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Baize S.,Institute for Radiological Protection and Nuclear Safety | Audin L.,French National Center for Scientific Research | Winter T.,Bureau de Recherches Geologiques et Minieres | Alvarado A.,National Polytechnic School of Ecuador | And 5 more authors.
Geomorphology | Year: 2014

The Pallatanga fault (PF) is a prominent NNE-SSW strike-slip fault crossing Central Ecuador. This structure is suspected to have hosted large earthquakes, including the 1797 Riobamba event which caused severe destructions to buildings and a heavy death toll (more than 12,000 people), as well as widespread secondary effects like landsliding, liquefaction and surface cracking. The scope of this study is to evaluate the seismic history of the fault through a paleoseismological approach. This work also aims at improving the seismotectonic map of this part of the Andes through a new mapping campaign and, finally, aims at improving the seismic hazard assessment. We show that the PF continues to the north of the previously mapped fault portion in the Western Cordillera (Rumipamba-Pallatanga portion) into the Inter-Andean Valley (Riobamba basin). Field evidences of faulting are numerous, ranging from a clear geomorphological signature to fault plane outcrops. Along the western side of the Riobamba basin, the strike-slip component seems predominant along several fault portions, with a typical landscape assemblage (dextral offsets of valleys, fluvial terrace risers and generation of linear pressure ridges). In the core of the inter-Andean valley, the main fault portion exhibits a vertical component along the c. 100 m-high cumulative scarp. The presence of such an active fault bounding the western suburbs of Riobamba drastically increases the seismic risk for this densely inhabited and vulnerable city. To the east (Peltetec Massif, Cordillera Real), the continuation of the Pallatanga fault is suspected, but not definitely proved yet. Based on the analysis of three trenches, we state that the Rumipamba-Pallatanga section of the PF experienced 4 (maybe 5) Holocene to Historical strong events (Mw > 7). The coseismic behavior of the fault is deduced from the occurrence of several colluvial wedges and layers associated with the fault activity and interbedded within the organic black soil sequence. According to a series of 14C datings, we document that these events occurred during the last 6500 years. The clear deformation of the shallowest layer (14C: 1633 AD) is most likely associated with the 1797 Riobamba earthquake. After retrodeforming one of the 3 trenches, we estimate coseismic vertical throws (0.70 to 0.90 m). Because of bad outcrop conditions, we could not determine the horizontal component of slip and we used the slip vector determined in a previous work with a tectonic geomorphology study. Assuming this slip vector, we obtain total coseismic offsets between 3.5 and 4.5 m, indicative of earthquake magnitudes around c. Mw 7.5. The estimated recurrence time intervals range between 1300 and 3000 years, indicating an average slip rate of c. 2.5 mm/a for the Rumipamba-Pallatanga section of the fault. © 2014 Elsevier B.V. All rights reserved. Source


Munoz G.A.,San Francisco de Quito University | Pazmino I.C.,Instituto Nacional Of Investigacion Geologico Minero Metalurgico Inigemm | Ayala D.K.,Instituto Nacional Of Investigacion Geologico Minero Metalurgico Inigemm | Espinosa P.A.,Instituto Nacional Of Investigacion Geologico Minero Metalurgico Inigemm | Velasquez P.C.,Instituto Nacional Of Investigacion Geologico Minero Metalurgico Inigemm
IPMI 38th Annual Conference "Precious Metals 2014: Back to the Future or Back to the Past" | Year: 2014

Gold has been recovered from the Nambija mining zone by gravity concentration since the discovery of the deposit in 1982. However, important amounts of the precious metal are lost in the tailings from the artisanal gravity concentration process that is being used to recover the gold. For these reasons, a particle size distribution of the gold of the discharge material from the mills that is fed to the gravity concentration devices was conducted. Results showed that the gold particle size is fine, and explains why gold cannot be recovered efficiently by these artisanal gravity concentration devices. A new gold recovery process is being proposed for the mining zone, which includes froth flotation of the tailings after gravity concentration. Source


Pazmino I.C.,Instituto Nacional Of Investigacion Geologico Minero Metalurgico Inigemm | Munoz G.A.,San Francisco de Quito University | Ayala D.K.,Instituto Nacional Of Investigacion Geologico Minero Metalurgico Inigemm | Espinosa P.A.,Instituto Nacional Of Investigacion Geologico Minero Metalurgico Inigemm | Velasquez P.C.,Instituto Nacional Of Investigacion Geologico Minero Metalurgico Inigemm
IPMI 38th Annual Conference "Precious Metals 2014: Back to the Future or Back to the Past" | Year: 2014

Small-scale gold mining in Ecuador takes place under precarious conditions basically due to lack of technology, illegality, informality and inequity. For these reasons, the Ecuadorian Government, through the Ministry of Natural Non Renewable Resources and the National Institute of Research in Geology Mining and Metallurgy (INIGEMM), is executing a project to improve the working conditions of small-scale and artisanal mining for gold and base-metal recovery. The project has seven different components in order to cover all the needs of the influence area, where one of these components is Technology Transfer. This paper presents the details of how this component is looking forward to boost technical education among small-scale miners, and to provide them of a better infrastructure to improve efficiency and performance of mining activities. Source

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