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Geology, hydrothermal alteration, paragenetic sequence and fluid inclusion analysis of La Maruja level, Marmato district, Caldas Department, Colombia




Bedoya Sanmiguel, Oscar Geovany, author
Hannah, Judith L., advisor
Ramirez, Jorge A., advisor
Thompson, Tommy B., committee member

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The Marmato goldfield is located in the Department of Caldas in the western Cordillera of Colombia. The area is topographically characterized by steep hills of abrupt relief. Rocks that range in age from the Cretaceous to the present appear in the area. Confined to the northeast of the area, the oldest units consist of sedimentary and volcanic rocks that have been metamorphosed to mid-amphibolite facies to amphibolites, hornblende schist and quartz-sericite schist. The metamorphic rocks form pendants within younger porphyry intrusions (Marmato Stock) and occur intermittently in a north-south belt along the Rio Cauca. The ore host at La Maruja level consists of dacite porphyry. A Late Miocene age has been assigned for this unit. This body has been affected by a tectonic event and it exhibits faulting, shearing and joint features. Structure is the primary control of ore mineralization. The fault surfaces are usually curved or arched and have a predominantly northwestern orientation with high dip angle. Sin Nombre, Porvenir, Santa Ines and Mucura are the veins at La Maruja level. The thickness of these veins can range from 0.30 to 2.5 m. The ore minerals of La Maruja level listed according to their relative abundance are: pyrite, pyrrhotite, arsenopyrite, sphalerite, chalcopyrite, gold, galena, marcasite and polybasite. The gangue minerals present are calcite, chlorite and quartz. Deposition of ore and gangue minerals in this level occurs in three stages. The early stage is characterized by abundant deposition of coarse euhedral pyrite crystals. The intermediate stage is characterized by abundant deposition of sphalerite and minor amounts of chalcopyrite and gold. A tectonic event occurred at the end of this stage. The late stage is a short period of fine-grained pyrite deposition which ended with great amounts of calcite and chlorite deposition. Silicic, sericitic, propylitic and albitic hydrothermal alteration assemblages occur at La Maruja level. Fluid inclusion homogenization temperatures, assumed to represent minimum ore fluid temperatures, range between 250°C and 350°C with mean values of about 310°C for Sin Nombre vein and 330°C for other veins; no evidence for boiling is present. The ore fluid salinity ranges from 3.7 to 10.3 equiv. wt% NaCl. Characteristics of the hydrothermal fluid in this level are: a relatively high temperature, moderate salinity and high in reduced sulfur.


1998 Summer.
Includes bibliographical references (pages 160-165).
Covers not scanned.
Print version deaccessioned 2020.

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Hydrothermal alteration -- Colombia -- Caldas (Department)
Fluid inclusions -- Colombia -- Caldas (Department)
Geology -- Colombia -- Caldas (Department)


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