gold mineralization in the northern andes_magmatic setting vs. metallogeny

8/10/2019 Gold Mineralization in the Northern Andes_Magmatic Setting vs. Metallogeny

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Northern Andes. Interesting historical and modern accounts of gold production in Colombia can be found inreferences listed within the selected bibliography presented at the rear of this document.

FIGURE 1: Historic Gold Producing Regions of the Northern Andes.

FIGURE 2: Distribution of Gold Occurrences vs. Magmatic Periods.

GEOLOGIC SETTING – METALLOGENY

With respect to historical through to modern-day gold production and the observed mineral occurrences and goldmetallogenic - exploration potential of the Northern Andes, the Central and Western Cordilleras of Colombia, andtheir bounding intermontane valleys are by far the most important regions of study. This history and potentialmay be extrapolated southwards into Ecuador (Figure 3 and 4) where it is manifest in portions of the CordilleraReal and Sierra del Condor (southern extension of the Central Colombian Cordillera), the Western Cordillera, andthe Inter-Andean Depression - El Oro metamorphic belt. It is noteworthy however that isolated, and locallyimportant, gold occurrences are observed elsewhere including in the Eastern Cordillera (e.g. Vetas-California- Angostura, Paipa), the Guiana Shield (Taraira, Naquen), the Sierra Nevada de Santa Marta, and the Guajira, all inColombia. With the exception of Vetas-California-Angostura, these occurrences are scarcely documented and notwell technically understood. This paper will focus primarily upon analysis of the gold metallogenic domains withinthe Colombian Cordilleras. Some extrapolation and supporting examples will also be drawn from Ecuador.

FIGURE 3: Major Tectonic Elements vs. Gold Metallogenic Domainsin the Northern Andes.

Figure 4: Geologic Correlation, SW Colombia - NW Ecuador.

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and subduction along the Pacific-South American margin is known to have been strongly oblique (right lateral).This scenario is further complicated by the Cenozoic break up of the Farallones plate into the Nazca-Cocossystem, and the subduction of a transverse spreading centre beneath south-central Colombia. Furthermore, thePacific margin subduction of alternating portions of older-dense, and younger-bouyant oceanic crust has caused

wide fluctuations in oceanic plate subduction angle throughout this time, strongly affecting both the style andchemistry of subduction-associated magmatism, and the high level structural - deformational rheologic regime inthe overlying plate.

Extrapolation of the geology of the Colombian Cordilleras southward into Ecuador provides realitively good broadtectono-stratigraphic correlation within the Central – Real Cordillera, the Inter-Andean Depression, and theWestern Cordillera (Figures 3 and 4). Geologic differences such as the apparent lack of Proterozoic metamorphicrocks in the northern Cordillera Real of Ecuador, or the paucity of Paleogene volcanic rocks in the WesternColombian Cordillera may be attributed to a general lack of detailed geologic coverage, differences in geologic

and age-date interpretation, or to the observation that much of the Northern Andes may be viewed as anamalgamation of distinct tectono-statigraphic terranes wherein abrupt geologic changes across structural breaksare normal (Litherland, et al., 1994).

The geological diversity of the metallogenetic domains of the Colombian Andes is emphasized below.

Eastern Cordillera

Underlain by a Proterozoic igneous basement complex, the Eastern Cordillera of Colombia consists primarily ofthick sequences of structurally juxtaposed low-grade Paleozoic metamorphic rocks, oxidised Mesozoicepicontinental strata, and Cenozoic through Recent continental and transitional deposits. The northern sector ofthe Eastern Cordillera contains a structurally superposed igneous-metamorphic complex of Triassic-Jurassic age,the Santander Massif. Known igneous activity, aside from the plutonic rocks observed in the Santander Massif, israre in the Eastern Cordillera, being constrained to isolated occurrences of rhyolite dome complexes of probableNeogene age (e.g. Paipa). The Eastern Cordillera essentially appears to represent an autochthonous forelandthrust-and fold province recording deformation caused by the collision and accretion of arc and terrane systemsalong both the Pacific and Caribbean margins of Colombia.

