El Espino Iron-Oxide Copper Gold District, Coastal Cordillera of North-Central Chile, The

The El Espino Iron Oxide Copper Gold (IOCG) mining district is located in the Coastal Cordillera of north-central Chile and includes the El Espino deposit which has a measured plus indicated geologic resource of 145 Mt at 0.55 percent Cu and 0.22 g/t Au. Mineralized bodies are distributed in a 7 x 10 km2 area and range in geometry from single veins to stockworks and breccias to manto-type deposits. The ore bodies are hosted primarily by Early Cretaceous volcanic, volcaniclastic, and sedimentary units, with fewer mineralized zones within a Late Cretaceous multi-phase intermediate pluton. Hydrothermal alteration and mineralization was coeval with plutonism at 88 Ma. Both plutonism and hydrothermal alteration/mineralization were localized within a dilatational jog along a major transtensional north-south fault system that controlled the distribution of alteration and mineralization. Sodic alteration is the most extensive style of alteration in the district and is best developed at stratigraphically deep levels. Sodic-calcic alteration is spatially more restricted and grades inward into a calcic alteration assemblage at intermediate levels, displaying a zoned pattern around the Late Cretaceous pluton. Potassic alteration is relatively restricted in extent and is not always spatially related to sodic, sodic-calcic, and calcic alteration zones. Late hydrolytic alteration is concentrated in the middle and upper portions of the stratigraphis sequence while argillic alteration is restricted to the highest part of the alteration system. Iron oxides and sulfides are largely confined to calcic and hydrolytic alteration assemblages. The fluids responsible for sulfide precipitation ranged in temperature from 350 to 425 degrees C with salinities between 32 and 34 wt. NaCl equivalent. Mineralization probably took place at a minimum depth of 3-4 km. Early high temperature fluids were magmatically derived while later hydrothermal fluids may have contained mixed meteoric fluids with marine-derived sulfate. The close spatial and temporal association of alteration zones with a plutonic suite suggests that plutons provided heat and contributed fluid and sulfur to the hydrothermal system. Lithogeochemical mass balance analyses indicate that early and deep alteration events leached elements that were fixed at later times higher in the stratigraphic sequence during the waning stages of hydrothermal alteration.

Name thesis:degree_name

Doctor of Philosophy (Ph.D.)

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Geology and Geological Engineering

Grantor dc:publisher

Colorado School of Mines. Arthur Lakes Library

Year dc:date.issued

2012

Author dc:creator

• Lopez Orrego, Gloria P.

Advisor dc:contributor.advisor

• Hitzman, Murray Walter

Committee members dc:contributor.committeemember

• Nelson, Eric P., 1951-
• Monecke, Thomas
• Humphrey, John D.
• Miller, Hugh B.

• Coastal Cordillera
• Chile
• Cretaceous
• IOCG deposit

Statement dc:rights

• Copyright of the original work is retained by the author.

Language dc:language.iso

eng, English

Identifier

T 7121

OAI identifier oai:identifier

oai:repository.mines.edu:11124/71537