THE METAMORPHIC BELTS OF ECUADORPREFACEThis Overseas Memoir reports on geological and mineral studies of the metamorphic rocks of Ecuador which are essentially confined to the Cordillera Real and EI Oro metamorphic belts. The objectives were the elucidation of their nature, structure, relationships. genesis and mineralisation, in response to the need for a geological and mineral database to support and promote a viable national mining industry. The work was carried out under the Cordillera Real Geological Research Project (19861993), a bilateral Technical Cooperation project between the Governments of Ecuador (Ministry of Energy and Mines) and the United Kingdom (Overseas Development Administration ODA), using geoscientists from the Ecuadorian Mining Institute (INEMIN), replaced in 1991 by the Geological and Mining Corporation (CODIGEM); and the British Geological Survey (BGS).ODA and BGS participation in the geological and mineral development of Ecuador began in 1969 and during the 1970s British and Ecuadorian geologists carried out the primary mapping and mineral exploration of the coastal area and the Western Cordillera. The present work thus completes the reconnaissance studies of the Ecuadorian Andes by Anglo-Ecuadorian teams, and provides the springboard for the regional plate tectonic interpretations outlined in this text and on the national maps (Geologic and Tectonometallogenic) prepared in ODA/BGS in cojunction with CODIGEM.BGS staff were contracted by ODA to serve on the project. Dr M Litherland (Project Leader) and Dr J A Aspden (Senior Geologist) were resident in Quito for the duration of the project and undertook the reconaissance studies of the Cordillera Real from 1986 to l990.From mid-1990 to 1993 Dr Aspden covered the El Oro metamorphic district whilst Dr R A Jemielita (Economic Geologist) carried out follow-up mineraI studies over the Cordillera Real. During the same period Dr Litherland compiled the national maps. In addition to the residential staff and their counterparts. other INEMIN/CODIGEM and BGS geoscients carried out geochemical, petrographic, geochronological and paleontological studies on project samples.Dr Litherland was responsible for the compilation of this Memoir and accompanying maps.

ONE INTRODUCTIONPHYSIOGRAPHYConsidering its small sizq (283 520 km2) mamland Ecuador is physiographycally very varied. The Andean range, or Sierra, is at its narrowest here ( 120 km9, being bounded to the west by the coastal lowlands (Costa) and to the cast by the upper Amazon basin (Oriente). The Sierra comprises two parallel ranges, the Cordillera Occidental (Western Cordillera) and the Cordillera Real or Cordillera Oriental (Eastern Cordillera) (Figure 1). The highest peak is Chimborazo (6310 M) The two cordilleras trend approximately NNE SSW, separated in central and northern Ecuador by the Inter-Andean valley which contains most of the major cities.The cordillera Real, the main subject of this memoir Is about 650 km long wide within Ecuador. Elevations along ots watershed are controlled in the north by a chain of of Plio Quaternary volcanoes (Plate I) from North to south the major peaks qre Cayambe (5790 m.) Antisana (5704), Cotopaxi (5897m.), Tungurahua (5016 m), Altar (5318 m) and Sangay (5230 m). To the west the floor of the Inter-Andean Valley occurs at 200-3500m, while de sub-Andean foothills of the castern slope are at altitudes of about 1000m. The highest peaks of metamorphic rock are Cerro Soroche (4730). Sra Urcu (4670) and Cerro Hermoso (4571m). Project expeditions visited these areas. Hermoso was climbed (Cover and Frontispiece).In the south of the Cordilllera Real, the watershed levels fall to 3000 3500 m the Inter-Andean valley disappears and the two cordilleras merge. West of this massif, and trending cast-west, at right angles to the Andes, is the coastal footbills range of the El Oro metamorfhic district, the other, smaller project study area (Figure 2)The Cordillera Real and the Sierra as a whole are deeply dissected by major perennial rivers. The Sierra is a major watershed dividing Amazon (Atlantic)-directed from Pacific-director drainage. I lowever, the following fuor rivers drain castwards to the Amazon from the Western Cordillera crossing the Cordillera Real and forming important lines of communication: the Chingual in the north, and, further south, the Pastaza, Paute and Zamora.