Central Cordillera

The Central Cordillera is comprised primarily of amphibolite-grade Proterozoic and greenschist-grade Paleozoicmetamorphic rocks (demarcating the western, deformed edge of the Guiana Shield, and it’s Paleozoic foredeepand marginal sedimentary cover sequence) which have been intruded by three Andean-type arcs, of roughlyJurassic, Mid- to Late Cretaceous, and Miocene to Recent ages. These arcs are all constructed upon continentalbasement and record the eastward subduction of oceanic lithosphere beneath the South American continentalblock. Jurassic magmatism is recorded in the Segovia, Sonson, and Ibague Batholiths, all of which are generallyof calc-alkalic, dioritic to quartz dioritic affinity. Associated intermediate volcanic and pyroclastic strata arepreserved in the northern portion of the Cordillera, in the Serranía de San Lucas, and in the south in theDepartment of Huila. The Cretaceous Antioquia, Sabanalarga, and Buga Batholiths are also of calc-alkalic affinity,however are of generally granodioritic to quartz monzonitic character. Finally, reactivated magmatic activity in thePaleogene and again beginning in the Mid- to Late Miocene and continuing through to the present is recorded inthe central through southern portions of the Central Cordillera, and is presently exemplified by the NNE trending





terranes, and a northern segment comprised of the Choco Segment of the Panama Arc, containing the Baudó andCañas Gordas Terranes (GEOTEC, 2000). Magmatic activity in the north is dominated by the Eocene Mandé- Acandí, Farallones, and Mistrato Batholiths, of calc-alkalic affinity and generally tonalitic composition. Theydemarcate the formation of island arcs constructed upon oceanic crust prior to it’s collision with northern

Colombia in the Neogene (GEOTEC, 2000). Magmatism in the southern segment is volumetrically more restricted,manifesting as Eocene tonalite plutons in the southern-central Western Cordillera (Piedrancha Batholith), andwidely dispersed but small diorite-granodiorite porphyry bodies of Neogene age.

Cauca-Patia Depression – Cauca River Drainage (Inter-Andean Depression)

This important geologic – geographic intermontane depression separates the Central and Western Cordilleras ofColombia. It records clastic shallow marine and intermontane sedimentation beginning in the Eocene. It is animportant feature from a metallogenic standpoint as it became the locus for eastward migrating magmatic activitybeginning in the Oligocene - Miocene, and hosts numerous hypabyssal porphyry intrusions of dioritic togranodioritic composition which intrude a generally reduced Palaeozoic metamorphic basement, andunconformably overlying Paleogene clastic sedimentary and volcanic sequences, which occur along it’s entirelength. Recent analysis of seismic reflection profiles indicates the Palaeozoic basement, and clastic sedimentarysequences in the southern portion of the Depression underwent thrust-and fold-belt style deformation both priorto and following hypabyssal porphyry intrusion (GEOTEC, 2000). A general three phase history for the Cauca-Patia Depression may thus be inferred – 1) as a coastal margin - intermontane basin receiving clasticsedimentation from the emerging Central and Western Cordilleras, 2) as a zone of foreland compression,

responding to the collision of Cretaceous oceanic terranes along the Colombian Pacific margin, and 3) as an arc-axial depression or zone of weak extension demarcating the thermal axis of Miocene calc-alkalic magmatism.Such a history contains obvious metallogenetic implications.

METALLOGENY

The integrated gold metallogeny of Northern Andes is complex, prolonged, and only marginally understood. InColombia the topic has been breached on the mine and lesser district-scale levels in various unpublished thesesor governmental geological (INGEOMINAS) bulletins, however virtually no integrated approaches have been taken

to assimilate the district-scale characteristics of gold mineralisation into a magmatogenic and/or metallogeneticframework (Northern Andean "magmatogenic" or "metallogenic" periods) with respect to the tectonic evolution ofthe Northern Andes sensu lato . In many respects this lack of conceptual integration simply reflects a paucity ofmodern, precise geochemical, especially geochronologic and broad-spectrum multi-elemental data, generatedpurposely with respect to gold metallogeny. It is noteworthy that the great majority of radiometric age-datesproduced from the Colombian Cordilleras are of the K-Ar (biotite, hornblende, sericite)-type, and in this contextare known to be highly susceptible to re-setting via subsequent thermal events, complicating in the process anyassociated time-contextual interpretations.

