Abstract
The Frontino-Morrogacho gold district is located on the western flank of the Western Cordillera, NW of Antioquia Province. Gold mineralizations in the area are spatially and genetically associated with the cooling of three mid- to late-Miocene age intrusive centers in the form of stocks and dikes (12-9 Ma): Cerro Frontino, La Horqueta and Morrogacho (El Cerro Igneous Complex). These composite magmatic pulses, with ultramafic to intermediate compositions, vary into diorite-, gabbro- and monzonitic-bearing phases. Mineralization in the complex is present as several structurally controlled fault veins, shear-related veins, sheeted quartz extension veins and quartz-carbonate tabular extension veins, with the development of swarms and nests of veins-veinlets, breccias and stockworks. Structures range from centimeter-wide individual veinlets to several meter-wide swarms of veins developed within broad mineralized structural corridors, with a metallic signature that consists of Au + Ag + Cu + Zn + Pb + As (± Te ± Bi ± Sb ± Hg ± W) assemblages. Veins are composed of multiple stages of mineralization, and the formation of these structures is enhanced by the presence of a local regime of extension and E-trending structures, including evidence of faults and shear zones with right-lateral displacement, which are likely involved in pluton emplacement and cooling. The ore mineralogy is composed of pyrrhotite, pyrite, chalcopyrite, sphalerite, galena and arsenopyrite assemblages formed in two or more mineralization stages, with complex Bi, Te, Sb and Hg mineral specimens associated with Au and Ag. Mineralized structures of the district present a preferential E-strike with dominant vertical to subvertical and occasional subhorizontal S-dips and secondary N- and NW-strikes that are steep to vertically E-dipping.
 The Frontino-Morrogacho Gold district presents characteristics related to the architecture, mineralogy and alteration of reduced (ilmenite-series) intrusion-related gold systems but is genetically associated with a parental oxidized magma source. The gold content is associated with three different families involving electrum, tellurides and alloys: gold rich (66 to 78% Au, 22 to 34% Ag), average (50 to 60% Au, 40 to 50% Ag) and silver rich (32 to 40% Au, 60 to 68% Ag). The formation of these bodies is associated with an N-S magmatic-metallogenic trend of Au-Ag-Cu deposits, which extend for more than 300 km along the Western Cordillera of Colombia. Similar plutonic suites span from the south of Chocó Province to the north of Antioquia Province, which indicates that the Frontino-Farallones-Botón arc can be proposed as an individual metallogenic belt.
Highlights
In Colombia, the Miocene represents a period of widespread continental subduction-related magmatism, which is represented in the Central and Western Cordilleras
The present study aims to characterize and classify the gold ore mineral occurrences related to the main intrusive centers of the El Cerro Igneous Complex: Cerro Frontino, Morrogacho and La Horqueta stocks
After the emplacement of the El Cerro Igneous Complex intrusive suite, Frontino arc magmatism ended and plutonism shifted eastwards, where arc migration was associated with the genesis of the Middle Cauca Belt (MCB) (Leal-Mejía et al, 2019; Shaw et al, 2019)
Summary
In Colombia, the Miocene represents a period of widespread continental subduction-related magmatism, which is represented in the Central and Western Cordilleras. Geology of the Frontino-Morrogacho Gold Mining District and metallogeny of the El Cerro Igneous Complex block (Zuluaga and Hoyos, 1978; Cediel and Shaw, 2003; Zapata and Rodríguez, 2011; Rodríguez and Zapata, 2012; Rodríguez and Arango, 2013; Rodríguez-García and Bermúdez-Cordero, 2015; Silva-Sánchez, 2018; Arrubla, 2018; Leal-Mejía et al, 2019; Shaw et al, 2019) In this collision, the Frontino-Botón arc was formed with the additional intrusion of different magmatic bodies on the western flank of the Western Cordillera, NW of Antioquia Province (Rodríguez and Zapata, 2012). It complements the regional and ore deposit geology information on the mid- to late-Miocene magmatic arc segment in the Colombian Western Cordillera, the metallogeny of gold mineralizations hosted and associated with mid- to late-Miocene intrusive bodies
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