CLIMATE AND VEGETATIONEcuador is an equatorial country with snow-peaked mountains. Crossing the Cordillera Real from west to cast there is a tremendous variation in climate and vegetation. The Inter-Andean Valley in the west is temperate with grassland vegetation and rainfall in the region of 700 mm per year (see rainfall for Quito and Cuenca.Table 1) Ascending the western slopes to the watershed one crosses cold, wer,windy, mountainous moorlands (paramos) scarred by recent glaciations and generally enshrouded in cloud: the snow line lies at about 1500 m. On the sheltered castern side, the tree line of the montane forest is at about 3500 m, and as one descends to the Amazonic lowlands the climate and vegetation become more tropical. Rainfall figures for the cordillera indicate no dry season, only that the period from October to March is slighty less wet. Indeed, the precipitacion during Puyos driest month is four times Quitos wellest.The Vilcabamba and El Oro areas near Peru have a more extreme dry season betwen May and November due to the influence of the Humbolt current (Table 1), whilst between December and June rainfall is high due to the El Nio current. With the low altitude, this produces hot, sticky conditions. This area supports only scrubby woodland.

a. b.

c.Plate 1. Cordillera Real a) El Altar volcano (5319 m): view of the volcanic cover sequence from the basement schist.b) Sangay (5230m), once of the highest active volcanoes in the world, wich straddles the Cordillera Real.c) The Cordillera Real rabge: view from the Rio Salado in the subtropical, sub-Andean Jowlands, to the snow-capped Cayambe volcano (5790 m) in the far distance.

HUMAN ASPECTThe population of Ecuador is approximately 11 million and rising fast, with a density of 37 per km2, the highest in South America. About 40 per cent are lndians, many of whorn are Quechua-speaking descendents of the inhabitants of the Incan Empire. They live mainly in remote regions of the Sierra, whilst whites and mestizos inhabit the towns.The Inter-Andean highway links the main towns of the Sierra from Tulcn (pop. 33 000) in the north, through Ibarra (80 000), Quito (1 250 000), Ambato (140 000), Riobamba (148 000), Cuenca (250 000) to Loja (160 000) in the south. Over the Cordillera Real the population is sparse; sizable towns (e.g. Baos) exist only along the main access routes. In the east, the unsurfaced sub-Andean highway links smaller towns, the largest of which are Puyo, Zamora, Macas and Tena.Population is relatively dense over the EI Ore metamorphic district, with towns such as Portovelo and Pias in the mapped area, bordered by Arenillas, Santa Rosa, Pasaje and the city of Machala (158 000) on the adjacent coastal plain.Subsistence farming is the traditional livelihood of the Indians in their Iands and of the more recent mestizo colonisers who clear the forests along new access routes. Cash crops such as potatoes are also produced. Gold panning is a common source of seasonal income and there is an embryonic hard-rock mining industry. The Cordillera Real is also the source of Ecuadors hydroelectric power from the plants at Agoyn, Pisayambo and Paute. Large inaccessible arcas have been designated as National Parks.