Similar problems exist in Ecuador, however the technical database has been greatly augmented over the lastdecade via locally intense activity by the international metals exploration community, especially in the Nambija-Zamora and El Oro districts, and via studies coordinated throughout the Ecuadorian cordilleras by CODIGEM inconjunction with the British Geological Survey. The complete publication, and integration of these data with thosefrom the Colombian cordilleras will provide many new insights in the interpretation of Northern Andeanmetallogeny.





however that a variety of "anomalous", isolated yet significant, gold deposits fall outside of the simplifiedclassifications presented below, and above all, emphasize the prolonged and complex nature of Northern Andeangold metallogeny, and the general lack of an integrated and coherent system for it’s understanding.

Jurassic

From the standpoint of historical and modern-day production, gold mineralisation associated with Jurassic-agedrocks, and their derived colluvial-alluvial occurrences, may be considered to be of the greatest importance inNorthern Andean gold mining. In Colombia these deposits have been worked extensively over the last 200 years,by artisanal miners, and by such companies as the Choco Pacific Mining Company (Anglo American Gold Mines),the Frontino Gold Mines, and the Pato Gold Mining Company (owned by Placer Development Inc., an earlyincarnation of Placer Dome Inc.). From a strictly hardrock perspective these deposits yield a variety of+1,000,000 oz. Au historical producers, including the El Silencio-Providencia Mine at Segovia, the La Bartola-Palmichela-La Castellana Mine at Remedios, and the El Limón camp near Zaragoza. The Nambija gold campassociated with the Jurassic Zamora Batholith is both historically and at present the most important goldproducing region in Ecuador.

Jurassic-aged magmatic rocks form an ENE-striking discontinuous curvilinear belt extending from southernEcuador along the eastern flank of the Central - Real Cordilleras, and the into northern portions of the EasternColombian Cordillera through to the Sierra Nevada de Santa Marta (Figures 2 and 5). Viewed south to north, themetallogenic entities of greatest importance include the Zamora Batholith (Ecuador), the Ibague Batholith, the

Segovia Batholith, the Santander Massif, and the Santa Marta Batholith. All of these units yield a rich goldmetallogeny, hosted within Jurassic-aged plutonic rocks as well as within the intruded Paleozoic and Precambrianmetamorphic complexes and Triassic - Jurassic-aged volcano-sedimentary sequences. The following generalcharacteristics are noteworthy;

FIGURE 5: Gold Mineralisation in the Jurassic.

Age of Plutons: Jurassic, 190 to 145 m.a.Pluton Petrology: Holocrystalline, medium grained biotite +\- hornblende diorite to quartz

diorite.Pluton Petrochemistry: Intermediate, metaluminous, calc-alkalic, I-type magmatismStyle of Mineralisation: Discrete, broadly mesothermal vein structures and clusters of vein structures.Structures range from 10´s of cm to metre-plus widths. Excellent strike, down-dip and grade continuity (Note,the El Silencio vein has been worked on 44 levels). Conspicuous lack of strong post-mineral ductile deformation.Strikes and dips highly variable however many cluster NW to NE, with 40 to 60° dips. (Note; Nambija – Zamora,Ecuador is characterised by exoskarn pockets, veins and replacement mantos in Triassic calcareous volcano-sedimentary rocks. Similar characteristics are locally observed in the central Ibague Batholith, Colombia).Ore Mineralogy: Mixed base-metal sulphides, pyrite (pyrrhotite)-sphalerite-chalcopyrite-galena (and magnetiteat Nambija), occasional tellurides. Generally good correlation Au (tellurides)-galena-sphalerite. Native goldcommon.Gangue Mineralogy: Predominantly quartz with calcite (ankerite), chlorite, adularia at Nambija.Wallrock Alteration: Pyritic sulphidation, carbonitisation, sericitisation proximal to mineralised structures,contained within a broad propylitic (epidote, lesser chlorite) halo in intrusive rocks. Grandite-epidote-cpx skarn atNambija.

