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| Author(s): |
Thais Andressa Carrino
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Campinas, SP. |
| Institution: | Universidade Estadual de Campinas (UNICAMP). Instituto de Geociências |
| Defense date: | 2015-02-03 |
| Examining board members: |
Alvaro Penteado Crósta;
Emilson Pereira Leite;
Jurandir Zullo Junior;
Teodoro Isnard Ribeiro de Almeida;
Jorge Silva Bettencourt
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| Advisor: | Adalene Moreira Silva; Catarina Labouré Bemfica Toledo; Alvaro Penteado Crósta |
| Abstract | |
Southern Peru contains important small- to medium-sized Au-Ag (± base metals) epithermal deposits, associated with the Miocene-Pliocene Andean orogeny. A synoptic analysis of the region covering the Chapi Chiara, Cerro Millo, San Antonio de Esquilache and Cerro Chucapaca targets ¿ each one located in distinct paleostratovolcanoes ¿ was done through the processing and analysis of ASTER data. These targets are characterized by extensive advanced argillic alteration zones, except San Antonio de Esquilache, that is marked by argillic alteration (AA) (smectite-illite) and advanced argillic alteration (alunite-kaolinite) (AAA) zones restricted to outcropping diorite intrusions. Unlikely, the Canahuire intermediate sulfidation epithermal Au-(Cu, Ag) deposit was discriminated by extensive NW-SE quartz-rich rocks (Yura Group/Juro-Cretaceous), and carbonate rocks (Gramadal Formation/Yura Group) and silica-poor phreatic and phreatomagmatic breccias that host the mineralization. Favorability model for "Canahuire-type" deposits was created through the integration of ASTER data using the fuzzy logic technique. A detailed study was conducted at Chapi Chiara prospect through petrography, geochemistry, reflectance spectroscopy, magnetic susceptibility (MS), images of the amplitude of analytic signal and of first vertical derivative of the anomalous magnetic field, besides the processing of HyMap hyperspectral remote sensing data. The main sampled volcanic rocks comprise porphyritic andesite (MS ~28×10-3 SI), and rhyolitic tuff and lapilli tuf (MS~0). The SW sector of the prospect is characterized by three sub-areas with extensive AAA zones, marked by quartz, K-alunite, intermediate alunite, Na-alunite, kaolinite, dickite (±topaz, ±huangite, ±APS minerals, ±pyrophyllite, ±diaspore, ±rutile) (MS ~0 to ~0,15×10-3 SI). Restricted AA zones (quartz, illite ± , paragonitic illite ± , smectite, ±pyrite, ±rutile) (MS ~0,01×10-3 SI), and of propylitic alteration (chlorite, quartz, calcite, epidote, smectite, ±kaolinite, ±pyrite, ±chalcopyrite, ±titanomagnetite and magnetite)) (MS ~3,45×10-3 to ~36,03×10-3 SI) occur in distal sectors. The central sector is marked by metric/decametric hydrothermal breccias with MS ~0 to 0,01×10-3 SI, composed of vuggy quartz-rich fragments. There is a considerable concentration of pyrite and strong geochemical association of Au, Ag, As, Bi, Hg, Se, Sb, e Te. The main supergene minerals comprise jarosite and goethite. The above mentioned hypogene mineral assemblages reveal a high sulfidation epithermal system similar to the Cerro Millo gold prospect and to Tucari and Santa Rosa gold deposits, allowing to infer a relative age between ~11 and ~4 Ma for the paleoestratovolcano and the concomitant hydrothermal activity in Chapi Chiara. Intense magmatic-hydrotermal leaching seen in the paramagnetic and diamagnetic AAA and AA zones generated two NW-SE extensive demagnetized zones, compatible with the regional Condoroma-Caylloma fault system. Smaller structures also occur (e.g., NE-SW, E-W). Although these trends are interesting exploration vectors, the exposure of minerals formed at higher temperature (e.g., alunite+topaz, alunite+dickite+pyrophyllite, diaspore, intermediate alunite in the SW sector), suggest possible eroded cores, reducing the local potential for mineralization, and/or indicating the proximity of the limit between epithermal and mesothermal domains in depth. In addition, there is a possible proximity of dioritic intrusion(s) near the surface of the prospect, similarly to the currently exposed intrusions at the surface in the analogous target of San Antonio de Esquilache (AU) | |
| FAPESP's process: | 11/00106-8 - GEOLOGY AND HYDROTHERMAL ALTERATION OF THE CHAPI CHIARA GOLD PROSPECT AND NEARBY TARGETS, SOUTHERN PERU, THROUGH GEOLOGICAL, REMOTE SENSING, GEOCHEMICAL AND MAGNETIC DATA |
| Grantee: | Thais Andressa Carrino |
| Support Opportunities: | Scholarships in Brazil - Doctorate |