ACCESSThere are five all-weather routes across the Cordillera Real connecting the Inter-Andean and Sub-Andean highways. From north to south these are: PapallactaBaeza, Baos-Puyo, CuencaLimon, LojaZamora and LojaZumba. The Guamore-Macas road is still under construction; the Tulcn - Lago Agrio road has reached La Bonita, and the Salcedo - Tena road has long been abandoned as a viable project.South of the Rio Paute there are a number of mule trails across the cordillera, but the north extensive segments are without access. These include the 120 km of cordillera between the Papallacta and Baos roads which contains the Llanganates mountains, recently traversed by the mountaineer Mclnnes (1984); and the stretch between the Papallacta and La Bonita roads, inaccessible since the destruction of the OyacachiEI Chaco trail by the March 1987 earthquake. A foot traverse across the heart of this area (e.g. SigsigpambaRio DoradoRio CofanesPuerto Libre) would take three or four weeks and would thus require at least one supply cache.Whilst rock outcrop is abundant along the road cuttings and over the paramos, t is generally sparse through the montane forest and often inaccessible along river gorge sections. Over many areas stream or talus blocks were used to identify the geology.PREVIOUS GEOLOGICAL WORKThe metamorphic rocks of the Cordillera Real and El Oro (Figure 2), the subject of this memoir, were depicted on the national geological maps of theodoro Wolf (1982) and Walter Sauer (1957). Wolfs descriptions incorporated economic geology as part of this naturalists magman opus. Sauers (1965) were very detailed and objective, representing some of the observations he made whilst traversing the country to its most inaccessible quarters . He recognized most of the metamorphic lithologies including ophiolites: distinguished the parafrom the orthogneisses, and located and named many of the post tectonic plutonic phases. His study was the most exhaustive before the present survey. In his review of the Sub-Andean region he utilized the pioneering works of Wasson and Sinclair (1923), Colony and Sinclair (1932) and Tschopp (1953).Reconnaisance mapping of the metamorphic rocks aided by photogeological interpretation began with the studies of Kennerley of the British Geological Survey over the Llanganates area (Kennerley, 1971) and Loja Province (Kennerley, 1973). Feininger (1978,1980) continued the mapping of the El Oro metamorphic belt westward, discovering the blueschist/eclogite/ophiolite complex at Raspas. Reconnaissance sheet mapping by DGGM/INEMIN/CODIGEM at a scale 1:100000 has continued over the years with little differentiation of the metamorphic rocks: overlying Plio-Quaternary volcanic sequences have attracted more detailed studies. Individual attempts to understand the metamorphic rocks of the Cordillera Real have also been under taken along the few road sections. These include the petrological and structural studies of Trouw (1976), a review by Feininger (1982), and unpublished metamorphic studies by Duque.Some K-Ar geochronology was undertaken (kennerley,1980;Aly,1980;Feininger and Silberman,1982;Hall and Calle,1982;Baldock,1982;Herbert and Pichler,1983;Pichler and Aly,1983); the available Rb-Sr geochronology was statictically invalid.Regional summaries of the metamorphic rocks in a national context (Kennerley, 1980; Baldock, 1982; 1985), whilst providing descriptions of the lithologies and dividing them longitudinally into various groups could only speculate on their age and correlation since there was only a range of metamorphic K-Ar ages from Precambriam to Tertiary and no palacomological data. Whilst most authors agreed with Sauer (1965) that the metamorphic rocks are of Paleozoic or Precambrian age as indicated by their equivalents along strike in either Peru or Colombia. Feininger (1975:1982) claimed the bulk of the Cordillera Real to comprise deeper-water equivalents of the Amazonic Cretaceous sequence to the cast. This supported the hypothesis of Bristow (1973), who, resurrecting an carlier suggestion by Liddke and Palmer (1941), claimed that the Upper Cretaceous sequence to the cast. This supported the hypothesis of Bristow (1973), who, resurrectiong an carlier suggestion by Liddle and Palmer (1941), claimed that the Upper Cretaceous sequences of the Cuenca area could be traced eastwards into their metamorphics equivalents.The Cordillera Real rocks thus appeared to be laterally Cretaceus and longitudinally Palaezoic.

MINING HISTORYAt the time of the Spanish conquest, the Incan kingdom of Quito was known for its gold, silver and platinum jewelery which, in those times, was without commercial importance. The Spanish rapidly located the alluvial gold, e.g. the Nambija and Zaruma districts. Indeed such was the gold fever that, of the thirty seulements they established, twenty were alluvial gold mining towns along the sub-Andean zone of the Cordillera Real (Navarro, 1986.Vol 1). However, due to Indian revolts, sisease and economic factors, mining ceased at the beginning of the 17th century, with the exception of the Zaruma district, which was worked at reduced production levels. But even this area was virtually abandoned in the 19th century.Foreing investors helped to reopen the Zaruma mines in the late 19th and gold polymetallic mines were also worked in the project area at Pilzhum, Peggy and San Bartolome. More recently, a hunting party rediscovered the forgotten mines of Nambija wich triggered an intense search for other deposits. Thus, during the destroyed almost all the larvest of the fertile coastal area, the impoverished campesinos dedicated themselves to the search for gold, first locating the Ponce Enriquez field. From this time an ever-increasing gold fever has seized wide sections of the poorer parts of the population.Gold production figures for 1990 were in the region of 13 tonnes: five tonnes from Nambija, three from of Zaruma- potovelo, two froim Ponce Enriquez and the remainder from Chinapintza, Guaysimi, Campanilla and alluvial workings.