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intrusive and/or volcanic rocks of like age. Mineralisation and alteration, dominated by symmetrical silicification,argillitisation-sericitisation, and pyritic sulphidation +/- propylitisation is intensely developed, and observed on akm-scale basis. Gold-silver mineralisation is hosted within dense networks of structurally-controlled cm to 10´s-of-cm scale veinlets and sheeted veins, and phreatic breccia zones. Vein-fillings are dominated by +50% pyrite,

with lesser quartz and minor base metal sulphides. In the case of Cerro San Carlos mineralisation is volcanic-hosted, and underlain by a plutonic root zone where chalcopyrite becomes the dominant veinlet sulphide, goldgrades diminish somewhat, and alteration approaches phyllic in character. Thus, metal and alteration zonations atSan Carlos suggest porphyry potential below the volcanic cover.

Cretaceous

Although of lesser importance to Colombian gold production history than the Jurassic-hosted occurrences, golddeposits hosted within generally Late Cretaceous plutonic rocks and their proximally located metamorphic andsedimentary cover sequences have produced significant quantities of gold. A number of historic +1,000,000 oz Aucamps including the Bramadora, Anorí, Amalfi, San Roque, and the Río Nus valley are documented. Thegeographic distribution of Cretaceous igneous rocks in Colombia is primarily restricted to the Central Cordillera,the vast majority of which are associated with a single geologic entity, the Antioquian Batholith (Figures 2 and 6),which is exposed over an area of some 8,000 sq. km in the northern portion of the Central Cordillera. No majorCretaceous-aged magmatic events are observed in Ecuador.

FIGURE 6: Gold Mineralisation in the Cretaceous.

Age of Plutons: Antioquian Batholith, Mariquita Batholith, Late Cretaceous (+\- 70 m.a.), Sabanalarga, BugaBatoliths, Mid-Cretaceous, 110 to 90 m.a.Pluton Petrology: Holocrystalline, medium to coarse-grained biotite +\- hornblende granodiorite to quartzmonzonite, local dioritic to gabbroic phases.

Pluton Petrochemistry: Intermediate to felsic, metaluminous, calc-alkalic, I-type magmatismStyle of Mineralisation: Broadly mesothermal, syn-to post-kinematic veins and reticulate to sheeted veinletand fracture networks cutting plutonic rocks and proximal or mantling sedimentary and metamorphic sequences.Ore Mineralogy: Pyrite, arsenopyrite, galena, sphalerite, chalcopyrite +/- stibnite, jamisonite, pyrrhotite, nativegold.Gangue Mineralogy: Predominantly quartz with late calciteWallrock Alteration: Pyritic sulphidation, silicification, local potassic alteration (k-spar, biotite, sericite),hydrothermal magnetite and carbonitisation in batholith, regional propylitisation (epidote, lesser chlorite).

Ag:Au ratio: Low, variable 1:1 to 10:1Geochemical Expression: Au, Ag, As, Sb, Hg, Pb,+\- Cu, Zn, Mo

Average Grades: Larger veins 5 to 20 g Au\t over life of mine, veinlet networks 3 to 4 g Au/t, local multi-ounceaccumulations.Most Active Producing Areas: Dept. of Antioquia: La Bramadora, Anorí, Amalfi, Gramalote – San Roque, SanJosé del Nus, Gomez Plata, San Vincente. Dept. of Valle del Cauca: Buga – Ginebra.

