometría, gamma espectrometría, Amazonia colombiana. Table 1. Geophysical methods commonly used in the exploration 1. Introduction of several important types of mineral deposits. Modern geophysical techniques are commonly used by geolog- Deposit type Gravimetry Magnetometry Resistivity Radioactivity ical surveys, academia, and industry around the world to aid in Iron formation M D M D D M geological mapping, provide basic information about mining Coal M D prospects, and strategic information to geological surveys even IOCG M D M D D D in areas where mining is restricted or prohibited (Dods et al., Magmatic M D M D D 1989; Geological Survey of Ireland, 2017; Nakamura, 2015; Primary diamonds M M Oliveira, 2014a; Oliveira, 2014b; Silva, 2014). Uranium M M M D For these objectives, the easiest and most inexpensive way Porphyry Cu, Mo M M D D D to cover large areas with geophysical data at regional to semi– SEDEX Pb–Zn M M D detailed resolutions is the use of fixed wing aircraft equipped Placer deposits M M with specific geophysical sensors suitable for the purposes of Skarns M M D the survey (Table 1; Dentith & Mudge, 2014; Reeves, 2005), Groundwater M D such as magnetic and gravimetric sensors over sedimentary ba- Petroleum M M M sins and offshore regions for hydrocarbon exploration (Graterol & Vargas, 2010a, 2010b) and magnetic and gamma spectro- Source: Data modified from Dentith & Mudge (2014). metric sensors for mineral resource and geological mapping (Oliveira, 2014a; Oliveira, 2014b; Silva, 2014). Note: M—geological mapping of prospective terrains; D—detection/delineation of the mineral environment. To increase the geological knowledge of the country and identify areas of interest for mineral resources, the Servicio Geológico Colombiano, in collaboration with external experts of the World Bank, selected areas of the country where geo- information, of which nearly 400 000 line kilometers are in the logical, geochemical, and metallogenical information could Amazonian region (Figure 1). be integrated with geophysical data to evaluate the miner- Regionally, the geological basement in eastern Colombia al resource potential of these areas (Andean region) and (Orinoquia and Amazonian regions; Figure 2) is composed other ones where the lack of geoscientific information could of rocks of the Amazonian Craton (Tassinari & Macambira, be complemented with the same geophysical information, 1999) and within Colombia corresponds to the Mitú Migma- such as the Orinoquia and Amazonian regions of eastern Co- titic Complex (PP–Mmg1 sensu Gómez et al., 2015) or the lombia (Moyano et al., 2016). Mitú Complex (Celada et al., 2006; López & Cramer, 2012; Airborne magnetometry and gamma spectrometry data ac- López et al., 2007; Rodríguez et al., 2011). These rocks include quisition surveys were designed for selected areas. The surveys gneisses and amphibolites with migmatites, granitoids of differ- were distributed in parallel lines at 500 to 1000 meter spac- ent compositions and alkaline and calc–alkaline affinities, and ings to attain a good resolution for the areal coverage (Reeves, doleritic dikes (Bruneton et al., 1982; Celada et al., 2006; Gal- 2005) and to acquire multi–purpose geophysical data (Olivei- vis et al., 1979; López & Cramer, 2012; Rodríguez et al., 2011). ra, 2014a; Oliveira, 2014b; Silva, 2014). This survey design The rocks of this complex outcrop in the Guainía, Vaupés, and represents more than 1 million line kilometers of geophysical Caquetá Departments. The U–Pb SHRIMP and Sm–Nd ages for 18 Contribution of New Airborne Geophysical Information to the Geological Knowledge of Eastern Colombia Puerto Carreño 6° 00' N 72° 00' W 70° 00' W 68° 00' W Tunja Yopal Villavicencio 4° 00' N IníridaInírida Venezuela San José del Guaviare 2° 00' N MitúMitú Brasil 0° Legend Fligth lines: 500 m Fligth lines: 1000 m 2° 00' S Perú 4° 00' S 0 65 130 km LeticiaLeticia Figure 1. Location and line spacing of the airborne geophysical surveys. the rocks of the Mitú Complex range from 2.2 Ga to 1520 Ma nas, 1988). Acid subvolcanic dikes in the Roraima Formation (Cordani et al., 2016; Tassinari et al., 1996). metasedimentites have a 1496 ± 30 Ma Rb–Sr whole–rock age The Roraima and Pedrera Formations (MP–Mvlg1 sensu and an