PROJECT OPERATIONSThe area of study was initially limited to the metamorphic rocks of the Cordillera Real and El Oro. Later it was decided to include the unmetamorphosed Zamora batholith and its envelope rocks on the accompanying map in order to augment the study of the pre-Cretaceous history of Ecuador and also include the important Nambija mining area. However, the field surveys over this, the Sub-Andean belt, were not as detailed as over the rest of the project area.The reconnaissance survey of the Cordillera Real (198690) was undertaken along a series of geotraverses using roads and trails where available. Litherland, with counterparts Bermudez or Pozo, mapped the area north of the Rio Pastaza, and Aspden, with counterparts Viteri or Bermudez, mapped the area south of the Rio Paute; the intervening ground was shared. The survey of the El Oro metamorphic belt (199O92) was undertaken by Aspden, with counterparts Silva, Bermudez or Bonilla.Outcrops and river boulders were sampled and geological observations made. Stream sediment samples (seived in the field to 175 mesh grain size) and panned heavy-mineral concentrates were collected where convenient.In terms of specialized field studies, the major economic follow-up programme was conducted by Jemielita and counterpart Bolaos.There was an economic investigation by Clarke and Viteri in 1988, regional geochronological studies by Rundle in 1987 and Harrison in 1989, and a palaeontological investigation by Woods in 1991.Microscopic petrographic studies and some stream, mineral and heavy-mineral geochemistry were undertaken in Quito, whilst geochronological, palaeontological, rock and most of te mineral analyses were carried out in the BGS laboratories (UK). Consultants reports are listed on pp.107108.REPORTS AND MAPSGeological field maps were constructed using IGM (Instituto Geogrfico Militar) base maps, normally on a 1:50000 scale. These became increasingly available for the Cordillera Real, replacing the old Census maps drawn from uncontrolled airphoto mosaics. The 1 :500 000 scale topographic base for the accompanying maps was compliled by project staff from IGM maps and satellite images.Annual reports were produced for the first four years of the project. These bilingual reports include appendices of specific field reports (in Spanish), laboratory analyses, reports by project consultants, and geotraverse maps.A summary of the first four years work on the Cordillera Real together with 1 :500 000 scale geology and metal maps were produced. The work on the El Oro region, with a 1:100 000 scale geological map, and the results of the economic followup of the Cordillera Real were produced as unpublished reports. All these are available as open-file reports at BGS (in English) and CODIGEM (in Spanish).Published and unpublished project-related reports and maps are listed separately on pp.107-109.NERC Isotope Geology Centre were able to date the rocks of the metamorphic- belts by different isotopic methods, including the most recent lead isotope studies by Sieve Noble.We are equally grateful to the staff in the INEMIN,Quito Polytechnic. and BGS laboratories who undertook the analytical work for the project, and to the scientific institutions and mining companies who collaborated with the project and who helped to make it a success within Ecuador. In this respect special thanks are due to Napoleon Baez, David Coochey, Pablo Duque, Arturo Egez, Minard Hall, Alex Hirtz, Luis Torres, Phil Townsend and Frank Van Thournout, We also appreciate the important contributions made by Rio Tinto Zinc (formery BP Minerals).In the field, locally recruited guides and porters carried, cut, chopped, cooked and fished, and tried to ensure (that the geologists arrived in one piece at the bottom of the Andes.Last, but not least, there is Manuel Celleri (Plate 15b),our CODIGEM field assistant, who also acted as driver, cook, panner and sergeant, who knows the Cordillera Real and remembers everything that happened.Brian Kennerley launched the ODA and BGS participation in Ecuadorian geology leading the first investigations and the firts project team. Following his untimely death in 1976, he now lies peacefully in a Quito cemetary. This memory is dedicated to his memory which is still treasured by many Ecuadorians.