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Cenozoic

Gold mineralisation hosted within Cenozoic-aged plutonic, volcanic, and sedimentary rocks, and proximalMesozoic and lesser Paleozoic cover sequences is widespread throughout the Western Cordillera, the Inter-

Andean Depression, and to a lesser degree the Central – Real Cordillera of the Northern Andes. Its occurrencespans the Cenozoic, manifesting in a wide variety of styles and associations. With some notable exceptionshowever, it is the historically least exploited, and in many respects, least understood of the Northern Andean goldmetallogenic pulses. Maintaining a "broad-brush" approach, mineralisation can be clustered into "Paleogene" and"Neogene" classifications, and the following generalisations can be made.

Paleogene

In Colombia Paleogene magmatism and related gold occurrences are primarily restricted to the allochthonousterranes of the Western Cordillera, as exposed in the north in the Mandé, Farallones, and Mistrato Batholiths(Figures 2 and 7). Additional significant gold mineralisation is observed in the southern Western Cordillera(Piedrancha Batholith), and in the Central Cordillera (El Bosque Batholith). In Ecuador mineralisation of possiblePaleogene age is exposed in the Ponce Enríquez (El Oro) and Guaranda (Western Cordillera) regions. Goldmetallogeny associated with the Paleogene in Colombia may be characterised as follows;

FIGURE 7: Gold Mineralisation in the Paleogene.

Age of Plutons: Paleocene - Early Eocene (+/-65 to 45 m.a.)Pluton Petrology: Holocrystalline, fine to medium grained biotite +\- hornblende tonalite, lesser doiritic andgabbroic phases.Pluton Petrochemistry: Mafic to intermediate, metaluminous, calc-alkalic, I-type magmatismStyle of Mineralisation: Broadly mesothermal veins, vein swarms and sheeted veining cuttings plutons andproximal reduced Cretaceous volcano-sedimentary strata.Ore Mineralogy: Pyrite, pyrrhotite, arsenopyrite, native gold, +\-local chalcopyrite, molybdenite.Gangue Mineralogy: Quartz, calcite, ankeriteWallrock Alteration: Strong, widespread carbonitisation, sulphidation (py-po-asp), silicification, minor biotite,distal epidote, chlorite (minor). Porphyries contain K-spar, magnetite, and argillic and propylitic alterations.

Ag:Au ratio: Low, variable 1:1 to 4:1Geochemical Expression: Au, Ag, As, +/- Cu, Mo

Average Grades: Individual veins 15 to 40 g Au/t. Grades of +/-10 g Au/t can be sustained over 5 to 15 m veinswarm widths. Multi-ounce values locally common.Most Active Producing Areas: Dept. of Nariño: La Llanada, Sotomayor, Cumbitará, El Diamante. Dept. ofRisaralda: Puerto de Oro, Mistrato, Las Camelias. Dept. of Antioquia: Santa Inés, Andes, Frontino (viejo) . Dept.of Quindio: Salento.

In addition to the above characterised "gold-only" occurrences, a variety of "porphyry-related" Cu-Mo+/-Ausystems of Paleogene age have been documented in Colombia. Associated primarily with the Mande-Acandí



within or along the margins of the regionally NNE trending Inter-Andean Depression (including in Colombia theCauca-Patia Depression, and its northern extension along the Río Cauca valley). Gold mineralisation, metalzonation and alteration are clearly related to the emplacement of numerous, generally small, often polyphase-polylithic, calc-alkalic dioritic through monzonitic and granodioritic stocks and plugs of hypabyssal, commonly

porphyritic affinity, and is hosted within the porphyry bodies themselves and the intruded Cenozoic, Mesozoic,and Palaeozoic sedimentary, volcanic and metamorphic sequences. Considered from north to south, importantknown mineralising centres of Neogene age (Figures 2 and 8) include; Buriticá, Guintar, Titiribí, Caramanta- Valparaíso (Dept. of Antioquia), Marmato-Echandía, Supia (Dept. of Caldas), Quinchia-Miraflores-Mina-Rica (Dept.of Risaralda), Buenos Aires-Suárez, El Tambo, Dominical, Altamira, Cerro Negro-La Concepción, and Cerro Bolívar(Dept. of Cauca) in Colombia, and the Zaruma-Portovelo and possibly Ponce Enríquez districts of Ecuador.

