22nd GEOLOGICAL CONGRESS OF BOLIVIA, Santa Cruz de la Sierra – 16th to 19th of November 2016 (original) (raw)
Related papers
AN OUTLINE OF THE GEOLOGY AND PALAEOGEOGRAPHY OF BOLIVIA
Extensive regional geological investigations by Compania Petrolera Bolivians Shell and Bolivia California Petroleum Co. from 1957 to 1961 led to a greatly improved understanding of the geological history of Bolivia, which is described and is illustrated with ten palaeogeographic figures. Physiographically, Bolivia is divided into four entirely different morphotectonic units. From east to west they are : the Andes, with the Altiplano; the Subandean foothill zone; the Eastern plains (Gran Chaco and Beni plains) and the Brazilian shield area in the NE part of the country. A marine Palaeozoic series from Ordovician to Devonian, and a predominantly continental sequence from Carboniferous to Recent with many gaps, are recognized. No geosynclinal conditions existed in this part of South America. Cambrian sediments are not proven in Bolivia, but have been tentatively assumed in a few places. Ordovician deposition has been found without interruption from Tremadocian to Caradocian, but its areal extent is little known except in the Andes. Glacial beds of the Silurian (Gothlandian) transgress with an angular unconformity, followed by shales which continue up into the Lower Devonian. Lower, Middle and Upper Devonian have been found, but uppermost Devonian is believed to be absent. Carboniferous follows, with a disconformity. Little Mississippian occurs, the Carboniferous being chiefly present in Pennsylvanian glacial "Gondwana" facies, mainly outcropping in the Subandean zone. The series is most complete in the south, and is gradually truncated northwards. Lower Permian, mostly fossiliferous Wolfcampian, is confined to the NW part of Bolivia. Bolivia was emergent during most of the Mesozoic and sedimentation only took place in a few scattered areas, but igneous intrusions occurred in the Cordillera. Part of the Andean region was strongly folded and eroded between Lower Permian and Lower Cretaceous. Cretaceous and Palaeogene deposits are known in two parts of the country : the Puca Group in the Andes and Lake Titicaca area, and the somewhat younger Beu-Tacuru Sandstones in the Subandean zone. The deposits rest with pronounced unconformity on 1 older rocks, and are in turn disconformably overlain by the Neogene. These sediments were derived dominantly from eastern sources. In mid-Tertiary the Andean uplift started with epeirogenic movements, creating two major Neogene depositional basins of completely different facies, which received material mainly from Andean sources: the Altiplano trough and the eastern foredeep. At the end of the Pliocene or perhaps the beginning of the Pleistocene the main Andean uplift created the high Cordilleras, which are now in a stage of erosion. Structurally, Bolivia can be divided into a tectonically higher northern half and a deeper southern half, separated by an old tectonic line or zone extending from Arica in the west to Santa Cruz and further in the east. In the northern half of the country, the Brazilian shield extends much further westwards than was previously assumed and is generally devoid of any sediments but Quaternary. In the south, the Chaco plain is underlain by a deep-seated cratonic arch covered by Palaeozoic sediments. The Andean mountain system of Bolivia is the result of mostly vertical uplift, showing a Germanotype style of block faulting and asymmetric folds.
Geology and Setting of the Miguela A-Zone, Guarayos Greenstone Belt, Eastern Bolivia
VMS deposits of Latain America, 2000
The Miguela A-Zone volcanogenic massive sulphide (VMS) deposit is a new discovery. It is located at the western border of the Pre-Cambrian shield of eastern Bolivia, hosted in a Proterozoic greenstone belt and metamorphosed to amphibolite facies. The mineralization occurs in a 400-meter thick felsic unit within a thicker succession of tholeiitic mafic volcanic rocks. The main rock types are meta-rhyolite and quartz-muscovite-rich meta-sediments close to the VMS mineralization, and silica and iron-rich mudstone and siltstone, magnetite or pyhrrotite-rich banded iron-formation on top and lateral to the known VMS mineralization. This litho-facies is informally known as the “La Pastora” formation and can be traced for at least 28 kilometers of strike length. This unit hosts all important geochemical and geophysical anomalies and gold and base metal showings of the area. The mineralization occurs in three lenses, is confined to two different stratigraphic levels, and is related to a system of synvolcanic growth faults. The texture of the mineralization is massive, semi-massive and finely laminated. The most important minerals are pyrite and chalcopyrite with lesser amounts of sphalerite and galena. Magnetite and pyrrhotite are rare in the A-Zone, but abundant in the northern El Bagre and southern El Porvenir zones. The lowermost A-3 lens is underlain and laterally surrounded by a zone of hydrothermal alteration, intense pyritization and sodium depletion. The main A-1 lens is the best investigated mineralized structure. It is tabular in shape, dips 45 degrees northwest, exhibits a true thickness between 12 and 23 meters and carries a quartz-rich layer on top with a significant enrichment of barium. It is continuous for 450 meters in strike, 350 metres down-dip and remains open along strike and to depth. It contains an Inferred Resource of 1.62 Million tonnes grading 3.76% Cu, 1.26 g/t Au, 11.3 g/t Ag and 0.33% and a geological resource potential of 4.25 million tonnes. This size compares well with the dimensions of the deposits of other VMS districts and places it in the median size category of known VMS deposits in Canada and Australia. The A-Zone is deeply weathered due to the intensive lateritization of the regolith since the Miocene. A 45-meter thick supergene chalcocite and a 40-meter thick oxide zone overlie the primary sulphide mineralization. The oxide zone is enriched in gold and depleted in base metals and silver, whereas copper is strongly enriched in the supergene zone. Routine geochemical and geophysical surveys, commonly used in massive sulphide exploration in Canada and elsewhere, have proved effective in the deeply laterized Bolivian Shield. Exploration on the Miguela and El Porvenir concessions have identified several targets with geochemical and geophysical signatures comparable to the A-Zone, which remain to be drill tested. Further exploration of the remainder of the Guarayos Greenstone Belt is a priority. Given the exploration success in a short period of time the Guarayos Greenstone Belt has excellent potential to host world class deposits.
This study is a synthesis of all the pyrolysis data concerning the Sub Andean Zone, the Chaco and the Madre de Dios basin that are available at YPFB (Yacimientos Petroliferos Fiscales Bolivianos) where they have been recently compiled in a database. This database contains actually more than 3000 data which have been used to build the present maps. The data come from more than 100 internal regional reports as well as from the final well reports; a few of them have been gathered by international oil companies and institutions working on Bolivia.
Sempere 1991 clarifications of Cz tectonics in Bolivia
6º Congreso geológico chileno, 1991
This work critically reviews the definition of the Cenozoic "tectonic phases" that have been described in Bolivia. Se efectua una revisión crítica de Ia definición de las "fases tectónicas" cenozoicas que han sido descritas para Bolivia.
Geology Abstracts: 4th Annual International Conference
2017
This book includes the abstracts of all the papers presented at the 3rd Annual International Conference on Geology, 5-8 June 2017, organized by the Athens Institute for Education and Research (ATINER). In total 18 papers were submitted by 20 presenters, coming from 14 different countries (Brazil, China, Egypt, France, Hungary, Iran, Malaysia, Mexico, Morocco, Namibia, Poland, Romania, Slovakia, Turkey). The conference was organized into 9 sessions that included a variety of topic areas such as Geological Exploration, Geological Characterization, Environmental Considerations and Sustainability of Water Resources and more. A full conference program can be found beginning on the next page. In accordance with ATINER’s Publication Policy, the papers presented during this conference will be considered for inclusion in one of ATINER’s many publications.