Loading...
Geology, alteration, and mineralization of the La Virgen high-sulfidation epithermal - porphyry district, northern Peru
Montesinos, Raul
Montesinos, Raul
Citations
Altmetric:
Advisor
Editor
Date
Date Issued
2024
Date Submitted
Collections
Research Projects
Organizational Units
Journal Issue
Embargo Expires
Abstract
This study seeks to fill a knowledge gap, enrich our understanding of high-sulfidation (HS) ore-forming processes in siliciclastic environments, and guide exploration in siliciclastic terranes, by studying the La Virgen district in northern Peru, 17 km east of the giant Lagunas Norte HS deposit, in which the HS mineralization is mostly hosted in the sandstone of the Chimu Formation and other siliciclastic rocks. In addition, this study is the first detailed study of the La Virgen District and discovered the porphyry style mineralization in the eastern part of the district, and that the eastern part of the district has mineralization significantly older than the western part based on mapping, geochronology, SWIR (Short Wavelength Infra-Red) spectral analysis, and whole rock geochemistry.
The sedimentary rocks of the La Virgen District are Low Cretaceous siliciclastic rocks with minor limestones that are folded at least twice and chopped up by many faults of various timing. The faults had multiple movements; some of them generated tectonic breccia that were later on altered and cemented by hydrothermal fluids, changing the breccias to tectonic-hydrothermal breccias. The sedimentary rocks were intruded by andesite porphyry, feldspar porphyry, and phreatomagmatic breccias of ~22-21 Ma, and later dacite porphyries and their related phreatomagmatic breccias of ~17 Ma. The alteration and mineralization occurred in two events and two domains: ~22-21 Ma porphyry-HS mineralization in the Escalerilla-Cuypampa Domain in the east, with the source being the feldspar porphyry in its Cuypampa block, and the ~18-17 Ma HS mineralization in the La Virgen Domain, with its magmatic center possibly below Cerro Alumbre. There are five types advanced argillic alteration (AA1: vuggy quartz + pyrite ± alunite; AA2: quartz + alunite + pyrite; AA3: dickite + pyrite ± alunite; AA4: kaolinite + pyrite ± illite; and AA5: quartz + pyrite + pyrophyllite.), intermediate argillic alterations (IA: illite and/or smectite + pyrite, and chlorite + smectite ± pyrite) in the HS deposits, and K-feldspar alteration and slightly later phyllic alteration (quartz-sericite-pyrite) associated with the porphyry-style mineralization. The alteration is structurally and lithology-controlled. The AA and IA alterations are typically zoned. The highly fractured and brecciated sandstone of the Chimu Formation are altered by AA alterations in which alunite, dickite, pyrophyllite, and quartz fill the interstitial open spaces between the resistant quartz grains, fill microfractures, and replace minor feldspar grains. The alteration is cryptic, with the altered sandstone appearing fresh. The alteration minerals also cement and alter clasts of tectonic-hydrothermal breccias. The Cu-Au HS mineralization consists of pyrite, enargite, and minor famatinite, luzonite, covellite, digenite, sphalerite, galena, tennantite, tetrahedrite, and visible gold. Gold also occurs in pyrite2, pyrite3, and enargite, as revealed by LA-ICP-MS mapping. HS mineralization is accompanied by silicification that occurs partly as black silica with fine-grained pyrite and partly as creamy silica. The silicification also fills interstitial open spaces between grains of the sandstone, fractures in sandstones, and as cement of breccias. The porphyry style mineralization consists of pyrite, molybdenite and chalcopyrite. The lesson for HS exploration in siliciclastic terranes is that SWIR analysis should be widely applied to identify cryptic clay minerals in reconnaissance exploration, even if the rocks look fresh.
Associated Publications
Rights
Copyright of the original work is retained by the author.