FIGURE 8: Gold Mineralisation in the Neogene.

In detail the characteristics of the associated gold mineralisation differ widely, given variations in plutonpetrochemistry, geologic structure, and the nature of the host sedimentary volcanic and/or metamorphic rocks.The following parametres are generally valid:

Age of Plutons: Miocene-Pliocene (+\-15 to 4 m.a.)Pluton Petrology: Fine to medium grained diorite to granodiorite. Plagioclase, quartz, biotite, hornblende occuras phenocrysts.Pluton Petrochemistry: Intermediate to felsic, metaluminous, calc-alkalic, I-type magmatismStyle of Mineralisation: Broadly epithermal to mesothermal. High-grade vein swarms and fracture systems cutplutons and surrounding host rocks. Disseminated and finely fracture-dispersed, sulphide-related mineralisation inhost sediments seen at Buriticá, Titiribí, La Concepción. Porphyry-related Cu (Mo)-Au associations seen at Titiribí,Guintar, Valparaíso, Buenos Aires-Suárez, Cerro Negro-Dominical. Intrusive-wallrock hosted breccia zones seen atBuriticá, Quinchía-Miraflores. Porphyry-associated "gold-only" mineralisation documented at Altamira, La

Concepción. Extensive fracture-controlled, breccia pipe and veinlet-type mineralisation within porphyry andvolcanic rocks at Mina Rica, Marmato-Echandía, Supia, Buriticá and Cerro Pelado, Ecuador. Sheeted regionalpolymetallic mega-vein systems in volcanic rocks at Zaruma-Portovelo.Ore Mineralogy: Variable; pyrite +/- sphalerite (marmatite), galena, chalcopyrite, arsenopyrite, stibnite, +/- Ag-sulphosalts, pyrrhotite, native gold, electrumGangue Mineralogy: Predominantly quartz with late calcite, poorly documented.Wallrock Alteration: Pyritic sulphidation, silicification, K-silicate (K-spar, biotite), hydrothermal magnetite,sericitisation, argillitisation, propylitisation (epidote), zoning notable in intrusives, subtle biotitisation, sulphidation,(de)carbonitisation in sedimentary rocks.

Ag:Au ratio: Highly variable 5:1 to 100´s:1Geochemical Expression: Au+/-Ag, Zn, Pb, Sb, As, Hg or Au+\- Cu, Mo, Ag: zoned.

Average Grades: Highly variable, dependant upon the intensity and/or density of mineralisation, alteration,fracturing, and nature of host the rocks.Most Active Producing Areas: Dept. of Antioquia: Buriticá, Titiribí, Guintar, Caramanta. Dept. of Caldas:Marmato-Echandía. Dept. of Risaralda: Miraflores, Mina Rica. Dept. of Cauca: Buenos Aires-Suárez, LaC ió El T b C B lí C P l d d Z P t l E d



The decisive factors inhibiting development of the gold exploration/exploitation sector in present-day Colombiaare clearly socio-political, and potentially involve security risks which most companies, both foreign and domestic,are not willing to accept. Such as the present case may be, similar situations in other regions of South Americaand the world have been observed to resolve relatively rapidly (Perú, for example, yields a "world-class"

example), and provide reasonable support to the philosophy that it is generally better to position early than tofind one’s self lost in a line-up of competitors.

Colombia is a country of wide-ranging, and in many cases, contradictory and unique attributes - geographic,physiographic, cultural, historical, botanical, and geological. It is a interesting point to ponder that virtually all ofthe pre-Colombian cultures which inhabited the Andean Cordilleras and intermontane valleys of Colombia yieldeda personalised, technologically advanced, and artistically profound gold craftsmanship, which is documented overa +2,500 year archaeological history. It may be considered rather poignant that the geographic region whichexhibits the most evolved pre-Colombian history of gold working in the Western Hemisphere remains the final

frontier for modern-day gold exploration and development in Latin America.

