Abstract
At El Chucho creek, located to the west of the Valle del Cauca department in Colombia, some hydrothermal alterations affecting the Buga Batholith rocks and dykes of porphyritic quartz-dioritic and tonalitic composition were identified. These lithological units host mineral occurrences of pyrite, chalcopyrite, and molybdenite that occur disseminated in the rocks or associated with quartz veinlets. The hydrothermal alterations identified were phyllic, propylitic, and, in minor quantity, potassic. The two firsts alterations’ distribution is related to structures and pervasive, whereas the last one seems restricted to contact zones of porphyritic dykes on tonalite. Microthermometric data were acquired i) on quartz veinlets of 1 cm thick over a phyllic alteration zone, and ii) on quartz veinlet of 1 cm thick with chalcopyrite ± molybdenite and copper silicates, both veinlets cutting the phaneritic tonalite. Those data suggest that the mineralizing fluids have an aqueous-saline chemical system and were trapped under low volatile content. The microthermal data allowed authors to identify two mineralizing events. One of them of higher temperature, with homogenization temperatures between 275°C-480°C; as the second event is characterized by lower homogenization temperatures that range from 100°C to 139°C.
Highlights
The mineral occurrences are disseminated in thin quartz veinlets (≤ 1cm) (3 veinlets); all of them complete almost 5 % vol; alteration minerals such as carbonate, chlorite, epidote, sericite and locally biotite complete 20 % vol; this mineral composition allow for classifying the rock as tonalite
The identified hydrothermal alteration are (1) moderate propylitic alteration, with a pervasive distribution and in a minor quantity present as straight veinlets of Ep + Qz + Cb ± Chl ± Py ± Mag, sulphurs and oxides as Py, Ccp and Mag are disseminated on the rock; (2) moderate phyllic alteration, with mineral association Qz + Ser + Py ± Chl and straight veinlents of Ccp and D-type veinlets (Gustafson & Hunt, 1975), this alteration
These results are presented separately according to the fluid inclusion type; the composition, and salinity of both type of inclusions were modeled on the BULK program from Fluids package (Bakker, 2003; Bakker & Brown, 2003)
Summary
Au-Ag mineralization and, according to Cediel & Shaw (2019), “were accreted to the Colombian margin along with slivers of Farallon – Caribbean Colombian. Batholith have been focused on Ginebra and Buga’s municipalities, located to the northwest of the study area. Afterward, Nivia et al (2017) dated the Buga Batholith through U/Pb in zircon and got two different ages (88 ± 1.64 Ma and 69 ± 1.41 Ma). Based on these ages, Nivia et al (2017) has classified the Buga Batholith on two differetn intrusive bodies
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