ACKNOWLEDGMENTS

This presentation would not have been possible without the full support of Mr. Robert Allen and the managementand staff of Grupo de Bullet S.A., in Medellín. Their expertise and patience is gratefully acknowledged.

Many special thanks are due to Drs. Fabio Cediel and Carlos Cáceres of GEOTEC Ltda. in Santafé de Bogotá, for

discussions and manuscript review, and the contribution of their unparalleled, newly published, Geologic Map ofColombia, 2000. The tectono-stratigraphic Chart was especially useful. Additionally, full appreciation must beexpressed for discussions regarding various unpublished aspects of Colombian geology and metallogeny, with avariety of fine Bogotá-based geoscientists including Hector Vargas C., Dr. Luis Jaramillo, and Rafael Alfonso R.

SELECTED REFERENCES AND BIBLIOGRAPHY

Alvarez, A. J., 1983, Geología de la cordillera central y el occidente colombiano y petroquímica de los intrusivos

granitoides mesocenozoicos, Boletín Geológico, INGEOMINAS, vol. 26, no. 2.

Aspden, J.A., McCourt, W.J., and Brook, M., 1897, Geometrical control of subduction-related magmatism: theMesozoic and Cenozoic history of Western Colombia, Journal of the Geological Society, London, Vol. 144.

CODIGEM – BGS, 1993, Mapas geologico y tectono-metalogenico de la Republica del Ecuador, escala 1:100,000,2 planchas complementarias.

Emmons, W.H., 1937, Gold Deposits of the World, First Edition, McGraw-Hill Book Co. Inc.

GEOTEC Ltda., 1987, Gold in Colombia: Historical overview, geologic framework, prospectivity, legal aspects.

GEOTEC Ltda., et al., 1999, Seismic Atlas of Colombia, produced in collaboration with Empresa Colombiana dePetroleos (ECOPETROL) and Robertson Research International Ltd.




INGEOMINAS, 1995, Colombia: Una Mina de Oro: Pontencial Aurífero en Colombia, 25 pp.

INGEOMINAS, 1998, Atlas colombiano de información geológico-minera para inversión (ACIGEMI), digital format.

Instituto de Estudios Colombianos, 1983, El oro en Colombia, Santafé de Bogotá, 290 pp.

Litherland, M., Aspden, J.A., and Jemielita, R.A., 1994, The metamorphic belts of Ecuador, British GeologicalSurvey, Overseas Memoir 11, 147 pp.

Liviaccari, R.F. et al., 1986, Cordilleran-style tectonics and Late Cretaceous – Cenozoic tectonic evolution inColombia, unpublished MagmaChem study, 120 pp. with time slice analysis.

Restrepo, V., 1883, Estudios sobre las minas de oro y plata en Colombia, Biblioteca Colombiana de CienciasSociales, Quinta Edición, 1979, Medellín, 220 pp.

Shaw, R.P., 2000, Gold mineralisation in Colombia: production history, tectonic setting, metallogeny, andexploration update, in 4th International Gold Symposium, Lima, Peru, May, 2000, CD-rom format.

Sillitoe, R. H., et al., 1982, Setting, characteristics, and age of the Andean porphyry belt in Colombia, Econ. Geol.,vol. 77, pp. 1837-1850.

Sub-Commission for the Metallogenic Map of the World, 1983, Metallogenic Map of South America, Ministerio deEnergía y Minas, Venezuela, Coordinador, escala 1:5,000,000, 2 planchas.

Wokittel, R., 1960, Recursos minerales de Colombia: compilación de los estudios geológicos officiales enColombia; Bogotá, Servicio Geológico Nacional, Edición Lumbre, vol. 10, 393 pp.

gold mineralization in the northern andes_magmatic setting vs. metallogeny

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